Severe Storm Outlook Narrative (AC)
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000
ACUS48 KWNS 220850
SWOD48
SPC AC 220849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Sat Jul 22 2017

Valid 251200Z - 301200Z

...DISCUSSION...
Medium-range models in relatively good agreement through the
forecast period, depicting gradual amplification of the flow field
aloft over the U.S.  This amplification appears likely to include
expansion/strengthening of troughing over the eastern U.S., and in
response ridging/anticylonic flow becoming more pronounced across
the Rockies.

As upper troughing expands gradually over the eastern states, a
surface cold front -- trailing from a primary low crossing the
eastern half of Canada -- will move gradually eastward across the
northeast U.S. and southward across the Plains/Ohio Valley.  By the
end of the period, models suggest that the front will reside off the
Atlantic coast, trailing westward across the southeast and southern
Plains.

Some severe risk will likely exist over the north-central U.S. Day
4/Tuesday, including portions of the northern Plains/upper
Mississippi Valley and into the western Upper Great Lakes.  This
risk area should spread east across the Great Lakes region Day
5/Wednesday, possibly extending west into the mid Missouri Valley
region.  Day 6 convective/severe potential would likely affect areas
farther east -- into the Northeast/New England and parts of the
Midwest.

At this time, will introduce 15%/slight risk across portions of the
north-central U.S. Day 4, and the upper Great Lakes region Day 5, to
highlight the aforementioned severe risk across these areas, but
will refrain from areal highlights through the latter half of the
period as uncertainty gradually increases.

..Goss.. 07/22/2017



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