U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus03 kwns 200820 
swody3 
Storm Prediction Center ac 200819 


Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0219 am CST Wed Feb 20 2019 


Valid 221200z - 231200z 


..there is a marginal risk of severe thunderstorms Friday afternoon 
through Friday night across parts of the lower Mississippi Valley 
into the Southern Plains... 


... 
Strong thunderstorms may impact portions of the lower Mississippi 
Valley Friday afternoon, into portions of the Southern Plains by 
late Friday night, accompanied by at least some risk for severe 
weather. 


... 
Models continue to suggest that mid/upper flow will undergo at least 
some transition across the eastern Pacific during this period, as a 
blocking ridge begins to become more prominent near the Gulf of 
Alaska. Downstream of this feature, another significant short wave 
trough is forecast to continue digging toward the U.S. Pacific 
northwest. As this occurs, guidance indicates that a vigorous short 
wave trough, initially near the southwestern U.S. International 
border area at 12z Friday, will remain progressive, and begin to 
more rapidly pivot east-northeastward across New Mexico and 
southwest Texas into the southern High Plains by late Friday night. 
It appears that this will provide support for a rapidly developing 
cyclone by the end of the period across the Texas Panhandle 
vicinity. 


Meanwhile, mid/upper ridging within the mid-latitude and subtropical 
westerlies is forecast to remain amplified across the Mississippi 
Valley through the Atlantic Seaboard, to the north/northwest of 
persistent prominent subtropical ridging (centered at mid-levels 
east of the bahamas). 


On the northwestern periphery of the subtropical ridge, weak 
elevated destabilization above a warm frontal zone may be supporting 
considerable thunderstorm development at the outset of the period in 
a corridor from The Ark-la-tex through the Tennessee Valley. This 
boundary may remain a focus for continuing convection through much 
of the period, while gradually shifting northward across the Ozark 
Plateau and lower Ohio Valley. 


Additional thunderstorm development appears likely across parts of 
the Southern Plains by late Friday night, in response to increasing 
large-scale ascent and destabilization associated with the impulse 
emerging from the southwest. 


..lower Mississippi Valley... 
Modest boundary-layer destabilization is forecast in a corridor 
south of the initial warm frontal convection, across parts of 
central Louisiana into western Mississippi by late Friday afternoon. 
This will be aided by daytime heating of a moistening air mass 
characterized by lower/mid 60s+ f surface dew points. Although it 
is possible that this may occur beneath increasingly capping 
mid-level warming, areas of enhanced low-level convergence may 
support the initiation of scattered thunderstorms. If this occurs, 
deep layer shear probably will be sufficiently strong to support 
storms capable of producing at least marginally severe hail and 
wind, which may linger into early evening. 


..Southern Plains... 
Late Friday night, increasing forcing for ascent and strengthening 
wind fields within the moistening and destabilizing warm sector of 
the developing cyclone may become supportive of increasing and 
organizing convective development. By 12z Saturday, forecast 
soundings suggest thermodynamic profiles will become characterized 
by increasing convective instability, and perhaps cape on the order 
of 500-1000 j/kg. It is possible that this may still be mostly 
based above a residual shallow stable near-surface layer, but storms 
capable of producing severe hail and wind may not be out of the 
question by daybreak. 


.Kerr.. 02/20/2019 


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