(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 190846
SPC AC 190846
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Sat Aug 19 2017
Valid 221200Z - 271200Z
The mid-latitude westerlies may undergo further amplification
through the middle of the coming work week, including the evolution
of large-scale troughing across much of the Great Lakes, Ohio Valley
and Northeast. Within this regime, models suggest that one
significant short wave impulse could support significant
cyclogenesis across Quebec, accompanied by a trailing cold front
which may advance through much of the eastern U.S. before weakening.
There remains a signal within model output that pre-frontal forcing
for ascent may be favorably timed with peak diurnal destabilization
across parts of the lower Great Lakes region and upper Ohio Valley
on Tuesday to support considerable vigorous thunderstorm activity.
In the presence of 30-50 kt deep layer mean flow and shear,
organized severe storm development appears possible, with
potentially damaging wind gusts the primary hazard. Continuation of
this threat across southern New England and the northern Mid
Atlantic on Wednesday remains more unclear, with possible early day
progression of the front off the coast.
Thereafter, late next week into early next weekend, upper
troughiness may linger across parts of the Upper Midwest/Great Lakes
and Atlantic Seaboard, as subtropical ridging becomes increasingly
prominent across the Intermountain West and Rockies. Although short
wave developments within this regime remain more uncertain, there
appears little obvious at the present time to suggest anything more
than perhaps generally low severe weather potential.
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