That’s because both precipitation and smoke are a possibility during the airshow (July 22-28), according to Scott Dennstaedt, author of the EZWxBrief and a FLYING contributor.

• READ MORE: FLYING Unveils ‘Oshkosh Live’ Video Programming Lineup

For starters, the wildfires in Canada and to the west may result in some smoky skies, Dennstaedt said. This was a factor last year, resulting in thick haze, poor visibility, and blood-red sunrises and sunsets. Photographs taken in the early morning hours had a sepia-tone look to them—a bonus if you are taking pictures of vintage aircraft.

In a forecast released Thursday, Dennstaedt predicted AirVenture attendees may smell the smoke earlier in the day but by later afternoon could expect some convective activity that should clear away the smoke due to the unstable atmosphere and ground heating up.

Dennstaedt presents an entertaining and educational look at the factors impacting aviators who are trying to get to the event as well as what to expect when they get there. The data is derived from atmospheric tools used by the National Oceanic Atmospheric Administration (NOAA).

EZWxBrief AirVenture Weather Roundup

The post Flying to AirVenture? What You Can Expect of the Oshkosh Weather appeared first on FLYING Magazine.

Answer: It depends on your mission and how many Ben Franklins you have to spare. Your sferics (short for radio atmospherics) equipment may represent the only real-time weather you’ll ever see in your cockpit.

Sure, panel-mounted and portable weather systems deliver their product in a timely fashion, but it will never be as immediate as your sferics device. Once you understand how to interpret your real-time lightning guidance, it can become a valuable asset in your in-flight aviation toolkit. 

Choices in the Cockpit

You have two options if you want lightning data in the cockpit: You can choose from ground-based lightning sensors or onboard lightning detection from a sferics device such as a Stormscope.

A Stormscope provides real-time data but does require some basic interpretation. Ground-based lightning, on the other hand, is a bit delayed and is only available through a data link broadcast at this time. Ground-based lightning is normally coupled with other weather guidance, such as ground-based weather radar (NEXRAD), surface observations, pilot weather reports, and other forecasts.   

Ground-Based Lightning

The ground-based lightning that’s now available through the Flight Information System-Broadcast (FIS-B) comes from the National Lightning Detection Network (NLDN). This network of lightning detectors has a margin of error of 150 meters for locating a cloud-to-ground strike. The ground-based lightning sensors instantly detect the electromagnetic signals given off when lightning strikes the earth’s surface.    

With 150-meter accuracy, I’d choose ground-based lightning any day. Don’t get too excited, though. Ground-based lightning is expensive (the data is owned by private companies like Vaisala), and you’ll not likely see a high-resolution product in your cockpit anytime soon.

SiriusXM satellite weather pulls from a different lightning detection network and includes both cloud-to-ground and intracloud lightning. It produces a 0.5 nm horizontal resolution lightning product. This means that you will see a lightning bolt or other symbol arranged on your display in a 0.5 nm grid.

Even if 50 strikes were detected minutes apart near a grid point, only one symbol will be displayed for that grid point. Same is true for the FIS-B lightning.

Stormscope Advantages

A Stormscope must be viewed as a gross vectoring aid. You cannot expect to use it like onboard radar.

Nevertheless, it does alert you to thunderstorm activity and will provide you with the ability to see the truly ugly parts of a thunderstorm.  Where there’s lightning, you can also guarantee moderate or greater turbulence.   

No lightning detection equipment shows every strike, but the Stormscope will show most cloud-to-ground and intracloud strikes. This allows you to see the intensity and concentration of the strikes within a cell or line of cells with a refresh rate of two seconds. It also lets you see intracloud electrical activity that may be present in towering cumulus clouds even when no rain may be falling.

Even if no cloud-to-ground strikes are present, intracloud strikes may be present. The Stormscope can detect any strike that has some vertical component (most strikes do). This is important since there are typically more intracloud strikes than cloud-to-ground strikes.

To emphasize this point, most of the storms in the Central Plains have 10 times more intracloud strikes than cloud-to-ground strikes. Moreover, during the initial development of a thunderstorm, and in some severe storms, intracloud lightning may dominate the spectrum. 

Also keep in mind that a sferics device does not suffer from attenuation like onboard radar. That is, it can “see” the storm behind the storm to paint cells in the distance out to 200 nm, but it does not see precipitation or clouds.     

Stormscope Disadvantages

It doesn’t take a full-fledged storm, complete with lightning, to get your attention.

Intense precipitation alone is a good indicator of a strong updraft (or downdraft) and the potential for moderate to severe turbulence in the cloud. Consequently, the Stormscope does not tell you anything about the presence or intensity of precipitation or the absence of turbulence.

Never use the Stormscope as a tactical device to penetrate a line of thunderstorm cells. Visible gaps in the cells depicted on the Stormscope may fill in rapidly. Fly high and always stay visual and you will normally stay out of any serious turbulence.        

A Stormscope display is often difficult to interpret by a novice. Radial spread, splattering, buried cables, and seemingly random “clear air” strikes can create a challenge for the pilot. It may take a couple years of experience to be completely comfortable interpreting the Stormscope display. Often what you see out of your window will confirm what you see on your display.    

Radial Spread

As the name suggests, the biggest Stormscope error is the distance calculation along the radial from the aircraft.

The placement of the strike azimuthally is pretty accurate. However, how far to place the strike from the aircraft along the detected radial is a bit more complicated and prone to error.

Lightning strikes are not all made equally. When the sferics devices were invented back in the mid-1970s, they measured the distance of the cloud-to-ground strike based on the strength of the signal (amperage) generated by the strike. An average strike signature of 19,000 amperes is used to determine the approximate distance of the strike.

Statistically, 98 percent of the return strokes have a peak current between 7,000 and 28,000 amperes. That creates the potential for error in the distance calculation. This error is a useful approximation, however, in that strokes of stronger intensity appear closer and strokes of weaker intensity appear farther away. 

In strike mode on the Stormscope, strikes are displayed based on a specific strike signature, whereas cell mode on the newer Stormscope models uses a clustering algorithm that attempts to organize these strikes around a single location or cell.

Cell mode will even remove strikes that are not part of a mature cell. Most thunderstorm outbreaks are a result of a line of storms. Cell mode provides a more accurate representation to the extent of the line of thunderstorms.

Radial spread is not necessarily always a bad thing. You can use it to your advantage to distinguish between false or clear air strikes and a real thunderstorm. Most of the strikes of a real storm will be of the typical strike signature and be placed appropriately.

As mentioned above, stronger than average strikes will be painted closer to the airplane. Looking at this in strike mode, a line of these stronger strikes will protrude toward the aircraft.  The result is a stingray-looking appearance to the strikes.    

You can confirm this by clearing the display.  The same stingray pattern should reappear with the tail protruding once again toward the airplane.

Clear Frequently

Clearing the Stormscope display frequently is a must.  How quickly the display “snaps back” will provide you with an indication of the intensity of the storm or line of storms.

You should be sure to give these storms an extra-wide berth.  Clearing the Stormscope in “clear air” will also remove any false strikes that may be displayed allowing you to focus on real cells that may be building in the distance.

Aging

Both ground-based and onboard lightning use a specific symbol to indicate the age of the data.

For Stormscope data shown on the Garmin 430/530, a lightning symbol is displayed for the most recent strikes (first six seconds the symbol is bolded). The symbol changes to a large plus  sign after one minute followed by a small plus  sign for strikes that are at least two minutes old. Finally, it is removed from the display after the strike is three minutes old.

Cells with lots of recent strikes will often contain the most severe updrafts and may not have much of a ground-based radar signature. Cells with lots of older strikes signify steady-state rainfall reaching the surface that may include significant downdrafts. 

Flight Strategy

A nice feature of a Stormscope is that you can quickly assess the convective picture out to 200 nm while still safely on the ground. Same is true for lightning received from the SiriusXM datalink broadcast.

However, for those with lightning from FIS-B, you won’t receive a broadcast until you are well above traffic pattern altitude unless your departure airport has an ADS-B tower on the field.  

As soon as your Stormscope is turned on, within a few minutes you’ll get a pretty good picture of the challenging weather ahead. If you are flying IFR, you may want to negotiate your clearance or initial headings with ATC to steer clear of the areas you are painting on your display. I’ve canceled or delayed a few flights based strictly on the initial Stormscope picture while I was still on the ramp. 

Another goal is to fly as high as allowable. You will benefit from being able to get above the haze layer, and the higher altitude will allow you to see the larger buildups and towering cumulus from a greater distance.

If you are flying IFR and you are continually asking for more than 30 degrees of heading change to get around small cells or significant buildups, then you should call it quits. You are too close, or you are making decisions too late.

Visual or not, the goal is to keep the strikes (in cell mode) out of the 25-mile-range ring on your Stormscope. If one or two strikes pop into this area, don’t worry. Just keep most of the strikes outside of this 25-mile ring.      

Don’t discount the value of a sferics device.  Add one of the data link cockpit weather solutions as a compliment, and you will have a great set of tools to steer clear of convective weather all year long.

The post Is Sferics Equipment Still Needed in the Cockpit? appeared first on FLYING Magazine.

Significant turbulence events are not particularly uncommon – a Hawaiian Airlines flight made headlines last year, and a Southwest flight was forced to divert due to turbulence earlier this spring – but the Singapore Airlines flight brought the first turbulence-related fatality in years.

• READ MORE: Severe Turbulence Blamed in Death Aboard Singapore Airlines Flight

This flight begs the question of how pilots, dispatchers, air traffic controllers, and other stakeholders can predict turbulence and avoid it. Detecting turbulence can be difficult, and not all turbulence is predictable, but there are ways to identify where it could occur.

Convective Activity

The biggest indicator of turbulence is convective activity. When unstable air is allowed to rise – by a lifting force such as a front or a mountain range – its movement becomes what we call turbulence. Pilots can identify where convective action is occurring to pinpoint areas where they could experience turbulence.

The easiest way to identify areas of convective turbulence is to look at clouds. When clouds become vertically developed – when they extend high into the sky in puffs – it is likely that turbulence is present because air needs to be pushed upwards considerably to allow moisture to condense into towering clouds. The same is true with heavy, showery rain: such comes about when air is forced upwards enough to create rain. In heavy storms, the turbulence is compounded by downdrafts that force rain to the surface, passing through the updrafts that allow the storm to develop in the first place.

Mountain Waves

Another place where turbulence is common is over mountain ranges. Mountains provide a natural lifting mechanism for unstable air, allowing air to rise and move around more strongly. This extra movement is often most noticeable the closer you are to the mountains, which is why mountainous areas often have the bumpiest takeoffs and landings. These are commonly referred to as mountain waves.

Pilots have additional tools to help them predict turbulence. In the United States, the Aviation Weather Center – part of the National Oceanic and Atmospheric Administration (NOAA) – creates aviation-specific weather reports and forecasts to help crew identify weather patterns conducive to atmospheric instability.

• READ MORE: Treat High-Altitude Turbulence with Knowledge and Respect

Most important are inflight aviation weather advisories called AIRMETs, SIGMETs, and Convective SIGMETs. AIRMETs apply mostly to smaller aircraft; they pertain to activies such as areas of low clouds and visibility and moderate turbulence. SIGMETs and Convective SIGMETs apply to all aircraft regardless of size.

Convective SIGMETs are the most applicable for finding areas of extreme turbulence. They may be issued for things such as lines of severe thunderstorms called squall lines; tornadoes; embedded thunderstorms; surface winds greater than 50 knots; and more. These provide pilots with information on the areas most critical to avoid inflight.

New Tools Available

There are also third-party apps that help crews and even passengers, predict where the smoothest rides will be. They take weather and pilot reports to make assessments and predictions about where the smoothest rides will be, allowing for safer, more comfortable trips. They also use real-time data to cross-check the accuracy of their systems.

In addition, pilots are able to use a reporting system – called PIREPs – to warn others of their observations, including icing and turbulence. Crews use these reports and predictions to make decisions about which routes to take, which altitudes to fly, or even whether to fly at all.

• READ MORE: ForeFlight Introduces Reported Turbulence Map

Not every bit of turbulence is predictable, though. There is another type of turbulence called “clear air turbulence” that can seemingly appear out of nowhere and will not show up on radar. This type of turbulence tends to take pilots by surprise and does not provide any possibility of avoidance. This is a big reason why pilots and cabin crew tell passengers to fasten their seatbelts whenever seated, even if the seatbelt sign is off: if turbulence suddenly takes an aircraft by surprise, passengers reduce their own risk if they are already strapped in.

Severe and extreme turbulence events are still exceedingly rare in the context of how many commercial flights operate each day.

Editor’s Note: This article first appeared on AVweb.

The post How Pilots Predict Severe Turbulence appeared first on FLYING Magazine.

I have been using 1800WXBRIEF.com and Aviation Weather Center for years since they don’t require a paid subscription. But according to the CFIs at the school I just started flying with, these are not considered legal weather briefings. 

Answer: The question asked begs another one: Legal to whom? 

FAA regulations, notably FAR 91.103, require pilots to obtain weather reports and forecasts. However, according to an FAA spokesperson, “the FAA does not prefer one weather source over another, nor do we define a ‘legal weather briefing.’ It is up to the pilot in command (PIC) to use a weather source that best suits their needs and allows them to meet the preflight planning requirements.“

That being said, there are some CFIs and flight schools that advocate paid subscriptions, such as ForeFlight, and free discreet login services, such as 1800WXBRIEF, because in addition to providing information, they also allow the pilot to file a flight plan. They also require an account, which means it’s easier to prove the pilot obtained a weather briefing prior to the flight because there will be a record of the login.

The latter is often one of the first things the National Transportation Safety Board checks when it investigates an accident or incident.

At the very least, a pilot should check TAFs, METARs, winds aloft, and NOTAMs prior to a flight. It is distressing how many pilots and pilots in training believe that listening to the ATIS/ASOS/AWOS at the airport or along their route constitutes a weather briefing. They don’t. 

Nor does looking out the window at the FBO. Any more than “pretty good” is a PIREP. 

The post Is There an Official Weather Briefing? appeared first on FLYING Magazine.

Northrop Grumman, I needed something that would challenge my mind, body, and spirit. There were two options on the table. I had just graduated with my master’s degree and was seriously thinking of taking the next leap of faith and earning a doctorate.

But that was quickly overshadowed by my second option—my childhood dream of learning to fly. And I wasn’t disappointed. It did challenge my mind, body, and spirit every step of the way.

What intrigued me the most about learning to fly was that it required mastering many disciplines. In other words, it’s more than just jumping into an airplane and learning stick-and-rudder skills. You have to become entrenched in subjects such as aerodynamics, radio navigation, geography, radio communications, airspace, map reading, legal, medical, and my favorite discipline, meteorology.

Despite my background as a research meteorologist, my aviation weather background was limited when I was a student pilot. So, I was very excited to discover what more I might learn about weather in addition to all of these other disciplines. If you are a student pilot, here are some tips that will help you achieve a good foundation with respect to weather.

It Isn’t Easy

First and foremost, weather is inherently difficult. It’s likely the most difficult discipline to master because of the uncertainty and complexity it brings to the table. Therefore, strive to understand what basic weather reports and forecasts the FAA effectively requires that you examine before every flight. It certainly doesn’t hide it. It’s a fairly short and succinct list that’s all documented in the new Aviation Weather Handbook (FAA-H-8083-28) and the Aeronautical Information Manual (AIM). Ultimately, knowing the nuts and bolts of this official weather guidance will help with your knowledge and practical tests and give you a head start once the ink is dry on your private pilot certificate.

Second, as a student pilot, plan to get your weather guidance from a single and reliable source. Try not to bounce around using multiple sites or apps. There are literally hundreds, if not thousands, of websites and apps that will deliver weather guidance to your fingertips such that you can become overwhelmed with all of the choices, and entropy quickly takes over. Besides, flight instructors love to show off their unique collection of weather apps on their iPhone. Sticking with the official subset of weather guidance will allow you to focus on what matters the most.

• READ MORE: Aviation Weather Center Website Upgrade—the Good, Bad, and Ugly

Once you receive your private certificate, then you can expand the weather guidance you use to include other websites and apps.

The two internet sources that should be at the top of your list include the Aviation Weather Center (aviationweather.gov) and Leidos (1800wxbrief.com). Both of these sites provide the essential weather guidance needed to make a preflight weather decision. Using one or both of these sites will help focus you on the official weather guidance the FAA demands you use.

Categorize Your Data

Third, when you look at the latest weather guidance, take a minute and characterize each product. It should fall into one of three categories: observational data, advisories, or forecasts. Knowing its category will tell you how to properly utilize that guidance. For example, if you come across a visible satellite image, that’s an example of observational data.

Observational data is always valid in the past and typically comes from sensors. What about a ground-based radar mosaic (e.g., NEXRAD)? That’s also an observation. Pilot weather reports (PIREPs) and routine surface observations (METARs) are also considered observational data. While not a pure observation, the latest surface analysis chart that is valid in the recent past will identify the major players driving the current weather systems.

• READ MORE: What Is the Criteria for Issuing a Convective SIGMET?

Observations are like the foundation when building a house. All other weather guidance you use will build on that foundation. A sturdy and well-built foundation is the key to a good preflight weather briefing. You can’t know where the weather is going until you know where it has been. Identifying the latest trends in the weather through the use of these observations is the cornerstone of this foundation. When possible, looping the guidance over time will expose these trends. Is the weather moving or stagnant? Is it strengthening or weakening over time?

Advisories such as the initial graphical AIRMETs (G-AIRMETs) snapshot, SIGMETs, and center weather advisories (CWAs) are the front lines of aviation weather. They are designed to highlight the current location of the truly ugly weather. Advisories build the structure that sits atop of this foundation. Essentially, these advisories summarize the observational data by organizing it into distinct hazards and areas of adverse weather to be avoided.

Forecasts are the springboard for how these observations and advisories will evolve over time. You can think of forecasts as the elements that protect the finished house, such as paint, shingles, and waterproofing. This also includes the alarm and surveillance system to alert you to the possible adverse weather scenarios that may occur during your flight. While forecasts are imperfect, they are still incredibly useful. Forecasts include terminal aerodrome forecasts (TAFs), convective outlooks, prog charts, and the remaining four snapshots for G-AIRMETs.

Dive into the Details…

Fourth, details matter quite a bit. Look at the guidance and identify what stands out. Don’t make a decision too early. Instead, carefully observe and gather facts. Is the precipitation occurring along the route limiting the ceiling and/or visibility? Is the precipitation expected to be showery? This is a clear indication of a convective process in place.

Are the surface observations reporting two or three mid- or low-level cloud layers? Again, this is another indication of a convective environment. This can be especially important to identify, especially when there’s a risk of thunderstorms that have yet to form.

…But Fall Back on the Big Picture

Fifth, get a sense of the big weather picture. This is likely the most difficult aspect of learning how to truly read the weather. Think about the big weather picture as the blueprint for building an entire community. It’s what brings everything together. When I do my own preflight briefings, my decisions are largely driven by what’s happening at that synoptic level.

Lastly, read, read, and read some more. Focus mostly on the weather guidance and less on weather theory. These are the specific weather products mentioned earlier. Weather theory is something you can tackle at a later time. The FAA’s Aviation Weather Handbook is a great start. You can download a PDF document for free from the agency website and add this to your online library. This was issued in 2022 to consolidate the weather information from six FAA advisory circulars (ACs) into one source document. My book, Pilot Weather: From Solo to the Airlines, was published in 2018 and is written for pilots at all experience levels in their journey to learn more about weather.

If you fly enough, you will eventually find yourself in challenging weather. The goal of any preflight weather briefing is to limit your exposure to adverse conditions, and that takes resources and time. Once you’ve mastered the weather guidance, then giving Flight Service a call at 1-800-WXBRIEF will allow you to sound like a true professional.

Yes, I eventually did earn that doctorate, but I am really happy that I took the step over 25 years ago to learn to fly. One guarantee with weather: You can never learn enough. I am still learning today.

This column first appeared in the March 2024/Issue 946 of FLYING’s print edition.

The post How to Wrap Your Head Around Weather appeared first on FLYING Magazine.

Answer: During the warm season, convective weather has a huge impact on the National Airspace System (NAS). As the amount of usable airspace diminishes on any given day, this ultimately engenders delays in the system. A departure within busy airspace usually means a delay. In the worst-case scenario, ground stops may be levied depending on route of flight and destination airport. Nevertheless, forecasters at the Aviation Weather Center (AWC) are busy at work issuing advisories to warn pilots of these dangerous convective areas.  

A single-cell, pulse-type thunderstorm is normally easy to spot in the distance and maneuver around while in flight. In this situation, a deviation around such a cell does not eat into your fuel reserves. However, when thunderstorms become embedded, severe, or dense in coverage within an area or along a line, they are considered a significant en route hazard to aviation. This often requires you to plan a more circuitous route, which means carrying extra fuel than if you flew a direct route. It is in this case that an AWC forecaster will issue a convective SIGMET (WST) to “protect” this airspace. 

When you hear “convective SIGMET” during your preflight briefing, don’t think of it as a forecast for thunderstorms. Instead, think of it as a “NOWcast” of organized convection that may be highly challenging or dangerous to penetrate. These active thunderstorms must meet specific criteria before a convective SIGMET is issued. Areas of widely scattered thunderstorms, such as shown in the XM-delivered satellite radar image below, are generally easy to see and avoid while in flight and often do not meet convective SIGMET criteria.

Nevertheless, on any particular eight-hour shift a single forecaster at the AWC’s convective SIGMET desk looks at all of the convective activity occurring throughout the conterminous U.S. on a continual basis. On an active convective weather day, they are likely the busiest forecaster on the planet. This forecaster is given the responsibility to subjectively determine if an area or line of convection represents a significant hazard to aviation using these minimum criteria:

• A line of thunderstorms is at least 60 miles long with thunderstorms affecting at least 40 percent of its length.
• An area of active thunderstorms is affecting at least 3,000 square miles covering at least 40 percent of the area concerned and exhibiting a very strong radar reflectivity intensity or a significant satellite or lightning signature.
• Embedded or severe thunderstorm(s) are expected to occur for more than 30 minutes during the valid period regardless of the size of the area. 

For reference, 3,000 square miles represents about 60 percent of the size of the state of Connecticut.

Will an advisory be issued as soon as the convection meets one or more of these criteria? Possibly. A special convective SIGMET may be issued when any of the following criteria are occurring or, in the judgment of a forecaster, expected to occur for more than 30 minutes of the valid period:

• Tornadoes, hail greater than or equal to three-quarters of an inch in diameter, or wind gusts greater than or equal to 50 knots are reported.
• Indications of rapidly changing conditions, if in a forecaster’s judgment they are not sufficiently described in existing convective SIGMETs.

However, special issuances are not the norm, especially when there is a lot of convective activity to capture. In most cases, a convective SIGMET is not issued until the convection has persisted and met the aforementioned criteria for at least 30 minutes. Given that these advisories are routinely issued at 55 minutes past the hour, any convection that has not met the criteria by 25 minutes past the hour may not be included in the routine issuance. Consequently, there are times where a dangerous line or area of developing thunderstorms could be present without the protection of a convective SIGMET. All convective SIGMETs will have a valid time of no more than two hours from the time of issuance.

• READ MORE: Surviving Thunderstorms: Cut Your Risk

Last but not least, these convective SIGMETs are often coordinated by an AWC forecaster with meteorologists at the various Center Weather Service Units (CWSUs) located throughout the country at the various Air Route Traffic Control Centers (ARTCCs). At times, a meteorologist at the CWSUs may issue a Center Weather Advisory (CWA) when building cells are approaching convective SIGMET criteria. The goal is not to duplicate advisories when possible and provide the best guidance for pilots.

The post What Is the Criteria for Issuing a Convective SIGMET? appeared first on FLYING Magazine.

But wait, is vertical visibility even a legitimate visibility? Actually, it’s a bit of a misnomer and not a true measure of visibility in the traditional sense. Vertical visibility is a close cousin to ceiling. That is, it represents the distance in feet a person can see vertically from the surface of the Earth into an obscuring phenomenon, or what is called an indefinite ceiling. What isn’t obvious is how vertical visibility is determined, and how this is different from a definite ceiling.

It’s arguable that an indefinite ceiling is perhaps the most misunderstood phenomenon reported in a routine (METAR) or special surface (SPECI) observation. Forecasters will add vertical visibility in a terminal aerodrome forecast (TAF) as illustrated in the image below for Bradford Regional Airport (KBFD) in Pennsylvania. Whether this occurs in a METAR or TAF, vertical visibility is coded as “VV” followed by a three-digit height in hundreds of feet above the ground level. For example, you may see “VV002,” which is a vertical visibility of 200 feet. While a definite ceiling can be broken or overcast, a vertical visibility always implies the sky is completely covered. Let’s explore the difference between a definite and indefinite ceiling and the operational considerations.

Automated Observations

In the early days, human weather observers used to employ what were called “pilot balloons” to estimate the ceiling height. Essentially the balloon was launched by the observer and, given the balloon’s known rate of ascent, they watched the balloon enter the base of the clouds and measured the time it took using a stopwatch to determine the ceiling height. Then new technology emerged called a rotating beam ceilometer that measured the height of clouds. While it was more effective than launching a balloon, this method was phased out around 1990 and replaced with the laser beam ceilometer, the technology still widely used today.

The task of walking outside and assessing the height of clouds is generally a thing of the past given that this technology is incorporated into the automated surface observing system (ASOS) or automated weather observing system (AWOS) present at many airports throughout the U.S. The trained observer simply logs in to the ASOS (or AWOS) and makes their observation based on the data gathered and reported by the automated system. Then the observation is edited and augmented by the observer as necessary. Depending on the airport, this process may be completely automated.

In all honesty, making an estimate of the height of the cloud base isn’t the difficult part. What’s difficult is to provide a representative description of the amount of cloud coverage (e.g., few, scattered, broken, or overcast) in the airport’s terminal area. A laser beam that points straight up may easily miss a scattered or broken cloud deck. To alleviate this issue, the automated systems process the data over a given amount of time since clouds are generally moving through the sensor array area. It was found that a 30-minute time period provided a representative and responsive observation similar to that created by a trained observer. The most recent 10 minutes of sky cover and ceiling height are double weighted using a harmonic mean. (A harmonic mean is used in the visibility and sky cover algorithms rather than an arithmetic mean because it is more responsive to rapidly changing conditions such as decreasing visibility or increasing sky coverage/lower ceiling conditions.) In the end, the goal is to provide an observation representative of the airport’s terminal area, which is the area within 5 sm from the center of the airport’s runway complex. Visibility, wind, pressure, temperature, etc., all have their own harmonic means accordingly.

In our everyday experience, we know that many cloud decks observed from the ground have a very well-defined base. For an untrained observer, it might not be a simple task to determine their height. However, it’s easy to pick out where the base of the cloud starts. Even in these cases, the cloud decks may vary in height and multiple cloud layers may exist. Visually, that may be more difficult to discern for the untrained eye, but automated systems do a reasonable job making that observation. In a convective scenario, it is not unusual to see multiple scattered and broken cloud heights. For example, at the West Michigan Regional Airport (KBIV) the following was observed:

KBIV 122353Z AUTO 08011KT 4SM RA BR FEW011 SCT048 OVC065 19/18 A2972

This observation includes three definite cloud layers, which are a telltale sign that a convective environment is in place even before the first lightning strike.

Nuts and Bolts

An ASOS continuously scans the sky. To determine the height(s) of the clouds, the backscatter returns from the ceilometer are put into three different bins. When there’s a “cloud hit,” the system identifies a well-defined and sharp signature pattern that you’d expect with the sensor striking the cloud base. Essentially this means most of the hits are aggregated around a particular height above the ground. Such a sharp signature is then incorporated into the 30-minute sky cover and cloud height harmonic average, and a new observation is born.

On the other hand, a “no hit” is recorded when there isn’t an ample amount of backscatter received, usually because there are no clouds below 12,600 feet agl over the sensor. Note that the ASOS (and AWOS) is designed only to detect clouds below 12,600 feet above the ground, although a trained observer can and does report higher clouds. Lastly, if the backscatter does not provide that sharp signature around a particular height, an “unknown hit” is recorded. It is this unknown hit that leads us down the path to an indefinite ceiling or vertical visibility.

Haze, Mist, and Fog, Oh, My!

So, isn’t an indefinite ceiling the same thing as a ground fog event? Not necessarily. Stratus is the most common cloud associated with low ceilings and reduced visibility. Stratus clouds are composed of extremely small water droplets or ice crystals (during the cold season) suspended in the air and may be touching the surface, so to speak. An observer along a coastal region or on the side of a mountain would likely just call this plain old fog. This is certainly understandable, since we grew up calling this kind of situation foggy.

Fog, however, is thought to be more of an obstruction to visibility from a surface observing standpoint. To understand the recording of obscurations, here’s how the ASOS automatically determines what to report. Once each minute, the obscuration algorithm checks the reported visibility. When the visibility drops below 7 sm, the current dew point depression (temperature-dew point spread) is checked to distinguish between fog (FG), mist (BR), and haze (HZ). If the dew point depression is less than or equal to 4 degrees Fahrenheit (~2 degrees Celsius), then FG or BR will be reported. Visibility will then be used to further differentiate between FG and BR.

Whenever the visibility is below five-eighth sm, FG is reported regardless of the “cloud” that produces it. So fog isn’t really about a cloud or ceiling as much as it is about visibility. Therefore, stratus and fog frequently exist together. In many cases, there is no real line of distinction between the fog and stratus; rather, one gradually merges into the other. Flight visibility may approach zero when flying in stratus clouds. Stratus over land tends to be lowest during night and early morning, dissipating by late morning or early afternoon. Low stratus clouds often occur when moist air mixes with a colder air mass or in any situation where temperature-dewpoint spread is small.

• READ MORE: Decoding the Weather

Moisture-Rich Environment

Essentially, an indefinite ceiling means there is something obscuring your view of the cloud base. When you look up, you won’t be able to see a well-defined cloud base like you would on a day where the sky isn’t obscured. According to the ASOS User’s Guide, “these ‘unknown hits’ are primarily caused by precipitation and fog that mask the base of the clouds.” The laser beam bounces off moisture at various heights, making it impossible to process this as a definite cloud hit. Instead, the ASOS identifies these unknown hits as a vertical visibility abbreviated as “VV” in the resulting routine or special observation.

Given the broad moisture field near the surface that scatters the laser beam signal, indefinite ceilings are guaranteed to be paired with low visibility situations. You are not going to see a surface visibility of 10 miles paired with a VV of 200 feet. Usually this means a low or very low IFR flight category anytime there’s an indefinite ceiling. Also keep in mind that an indefinite ceiling in a terminal forecast will result in a low visibility forecast.

In general, the higher the vertical visibility, the better the surface visibility. Therefore, a vertical visibility of 200 feet (VV002) is usually met with a visibility of one-half sm. Furthermore, a vertical visibility of 700 feet (VV007) will likely be associated with a visibility between 1 and 2 sm. While rare, you may even see a fairly high vertical visibility over 1,000 feet (e.g., VV012). In this case, the surface visibility may be over 3 sm. The really bad stuff, however, occurs with a visibility of one quarter sm (or even “M1/4 SM” denoting less than that) and a vertical visibility of zero feet (VV000) as illustrated in the image below for Bradford Regional Airport. This very low indefinite ceiling is not all that common unless you are stationed on the summit of Mount Washington in New Hampshire, where this low vertical visibility happens quite often throughout the year. It also occurs fairly often at airports along West Coast regions of the U.S., especially during their “May gray” or “June gloom” time frame.

As mentioned earlier, fog and precipitation are the two primary reasons the base of the cloud deck is obscured. Therefore, it’s common to see vertical visibility reported when light rain, drizzle, or even snow is falling from the cloud base.

Precipitation or not, it’s generally rare to see a single station reporting an indefinite ceiling. Most of the time, you will see indefinite ceiling reports embedded in a widespread area of low or very low IFR conditions, especially at coastal airports. Although airports such as Nantucket Memorial Airport (KACK) in Massachusetts can be reporting a low indefinite ceiling, at stations farther inland near Cape Cod the sky can be clear or nearly so.

It’s important to note that conditions producing an indefinite ceiling often take longer to improve. Normally there will be a transition from an indefinite to definite ceiling once the moisture begins to mix out with the help of the sun. However, the visibility may still be quite low for the next few hours. Keep this in mind when flight planning to an airport reporting an indefinite ceiling.

Operational Significance

From a practical standpoint, you should treat an observation or forecast for a vertical visibility the same as you’d treat a definite ceiling. Given the nature of conditions that produce an indefinite ceiling, you can expect a longer transition as you depart into such a ceiling under IFR. It’s easy to get spatial disorientation because of the gradual change.

An indefinite ceiling restricts the pilot’s flight (air-to-ground) visibility. Therefore, an instrument approach may be a bit more challenging even after you drop below the reported ceiling height because of the reduced visibility. Most importantly, a circle-to-land approach with an indefinite ceiling will make it quite difficult to keep the runway in sight, especially at night. And, as a final consideration, with an indefinite ceiling, don’t be surprised to see runway visual range also pop up in the observation for airports with such equipment.

This feature first appeared in the October 2023/Issue 942 of FLYING’s print edition.

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On Monday, Santa Barbara Municipal Airport (KSBA) was closed due to flooding from as much as 10 inches of rain. According to the airport website, the facility will remain shut down until further notice—more specifically until the water recedes and authorities can check for and repair any damage.

The airport saw 35 flights were canceled on Monday.

According to multiple media sources, Santa Barbara County has been hammered by heavy rain, leading to landslides, downed power lines, and flooding in multiple areas, including the airport that sits at an elevation of just 13.5 feet above sea level. The facility is located in the city of Goleta and bordered by a wetland area known as the Goleta Slough. Local aviation sites note the airport closes frequently due to flooding caused by heavy rains. The entire area is under a flood warning, and there have been multiple evacuations.

FAA NOTAMs have been published to warn pilots that Runways 15R/33L and 15L/33R are closed, and the safety area of Runway 07/25 has standing water.

• READ MORE: California Airports Reeling from Heavy Rain

Early in its use, the airport, opened in 1914, had a seaplane base established by the Lockheed brothers. In 1942 the government took over the airport to create Marine Corps Air Station Santa Barbara, but it reverted to civilian use in 1946. Today it covers 948 acres with three runways and is served by several major airlines in addition to general aviation operations.

The post Santa Barbara Airport Closed Due to Flooding appeared first on FLYING Magazine.

Answer: There is an opinion in the aviation community that flying through snow is not only an icing hazard but also against FAA regulations for pilots in aircraft without a certified ice protection system. Keep in mind that each weather system is unique, and there are many exceptions to the general view presented here.

Let’s discuss some of the many factors associated with flying through snow.

Snow falling out of the base of a cloud means there are fairly deep, saturated conditions aloft. To produce snow typically requires that the cloud top temperature (CTT) be sufficiently cold. That usually means a CTT of minus-12 degrees Celsius or colder—the colder the air, the more likely the precipitation type is snow. In this situation, ice crystals can dominate any supercooled liquid water in the cloud and lead to the development of snowflakes in the cloud aloft. If you are flying through snow below the cloud base, does that imply icing conditions exist? Just to be clear, this is not a discussion of flying in the clouds producing the snow but below the cloud base. 

Snow is considered visible moisture. It can be mixed with other precipitation types that may include rain, freezing rain, or ice pellets. In general, snow falling from the base of a cloud doesn’t represent a significant airframe icing hazard unless it is mixed with other types of precipitation such as freezing rain. It can be an issue with induction icing but not airframe icing. In the unlikely case that snow does adhere to the airframe, an exit plan should be executed. 

• READ MORE: What Is Mixed Icing?

Outside of a mixed-precipitation scenario, snow is usually classified as wet or dry. Wet snow occurs when the static air temperature is at or above 0 degrees Celsius. That is, the snow falls into an atmosphere warmer than freezing and begins a melting process. Although liquid water doesn’t necessarily freeze at a temperature below 0 degrees Celsius, snow must begin to melt at a temperature warmer than that. If the temperature is warm enough, it will completely melt the snowflake into a raindrop before reaching the surface. You may have experienced this while driving in your car. You’ll see the wet snowflake splat on your windshield and quickly melt. Wet snow can begin to accumulate on grassy surfaces or other vegetation but usually melts quickly on other surfaces.

Moreover, because you are flying at an airspeed where kinetic heating occurs on the leading edge, even at a static air temperature of 0 degrees Celsius, snow will typically not accrete on the leading edges of the wings and horizontal stabilizer as a result of this kinetic heating driven by adiabatic compression. This is typically referred to as ram air rise. And certainly, with a static air temperature above 0 degrees Celsius, ice is very unlikely to accrete with the additional ram air temperature rise. In fact, even at a static air temperature of minus-1 or minus-2 degrees Celsius, accreting ice is difficult at best. Once the static air temperature gets colder than minus-3 C, then you are no longer dealing with wet snow since no melting is occurring.   

Certainly, wet snow can be problematic while taxiing. Or, if you pull your airplane out of a warm hangar, even dry snow will melt and begin to collect on some surfaces and may accumulate over time. It is recommended that you never depart with any of the aircraft surfaces contaminated, including wings and the horizontal stabilizer. Doing so may cause the aircraft not to develop the lift necessary to take off and climb, creating a risk of impact with terrain. 

Another metric to use is the Current Icing Product (CIP) found on the Aviation Weather Center website. CIP utilizes a recent three-hour forecast from the Rapid Refresh (RAP) model for parameters such as temperature, moisture aloft, supercooled liquid water content, and other useful model data. This is mainly to “seed” the forecast for these items, given that observational data is rather sparse throughout the atmosphere for these important parameters. Nevertheless, it combines this with surface observations, ground-based radar, pilot weather reports, satellite imagery, and lightning to produce an hourly analysis of icing probability, icing severity, and supercooled large-drop icing potential from the surface through 30,000 feet.  

CIP looks for information about the presence or absence of six precipitation types—freezing rain (FZRA), freezing drizzle (FZDZ), ice pellets (PL), rain (RA), drizzle (DZ), and snow (SN). A report of any of the first five means that altitudes below cloud base need to be considered for possible icing and SLD, because subfreezing liquid precipitation may be present. However, in an observation in which only snow is reported at the surface, ice crystals are clearly present beneath and within the lowest cloud layer, and those are not considered an icing threat, especially below the lowest cloud base. 

For example, if an airport is reporting an overcast sky at 2,500 feet and only snow is being reported, the CIP algorithm will remove any possible occurrence of icing from the cloud base down to the surface, regardless of what other sources may say. This is because snow not mixed with other precipitation types, such as freezing rain, is not seen as an icing hazard…even wet snow.  

Is it legal to fly through snow in an aircraft without a certified ice protection system? First you may want to read this letter from the FAA’s Office of the Chief Counsel. An excerpt  states: 

The formation of structural icing requires two elements: 1) the presence of visible moisture, and 2) an aircraft surface temperature at or below zero degrees Celsius. The FAA does not necessarily consider the mere presence of clouds (which may only contain ice crystals) or other forms of visible moisture at temperatures at or below freezing to be conducive to the formation of known ice or to constitute known icing conditions. There are many variables that influence whether ice will actually be detected or observed, or will form on and adhere to an aircraft. The size of the water droplets, shape of the airfoil, and the speed of the aircraft, among other factors, can make a critical difference in the initiation and growth of structural ice.

Yes, snow is definitely visible moisture, but will it adhere to the airframe? Dry snow is not going to adhere to the airframe while in flight. Wet snow, as mentioned above, is more of an induction icing or ground icing concern than airframe icing while in flight. 

Sometimes it’s not about airframe or induction icing. Flying through falling snow can also be very disorienting at times, especially when the snowfall is moderate or greater, or you are flying at night. It will often lower flight visibility to 3 sm or less and can make runways extremely slick. Landing while it is snowing on a snow-covered runway can lead to a flare at an altitude higher than normal, making for a hard landing.      

One last point. Often when snow falls into a fairly deep, dry layer below the cloud base, it can sublimate on its way down. This usually occurs with the onset of precipitation as a weather system approaches. Evaporation and sublimation are both cooling processes, and they will lower the temperature of the dryer air. An atmosphere that is a few degrees above freezing can lead to melting wet snow, and this process can quickly move the temperatures to below freezing, allowing for snow to reach the surface instead of melting.

The post Is Flying Through Snow an Icing Hazard? appeared first on FLYING Magazine.

“You’ve been watching, and you still want to go?” the briefer asked.

“Baby needs a wash,” joked the pilot, 66, a recently retired judge who was known for his “well-honed” sense of humor.

“Oh, he’s going to get a wash job,” the briefer said. “We do have a lot of rain and convective activity. It’s becoming pretty solid. I can’t see you doing much dodging trying to get around.”

“It looks like it subsides as it goes east,” the pilot suggested, and then added, “Question mark.”

“Well, yeah, question mark,” said the briefer. “If you take a line drawn directly north, it’s heavy precipitation until you get over to about Bowling Green (Kentucky), and that’s when the thunderstorms start again. But all this is moving northeast about 34 knots, so you head east as it is heading east, and then you get blocked off, and it’s building behind so…you have to go today?”

“Well, maybe not.”

“We will have some rain tomorrow, but at least it will break up enough and begin to move to where, you know, that Arkansas and Missouri area won’t be getting so smashed.”

“I might just go up and take a look at it and see what it looks like out of the windshield,” the pilot mused. “I don’t have anything better to do today.”

“Well,” said the briefer, “think of a good reason to go.”

He issued the required “VFR not recommended” warning—under the circumstances it was hardly necessary—and the pilot filed an IFR flight plan, estimating 2 hours and 15 minutes for the 520 nm trip.

His airplane was a Lancair Legacy, a small, very fast two-seat retractable homebuilt with a 310 hp engine. After climbing VFR to 6,000 feet, the pilot contacted Memphis Approach at 9:50 a.m. The controller asked whether he wanted to continue on his present heading of 356 degrees or deviate eastbound to try to go around the weather. The pilot said he would like to avoid the weather, and the controller gave him a vector of 060. The pilot, however, asked to continue on his present heading for a couple of minutes, and the controller agreed.

A minute later, the pilot came back. “The route ahead, as far as I can see, looks VMC. I can’t be sure on that, but I’d appreciate your input.”

“All right,” the controller replied, “stay on course and let me know if that weather starts to become a problem for you.”

Four minutes later, the controller said, “You are just going to run into about a 10-mile-wide band of showers that’s crossing in front of you. The quickest way through the weather, if you want a direct 90-degree cut, is about a 330 heading. There’s a lot of rain for about 10 miles, and then it should clear up on the other side.”

“All right, thanks,” replied the pilot. “We’ll go to 330, and we’ll slow down a little bit.” Two minutes passed.

“Looks like you are getting an updraft there,” the controller said. “I don’t have any targets around your altitude. Do what you can to hold it, but just take care of yourself through that weather. You’ve got another 10 miles before you’re going to clear it up a little bit.”

“Thank you, sir,” the pilot said.

Twenty seconds later, the controller asked the pilot whether he was OK. There was no reply. The controller’s transmissions became increasingly urgent.

“You’re going through a heavy area of weather, sir. If you can hear me, you, climb, altitude whatever, deviate, reverse course is also approved, sir…Radar contact is lost 30 miles northeast of Memphis, sir…You’ve got another 15 or 20 miles in that weather. If you can hear, sir, suggest a heading northwest bound to get through the weather. You’re in a level 4 and level 5 cell in that area, sir.”

The controller was not long in guessing what had happened. “I think he might have crashed,” he told a colleague.

Three hours later, searchers in a helicopter spotted fragments in a rain-soaked field. The recovery team found the engine and propeller buried almost 9 feet below the surface.

About an hour before the flight took off—but after the pilot’s conversation with the weather briefer—the National Weather Service had issued a SIGMET for the area through which the flight would pass. It warned of severe thunderstorms with tops to 38,000 feet, possible 50-knot gusts and 1-inch hail. The pilot most likely never saw the SIGMET. A retrospective analysis of Doppler weather radar recordings confirmed that at the time of the crash the pilot was just crossing the leading edge of a level 5 storm.

The National Transportation Safety Board limited its finding of “probable cause” to the trivial insight that the pilot had lost control of the airplane. A factor in the accident, it added, was “insufficient information” provided by the controller, who did not convey the storm’s intensity level to the pilot until he was already in it. Exactly how and why the loss of control occurred was not discussed. The wreckage was too badly fragmented for forensic analysis, and significant portions of it were not recovered at all. It did not appear that the airplane had broken up in flight, however. The wreckage was confined to a small area among plowed fields where more widely scattered debris would have been easy to find.

• READ MORE: The Road Not Taken

This accident occurred in 2004. In the intervening years, the NTSB has moved away from mechanistic analyses such as “loss of control” and toward more judgment-oriented ones signaled by the phrase, “the pilot’s decision to…” Today, I think, the finding of probable cause would put more emphasis on decision-making on the parts of both the pilot and controller, although the board’s investigations seldom satisfactorily dissect the nuances of decisions made by two people unconsciously influencing one another. The pilot’s assertion that it looked like VMC ahead probably affected the controller’s interpretation of his own weather display. The controller’s mention of 10 miles of “showers”—two and a half minutes in the Legacy—probably alleviated the pilot’s concern about the storm.

At the risk of venturing into groundless speculation, I am inclined to note that, as a judge, the pilot was accustomed to being the final arbiter of complex questions. As the builder-pilot of a beautiful—the word he used when filling in the “color” field in his flight plan—high performance airplane, he also probably experienced a little of the feeling of untouchable power that comes with fast airplanes and fast cars. The weather briefer hinted, warned, cajoled—but his objections were overruled.

This review first appeared in the July 2023/Issue 939 print edition of FLYING.

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