U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 180817 

Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0217 am CST Mon Feb 18 2019 

Valid 201200z - 211200z 

..there is a marginal risk of severe thunderstorms into the day 
Wednesday across parts of southeastern Louisiana and Mississippi 
into adjacent portions of southwestern Alabama... 

Strong thunderstorms may continue to impact parts of the lower 
Mississippi Valley into the day Wednesday, accompanied by at least 
some risk for severe weather. 

Models indicate little change to the general large-scale pattern 
from Tuesday into Wednesday. A belt of mid-latitude westerlies 
likely will remain amplified across the eastern Pacific into western 
North America, while flow remains broadly confluent downstream, 
across eastern North America, to the north of prominent subtropical 
ridging centered to the east of the Bahamas. 

While another strong short wave impulse continues to dig along the 
U.S. Pacific coast, toward the base of the larger-scale western U.S. 
Troughing, a downstream impulse emerging from the troughing is 
forecast to progress around the crest of the larger-scale eastern 
U.S. Ridging. At the same time, a gradual erosion of cold surface 
ridging appears likely to proceed to the east of the Mississippi 
Valley, and it appears that a modest cyclone may evolve within 
deepening surface troughing accompanying the lead short wave 
impulse, across the upper Midwest and Great Lakes region Wednesday 
through Wednesday night. 

Considerable convective development, including embedded 
thunderstorms, may be ongoing early Wednesday across the lower 
Mississippi and Ohio valleys, largely driven by warm advection and 
moisture return above the residual cold/stable surface-based air. 
Forcing for this elevated destabilization and convection is expected 
to spread east-northeastward across the Appalachians and northern 
mid Atlantic region through the period, while additional convective 
development persists along a trailing quasi-stationary baroclinic 
zone across the Tennessee and lower Mississippi valleys into the 
Texas Gulf Coast vicinity. 

Much of this convection may remain rooted above a cold/stable layer. 
However, a corridor of weak to modest boundary-layer instability 
developing across parts of the lower Mississippi Valley by 12z 
Wednesday may linger into at least midday, while slowly spreading 
eastward. It appears that vertical shear will remain strong enough 
across this region to maintain an environment at least marginally 
conducive to organized severe thunderstorm development, perhaps 
including supercells with the risk for a tornado or two. 

.Kerr.. 02/18/2019