IRFP-01
Metro Review
(5) Three bulletins issued for eastern (E), central (C), and
western (W) regions
(a) Boundaries at 87 and 107 degrees west
b. WSTs shall be issued when either of the following occurs and/
or is forecast to occur for more than 30 minutes of the valid
period, regardless of the size of the area affected (i.e.,
including isolated)
(1) Severe thunderstorms
(a) May include specific information on tornadoes and/or
hail 3/4-inch or greater and/or wind gusts of 50 kts or
greater
(2) Embedded thunderstorms
(a) Occurring within and obscured by haze, stratiform
clouds, or precipitation from stratiform clouds
(b) Intended to alert pilots that avoidance by visual or
radar detection could be difficult or impossible
(3) A line of thunderstorms
(a) At least 60 miles long with thunderstorms affecting at
least 40% of the length
(4) An area of active thunderstorms affecting at least 3,000
square miles
(a) Thunderstorms having a reflectivity intensity (VIP LVL)
of 4 or greater and/or having significant satellite
signature affecting at least 40% of the area outlined
8. Special Convective SIGMETs - A WST special shall be issued
anytime when either of the following criteria are met and/or
forecast to be met for more than 30 minutes of the scheduled
WST's valid period
a. Tornado, hail 3/4-inch or greater, or wind gusts to 50 kts or
greater reported to the NAWAU forecaster or indicated when
previous WST did not mention severe thunderstorms
b. Indications of rapidly changing conditions if in the forecaster's
judgment, not sufficiently described in existing SIGMET
9. Nonconvective SIGMETs (WS)
Fig 32:
SIGMET (WS)
a. Not issued on a regular scheduled basis
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