Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 180845
SWOD48
SPC AC 180844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 AM CST Mon Dec 18 2017

Valid 211200Z - 261200Z

...DISCUSSION...
...Thursday/Day 4 and Friday/Day 5...
The medium-range models including the ECMWF, GFS, UKMET and Canadian
move an upper-level trough across the Desert Southwest on Thursday
and into the southern Plains on Friday. Low-level moisture is
forecast to return northward into the western Gulf Coast states on
Thursday moving eastward into the central Gulf Coast states on
Friday. It appears that thunderstorm development will be possible
from east Texas northeastward into the Mid Mississippi Valley on
Friday. Surface dewpoints in the 60s F coupled with strong
deep-layer shear may be enough for an isolated severe threat.
However, instability is forecast to remain weak which should keep
any severe threat marginal.

...Saturday/Day 6 to Monday/Day 8...
On Saturday, the ECMWF, UKMET and Canadian remain in reasonable
agreement with an upper-level trough in the western states and
southwest mid-level flow over the southern and eastern U.S. The
ECMWF keeps a moist airmass in place across the Gulf Coast states
while the GFS drives a cold dry airmass to western and central parts
of the Gulf Coast. If the ECMWF is closer to being correct, a
marginal severe threat would be possible in the lower Mississippi
Valley near a strengthening low-level jet on Sunday. On Monday,
model forecast differ markedly on the details but several solutions
have a dry airmass in place across much of the CONUS. This would
limit thunderstorm potential.

..Broyles.. 12/18/2017



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