Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 210736
SWOD48
SPC AC 210734

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0234 AM CDT Mon May 21 2018

Valid 241200Z - 291200Z

...DISCUSSION...
Medium-range models continue to suggest seasonally weak steering
currents across much of the CONUS this week. This flow regime is
problematic in a predictability perspective beyond a day or two due
to influential convective clusters that may or may not be resolved
by current model guidance. Much of this convection may ultimately
produce some severe due to a gradually moistening and increasingly
buoyant air mass.

One region where predictability is somewhat higher will be across
the northern Plains/upper MS Valley region. There is reason to
believe a notable, but weak, short-wave trough will top the Plains
ridge during the day4 period over the Dakotas, then dig southeast
into MN Friday. While forecast deep-layer shear will not be that
strong, it appears steep lapse rate plume and increasing instability
should lead to convection across this region, some of which may be
severe. Will not introduce 15% severe probs across this are due to
aforementioned caveats; however, a severe risk may be issued across
this region in subsequent outlooks if confidence increases.

..Darrow.. 05/21/2018



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