(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 190957
SPC AC 190957
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0357 AM CST Tue Feb 19 2019
Valid 221200Z - 271200Z
Medium-range models suggest that blocking will become more prominent
at a higher latitude of the northeastern Pacific this coming weekend
through early next week. As this occurs, split downstream
westerlies will generally converge inland of the Pacific coast, with
the southern mid-latitude and subtropical westerlies generally
decreasing in amplitude across the southern tier of the United
Prior to this transition, at least one more vigorous short wave
impulse is forecast to emerge from persistent larger-scale western
U.S. troughing late this week, as a significant upstream
perturbation digs into the U.S. Pacific Northwest. Latest model
output remains similar to prior runs indicating that the lead
impulse will support strong cyclogenesis to the lee of the Rockies,
likely from the Texas/Oklahoma Panhandle vicinity through the Great
Lakes on Saturday. It still appears probable that there will be
sufficient boundary layer moisture return across the evolving warm
sector to contribute to weak to modest destabilization in the
presence of intensifying wind fields (including 50-70+ kt in the
850-500 mb layer), from portions of the lower southern Plains and
Ozark Plateau through portions of the lower Mississippi and Ohio
Valleys. Forcing for ascent may support the evolution of a
mesoscale convective system capable of producing damaging wind
gusts. This could be preceded by discrete supercell development and
an associated risk for tornadoes.
Although more uncertain, it is possible that severe weather
potential could continue eastward into portions of the Allegheny and
Cumberland Plateaus by late Saturday night. Uncertainty concerning
this potential increases further for Sunday, eastward and
southeastward across the Mid Atlantic and Southeast.
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