Severe Storm Outlook Narrative (AC)
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955
ACUS48 KWNS 200821
SWOD48
SPC AC 200820

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0320 AM CDT Wed Sep 20 2017

Valid 231200Z - 281200Z

...DISCUSSION...
A slowly evolving western trough/eastern ridge pattern should
continue throughout the extended forecast period, although models
suggest that the trough may begin to weaken and migrate eastward
with time - especially after D6/Monday.  Meanwhile at the surface, a
nearly stationary, NNE-SSW oriented cold front will gradually shift
southward across portions of the Plains in advance of a building
surface ridge across the Dakotas.  A lee surface trough will also
remain nearly stationary across eastern New Mexico and vicinity.
Although model variance regarding specific surface boundary
positioning increases with time, the overall pattern suggests that
areas of showers and thunderstorms will continue (especially
during/after peak heating hours) from eastern New Mexico northward
to central Nebraska and into portions of the Upper Midwest around
D4/Saturday and D5/Sunday.  This general region of convection should
shift southeastward into the central and southern Plains from
D6/Monday onward.  At least a Marginal risk for severe storms should
exist during each of these periods - especially in eastern New
Mexico nearer to steeper mid-level lapse rates.  General uncertainty
regarding frontal position and magnitude of buoyancy preclude severe
probabilities at this time.

..Cook.. 09/20/2017



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