Severe Storm Outlook Narrative (AC)
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000
ACUS48 KWNS 270847
SWOD48
SPC AC 270846

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Sat May 27 2017

Valid 301200Z - 041200Z

...DISCUSSION...
...Tuesday/Day 4 and Wednesday/Day 5...
Both the ECMWF and GFS solutions move an upper-level trough across
the Upper Mississippi Valley on Tuesday and into the Ohio Valley on
Wednesday. Both models also maintain a broad moist sector from the
Texas Coastal Plains east-northeastward across the lower Mississippi
Valley into the Carolinas from Tuesday into Wednesday. Areas that
heat up the most along this corridor may develop a severe threat
mainly during the afternoon and evening for both days. Spatial
uncertainty is substantial at this point.

...Thursday/Day 6 to Saturday/Day 8...
Both the ECMWF and GFS develop strong moisture advection in the
Great Plains on Thursday but differ on how much instability will be
in place by Thursday afternoon. Both models show an upper-level
ridge over the high Plains which could dampen the severe threat
across much of the region in spite of the low-level moisture. The
models move the upper-level ridge eastward across the north-central
states on Saturday as an upper-level trough moves into the southern
High Plains. If this occurs, then severe thunderstorms would be
possible in the southern and central High Plains Saturday afternoon
especially if a dryline can develop. Uncertainty concerning the
spatial distribution is still substantial for Thursday and Friday.
The ECMWF and GFS solutions are quite different on Saturday
suggesting that predictability is very low late in the Day 4 to 8
period.

..Broyles.. 05/27/2017


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