Hello and thank you for taking the time to read the 42nd issue of EZNews!
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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 instructions in this video or visit the 180+ page Pilots Guide for more information on how to install EZWxBrief as a PWA on all of your devices.
Coming soon...
Mark your calendars, based on many requests by attendees of the previous two classes, we are looking to offer another live class early next year. The 10-week class will be held on Monday evenings at 8 pm EST beginning January 13, 2025. This will follow on the heels of the Weather Essentials for Pilots and Skew-T Weather Essentials classes held earlier this year and focus primarily on preflight route planning using live weather guidance from the EZWxBrief progressive web app. The goal of this class is to integrate and apply all of the training found in both of these previous classes. While it is not necessary to have attended these other two classes, it will be highly beneficial to at least have attended the Weather Essentials for Pilots class which can be purchased here. If you are interested in attending this new class, please contact us and we'll be sure you are on the reminder list when we make the official registration announcement at the end of September or early October.
NEW! Weather Essentials for Pilots: The Skew-T Edition eBook now on sale!
We have exciting news! There's a new eBook available for purchase that takes the best selling book, The Skew-T log (p) and Me: A Primer for Pilots, to a whole new level. Debuted this year at AirVenture, Weather Essentials for Pilots: The Skew-T Edition has taken the reigns from the Skew-T with Updates limited series that was offered for nearly two years and adds 150 more pages to the original Skew-T log (p) and Me eBook. This new eBook now incorporates material beyond the Skew-T diagram to include important weather topics such as air masses, low pressure areas and fronts, cloud classifications, terminal aerodrome forecasts and much more. It's now shaping up to be a basic weather book with the Skew-T diagram as the centerpiece. Given its 472 page length, we've opted to only provide this in PDF form as an eBook.
If you previously purchased the Skew-T with Updates eBook option, you already have this new eBook in your hands. An email was sent out in July with the latest update. In fact, you will continue to receive free updates to this new eBook for the next few years as it continues to evolve. For those that purchase this new eBook today, you will be notified of updates and will be able to purchase the next edition for a small fee. Before Scott retires he's hoping to document in this eBook all that he's learned about aviation weather over the last 30+ years for the benefit of general aviation pilots flying today and to those learning to fly in future generations. Your support of this effort is greatly appreciated.
Check out these two new videos on the EZWxBrief YouTube channel (@ezwxbrief)
Preflight planning in EZWxBrief - This discusses the remnants of Hurricane Debby as it moved up through the Mid-Atlantic and Northeast. It's important to understand the difference between most convective outbreaks and those that are part of a dissipating tropical system.
Preflight planning in EZWxBrief - This video discusses how to use forecast guidance in EZWxBrief to plan a flight early the next morning from Salisbury, Maryland to Monroe, North Carolina.
"Who's who in Aviation & Weather" YouTube series continues...
We are looking forward to bringing 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 industry 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.
This past month we really enjoyed talking with John Covino who is a pilot and retired air traffic control supervisor at the Boston Logan Airport. We talked to John about how complex weather can make an air traffic controller's job even more difficult, especially in a busy airspace. You can watch this new episode here.
Stay tuned for our next live program on Tuesday, October 8th at 2 pm EDT as we'll be speaking with one of our good friends, Robert O. Buck. He's a retired airline pilot and also one of the authors of the legendary book, Weather Flying, Fifth Edition. We also look forward to chatting with Matt Johnson in November. Matt is an EMS helicopter pilot and DPE located in Ohio. We'll talk with him about the unique aspects of flying a helicopter in adverse weather. Then in December, plan on tuning in as we speak with Tammy Barlette who is a motivational speaker and expert in mental performance training in aviation. Now retired from the military, Lt Col Barlette has flown the T-37 Tweet, the A-10 Warthog, the MQ-1 Predator and the MQ-9 Reaper.
> 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.
Termination of the TAF for Troy Municipal Airport
Over the past several years, airport statistics show that aircraft operations per day at the Troy Municipal Airport (KTOI) in Troy, Alabama are mainly from nearby Fort Novosel. Consequently, the termination date for the KTOI TAF is October 1, 2024 at 1800Z.
Are weather observations instantaneous?
Whether in the form of a METAR or by the ground-to-air radio broadcasts, every pilot uses surface observations to make many routine operational decisions during any particular flight. As we listen to the broadcast prior to taxi, it provides us with an altimeter setting and will likely determine the runway we use for departure. When approaching an airport under instrument flight rules (IFR), it will help us determine if we’ll be flying a visual approach or need to execute a standard instrument approach procedure. And when Mother Nature is at her worst, it will let us know when we should skip the airport altogether and fly to our alternate destination.
Surface observations are one of those data points that we often take for granted. The truth is that they play a monumental role in many of our most routine decisions even as we are taxiing to depart. They are not just used by pilots, however; surface observations also provide air traffic controllers, dispatchers and weather forecasters with a reasonable depiction of the weather conditions at an airport. Even with something as ubiquitous as a surface observation, there are some nuances you should understand.
Pilots at all experience levels should be familiar with the two primary automated observing systems deployed at many airports throughout the United States. This includes the Automated Surface Observing System (ASOS) and the Automated Weather Observation System (AWOS). Both of these automated systems consist of a collection of electronic sensors that measure the environment, and then process the data to create an observation once every minute.
It all about sampling the atmosphere
While many high-impact airports throughout the U.S. still rely on a trained weather observer to construct the routine or special observation (SPECI), automated systems supply them with uniform and objective data for the observation. However, automated systems measure only the weather that passes directly through the sensor array so it is not able to report what’s happening outside the airport’s runway complex or what is referred to as the airport’s vicinity. Weather observers can certainly augment the observation to add these details.
At airports without a trained observer, pilots must completely rely on the “raw” automated observation. This observation, however, isn’t as raw as you might think. In order to provide a representative observation, the automated hardware must continuously collect the sensor’s real-time data over a period of time. The automated system applies an algorithm to the collected data to extrapolate the weather to cover a wider area referred to as the terminal area.
When the weather is sampled over a specified period it will tend to “smooth out” the conditions but also will account for the normal meteorological variations that we see in the weather. Each of the various weather elements shown in the table below identifies the required sample times for its algorithms and provides a summary of where the data are considered valid.
For example, 30 minutes of data provides a fairly reasonable description of sky conditions. This means that the system will detect and process all the clouds (if any) passing over the sensor in the past 30 minutes. To account for the latest sky conditions, the result is biased by double weighting (counting twice) the last 10 minutes of data. Using the last 30 minutes of data in this way will allow the system to determine the cloud base height and sky coverage included in the surface observation and becomes a reasonable estimate of the sky conditions over a three to five statute mile radius around the location of the sensor (usually sited on the field).
Beware of rapidly changing weather
Even though an ASOS creates a completely new observation every minute, automated systems must have adequate sensor samples to develop an accurate observation. Therefore, in rapidly changing conditions, pilots should expect that most of the weather elements from the automated observations to trend slightly behind the actual weather. For example, if skies are clear and a sudden broken sky appears on the sensors, ASOS will take only two minutes to report a scattered deck of clouds even though a trained observer may report a broken sky cover. It’ll take nearly 10 minutes before the observation system will catch up and indicate a broken cloud layer.
This may or may not trigger a SPECI (special observation) for an ASOS (most AWOSs cannot report a special observation). It depends on the height of the broken layer. In other words, a sudden broken ceiling at 600 feet has a significant operational impact and will generate a SPECI since the flight category changed from VFR to IFR. But it will take nearly 10 minutes before the SPECI is issued given the discussion above.
Each minute an ASOS processes the most recent 10 minutes of visibility sensor data to obtain a representative value. Therefore, when visibility drops suddenly (in one minute) from 7 statute miles to 1 statute mile, the ASOS needs about four minutes before the 10-minute mean values reach the 3 statute mile criteria. This criterion forces SPECI to alert pilots to a significant change in visibility in this instance. A total of nine minutes will pass before the ASOS will report the 1 statute mile visibility.
On the other hand, when the visibility rapidly improves from 1 mile to 7 miles, the ASOS generates a SPECI four minutes after reaching the 1.5 statute mile threshold. In about 11 minutes, the ASOS will report 7 statute miles. The system is intentionally designed to raise surface visibility more slowly than to lower it. This design provides a margin of safety and buffers rapid changes when the visibility is widely fluctuating over a short period.
Hourly and special observations are the only ones created by human observers. In contrast, ASOS relentlessly measures the weather and could inundate pilots with more frequent special observations than a human observer when the weather is changing rapidly. Thus, the system is purposely throttled to only provide SPECIs at no more than a 5-minute interval to limit the number of observations that can be transmitted during the hour. An even slower response is seen at controlled airports where only the hourly and special observations must be prepared and broadcast on the Airport Terminal Information System (ATIS). At uncontrolled airports pilots can also receive the 1-minute weather by calling the voice phone link or by the ground-to-air radio broadcasts.
The FAA has created a Google map presentation online of the locations of all automated weather systems across the country. This includes including the frequency and phone numbers for each ASOS and AWOS currently in operation. Open a browser and visit https://www.faa.gov/air_traffic/weather/asos.
The lockout period
If you pay attention to the issuance time on METARs, you will notice that many are issued a few minutes before the top of each hour. This allows the observation to be transmitted and ingested into other computer systems such as numerical weather prediction models. Some models get executed at the top of the hour or shortly thereafter. Starting at 47:20 past the hour, the ASOS begins to make its routine observation. By 53:20, the hourly observation has been prepared and edited and should be ready for transmission.
This period of time between 47:20 and 53:20 minutes after the hour is known as the lockout period. During this period, the ASOS is prevented from issuing any other reports including SPECIs. The ASOS still continuously monitors and records the weather during the lockout period; however, it just can’t issue a formal surface observation. This does not affect the 1-minute weather you receive by calling the voice phone link or by the ground-to-air radio broadcasts, but it will affect any formal observations that get transmitted that you may see on your datalink weather broadcast.
Can I trust observations?
All observations, whether automated or taken by human observers, should be used with care. Pilots must be aware of how long ago the observation was taken, under what conditions, and whether or not they are special observations. Even though automated systems are totally objective and maintain a certain uniformity among all sites, it does not mean they match what a pilot sees out the windscreen.
ASOS may occasionally report cloud decks lower than what is actually encountered. Sometimes precipitation, lower cloud fragments or fog triggers these lower values. Pilots have said that these "lower" reported values often indicated the height below which they had to fly before gaining enough forward visibility to see an airport and land. The key lesson here is to evaluate all reports closely before dismissing them as inaccurate.
Even though the visibility sensor is designed to objectively represent the visibility of the atmosphere over a wide range of weather conditions, day or night, it occasionally reports a visibility more optimistic than what a human perceives. During the day, the human eye can be overwhelmed by bright light reflected in clouds, light precipitation, fog or haze. Many pilots will resort to wearing sunglasses to obtain some relief from the glare. The ASOS visibility sensor is not as sensitive to this condition and sometimes reports a visibility approximately twice as high as what an individual may determine. Be alert for these bright conditions and expect a more optimistic value from the automated system.
What will automation not provide?
We can easily become complacent when it comes to automation. We learn to trust automation and sometimes don’t acknowledge that it has real limitations. Therefore, to finish this discussion, it is just as important to know what automation will not provide.
Automation systems can only report the weather that passes through the sensor array. They do not provide a horizon-to-horizon evaluation of the weather. This means that weather in the vicinity of the airport will not be measured. A rain shower as shown below that passes just to north of the airport, for instance, may reduce visibility in that immediate area but will not be reported by the automated system.
Next, the ASOS only reports clouds that are below 12,000 feet. This means that an overcast cloud deck at 14,000 feet will be reported as clear. Effectively, a clear sky report from an automated station means clear below 12,000 feet. For airports with a human observer, this report can be augmented to include clouds above 12,000 feet. Some of the new AWOSs being installed can automatically report clouds above 12,000 feet up to and including 30,000 feet.
Automated systems can only report one precipitation type at a time. For instance, if freezing rain and snow are detected, snow is reported. Certainly, weather observers can edit the observation before transmission to include additional precipitation types.
Lastly, the ASOS is not designed to report virga, tornadoes, funnel clouds, ice crystals, snow pellets, ice pellets, drizzle, freezing drizzle and blowing obstructions such dust or sand. All of these elements can be provided at locations that employ a trained observer. Often with drizzle, freezing drizzle, ice pellets or a mixture, you will see the automated system report an unknown precipitation type (UP).
Nevertheless, automated reporting is in its infancy so it’s likely new sensors will be added to measure some of these other weather elements in the future.
EZWxBrief v2 news
Canadian GFAs are back! After NAV Canada changed their website and made it much more difficult to scrape these images from their site, EZWxBrief now provides access to these forecasts like the one shown below. At the moment, the only region that is not provided is the Arctic GFA.
Access to the Skew-T diagrams within EZWxBrief has been temporarily removed. These diagrams were being rendered through the government site, https://rucsoundings.noaa.gov. However, we have been informed that NOAA management has decreed that all of their web pages must be Section 508 compliant (see https://www.section508.gov). If not, NOAA is requiring them to be shut down to the public. The researchers that administer this site are currently working on reaching compliance. They hope they can have the site available to the public again soon, but there's no estimated date when that will occur. Once NOAA restores public access, then they will be made available again within EZWxBrief. Therefore, the Skew-T option in the Airport Wx sitemap dropdown menu as been temporarily removed until further notice.
Otherwise, no other updates have been released in September except for a few minor "under the hood" changes to increase reliability, stability and performance. Please note that starting January 1, 2025, the monthly subscription price will increase to $7.99/month (currently $6.99/month) to account for increased cost in computing resources for the servers used by the EZWxBrief progressive web app.
Most pilots are weatherwise, but some are otherwise™
Dr. Scott Dennstaedt
Weather Systems Engineer
Founder, EZWxBrief™
CFI & former NWS meteorologist
