If you surveyed a group of general aviation pilots, it would probably not surprise you to learn that Center Weather Advisories are not a weather source that pilots use very frequently when planning a flight. They have always been included within the ForeFlight Mobile app by tapping the Brief button under File & Brief. But this standard briefing only provides the advisory in raw text form—unless of course you are using the new and improved ForeFlight Briefing where it is also displayed graphically. In ForeFlight Mobile 7.4, Center Weather Advisories are now depicted graphically within the existing AIR/SIGMET layer on the Map view making them even more useful.
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. While they smell a lot like 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. Now is a good time to mention that CWAs are not part of the ADS-B broadcast so you will not receive them while connected to a Stratus.
CWAs are issued by highly trained meteorologists at the Center Weather Service Units (CWSUs) located at the various Air Route Traffic Control Centers (ARTCCs) pictured below.
CWAs are issued to warn pilots of the following in-flight weather hazards:
- Conditions meeting or expecting to meet convective SIGMET criteria
- Moderate or greater airframe icing
- Moderate or greater turbulence
- Heavy precipitation
- Freezing precipitation
- Conditions at or approaching Low IFR
- Sustained surface winds/gusts > 30 knots
- Non-convective low level wind shear below 2,000 feet AGL
- Volcanic ash, dust storms, or sandstorms
Short lead time
Unlike their 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 20 minutes past the hour to describe adverse weather that has evolved very rapidly. Once issued, CWAs are valid for two hours or 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.
Complementary guidance to other advisories
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. 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. An 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 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). As shown below, given the number of stations reporting low IFR conditions (magenta markers) within the AIRMET region, the Denver CWSU issued a CWA for ceilings at or below 500 feet and visibility at or below 1/2 statute miles.
While CWAs can be issued at any time, they are generally coordinated with other agencies within NOAA to ensure meteorological consistency between products. This includes meteorologists at the AWC who are responsible for issuing the area forecast, AIRMETs, SIGMETs and convective SIGMETs. It’s pretty typical for the meteorologist at the CWSU to have a brief phone conversation with the appropriate meteorologist at the AWC before issuing a new CWA.
Finding CWAs in ForeFlight
The CWA layer can be displayed from the Map view in ForeFlight Mobile 7.4. Simply tap the Map mode button in the upper left and select AIR/SIGMET/CWAs from the menu as shown below:
Once the layer has been selected you will see CWAs depicted on the ForeFlight map view as cyan-colored polygons regardless of the hazard type. In most cases, these areas will be smaller in size than an AIRMET or SIGMET because of their complementary nature and short duration. To see the associated uncoded text of the CWA, simply tap on the polygon in the same way that you view the uncoded text for AIRMETs and SIGMETs. Be sure to always read the text of the CWA since it will have additional details about the flight conditions such as the altitudes affected and an indication of whether or not conditions are expected to improve or persist beyond the valid time.
Lastly, given that CWAs are a complementary product to AIRMETs, SIGMETs and convective SIGMETs, with ForeFlight Mobile 7.4 you can overlay them with other advisories. Tapping on the buttons at the bottom labeled Ice, Turb, IFR and TS, will permit you to add or remove CWAs from the Map based on hazard type. In this example above, only IFR hazards are selected which includes AIRMETs for IFR conditions and mountain obscuration as well as a single CWA for low IFR conditions captured by the cyan-colored polygon. Any advisories for icing, turbulence and convection (if any) have been filtered from the Map.