Severe Storm Outlook Narrative (AC)
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000
ACUS03 KWNS 260721
SWODY3
SPC AC 260721

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0221 AM CDT Fri May 26 2017

Valid 281200Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS...ARKLATEX...MID MISSISSIPPI VALLEY AND OHIO
VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
SLIGHT RISK ACROSS PARTS OF THE SOUTHERN PLAINS...ARKLATEX...MID
MISSISSIPPI VALLEY...OHIO VALLEY...GREAT LAKES...CENTRAL
APPALACHIANS AND CAROLINAS...

...SUMMARY...
Scattered severe thunderstorms with a threat for large hail, wind
damage and a few tornadoes will be possible on Sunday across parts
of the mid Mississippi and Ohio Valleys. Large hail and wind damage
will also be possible across parts of the southern Plains and
Arklatex.

...Mid Mississippi Valley/Ohio Valley...
An upper-level trough is forecast to move eastward into the mid to
upper Mississippi Valley on Sunday as a cold front advances
southeastward into the Ohio and mid Mississippi Valleys. A moist
airmass is forecast ahead of the front with surface dewpoints in the
mid to upper 60s F. This should be enough for the development of
moderate instability by afternoon across prats of western Tennessee,
Kentucky, southern Indiana and Ohio. Model forecasts along this
corridor generally develop scattered convection during the late
afternoon as the upper-level trough approaches. GFS forecast
soundings at 00Z/Monday from Memphis, Tennessee northeastward to
Louisville, Kentucky show MLCAPE values of 2000 to 2500 J/kg with
0-6 km shear values from 40 to 50 kt. If the convection can develop
into clusters with discrete cells, then the environment would
support supercells with large hail, wind damage and possibly a
tornado threat. If convection tends to organize into line segments,
wind damage could be the primary threat. A tendency to go linear may
be the more likely outcome due to unidirectional wind profiles and
the deep-layer shear vectors being somewhat parallel to the
boundary. The exact corridor with the highest severe threat will
likely depend upon the position of the cold front by late Sunday
afternoon.

...Southern Plains/Arklatex...
Westerly to west-southwesterly mid-level flow is forecast to be in
place across the Southern Plains and Arklatex on Sunday as a cold
front advances southeastward across the region. Ahead of the front,
surface dewpoints are forecast to be in the upper 60s and lower 70s
F with a corridor of moderate to strong instability in place by
afternoon. Model forecasts appear to develop convection along the
front and on the cool side of the front Sunday afternoon and
evening. GFS forecast soundings near the front at 00Z/Monday across
the Texas Hill Country and Arklatex show strong instability (MLCAPE
of 2500 to 4000 J/kg) with 0-6 km shear in the 30 to 40 kt range.
This combined with steep lapse rates in the 500-300 mb layer would
support supercell development with isolated large hail. Wind damage
would also be possible especially with storms that can persist and
develop mature downdrafts.

..Broyles.. 05/26/2017

$$



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