Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Wed Sep 20 2023 08:38:01

ACUS48 KWNS 200837
SWOD48
SPC AC 200836

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0336 AM CDT Wed Sep 20 2023

Valid 231200Z - 281200Z

....DISCUSSION...
An active start to the extended period is expected, with a
pronounced mid-level trough traversing the northern U.S. and an
associated surface cold front sweeping across the Plains states this
weekend. On Saturday, the primary surface low will drift eastward
across the northern Plains, with the cold front progressing eastward
across eastern portions of the Plains toward the Mid MS Valley.
Adequate overlapping shear and instability should precede the cold
front, supporting scattered severe storms across IA into eastern KS
and MO. More isolated severe storms may also form farther south
along a trailing dryline from southeast KS into northeast OK. 15
percent severe probabilities have been maintained where medium-range
guidance is in best agreement for greater storm coverage. The severe
threat may persist into Sunday as the cold front continues to sag
southward into the southern Plains. Again, adequate buoyancy and
shear may support at least an isolated severe threat. However, the
timing and position of severe storms on Sunday is highly dependent
on cold-front placement, and given that uncertainty, severe
probabilities have been withheld for Sunday.

Next week, the upper trough should deamplify, with upper ridging
gradually building into the central CONUS. Despite the upper
ridging, surface lee troughing and favorable northward moisture
transport may persist over the Plains/Midwest states, potentially
encouraging bouts of scattered thunderstorms. However, widespread
severe storms do not appear likely, and details regarding local
severe-thunderstorm evolution are too unclear to pinpoint in the
Days 6-8 time frame.

...Squitieri.. 09/20/2023

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