Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Nashville, TN...New Orleans, LA...Virginia Beach, VA...Atlanta, GA...Raleigh, NC...
SPC AC 221623
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1123 AM CDT Sat Apr 22 2017
Valid 221630Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
LOWER MISSISSIPPI AND TENNESSEE VALLEYS...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN
VIRGINA AND NORTHERN NORTH CAROLINA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ELSEWHERE FROM
LOUISIANA TO THE VIRGINIA/NORTH CAROLINA BORDER REGION...
A few severe thunderstorms capable of damaging wind gusts and large
hail will be possible this afternoon and evening from Louisiana to
the southeastern Virginia/North Carolina Tidewater region. The
best-organized potential appears to be from parts of Mississippi
into western/northern Alabama and southern Tennessee, and over
southern Virginia and extreme northern North Carolina.
...Mississippi and Tennessee Valleys...
A well-defined vorticity maximum over Missouri is forecast by model
guidance to move eastward over the Mississippi Valley tonight as the
associated upper trough amplifies during the period. A strong band
of mid/upper level winds is located on the southern periphery of the
system with a 60-70 kt mid-level jet streak progressing toward the
lower Mississippi Valley.
At the surface, a low near the Mississippi Delta will move slowly
eastward across northern parts of Mississippi and Alabama through
tonight, as a trailing cold front moves southeastward across the
lower Mississippi Valley. A quasistationary front extending eastward
from the low is forecast to sag slowly southward with time.
Earlier clouds over northern/central Mississippi into northern
Alabama and southern middle Tennessee have diminished substantially
permitting stronger diabatic heating to occur in advance of the
approaching cold front. With surface temperature warming into the
70s and dew point values in the low-mid 60s, further destabilization
is likely in the pre-frontal environment with MLCAPE reaching
1000-1500 J/kg this afternoon. CAM guidance indicates stronger
storms will develop along/ahead of the cold front during the early
afternoon with activity spreading eastward through the evening
hours. Effective bulk shear of 35-40 kt will promote organized
storm structures including isolated supercells. Stronger cells will
be capable of producing mainly damaging wind gusts and severe hail.
...Southern Virginia/Northern North Carolina...
The environment is undergoing strong diabatic heating over North
Carolina where visible satellite imagery indicates few clouds, and
low-level warming is spreading northward into far southern Virginia
as cloud cover thins near an east-west frontal zone. Despite modest
mid-level lapse rates, surface dew points in the low-mid 60s coupled
with diurnal heating will result in further destabilization with
MLCAPE near 1500 J/kg expected this afternoon. Storms are beginning
to develop at this time over northwest North Carolina and southwest
Virginia within a weakly-capped environment. Activity is expected
to increase in coverage and intensity and spread/develop eastward
during the afternoon with a few severe storms possible. See
Mesoscale Discussion 545 for more details.
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