Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 300821
SWOD48
SPC AC 300819

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0319 AM CDT Tue May 30 2017

Valid 021200Z - 071200Z

...DISCUSSION...
...Friday/Day 4 and Saturday/Day 5...
The ECMWF and GFS models are somewhat in agreement on Friday with a
shortwave ridge over the northern Plains, an upper-level trough over
the Great Lakes and a relatively weak mid-level flow pattern over
much of the central and southern U.S. The two models do show a
northwest-to-southeast gradient of low-level moisture from the upper
Mississippi Valley into the Great Lakes with moderate instability on
the warm side of the gradient. Convection that develops along this
corridor could have a severe threat Friday afternoon and evening
mainly due to the presence of a mid-level jet in the Great Lakes
which would enhance deep-layer shear. The mid-level jet is forecast
to move eastward across the Northeast on Saturday. Although the
upper-level pattern is different on Saturday for both the ECMWF and
GFS solutions, the models suggest the moisture gradient may still be
in place across parts of the southern Great Lakes. This would be the
area with the greatest potential for a severe threat Saturday
afternoon and evening. Spatial uncertainty is substantial for Friday
and Saturday.

...Sunday/Day 6 to Tuesday/Day 8...
The ECMWF and GFS solutions are in a bit more agreement for Sunday
with an upper-level ridge in the Rockies and an upper-level trough
in the Upper Midwest. The two solutions suggest a front could be
located from parts of the mid Mississippi Valley eastward in the
central Appalachian Mountains on Sunday. If a front ends up in that
general area, then an isolated severe threat would be possible with
thunderstorms that form along the front Sunday afternoon. On Monday,
the ECMWF and GFS solutions move the upper-level trough in the lower
Great Lakes and show a potential for convection in the Carolinas on
the southern part of the trough. This would be the area with the
greatest potential for a severe threat Monday afternoon. For
Tuesday, both solutions develop instability in the central high
Plains and show convective potential there. However, predictability
is low on Tuesday as is the case for the entire day 4 to 8 period.

..Broyles.. 05/30/2017



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