top of page

February 2023 EZNews

Updated: Feb 9, 2023

Hello again and thanks for reading the 22nd edition of EZNews!

At EZWxBrief we appreciate those customers that have recently joined, renewed their membership or signed up for auto-renewal. A big thanks goes out to Bill M. who renewed his annual membership for $100 and David D. who renewed for $74. We truly appreciate your generosity which helps support our continued innovation and growth 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 and reliability. More information about this new version will be released during the late spring. Stay tuned for that.


Minor change in SIGMET format


Effective April 20, 2023 at 19Z, Blowing Dust (BLDU) will replace Widespread Dust storm (WDSPR DS) and Blowing Sand (BLSA) will replace Widespread Sandstorm (WDSPR SS) in SIGMETs. The format change is necessary for the advisory to comply with NWS Instruction 10-811, En Route Forecasts and Advisories.


Current format for WDSPR DS:


WSUS04 KKCI 272310

MKCWS4O

DFWO WS 272308

SIGMET OSCAR 1 VALID UNTIL 280308

OK TX KS CO NM

FROM 60NW ICT TO 20NE ABI TO 60SSE CME TO 30SSW PUB TO 60WNW ICT

OCNL VIS BLW 3SM IN WDSPR DS BLW 030. CONDS CONTG BYD 0308Z.


New format for BLDU:


WSUS04 KKCI 272310

MKCWS4O

DFWO WS 272308

SIGMET OSCAR 1 VALID UNTIL 280308

OK TX KS CO NM

FROM 60NW ICT TO 20NE ABI TO 60SSE CME TO 30SSW PUB TO 60WNW ICT

OCNL VIS BLW 3SM IN BLDU BLW 030. CONDS CONTG BYD 0308Z.


Surface wind forecasts in EZWxBrief


Current federal standards for siting meteorological equipment at airports specify (with some variance permitted) a height of 10 meters (32.8 feet). Therefore, the typical ASOS wind sensor heights are 33 feet or 27 feet, depending on local site-specific restrictions or requirements. The wind information you get in a surface observation (METAR) is actually about 30 feet off the ground (different than you'd get looking at the wind sock which is typically lower to the surface).


When you are viewing surface wind and wind gust forecasts on the EZMap like you see below or in the Meteogram, you should be aware that the forecast is not like what is shown in surface observations. It is actually the 30 meter wind which is approximately 100 feet above the surface and about what you'd experience when flying "over the fence" as you are on short final. The wind near the surface is very difficult to predict with any certainty due to the local effects of terrain. Even so, EZWxBrief v2.0 will be providing a 10 meter wind when that is released later this summer.

For now, expect the wind forecast for EZWxBrief to be a bit higher than what you'd likely see in a terminal forecast or in a surface observation.


What is non-convective LLWS?


There’s no doubt that terminal aerodrome forecasts, simply known to pilots as TAFs, are perhaps the most detailed aviation forecasts available. If you call Flight Services for a standard briefing or get an automated briefing through one of the heavyweight apps, you can bet the farm that any TAFs along your proposed route and at your departure and destination airports will be a part of this briefing. There are, however, some finer details about TAFs that instructors fail to pass along to their students. The top one on the list includes a forecast for non-convective low level wind shear (LLWS). Below is a non-convective LLWS G-AIRMET as shown in EZWxBrief.

Probably the most misunderstood aviation forecast among pilots and instructors is one for non-convective LLWS. In a TAF, this forecast appears in coded form with a WS code such as WS020/15035KT. Such a forecast can also appear in a G-AIRMET. In a preflight briefing, pilots hear the term “wind shear” and immediately equate this with thunderstorms and severe turbulence. It’s a common misconception, but non-convective LLWS as it appears in a TAF is not a forecast for turbulence. In fact, in most cases when this is forecast, the air is glassy smooth.


This form of wind shear is typically found in the warm sector east of the surface cold front and south of the surface warm front. But it’s also quite prevalent in the overnight hours during fair weather conditions coupled with clear skies and calm wind at or near the surface. Even though wind seems to be the common denominator, atmospheric stability is the catalyst behind most non-convective LLWS occurrences.


We know that wind naturally tends to increase in speed with increasing height, but it normally does so fairly gradually. But what if the winds are nearly calm at the surface and increase to 45 knots just 2,000 feet above the ground? That’s an example of vertical speed shear also known as non-convective LLWS.


When the winds are expected to increase rapidly with height within 2,000 feet of the airport’s surface a forecast for non-convective LLWS will likely be issued in a TAF for that airport. The forecast for non-convective LLWS found in a TAF tells the pilot about the potential for the wind speed to increase quickly with height above the ground within a shallow layer. That is, faster air at the top of the wind shear layer is moving over slower air near the bottom of that layer. There also may be an accompanying shift in wind direction with height in this layer as well.


Keep in mind that it’s not the same horizontal and vertical wind shear that may be experienced in the vicinity of deep, moist convection or thunderstorms, hence the name non-convective LLWS. Forecasts for convective and non-convective LLWS have very distinct differences. In a TAF, convective LLWS will typically contain a reference to thunderstorms (TS or VCTS) and will contain CB - which stands for cumulonimbus - in the cloud group. Also, the surface winds are typically forecast to be strong & gusty. While convective LLWS can occur at any time of the day or night, most convective LLWS occurs in the afternoon and early evening when thunderstorms are the most prevalent. Here are three examples of forecasts for convective LLWS.


– FM132200 33010G20KT P6SM VCTS SCT015 BKN040CB

– FM131600 22013G35KT 3SM TSRA BR BKN035CB

– FM140000 VRB20G55KT 1/2SM +TSRA FG BKN015CB


Non-convective LLWS can occur in the warm sector of an area of low pressure, but it can frequently occur in the presence of a strong nocturnal surface-based temperature inversion. Frontal non-convective LLWS can occur any time of the day or night and normally has the characteristics of light winds at the surface and cloudy skies, but can be strong and gusty when the weather system is associated with an intense area of low pressure. Here are three examples of TAFs non-convective LLWS when associated with a frontal system.


– FM111600 13010KT 5SM -RA OVC015 WS020/27055KT

– FM120100 VRB03KT 4SM BR OVC008 WS015/25045KT

– FM120900 19018G30KT 3SM +SHRA BR OVC005 WS020/17075KT


On the other hand, nocturnal non-convective LLWS occurs in the overnight or early morning hours often with light winds and clear skies. This is a manifestation of radiational cooling and likely occurs in the region under an area of high pressure. Here are three examples of the nocturnal version of non-convective LLWS you might see in a TAF.


– FM221100 19004KT P6SM SKC WS015/17040KT

– FM230800 VRB03KT P6SM SCT010 WS010/22035KT

– FM230400 00000KT P6SM SKC WS020/23055KT


In both cases of non-convective LLWS, the LLWS code - WS - will be included in the TAF immediately after the cloud group. Let’s take a closer look at this misunderstood forecast group. Assume the following from a TAF -


– FM130300 17005KT P6SM SKC WS020/23055KT


The first element to the immediate right of the WS code is a height above the airport – in this case 020 or 2,000 feet. This represents the top of the wind shear layer. This altitude is "typically" one of three values; 010 for 1,000 feet AGL, 015 for 1,500 feet AGL or 020 for 2,000 feet AGL. Even if the WS layer extends higher, the maximum height that is forecast is 2,000 feet.


Following the forward slash, the next group contains the true wind direction followed by the wind speed in knots at the indicated height or 230 degrees at 55 knots in this example. This implies indirectly that the wind is rapidly increasing from the surface through the indicated height although this says nothing about the wind direction throughout this shear layer. Effectively this forecast translates into “the wind at 2,000 feet is 230 degrees at 55 knots.” But it does not imply there will be turbulence at 2,000 feet AGL or below. In most cases, you’ll find smooth conditions in this wind shear layer, especially for the nocturnal instance of non-convective LLWS.


The catalyst for the development of all non-convective LLWS is atmospheric stability. We also know that temperature normally decreases with increasing altitude. This is generically referred to as a lapse rate. A lapse rate is simply a change of temperature over a change of increasing altitude. Anytime the temperature decreases with increasing altitude it’s referred to as a positive lapse rate. If the temperature increases with altitude, that’s referred to as a negative lapse rate or more commonly labelled a temperature inversion. The larger the lapse rate, the greater the atmospheric instability. An unstable environment (large lapse rate) promotes vertical mixing and provides for a more turbulent air flow potential. On the other hand, a stable atmosphere (small or negative lapse rate) inhibits vertical mixing and provides for a laminar and non-turbulent flow.


One might suspect that vertical speed shear (faster air flowing over slower air) could cause the air to overturn and produce turbulent eddies within this wind shear layer. However, just about all non-convective LLWS occurrences feature a strong temperature inversion. Any kind of overturning or vertical mixing introduces the potential for turbulence, however, an extremely stable layer such as this tends to dampen or resist vertical mixing. Simply put any air that is forced to ascend within this stable layer will expand and cool and immediately finds itself in warmer temperatures aloft due to the inversion. The air is forced to return back to its original altitude almost immediately. In other words, this air has neutral buoyancy and doesn’t want to rise or sink.


So why does the air accelerate rapidly with height? The extreme stability courtesy of the temperature inversion eliminates upward and downward motion or vertical mixing (neutral buoyancy). This promotes a laminar flow and the effects of surface friction are no longer “felt” at heights a few hundred feet above the surface. This allows the flow of air just above the tree tops to accelerate uninhibited and insulated from surface friction below through the depth of the wind shear layer. You can think of this as a faster flowing river of air (called a low level jet) located just above the surface. The stronger and deeper the inversion, the less likely there will be any kind of turbulence.


So if non-convective LLWS isn’t a forecast for turbulence, why is it forecast at all? When the sky is clear and surface winds are light, the nocturnal version of this phenomenon is just as common as low level thermal turbulence is during the afternoon in the summer. Unless you were fixated on your groundspeed approaching an airport late at night or in the early morning hours, you probably flew right through it without even noticing that it existed. In most cases, nocturnal non-convective LLWS isn’t usually forecast.


Nevertheless are several situations where you should pay close attention. First, if you are departing out of an airport with a high density altitude, non-convective LLWS can make for a difficult climb if the low level jet is off your tail. It’s not uncommon for the winds to be light or calm at the surface although they may be 30 knots are more just above the tree tops. With light or calm winds at the surface, you may not realize that during the initial climb to pattern altitude, the prevailing wind is at your back.


The most important one to watch out for is when non-convective LLWS of 50 knots or greater is coupled with the potential for moderate to heavy rain showers (SHRA or +SHRA) or even thunderstorms (TSRA or +TSRA) as shown below.


– FM120900 19018G30KT 3SM +SHRA BR OVC005 WS020/17075KT


As the moderate to heavy rain falls through the low level jet, some of the momentum of the jet gets directed downward toward the surface of the earth. This is like taking a fire hose and deflecting it downward toward the ground. The downward momentum of that low level jet creates the potential for wet microbursts or downbursts. In this case, the magnitude of the non-convective LLWS event and convective outflow can make for a real interesting approach to land.


In the end, don’t get too excited when you see a forecast for non-convective LLWS especially when it occurs in the overnight hours. It’s not a forecast that should instill fear in a pilot like it often does. In most cases, it’s a non-event that you may not even notice was there.


TAIWIN


This is likely an acronym that you'll be hearing more about in the coming years. It stands for Terminal Area Icing Weather Information for NextGen. The overarching goal of TAIWIN is to provide pilots with timely and critical icing and non-icing condition information to aid in decision-making and operate more safely during flight planning, departure, and landing. Below is an early depiction of the user interface that could be used.

The intention is to develop a capability for icing diagnosis and forecasting in the terminal area with an emphasis on FZDZ and FZRA identification. Unlike the size of the terminal area used for TAFs which is the region five statute miles from the center of the airport's runway complex, TAIWIN uses a much larger 30 nautical mile radius, from the surface to 12,000 feet AGL.


Here are some of the features and improvements incorporated into TAIWIN:


1) Enhances the use of satellite datasets to improve the differentiation between the phase of a cloud (e.g., liquid vs solid) and the size of cloud drops.


2) Improves estimates of cloud top height and height of the icing layer.


3) Corrects for well-known errors that exist in automated surface observations. Surface observation reports (i.e., METARs) are especially critical to the diagnosis of supercooled large drop (SLD) icing.


4) Maps surface observation information using meteorological factors, including elements evident in satellite, radar and forecast model data.


5) Employs a 3-D radar mosaic dataset.


6) Provides a high-quality, 24 hour cloud shield/mask, which is essential for high-quality icing diagnostics.


7) Employs the High Resolution Rapid Refresh (HRRR) model, both in a deterministic mode and as a time-lagged ensemble (TLE) of up to seven HRRR model runs all valid at the same time.


8) Differentiates SLD into freezing drizzle (FZDZ) and freezing rain (FZRA) categories. Also differentiates these from small drop (i.e., Appendix C) icing and non-icing conditions that can vary in time and space.


Updates will be every 15 minutes using a 1-km resolution horizontally and approximately 500 feet resolution vertically. The high-resolution gridded icing fields are examined across the entire terminal area to provide a simplified singular answer for the entire terminal area. This is just a quick summary of many of the interesting things about this new tool that is under current development.


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! Print supplies are limited, so order your copy today.


Most pilots are weatherwise, but some are otherwise™


Dr. Scott Dennstaedt

Weather Systems Engineer

Founder, EZWxBrief™

CFI & former NWS meteorologist






234 views0 comments

Recent Posts

See All
bottom of page