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.
SPC AC 202007
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0307 PM CDT Fri Jul 20 2018
Valid 202000Z - 211200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR
WESTERN/MIDDLE TN...WESTERN/CENTRAL KY...FAR SOUTHERN IN...
The greatest threat for severe thunderstorms reamins across portions
of the Ohio and Tennessee Valley regions into the Mid-South today
into tonight, with damaging gusts, large hail and a few tornadoes
The primary change with this outlook is to reduce probabilities in
areas where significant redevelopment is not expected in the wake of
ongoing convection, and also in areas where the potential for
substantial destabilization now appears limited. Some adjustment
eastward has been made for the Slight Risk into portions of
WV/western VA, where some damaging wind threat may spread in from
To the southwest of the ongoing convection across the Ohio Valley,
redevelopment of scattered severe thunderstorms is still expected
across the Enhanced and Moderate Risk areas, though the timing and
exact location of initiation remains uncertain. A very favorable
combination of instability and effective shear continues to support
significant hail, damaging wind, and a few tornadoes with any
development over the next several hours. Multiple rounds of severe
convection remain possible, with additional storms possible into
late this evening spreading out of the central Plains into portions
of the MS Valley.
.PREV DISCUSSION... /ISSUED 1128 AM CDT Fri Jul 20 2018/
...Mid MS/OH/TN Valleys...
Morning water vapor loop shows a significant upper low tracking
southeastward across southern WI. A strong mid level jet lies to
the south of the low, extending from the northern Plains into MO.
As this upper wind max overspreads the warm sector over parts of the
Mid MS, OH, and TN Valleys, the risk of rather widespread severe
thunderstorms will develop this afternoon into tonight. A very
moist and unstable air mass has developed across this region with
pockets of MUCAPE in the 5000-6000 J/kg range. Steep low and mid
level lapse rates combined with strong effective shear values will
result in a conditional risk of severe storms throughout the region.
The primary forecast uncertainty is the timing and location of
12z model guidance shows wide diversity in where/when the most
intense convective clusters will occur later today. Due to this
uncertainty, few changes have been made to the ongoing outlook.
Discrete supercell development is possible along/ahead of the
approaching cold front due to shear vectors orthogonal to the front
and favorable shear magnitudes. Any storms that remain discrete
will pose a risk of very large hail and a tornado or two. It
appears likely that multiple clusters of storms will congeal into
fast-moving bowing structures posing a risk of rather widespread
damaging winds. This threat will likely spread as far east as
eastern KY/TN overnight.
...KS/MO/OK/AR this evening...
A surface boundary will extend from western KS into southwest MO and
northwest AR later today. Given the intense heat to the south of
boundary, and a corridor of high dewpoints immediately north of the
boundary, a zone of high CAPE values will result. There is
relatively good consensus of 12z models that show clusters of storms
forming over KS late this afternoon and tracking along this corridor
though the evening. Damaging winds and large hail will be possible
if this scenario unfolds.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z