Severe Storm Outlook Narrative (AC)
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731
ACUS03 KWNS 240725
SWODY3
SPC AC 240725

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0225 AM CDT Fri Mar 24 2017

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS OUTSIDE OF THE SLIGHT RISK AREA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN AND CENTRAL APPALACHIANS...

...SUMMARY...
Large hail, isolated wind damage and a perhaps a tornado or two will
be possible in parts of the southern Plains on Sunday. Isolated
strong wind gusts and hail may also occur in the southern and
central Appalachians on Sunday.

...Southern Plains...
An upper-level trough will move into the southern Plains on Sunday
as a surface low develops in the Texas Panhandle and moves
southeastward into the upper section of the Red River Valley. A
dryline is forecast to become established across the southern
Plains. Surface dewpoints by 00Z/Monday in north-central Texas
appear likely to reach the lower 60s F with 50s F across southern
and central Oklahoma. This should result in a narrow corridor of
moderate instability by late afternoon from the Dallas/Fort Worth
Metro extending northward to near Oklahoma City. The NAM, GFS and
ECMWF all suggest that convection will initiate along the dryline
and move eastward across eastern Oklahoma and northeast Texas during
the late afternoon and evening.

NAM forecast soundings along the corridor of instability during the
late afternoon show a supercell profile with MLCAPE of 1000 to 1200
J/kg and 0-6 km shear values of 40 to 50 kt. In addition, the
forecast soundings show steep mid-level lapse rates approaching 7.5
C/km suggesting that large hail will be possible if supercells can
form. The relatively dry airmass to the east of the dryline could
also contribute to downdraft acceleration making a few damaging wind
gusts possible as well. Although a tornado or two can not be ruled
out, the dry airmass may confine this threat to the strongest couple
of storms. Forecast soundings also suggest that convective
inhibition will increase across the southern Plains during the
evening. For this reason, severe storms that develop during the late
afternoon or early evening may become elevated after maturation.
This may prioritize a large hail threat a couple hours after
initiation. A marginal severe threat could extend south
southwestward into northern sections of the Texas Hill country but
convective initiation will likely be conditional that far south due
to less lift with southward extent.

...Southern and Central Appalachians...
A shortwave trough is forecast to move northeastward across the
southern and central Appalachians on Sunday as moisture advection
takes place due to southerly flow at the surface. The NAM suggests
that a corridor of upper 50s and lower 60s F surface dewpoints will
be established by afternoon from northern Alabama extending
northeastward into eastern Kentucky with the northern end of the
moist corridor extending into the central Appalachians. As surface
temperatures warm during the day, isolated to scattered
thunderstorms should develop along the moist corridor aided by
topographic lift associated with the Appalachians mountains.
Forecast soundings across the southern Appalachians at 21Z show
SBCAPE values of 500 to 1000 J/kg with 30 to 35 knots of 0-6 km
shear. This environment may support a marginal wind damage threat.
Hail could occur with the stronger updrafts.

..Broyles.. 03/24/2017

$$



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