METEOROLOGY FLIGHT PLANNING
While this is indeed the first SIGMET issued for this phenomenon in the DFW area, it is actually
the fourth issuance for the phenomenon since it met SIGMET criteria, and the previous three
issuances occurred in the SLC area.
While SIGMETs may be issued up to two hours before the onset of any condition forecast to meet
a criterion, note the time in line 1 (Figure 3-5) is the issuance time, not the onset time. The time
indicated in the VALID UNTIL 052100 statement is the SIGMET expiration time. The difference
between the two will not exceed four hours. If it is expected to persist beyond four hours, a
statement to this effect will be included in the remarks of the text. If the conditions do persist
beyond the forecast period, then the SIGMET will be updated and reissued. However, if
conditions end, a SIGMET cancellation will be transmitted.
Center Weather Advisory (CWA)
CWAs are unscheduled in-flight, flow control, air traffic, and aircrew advisory. By nature of its
short lead-time, the CWA is not a flight-planning product. It is generally a nowcast for conditions
beginning within the next two hours. CWAs will be issued:
As supplement to an existing SIGMET, Convective SIGMET, AIRMET, or FA.
2. When an In-flight Advisory has not been issued, but observed or expected weather
conditions meet SIGMET/AIRMET criteria based on current PIREPs and reinforced by other
sources of information about existing meteorological conditions.
3. When observed or developing weather conditions do not meet SIGMET, Convective
SIGMET, or AIRMET criteria; e.g., in terms of intensity or area of coverage, but current Pilot
Weather Reports or other weather information sources indicate existing or anticipated
meteorological phenomena will adversely affect the safe flow of air traffic within the Air Route
Control Center (ARTCC) area of responsibility.
The following example (Figure 3-6) is a CWA issued from the Kansas City, Missouri ARTCC. The
"3" after ZKC indicates this CWA has been issued for the third weather phenomenon to occur for the
day. The "301" in the second line denotes the phenomenon number again (3) and the issuance
number, "01," for this phenomenon. The CWA was issued at 2140Z and is valid until 2340Z.
ZKC3 CWA 032140
ZKC CWA 301 VALID UNTIL 032340
ISOLD SVR TSTM OVER KCOU MOVG SWWD 10KTS
Figure 3-6 CWA Example
AIRMETs also advise of significant weather phenomena other than convective activity but indicate
conditions at intensities lower than those that trigger SIGMETs. Both are intended for dissemination
to all pilots in the en route phase of flight to enhance safety, and are available for preflight planning,
SEVERE WEATHER WATCHES, MILITARY ADVISORIES, AND PIREPS