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September 2023 EZNews

Updated: Oct 21, 2023

Hello and thanks for reading the 29th edition of EZNews!

We really appreciate those that have recently joined, renewed their annual membership or signed up for auto-renewal. A big thanks goes out to Clayton W. who renewed for $75, Stu P. who renewed for $85, Alan Z., Douglas S., and Glenn B., who renewed for $100, and William P. who renewed his annual membership for $120! We truly appreciate your generosity which helps support our continued innovation and growth moving forward.

For members new to EZWxBrief, you won't find EZWxBrief in the App Store or Google Play Store. For the best user experience, EZWxBrief is optimized to run as a progressive web app (PWA) and must be installed on your device which takes less than 10 seconds per device. Follow the link above or see the 140+ page Pilots Guide for more information on how to install EZWxBrief as a PWA on all of your devices. Also check out our playlist on YouTube for some helpful videos on how to use the various features found in EZWxBrief.

"Who's who in Aviation & Weather" YouTube series continues...

We had a great time chatting with Dave Hubner of SiriusXM in our latest "Who's Who in Aviation & Weather" series that recently aired. You can view this 30 minute interview with Dave who is the Senior Director, Aviation Services at SiriusXM Aviation.

This new program will bring you the latest news and insights from the top minds in the aviation and weather industries. With a focus on weather, each month we'll feature interviews with leading experts on topics such as air traffic control, flight safety, forecasting, flight instruction and more. We'll also explore the latest trends and developments in these fields, and provide you with the information you need to stay ahead of the learning curve. So join us every four to six weeks as we explore the latest news and trends in these two fascinating industries.

Stay tuned for our next live program on Friday, September 15th at 1 pm EDT. We are very excited to be talking with Ben Bernstein of Leading Edge Atmospherics. He's one of the leading icing experts in the U.S. if not the world. We'll be chatting with Ben about his career as a meteorologist and his contribution to icing research throughout the last 30+ years.

On the schedule for the remainder of this year, we will be interviewing some other industry experts to include Dan Adriaansen of NCAR in October, Gary Reeves of in November, John Zimmerman of Sportys in early December, and Max Trescott of Aviation News Talk, Mark Robidoux of and Julie Boatman of FLYING magazine early next year.

> How to watch <

The program will be hosted live on EZWxBrief's YouTube channel. If you cannot attend live, the episodes are recorded and will become available on the same channel shortly after the live broadcast ends. You can also find them in the Who's Who in Aviation & Weather playlist. The exact date and time for future episodes will be announced through this blog and will appear on the EZWxBrief YouTube community page.

The Daily EZ Weather Brief has transitioned to three days a week

The Daily EZ Weather Brief will be broadcast Monday, Wednesday and Friday only until further notice. This change is primarily a result of the reduced number of views for each recorded video and also due to the reduction in subscribers over the last six months. The broadcast on Monday will continue to feature a route-based planning scenario such as the one presented here.

If you watch these regularly and want to see these continue into the next year without any cost, please take a few minutes today to send an email to pilots that you know and post a link to the YouTube channel on your social media accounts or aviation forums. There are tens of thousands of pilots out there that would greatly benefit from the content presented in these videos.

Here's what other are saying about The Daily EZ Weather Brief...

"Thank you Scott for investing your time in these wonderful daily weather briefs. I am learning a tremendous amount of information - these briefings bring many of the topics you discuss in 'Pilot Weather' and apply to your EZWxBrief app to the real world. Please, please keep doing these presentations. I love them."

- James W.

"I appreciate the direction you're taking with your format. I'm glad it's not just focused on the forecast but also includes a higher level of discussion on the tools. I still enjoy the content that involves experienced pilots with varying levels of aircraft capabilities discussing practical applications. It's important to note that a forecast that may not be suitable for a single normally aspirated aircraft could be okay for a turbo twin. However, turbulence and icing are among other factors to consider. A turboprop has additional options and considerations for a comfortable flight, and jet aircraft have even more."

- Trae W.

"This new series is great. It is helping me to understand the nuances of the various charts and their utility in real life. Keep up the great work."

- YouTube commenter

The update to the Aviation Weather Center website has been delayed

The Aviation Weather Center (AWC) website at was set to be updated on September 12, 2023. However, the switchover to the new website has been put on hold. Right now, the web group is on the outside looking in on the approval process. So, there is no clear definition of when this will be released and the old site will disappear. Currently you can visit for the new look and feel.

One of the ancillary goals of the new website was to eliminate the static imagery. The NWS seemed to think using the Graphical Forecast for Aviation (GFA) would remove the need for those images. They want to free up CPU cycles now used to generate thousands of static images. Instead of removing all of them, they decided to keep those static images from products AWC produces such as SigWx, SIGMETs, Prog Charts, Icing and Turbulence and remove the rest. Eventually the plan is to remove them all.

What does this mean for EZWxBrief? Well, given that some of the static imagery is scraped from the AWC website, this means we (and any other heavyweight app that also scrapes the same imagery) will likely lose the ability to repost those images to the app since they will no longer exist. Some of the same information us displayed on the map, and therefore, static imagery for these will become unnecessary (e.g., G-AIRMETs). In other cases, we need to determine if there are any replacements for this imagery or if EZWxBrief can build it's own images from other data sources like we did with the LAMP static imagery that was unreliable.

The bottom line is that on the immediate chopping block is the static satellite imagery, NAM/RAP temperature and wind imagery, PIREP imagery and the TFM Convective Forecast and extended TFM (both under CCFP), and Extended Convective Forecast Guidance will no longer be available. Again, this is just under the static imagery and does not affect other data shown on the map. For now, the EZWxBrief static imagery will remain, but you may notice in the next few months ahead that some of this imagery will likely be eliminated.

The tropics are heating up

If you live and fly anywhere along the eastern seaboard from the Mid-Atlantic down through Florida and along the Gulf Coastal regions of the U.S. and Mexico, you should be prepared for an active hurricane season this year from NOAA's updated forecast here. Visit to stay informed of any impacts that these storms may have in these areas.

The peak of hurricane season is September 10th and we've already had eleven named storms as of September 1st. Based on the NOAA forecast, we will see a high probability that the number of named storms will be above normal. This is, in part, due to the extremely warm sea surface temperatures this season in the Atlantic and Gulf of Mexico. Warmer waters lead to more condensation and release of latent heat which is the fuel for these tropical systems.

Negative icing at -3°C in visible moisture?

As convective SIGMETs begin to morph into G-AIRMETs for airframe ice over the next several months, it's quite common to hear pilots unsure about what temperatures are prevalent to begin worrying about airframe ice. So, is it possible to be flying in visible moisture at a temperature of -3°C and not accrete ice? That's a complex question because there are many, many factors that contribute to whether or not ice will/can accrete on the airframe.

Before answering this question, we need to first define what constitutes an icing environment. At the most primitive level, an airframe icing environment (not induction ice) is one that consists of three environmental or meteorological factors. These primary factors include total air temperature, liquid water content and drop size.

Airframe icing can only occur when supercooled liquid water exists at the altitude you are flying. If no supercooled liquid water is present, then airframe icing is extremely unlikely (with a very few rare exceptions). Although it is reasonable to expect that as the static air temperature drops even a sliver below 0°C, that any liquid water will freeze into an ice crystal. After all, consider a puddle of water outside on your driveway on a cold winter morning. Even at a warm -1°C, there's usually a thin layer of ice that forms on top of the puddle. So why doesn't that happen in the atmosphere? In other words, we should expect a cloud drop to freeze just as the temperature drops below freezing.

For a cloud drop to freeze into an ice crystal, the static air temperature must first be colder than 0°C. However, water in the atmosphere (e.g., a cloud droplet) is happy to exist in the liquid state even to a temperature as cold as -40°C. (By the way, it is very common to use Celsius when discussing airframe icing.) When liquid water exists at a temperature below 0°C, this is referred to as supercooled liquid water and that's what creates an icing hazard. There's a whole lot of "sausage theory" behind the discussion to follow, but for water to freeze at a temperature below 0°C, it prefers something to freeze on...that's called a nucleus.

The fancy term used by scientists for this freezing process is heterogeneous nucleation. That is, a drop of water will immediately freeze on this nucleus. The catch is that these submicron-sized nuclei are fairly rare in the atmosphere aloft because they must have a similar molecular structure to an ice crystal to serve as an ice nucleus. So not just any tiny particulate floating around will do the trick.

Many different types of atmospheric particulate matter can act as ice nuclei, both natural and anthropogenic. Natural ice nuclei include fine particles of clay such as kaolinite stirred up from the soil by the wind. Certain bacteria and amino acids such from plants also can nucleate ice. Byproducts of combustion from forest fires contain many ice nuclei. Same is true of volcanic ash. Also, ice crystals from a higher cloud can fall into one that is lower, triggering ice crystal formation in that lower cloud...also referred to as "seeding" the cloud.

It turns out that ice crystals make the best ice nuclei. Therefore, once ice crystals begin to form in a cloud, it will begin transitioning the cloud from all liquid to a mixed-phased cloud containing both ice crystals and supercooled liquid water. Keep in mind that ice nuclei are more likely to activate as the temperature trends to below -12°C where activation becomes the most efficient.

What about at a temperature of -40°C or colder? At those temperatures, it's all about kinetic energy. Even the most pristine drop will freeze due do to homogeneous nucleation. In this case, ice crystals form by chance when clusters of water molecules in a cloud drop happen to come together with the correct orientations to create an ice embryo which now becomes the nucleus (instead of the ice nuclei). In other words, the molecules of water in the drop lose much of their kinetic energy to cause them to slow down their motion so they begin to line up in a crystal-like pattern to produce a frozen embryo. This is not a common scenario in the atmosphere...supercooled liquid water rarely survives to a temperature colder than -35°C. This usually occurs in deep, convective clouds.

Remember that puddle of water mentioned earlier? This is referred to as "bulk water." And in and around the puddle there's often plenty of ice nuclei or other structures to start the freezing process. However, in the atmosphere, you need to think of every cloud drop as a separate puddle of water that must go through a nucleation process to freeze. Given the limited amount of ice nuclei in the atmosphere, the more likely supercooled liquid water will exist. Moreover, many of the ice nuclei originate from the surface of the earth. Therefore, snow cover, temperature inversions and other elements that limit the ability for these particulates to get to a height where supercooled liquid water exists will also determine how much supercooled liquid water can survive in a cloud. In other words, "cleaner" clouds will produce supercooled liquid water down to colder temperatures.

So far this has described the environment that will produce supercooled liquid water and create an icing hazard. Let's circle back to the original question, that is, if the temperature aloft is reported to be -3°C, is it possible that supercooled liquid water may not exist or that ice will not accrete on the airframe? Yes! The first thing to ascertain, however, is the source of this temperature. Is it the static air temperature, outside air temperature, total air temperature or possibly an upper-air temperature from a forecast?

In general, immersion thermometers that measure the outside air temperature are notoriously inaccurate when the probe has accreted ice or is wet. As the sensor gets wet, evaporative cooling begins to occur and this can cause the probe to record a temperature that is several degrees colder than is actually occurring in the atmosphere. So, it is possible at these warmer subfreezing temperatures from -3°C to 0°C, the static air temperature (the undisturbed air around the aircraft) could be near or slightly warmer than 0°C. Essentially, the probe is lying to you.

One other explanation depends on the other two meteorological factors, namely, liquid water content and drop size. Smaller supercooled cloud droplets will often flow over the boundary layer of the wing's surface without striking the surface of the aircraft. Although these droplets are not moving let's pretend for a minute that the aircraft is stationary and the droplets are moving toward it at the speed of the aircraft.

The larger the size of the cloud drop, the more momentum it has and the greater chance it has to impinge on the aircraft surface. In fact, very large supercooled drops will penetrate the boundary layer well behind the leading edge of the wing. At warmer subfreezing temperatures, this can create runback ice that does not freeze on contact. Instead, it freezes behind the protected surfaces of some ice protection systems (e.g., boots).

Smaller cloud droplets, on the other hand, have very little momentum and tend to only strike the immediate leading edge of the wing creating light or trace rime ice. For extremely small cloud droplets, they may literally flow around the aircraft surface and not impact the the surface at all. Even with a static air temperature of -3°C, a small drop icing environment may not create any noticeable accretion on any aircraft surfaces. Moreover, smaller droplets can remain in the liquid phase at much colder temperatures than larger drops.

Liquid water content or drop concentration is another factor that may allow for negative icing at -3°C. Some clouds have a greater concentration of drops than others. That is, there is more supercooled liquid water packed into the same cubic space. The more liquid water content, the more drops there are to have the opportunity to accrete on the aircraft surface regardless of the size of the cloud drops.

Lastly, if the drop size is small and liquid water content low, the immediate leading edge of the wing will be warmer than the rest of the aircraft surfaces due to kinetic heating. This is primarily dominated by what is called adiabatic compression. As the air mounds up against the immediate leading edge of the wing as it moves through the air, that air gets compressed adiabatically. This causes the air a millimeter or two above the wing's leading edge surface to heat up. It may cause that air to be several degrees warmer than the static air temperature depending on the aircraft's true airspeed as shown in the table above.

As you can see, the factors are plenty. There are definitely scenarios where airframe ice is unlikely at a temperature of -3°C or even colder. In the end, even a small amount of ice accretion will begin to affect the flying characteristics of the airplane. Aircraft such as helicopters are extremely sensitive to any amount of ice. Keeping the airframe clean of ice is paramount no matter what type of aircraft you are flying. At speeds below 250 knots, most aircraft will begin to accrete some ice once the temperature drops to below -6°C when exposed to supercooled liquid water with larger drop sizes and higher liquid water content.

Most pilots are weatherwise, but some are otherwise™

Dr. Scott Dennstaedt

Weather Systems Engineer

Founder, EZWxBrief™

CFI & former NWS meteorologist

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