Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 210844
SWOD48
SPC AC 210843

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0343 AM CDT Thu Sep 21 2017

Valid 241200Z - 291200Z

...DISCUSSION...
The persistent, nearly stationary longwave trough over the West will
finally begin to weaken while ejecting northeastward toward Ontario
late D6/Tuesday as mid/upper ridging builds along the West Coast.
Ridging will also persist along the Gulf of Mexico, and weaker
disturbances will linger across the Southwest in the wake of the
trough.

At the surface, a meridionally oriented boundary will remain nearly
stationary across the central Plains and western Great Lakes region
through D6/Tuesday, before migrating into the southern Plains and
Lower Mississippi Valley as a surface ridge builds into the High
Plains and adjacent Rockies.

Given the overall pattern, any organized severe threat is expected
to be isolated at best - primarily due to marginal lapse rates and
relatively weak synoptic forcing.  This isolated threat should also
remain limited mostly areas near the front and along/east of a weak
surface trough in the lee of the southern Rockies.

..Cook.. 09/21/2017



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