Section 11. Center Weather Advisory (CWA)

9-11-1. GENERAL

A Center Weather Advisory (CWA) is an unscheduled weather advisory. It is issued for the guidance of ARTCC personnel, designated FAA facilities, Air Traffic Control System Command Center Weather Unit (DCCWU) meteorologists, and air crews inflight to anticipate or avoid adverse weather conditions in terminal and en route environments.

9-11-2. CRITERIA

a. The CWA is not a flight planning document. By nature of its short lead time, it reflects weather conditions in existence at the time of issuance or conditions beginning within the next 2 hours. If conditions are expected to persist beyond the time of the valid period and/or if conditions extend beyond the ARTCC area, statements to this effect should be included in the text. The CWSU will issue a CWA:

1. When necessary as a supplement to an existing WS (including WSTs), to an existing WA, or to an existing FA section. The issuance of a CWA under these circumstances should be limited to occasions when, in the judgment of the CWSU meteorologist, real time information adequately supports the issuance of a redefining statement update or advanced amendment. Such real time information regarding the phenomenon covered by a NAWAU product may be pilot reports, radar satellite, or information from other sources. The purpose of the CWA, under these circumstances, is to improve or to update the definition of the phenomenon in terms of relevance to users in the ARTCC area regarding the phenomenon's location, movement, extent, and intensity. A CWA, for example, describing an IFR WAs area of low IFR (LIFR) conditions in terms of ARTCC reference points would be a valid redefinition of the location and intensity relevant to the ARTCC's area and would meet documented requirements.

2. When an inflight advisory has not yet been issued, but the observed or expected weather conditions meet WS or WA criteria based on current pilot reports and reinforced by other sources of information concerning existing meteorological conditions. In this situation, the CWSU meteorologist should call the appropriate forecaster at the NAWAU or appropriate Alaska WFO. If the CWSU forecaster determines that it is necessary to issue a CWA to allow lead time while the WS/WA is being prepared, the CWA will be issued, and the CWA should indicate that a WS/WA will be issued shortly.

3. The CWSU meteorologist may issue a CWA when observed, or developing weather conditions do not meet WS (including WST) or WA criteria but current pilot reports or other weather information sources indicate that an existing, or anticipated, meteorological phenomena will adversely affect the safe flow of air traffic within the ARTCC area of responsibility. In this situation, the data available must be sufficient, in the judgment of the CWSU meteorologist, to support both the issuance of such an advisory and, if necessary, its continuation.

b. The CWA will describe the location of the phenomenon using ARTCC relevant points of reference, such as VORs, and will include the height, extent, intensity, and movement of the phenomenon. Each CWA will have a phenomenon number (1 through 6) immediately following the ARTCC identifier in the CWA message heading. A separate phenomenon number will be assigned to each meteorologically distinct condition or group of conditions, such as jetstream clear air turbulence or LIFR/icing conditions northwest of a low pressure center. The use of phenomenon numbers make it possible to store and disseminate up to six unrelated CWA conditions with each condition capable of being updated. Forecasters should be aware that the CWA is stored and disseminated as a replaceable product. This means that each subsequent CWA issuance must contain all the pertinent and known details of the conditions meeting CWA issuance criteria, including the continuing conditions described in the previously issued CWAs. CWAs will also be numbered sequentially, beginning at midnight local time each day. The sequential CWA issuance number will be followed by the related two-digit, alphanumeric designator for inflight advisories in effect if applicable. The CWA communications heading will also contain the CWA date/time of issuance in UTC and the “valid until” date/time in UTC. The difference between these two times will not exceed 2 hours.

c. The format of the CWA communications header is: (ARTCC designator)(phenomenon number) CWA (date/time issued in UTC)/(ARTCC designator) CWA (issuance number) VALID UNTIL (date/time in UTC)/(FROM) (affected area)/(text).

EXAMPLE-
ZOB1 CWA 032141
ZOB CWA 101 VALID UNTIL 032300
FROM 10S DET TO 40N DJB TO 40E SBN TO 80SE MKG
LN SEV TSTMS WITH EXTRM PCPN MOVG FROM 2525 3/4 INCH HAIL RPRTD LAST 5 MINS 20 SW YIP.
TSTMS WITH HVY TO EXTRM PCPN CONTG DTW AREA BYD 2300

ZKC1 CWA 121528
ZKC CWA 102 VALID UNTIL 121728
STL DIAM 30 NM. NMRS RPTS OF MOD TO SEV ICG 080/090.. LGT OR NEG ICG RPTD 040/120 RMNDR OF ZKC AREA AND NE OF AREA.

NOTE-
The format of the CWA communications header must be followed exactly if the product is to be distributed through the AISR.

9-11-3. DISTRIBUTION

The CWA will be distributed to ARTCC area supervisors and traffic management coordinators and will be entered through FAA AISR and other communications media to make it available for dissemination to other FAA and NWS facilities. Distribution may be made directly by the CWSU meteorologist or through the weather coordinator position.