(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 150915
SPC AC 150915
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0315 AM CST Fri Dec 15 2017
Valid 181200Z - 231200Z
...Monday/Day 4 and Tuesday/Day 5...
The medium-range models including the ECMWF, GFS, UKMET and Canadian
show anticyclonic southwest mid-level flow across the Southeast on
Monday and Tuesday. A moist airmass is forecast to be in place
across the Gulf Coast region where scattered thunderstorms should
persist early in the week. Although large-scale ascent will be
lacking across the Gulf Coast States, lift associated with enhanced
low-level flow should support scattered thunderstorm development
Monday and Tuesday. Strong low-level and deep-layer shear will be
enough for a marginal severe threat. A few damaging wind gusts and a
marginal tornado threat will be possible.
...Wednesday/Day 6 to Friday/Day 8...
On Wednesday, the models develop an upper-level trough in the
northwestern states and move this feature quickly into the central
U.S. on Thursday. West to southwest mid-level flow is forecast to
remain in the Southeast as a cold front moves into the region on
Friday. Thunderstorm development will be possible along the front
during the day. This convection may move eastward to southern
sections of the Eastern Seaboard Friday afternoon as is suggested by
the GFS solution. However, other model solutions do not move the
front that quickly east and show much less convective potential. For
this reason, uncertainty is substantial on Thursday and Friday.
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