U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 201727 
Storm Prediction Center ac 201727 

Day 2 convective outlook resent 1 
National Weather Service Storm Prediction Center Norman OK 
1127 am CST Tue Feb 20 2018 

Valid 211200z - 221200z 

..there is a marginal risk of severe thunderstorms from East Texas 
into Louisiana... 

Showers and embedded thunderstorms are expected from Texas through 
the lower Mississippi Valley to the Ohio Valley Wednesday. 
Marginally severe storms are possible from East Texas into 
Louisiana, with small hail possible into central Texas. 

An amplified large-scale pattern will persist into Wednesday with an 
upper ridge centered over the western Atlantic, and a large upper 
trough across the western Continental U.S.. in between, a broad region of 
strong southwest flow will exist from the Southern Plains into 
eastern Canada. Within this area of southwest flow, an intense 
low-amplitude shortwave trough will move from the upper Great Lakes 
into Quebec, with an impressive 200+ kt upper level jet Max, with 
generally neutral height tendencies aloft to the southwest, although 
a weak impulse is expected to move across Texas. 

At the surface, a cold front will extend from a low in Quebec 
southwestward across the Ohio/Tennessee valleys, and across the lower MS 
valley across southern Texas. A moist air mass with 60+ dewpoints will 
exist ahead of the front from Texas into the Ohio Valley, with dewpoints 
near 70 f across coastal Texas to the Sabine River. Warm advection in 
the lower levels coupled with lift along and north of the cold front 
will result in thunderstorm activity from Texas to OH, the strongest of 
which will exist from Texas into la. 

..East Texas into Louisiana... 
Moderately strong southwest flow aloft will persist over the area 
along with warm, moist southerly low-level flow. This is expected to 
counteract/stall the front, perhaps resulting in a weak surface wave 
along it. Models are in good agreement depicting a zone of 
thunderstorms developing by late morning through afternoon across 
east TX, continuing into western la. Low-level shear appears 
marginally supportive of rotating storms should storm Mode be 
cellular. However, a large number of storms could have negative 
impacts as far as supercell potential. Any threat is expected to end 
after 00z as lift from differential divergence tied to the large jet 
Max to the north moves away from the area. 

..much of central Texas... 
The cold front will continue to drift southward during the day, 
undercutting a moist and marginally unstable air mass and resulting 
in elevated instability. This will be maintained by a broad region 
of warm advection with 20-30 kt southerly 850 mb flow. Lift will 
occur mainly via warm advection, although a storm or two cannot be 
ruled out along the actual front across southern TX, but 0-3 km 
lapse rates will be poor there. Given cool temperatures aloft and 
sufficient instability, a few storms may be capable of marginal 
hail, but the threat does not appear high enough for a marginal risk 
at this time. 

.Jewell.. 02/20/2018