Revision 6 Feb/2009
KMD 550/850 FIS Addendum
11
Basic Service Weather Products
When an SIGMET is cancelled, neither the original report nor the cance-
lation message can be displayed.
See Appendix A for instructions on decoding textual SIGMETs.
CONVECTIVE SIGMET
A Convective SIGMET (Convective Significant Meteorological Information)
is an advisory of convective weather that the forecaster believes haz-
ardous to all aircraft. Convective SIGMETs address details regarding
severe thunderstorms, embedded thunderstorms, a line of thunderstorms,
or thunderstorms producing heavy precipitation affecting an area 40 per-
cent or more of an area at least 3,000 square miles. Convective SIGMETs
are issued hourly with a maximum forecast period of 2 hours. A
Convective SIGMET will contain elements in the following order:
1.
Region Identifier and issue date and time
2.
Report designator
3.
Validity period
4.
Area of coverage
5.
Location details
6.
Weather phenomena details
NOTE: Convective SIGMETs older than the forecast period are dis-
carded. Amended, updated or corrected Convective SIGMETs generated
withing the issuance period are provided as soon as they are available,
and the previous outdated Convective SIGMET is no longer transmitted.
See Appendix A for instructions on decoding textual Convective
SIGMETs.
ALERT WEATHER WATCHES (VDL ONLY)
Alert Weather Watches (AWW) are Alert Severe Weather Watch
Bulletins that describe areas of possible severe thunderstorm or tornado
development. These are watches, not warnings; and are issued as
needed. Severe weather may not actually develop. An Alert Weather
Watch will contain elements in the following order:
1.
Report designation and date and time of issuance
2.
Watch number, reason for issuance, area of coverage and validity
period.
3.
Watch coordinates
4.
Forecast
NOTE: Alert Weather Watches older than the forecast period are discarded.
See Appendix A for instructions on decoding textual Alert Weather
Watches.
