(All days are valid from 12 UTC - 12 UTC the following day)
Note: A severe weather area depicted in the Day 4-8 period indicates 15%, 30% or higher probability for severe thunderstorms within 25 miles of any point.
PREDICTABILITY TOO LOW is used to indicate severe storms may be possible based on some model scenarios. However, the location or occurrence of severe storms are in doubt due to: 1) large differences in the deterministic model solutions, 2) large spread in the ensemble guidance, and/or 3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of organized severe storms appears unlikely (i.e., less than 15%) for the forecast day.
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 220759
SPC AC 220759
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 AM CDT Fri Sep 22 2017
Valid 251200Z - 301200Z
The slow-moving longwave trough over the West will finally begin to
weaken and eject northeastward toward the western Great Lakes region
around D5/Tuesday. Ahead of this trough, surface cyclogenesis
should occur in Wisconsin that, when combined with weak
surface-based destabilization, may result in a risk for isolated
severe storms during the afternoon and evening.
Beyond this period, models diverge substantially with regard to a
remnant cut-off low over the Southwest and a downstream trough near
the Great Lakes. Despite differences in the mid/upper synoptic
pattern, models generally suggest varying degrees of surface ridging
across the northern Rockies and central Plains that should result in
a cooler, drier airmass spreading into these areas. With modified
maritime air shunted south of more active westerlies (nearer the
Great Lakes and vicinity), it appears that any organized severe risk
should be on the decrease.
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