Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 170656
SWOD48
SPC AC 170655

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0155 AM CDT Thu Aug 17 2017

Valid 201200Z - 251200Z

...DISCUSSION...
Northwesterly flow should relax and become more zonal across the
northern Plains during the day4 period as westerlies retreat to near
the international border. Latest medium-range guidance is in general
agreement regarding this evolution and a potentially meaningful
short-wave trough is expected to progress across the northern Plains
Sunday. Higher PW plume should advance northward across the Plains
prior to this short wave and significant instability is expected to
develop along southern fringe of westerlies where strong buoyancy
should aid strong/severe thunderstorm development. Models suggest
thunderstorms will develop during the late afternoon along a frontal
zone draped across SD. This activity would then propagate toward the
upper MS Valley during the overnight hours as the short wave
progresses toward MN. Beyond day4, strong/severe convection may also
develop across portions of the upper MS Valley into the upper Great
Lakes Monday but uncertainty increases due to possible extensive
convective event the prior day and the potential for boundary-layer
air mass disruptions.

..Darrow.. 08/17/2017



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