U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus03 kwns 170817 
Storm Prediction Center ac 170816 

Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0216 am CST sun Feb 17 2019 

Valid 191200z - 201200z 

..there is a marginal risk of severe thunderstorms late Tuesday 
through Tuesday night in a corridor across south central through 
northeast Louisiana...southwest and west central Mississippi...and 
adjacent portions of southeast Arkansas... 

Strong thunderstorms may impact parts of the lower Mississippi 
Valley late Tuesday through Tuesday night, accompanied by at least 
some risk for severe weather. 

As another strong short wave impulse digs off the British Columbia 
coast, toward the U.S. Pacific northwest, models indicate that a 
fairly significant downstream impulse will emerge from the 
persistent larger-scale western U.S. Upper troughing during this 
period. It appears that strongest associated mid-level height falls 
will spread from the southwestern international border area, near El 
Paso, Texas early Tuesday, through the middle Missouri Valley by 12z 
Wednesday, as the northwestern periphery of subtropical ridging 
(centered east of the bahamas) maintains considerable strength. 

On this track, strongest mid-level forcing for ascent and cooling 
will remain focused well to the cool side of a quasi-stationary 
frontal zone near the northwest Gulf Coast. However, warming and 
moistening associated with a strengthening southerly return flow off 
the western Gulf of Mexico, above the surface front, appears likely 
to contribute to considerable erosion of the southwestern flank of 
the initially expansive cold surface ridging centered across the 
upper Midwest into lower Great Lakes. 

Models continue to indicate the gradual development of weak surface 
troughing along the strengthening low-level jet axis (including 
50-70 kt at 850 mb), across the lower Mississippi Valley toward the 
lower Ohio Valley by late Tuesday night. Across parts of Louisiana 
and Mississippi, this corridor may become a focus for weak 
boundary-layer destabilization by Tuesday evening, as surface dew 
points begin to increase through the lower/mid 60s f. Although this 
probably will take place in the wake of the strongest 850 mb flow 
(forecast to shift into the lower Ohio valley), lower to 
mid-tropospheric wind fields may remain sufficiently strong and 
sheared to contribute to an environment at least marginally 
conducive to organized severe thunderstorm development. 

The evolution of a narrow squall line appears possible Tuesday 
night, with isolated supercells perhaps also possible within and 
just ahead of the line, accompanied by at least some risk for a 
tornado or two, in addition to potentially damaging wind gusts. 

.Kerr.. 02/17/2019