U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus02 kwns 190540 
swody2 
Storm Prediction Center ac 190539 


Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1139 PM 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 portion 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. 


... 
Latest model output suggests little appreciable change from prior 
runs. The westerlies emanating from the mid-latitude Pacific appear 
likely to remain amplified, with at least some further amplification 
of embedded ridging over the northeast Pacific into downstream 
troughing inland of the U.S. Pacific coast. The cyclonic regime is 
likely to be reinforced by a strong short wave trough digging along 
the coast, as a vigorous downstream impulse emerges from the 
larger-scale western U.S. Troughing. 


As the northwestern periphery of a prominent subtropical ridge, 
centered east of the Bahamas, remains strong across parts of the 
southeast, the lead impulse is forecast to accelerate around it, 
into a broadly confluent regime near/north of the Great Lakes 
region. Although it may undergo considerable deformation, models 
suggest that it may still support the evolution of a modest cyclone 
within deepening surface troughing across the upper Midwest and 
Great Lakes region, as a gradual erosion of cold surface ridging 
proceeds to the east of the Mississippi Valley. 


Above the residual cold/stable surface-based air, weak 
destabilization associated with a moist southerly return flow off 
the western Gulf of Mexico may be contributing to considerable 
convective development, including embedded thunderstorms, at the 
outset of the period across the lower Mississippi and Ohio valleys. 
Across the Ohio Valley, this likely will be aided by warm advection 
associated with a strong low-level jet (including 50-70 kt at 850 
mb). This jet is forecast weaken while shifting east-northeastward 
across the central Appalachians and mid Atlantic region, but models 
indicate forcing for ascent will support secondary frontal wave 
development near/east of the northern mid Atlantic coast late 
Wednesday night. 


By 12z Thursday, the primary low-level frontal zone is expected to 
become quasi-stationary to the west-southwest of this feature, 
across the mid Atlantic coast and southern Appalachians through the 
lower Mississippi Valley and Texas Gulf Coast region. This boundary 
is expected to provide a continuing focus for mostly weak 
thunderstorm development, associated with moist return flow above/to 
the cool side of it. 


..southeast Louisiana/Mississippi/adjacent Alabama... 
Weak surface troughing is expected to provide the focus for boundary 
layer moisture return (including surface dew points rising through 
the lower/mid 60s f) and associated weak to modest destabilization 
Tuesday night. It appears that this will linger in a corridor 
inland of the coast through the day Wednesday, gradually shifting 
across/east of the lower Mississippi Valley, but with little 
enlargement, with a residual near-surface stable layer expected to 
linger northward/northeastward into the Tennessee Valley and 
Piedmont to the Lee of the southern Appalachians. 


Before the strong low-level jet to the north progresses further away 
from the region, it appears that lingering 30-40 kt southerly 850 mb 
flow may contribute to sizable low-level hodographs and the 
maintenance of an environment at least marginally conducive to 
organized severe thunderstorm development, including supercells, 
into the day Wednesday. This may include a risk for a tornado or 
two, in addition to a few potentially damaging wind gusts. 


..Pacific coast/intermountain west... 
Despite the strength of the digging upper trough, a generally cold 
low-level environment inland of coastal areas appears likely to 
minimize the potential for thunderstorm activity. 


..maximum risk by hazard... 
Tornado: 2% - marginal 
wind: 5% - marginal 
hail: 5% - marginal 


.Kerr.. 02/19/2019 


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