- Day Three
acus02 kwns 210541
Storm Prediction Center ac 210540
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1240 am CDT Tuesday Apr 21 2015
Valid 221200z - 231200z
..there is an enh risk of severe thunderstorms across parts of southern OK and
north to northeast Texas...
..there is a slight risk of severe thunderstorms across parts of OK...SW
Arkansas...TX...la and MS...
..there is a marginal risk of severe thunderstorms across parts of the Southern
Plains...arklatex...lower MS valley and central Gulf Coast states...
..there is a marginal risk of severe thunderstorms across parts of South Florida...
thunderstorms with wind damage...large hail and possibly a few
tornadoes are expected to develop from the Southern Plains
southeastward across the arklatex and into the lower Mississippi
Valley. Other storms with hail and wind damage may develop in
central Texas and the Texas coastal plains. Marginally severe
thunderstorms may develop across parts of the southern High Plains
and in south Texas. Thunderstorm development may also occur across
parts of the central to northern rockies and Sierra Nevada.
..srn plains/arklatex/lower MS valley...
An upper-level ridge is forecast to build north-northwestward across the southern High
Plains into the central rockies on Wednesday. At the surface...a low is
forecast to deepen in NE nm with a warm front extending eastward across
scntrl OK into central Arkansas. South of the boundary...surface dewpoints
should be in the lower to middle 60s f across North Texas and southern OK where
moderate instability should be in place by afternoon. Convection
appears likely to initiate by late afternoon along the warm front in
SW OK with an mesoscale convective system organizing and moving east-southeastward across southern OK into NE
Texas. There is still some question about timing but the GFS solution
seems to be reasonable with a late afternoon and early evening mesoscale convective system.
NAM forecast soundings for 00z/Thursday at Frederick OK and Vernon Texas
show 1500 to 2000 j/kg of MLCAPE with very steep middle-level lapse
rates approaching 9.0 c/km. In addition...an impressive wind-shear
environment is forecast with substantial veering with height below
850 and 0-6 km shear near 60 knots. This would favor the development of
supercells with large hail and wind damage early in the event.
Hailstones of greater than 2 inches in diameter will be possible
with the more dominant cells. A few tornadoes may occur especially
with persistent rotating storms. A relatively fast-moving mesoscale convective system may
develop a linear structure and cold pool early Wednesday evening
which could result in an enhanced wind-damage threat. The severe
threat from this convective system could extend as far southeast as
East Texas and northwest la during the evening and possibly during the early
overnight over parts of the lower MS valley.
..TX Hill Country/Texas coastal plains...
An upper-level ridge is forecast to be maintained across the Texas Hill
country and southern High Plains on Wednesday as a warm sector remains
located over much of the southern two-thirds of Texas. The airmass across
the Texas Hill country and the Texas coastal plains...away from the
immediate coast...is forecast to become moderately to strongly
unstable by Wednesday afternoon. Forecast soundings for 00z/Thursday at
Austin and College Station show MLCAPE above 3000 j/kg with lower
70s f dewpoints. In addition to the impressive
thermodynamics...deep-layer shear should be in the 50 to 60 knots
range. This should support severe thunderstorm development with
supercells the favored storm Mode. Convective coverage is the main
uncertainty with the upper-level ridge to the west. Even though
storm development should remain isolated...supercells should be
capable of producing large hail...wind damage and possibly a
An upper-level trough is forecast to move slowly eastward across the East
Coast as a belt of stronger middle-level flow moves eastward across the northern
Gulf of Mexico. A moist airmass is forecast across South Florida where
moderate instability should develop by midday. Cells that can
initiate across South Florida during the early afternoon may obtain a
marginal wind damage threat due to moderate deep-layer shear and
unidirectional wind profiles.