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EZTip No. 24 - Center Weather Advisories (CWAs) in EZWxBrief

Updated: Jan 29

Center Weather Advisories, or CWAs, are the “front lines” of aviation weather in the U.S. for adverse weather such as low IFR conditions, thunderstorms, icing, and turbulence, just to name a few. While they smell a lot like Graphical AIRMETs and SIGMETs, they are more of an in-flight advisory about current conditions than they are a planning tool or forecast. Therefore, it’s critical to look for these while en route to your destination and just before you close the door to depart.

These are issued by highly trained meteorologists located at the Center Weather Service Units (CWSUs) co-located at the FAA’s 21 Air Route Traffic Control Centers

(ARTCC) as shown above. A CWA is an unscheduled weather advisory for conditions meeting or approaching national in-flight advisory criteria for non-convective SIGMETs, G-AIRMETs and convective SIGMETs. It is primarily used by pilots to anticipate and avoid adverse weather conditions in the en route and terminal environments.

Adverse weather includes, but is not limited to:

a. Convective weather including thunderstorm timing, tops, movement, intensity,

and character such as broken and solid lines or large clusters

b. Operationally significant ceilings/visibility

c. Cloud tops

d. Winds and temperatures, surface and aloft

e. Wind shear

f. Operationally significant pressure changes

g. Precipitation

h. Turbulence

i. Icing

j. Volcanic ash

Unlike their G-AIRMET counterpart, CWAs are not routinely issued and have no defined schedule. Moreover, they have a very short lead time since they are issued on an as-needed basis. So, it’s not unusual to see a CWA issued at 22 minutes past the hour to describe adverse weather that has evolved very rapidly. Once issued, CWAs are valid for two hours or sometimes less. If conditions are anticipated to persist beyond two hours, it will be indicated in the last line of the CWA text. As mentioned earlier, CWAs are not as valuable of a preflight planning tool because of its short lead time and duration. They tend to pop up as adverse weather evolves or develops throughout the U.S. and along its coastal waters.

Forecasters at the CWSUs have a fair amount of latitude when issuing a CWA. Conditions do not have to meet national in-flight advisory criteria in terms of intensity or areal coverage. For example, unlike convective SIGMETs, CWAs for convection can be issued before thunderstorms have formed. That is, they can describe a broad area of towering cumulus or showery precipitation that is trending toward an aviation hazard within the next two hours especially in regions that may affect flow into or out of busy airspace. On the other hand, convective SIGMETs issued by forecasters at the Aviation Weather Center (AWC) are more of a NOWcast that warn pilots about active areas of thunderstorms that have already met specific hazard criteria.

A good example of its complementary nature is a CWA for low IFR conditions. A G-AIRMET for IFR conditions is primarily directed at pilots flying under visual flight rules (VFR). It describes an area that may experience a ceiling and/or visibility below VFR minimums. However, what if a portion of the G-AIRMET region is also plagued with persistent low IFR conditions? This would be critical information for all pilots including those flying under instrument flight rules (IFR). Therefore, it is common for meteorologists at the CWSU to issue a CWA for areas within a G-AIRMET for ceilings at or below 500 feet and/or visibility at or below 1/2 statute miles.

CWAs in EZWxBrief can be found on the EZMap. The layer selector attributes allows you to filter these by the hazard to include Airframe Icing, Turbulence, IFR conditions, Convection and Other. Other may include volcanic ash (very rare in the lower 48) and any CWAs that could not be properly decoded (CWAs have no hard rules for the format of the text, so some are easier to decode than others).

They show up as a cyan-colored polygon on the EZMap like the ones shown below for icing. A click or tap on that polygon will display the associated CWA text where you can find out other important details. In this case, the remarks include "Several airports reporting FZRA."

In order to see the CWAs on the map, be sure that the time set on the EZDeparture Advisor is at the far left. This is due to the nature of their short valid time span that is usually two hours or less. If you happen to select CWAs from the layer selector and there are none or you have the time set too far into the future, you will see an informational message in the upper-right of the EZMap like the one shown below.

If you want to learn more about the Skew-T diagram, you can order your copy of The Skew-T log (p) and Me book that is available in soft cover or eBook format.

Most pilots are weatherwise, but some are otherwise™

Dr. Scott Dennstaedt

Weather Systems Engineer

Founder, EZWxBrief™

CFI & former NWS meteorologist

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