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Center Weather Advisories (CWA)

     Center Weather Advisory (CWA). The CWA is an aviation weather warning for conditions meeting or approaching national in-flight advisory (AIRMET, SIGMET or SIGMET for convection) criteria. The CWA is primarily used by air crews to anticipate and avoid adverse weather conditions in the en route and terminal environments. It is not a flight planning product because of its short lead time and duration. Additionally, the CWA should be meteorologically consistent with other products and reflect conditions at the time of issuance and/or in the near future. If a CWA has been issued prior to coordination, notification to the appropriate offices, national center, or WFO should follow as soon as higher priority duties permit.

     CWAs are valid for up to two (2) hours and may include forecasts of conditions expected to begin within two (2) hours of issuance. If conditions are expected to persist after the advisory's valid period, a statement to that effect should be included in the last line of the text. Follow-up CWAs should be issued as appropriate. Notice of significant changes in the phenomenon described in a CWA should be provided by a new CWA issuance for that phenomenon. If the forecaster deems it necessary, CWAs may be issued hourly for convective activity. This may improve the usefulness of the Hazardous In-flight Weather Advisory Service (HIWAS) recordings which include those CWAs.

     The Urgent CWA (UCWA) communications header is intended for those situations when weather conditions occur that have not been forecast and have an immediate effect on the safe flow of air traffic within the ARTCC area of responsibility. It should only be used when the CWSU meteorologist believes any delay in dissemination to FAA facilities would impact aviation safety. Use the routine CWA header for subsequent issuances of the same phenomenon. CWAs may be issued for the same phenomena described in advisories and forecast products issued by WFOs, the AWC, or the National Centers for Environmental Prediction (NCEP).

     The first line of each CWA's FAA communications system header must have an ARTCC identifier immediately followed by a Phenomenon Number (1-6). The Phenomenon Number must be assigned to each meteorologically distinct condition, group of conditions, or to each set of similar condition(s) in distinctly separate areas. The first meteorological event of the local calendar day which requires the issuance of a CWA should be assigned phenomenon number 1. The latest CWA issuance with this number can replace and update the previous issuance. This numbering makes it possible to disseminate CWAs for up to six (6) unrelated events with each event issuance capable of being individually updated.

     CWAs should be issued for any of the following events when they are expected to occur within two hours and have not been previously forecast by AWC or AAWU products, or to supplement the AWC and AAWU products.

          a. Any of the following conditions occur, are forecast to occur, and, if previously forecast, are no longer expected:

                 (1) Conditions meeting convective SIGMET criteria
                 (2) Icing - moderate or greater
                 (3) Turbulence - moderate or greater
                 (4) Heavy precipitation
                 (5) Freezing precipitation
                 (6) Conditions at or approaching Low IFR
                 (7) Surface winds/gusts >30 knots
                 (8) Low Level Wind Shear (surface - 2,000 feet)
                 (9) Volcanic ash, dust storms, or sandstorms; and

 b. In the forecaster's judgment, the conditions listed above, or any others, may adversely impact the flow of air traffic within the ARTCC area of responsibility.