Updated: Jan 1
Hello again and thanks for reading the 21st edition of EZNews!
Happy new year! At EZWxBrief we appreciate those that have recently joined, renewed their membership or signed up for auto-renewal. A big thanks goes out to Keith A. who renewed his annual membership for $100. We truly appreciate your generosity which helps support our continued innovation moving forward. There have been no new releases this past month, but we are moving forward to more continued growth with the development of EZWxBrief v2.0 that is due to be released the summer of 2023. Version 2.0 will have a new look and feel and will have the benefit of additional horsepower to help with app performance.
Retirement of the legacy AvWxWorkshops domain
As mentioned in previous EZNewsletters, the AvWxWorkshops domain is being retired on March 1, 2023. This was the predecessor to the current EZWxBrief website and at the moment simply points to EZWxBrief. At this point in time, any email addresses under this domain such as firstname.lastname@example.org have been depreciated. Sending an email to this address will bounce back as unreachable. The best way to reach us now is to visit our contact page.
FAA's new Aviation Weather Handbook has been released
It has been years since the FAA embarked on a mission to release a single handbook for aviation weather. Well, the wait is finally over. On December 22, 2022 the FAA published FAA-H-8083-28 Aviation Weather Handbook. It is now available for download from the FAA's website.
It has been the FAA's goal to consolidate the weather information from many advisory circulars (AC) into a one-stop shopping experience. This new handbook now incorporates most (if not all) of the technical guidance found in the following ACs:
• AC 00-6, Aviation Weather • AC 00-24, Thunderstorms • AC 00-30, Clear Air Turbulence Avoidance • AC 00-45, Aviation Weather Services • AC 00-54, Pilot Wind Shear Guide • AC 00-57, Hazardous Mountain Winds
All the latest versions of these ACs will continue to remain in effect as non-regulatory FAA guidance, but the expectation is that all of them will eventually fall victim to cancellation sometime within this decade. This will mean that the FAA knowledge tests and certification standards for new certificates or ratings will point to this new handbook sometime in the future under the required areas of knowledge as references to these legacy ACs are eventually phased out. But, don't place your bets this will happen anytime soon.
Now that the new handbook is out, is there anything new to chew on? For all intents and purposes, not really. As someone who has authored two weather books, I'll be extremely reticent about my own personal feelings. Let's see how well I do. The FAA clearly took the Aviation Weather Services AC (00-45H, Change 2) and the Aviation Weather AC (00-06B) last updated in 2016 and mashed them together and backfilled with a couple of the other ACs mentioned above. Well, it was more like they very loosely shuffled two decks of cards together to produce the new handbook. Of course, if you haven't read these ACs in the last 10 years, then you might find some new material in this handbook.
The thing that is most obvious is that the FAA didn't take the time to make any significant updates to the ACs they were surgically merged together. For example, Graphical AIRMETs or more simply G-AIRMETs have been the operational product issued by forecasters at the Aviation Weather Center (AWC) when they officially replaced the existing traditional or "legacy" textual AIRMET on March 16, 2010 as I discuss in this FLYING magazine article. This is very important since the legacy AIRMET is being retired in early 2023 as I discussed in this other FLYING magazine article.
The new handbook never mentions the term "G-AIRMET" in the text. Clearly the handbook attempts to describe the G-AIRMET concept in the text but doesn't update the terminology that has been in use for over a decade. In fact, you can see in one of the figures in the new handbook shown below, the caption clearly states that this is an AIRMET, but you can see in the upper left, the product itself from aviationweather.gov is labeled as "G-AIRMET."
This may seem like a minor technicality or nit-picky detail, but while the legacy AIRMET and G-AIRMET are related products (the legacy AIRMET and its outlook are automatically generated from the five G-AIRMET snapshots) they must be interpreted differently. The G-AIRMET is based on five snapshots valid at specific times (coverage of that adverse weather element) and the legacy AIRMET text is a time-smeared forecast valid over six hours with a six hour time-smeared outlook. There are other critical differences as well that are simply overlooked that I cover in the two FLYING magazine articles lined above. It's as if you were hanging a picture and ask someone to "hand you a hammer" and they handed you a sledge hammer instead of the ball-peen hammer. The correct terminology is important or you end up with a major hole in your wall.
Given that weather is likely the single biggest physical factor affecting your flying activity and is listed as the primary cause of 35% of general aviation accidents, the new handbook is simply too rigid and lacks depth from a practical standpoint. Like many ACs and handbooks, it reads more like a user's manual rather than a text to learn more about weather. If you are using it for a reference (e.g., How often are TAFs issued each day?), it's a great resource for those "trivial" types of knowledge. Certainly, the update of AC 00-6B in 2016 was a significant improvement to its earlier predecessor that was originally issued back in 1977. In that light, this new handbook represents a good resource for CFIs and their students as a study guide to pass the FAA knowledge and practical tests, but you'll likely need to seek out additional training to learn the practical components of preflight planning as well as inflight strategies that are not typically taught during a pilot's primary training.
Precipitation type on the Skew-T
Looking at this 1-hour forecast sounding below, what precipitation type do you believe is expected to reach the surface?
There is a lot of complexity to this particular forecast sounding to determine the precipitation type that is expected at the surface. The surface temperature is the key to whether or not you get RA (rain), FZRA (freezing rain), DZ (drizzle) or FZDZ (freezing drizzle) at the surface. In this sounding the temperature at the surface is exactly 0°C as shown below. That doesn’t bode well for any freezing precipitation types such as FZRA or FZDZ, but keeping in mind that just 20 miles away from this point, the surface temperature could be below 0°C creating a FZRA hazard nearby.
The saturated layer extends to about 13,000 feet MSL which is deep enough to produce precipitation. Cloud top temperature (CTT) is the key to determine if the primary precipitation type is snow, drizzle or perhaps rain in the clouds. In this case, the CTT is roughly -13°C. This is right at the edge where ice nuclei being to activate to allow for ice crystal growth. What is not shown is a “potential” higher glaciated cloud layer above at 25,000 ft MSL. This can provide ice crystals to gently fall into the lower cloud to help seed it. The relative humidity between the cloud top and the higher cloud deck remains fairly high (no considerable dry slot) allowing for those ice crystals to survive (and not sublimate before reaching the clouds below) down to seed the lower cloud deck.
There is also an inversion from 800 ft MSL to 3,500 ft MSL. This is creating an overrunning situation and a “warm nose” that hovers right around 0°C from 2,500 ft MSL to 3,500 ft MSL. In order to get ice pellets, snow must be the primary precipitation type aloft. If snow was the dominant precipitation type, those warmish temps might be enough to melt some of those snow flakes into a drop that will likely retain a slushy core that could possibly freeze into a nugget in the colder temps below 2,500 feet. So that would give rise to a mixed precipitation scenario.
This particular sounding was valid at 17Z. At 1635Z, the weather was +SN FZFG (FZFG is due to the vis being less than 1/4th of a mile with the temp below 0°C). And that was the dominant precipitation type occurring since 1535Z. At 1517Z, UP (unknown precipitation type) was being reported based on the remarks from the 1535Z observation, but that changed over to snow at 1526Z. Perhaps this started out as a mixed precipitation type of snow and ice pellets. Temperature at the surface was -1°C for most of this period.
261635Z AUTO 17010KT M1/4SM +SN FZFG OVC024 M01/M01 A3025 RMK AO2 OVC V BKN P0000 T10111011 $ 261615Z AUTO 17010KT M1/4SM +SN FZFG OVC021 M01/M01 A3025 RMK AO2 P0000 T10101012 $ 261555Z AUTO 20007KT M1/4SM +SN FZFG OVC024 M01/M02 A3027 RMK AO2 P0000 T10071018 $ 261535Z AUTO 20009KT M1/4SM +SN OVC033 00/M03 A3026 RMK AO2 UPB1517E1526SNB1526 P0000 T00011035 $
Although the temperature was about the same, the precipitation changed over to rain with freezing fog. Hard to know for sure if this observation was correct given that the snow ended at 1655Z and rain began at 1655Z. This is an automated observation and there’s no way to know for sure from the METAR alone.
261655Z AUTO 18009KT M1/4SM +RA FZFG FEW006 OVC030 M01/M01 A3024 RMK AO2 SNE1655RAB1655 P0000 T10081008 $
At other nearby locations that were issued by a human observer, snow was being reported as shown below. So it is suspect that the report of heavy RA was more of a moderate wet snow being misreported.
261612Z 21013G20KT 4SM -SN BKN026 BKN050 OVC070 01/M02 A3023 RMK AO2 SNB00 P0000 T00111022 $ 261608Z 21008KT 7SM -SN SCT026 BKN050 OVC065 01/M03 A3023 RMK AO2 SNB00 P0000 T00111028 $
In the end, this sounding tends to support a wet snow scenario possibly mixed with ice pellets or even rain.
Let's say you were departing out of Friday Harbor (KFHR) in NW Washington tomorrow morning at 13Z. The sounding below shows a fairly good saturated layer from 6,500 feet to 11,500 feet pressure altitude. Is it safe to assume that you’d be above the clouds at 12,000 feet? Or below the clouds at 6,000 feet? Not exactly. There’s really high certainty you are in the clouds between 6,500 and 11,500 feet, but the certainly decreases above and below this saturated layer.
In fact, if you look at the EZWxBrief EZRoute Profile for icing severity shown below, this uncertainty drives the forecast you ultimately see. That saturated layer above can be characterized as moist instability and given the temperatures aloft at those altitudes of -7°C to -15°C, icing is a darn good bet. Moreover, that moist instability also drives up the liquid water content (LWC) in the clouds at those altitudes and it will be quite high, hence, the heavy icing forecast in EZWxBrief.
However, you’ll notice that the icing severity extends above and below those core altitudes. This is because the models being used exhibit a high degree of agreement for that saturated layer showing heavy icing (dark blue), but are not as certain where the icing ends above and below it. Therefore, EZWxBrief phases out the icing from heavy to trace (cyan) below that layer and heavy to light (light blue) above that layer to better quantify the uncertainty that clearly exists. In other words, there’s a strong signature of saturation between 6,000 and 10,000 feet, but not as strong outside of this range. That tends to match the RAP model forecast in the Skew-T above.
For the EZRoute Profile cloud depiction above, however, the models used to determine cloud coverage and depth are similar to the icing profile, but have a little stronger certainty where the bases and tops are located in this case. EZWxBrief makes every attempt to make sure that if icing is depicted, clouds are also depicted (except for freezing precipitation situations where you can have icing below the cloud base). When specifically checked (hovering the over the areas on the icing probability profile), the actual icing probabilities (not shown) above and below where clouds are about 6-7% (the cutoff for icing severity is 5%) and the cloud depiction certainties were below 5% in these areas. Consistency is difficult.
The determination of icing and clouds are rarely black and white, but shades of gray. Consequently, it can be quite difficult to determine where the clouds start and stop…same is true for airframe icing.
Looking to expand your weather knowledge in 2023?
If so, then get online today and purchase your copy of the The Skew-T log (p) and Me: A primer for pilots. You can purchase the softcover version for $59.95 plus $10 for domestic shipping or if you can't wait for the book to arrive, save even more by purchasing the eBook for $49.95 that you can download and start reading today!
Most pilots are weatherwise, but some are otherwise™
Dr. Scott Dennstaedt
Weather Systems Engineer
CFI & former NWS meteorologist