U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 210542 
Storm Prediction Center ac 210541 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1141 PM 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 

While amplified large-scale ridging, within the mid-latitude and 
subtropical westerlies, prevails across much of the eastern U.S., To 
the north of persistent prominent subtropical ridging centered near 
the Bahamas, models suggest that mid/upper flow will undergo 
transition across the eastern Pacific. It appears that a blocking 
mid/upper ridge will become increasingly prominent near or just 
southwest of the Gulf of Alaska. Downstream of this feature, one 
short wave impulse is forecast to turn inland of the Pacific 
northwest coast and weaken, while another more vigorous perturbation 
digs to the west of the British Columbia coast. 

In response to the upstream developments, a vigorous short wave 
trough (and embedded mid-level closed low), initially near the 
southwestern U.S. International border area at 12z Friday, likely 
will remain progressive. Models suggest that it will come 
increasingly in-phase with the subtropical stream and take on an 
increasing negative tilt while accelerating across New Mexico and 
southwest Texas, into the southern High Plains. It still appears 
that associated forcing for ascent will provide support for a 
rapidly developing cyclone by 12z Saturday across the Texas 
Panhandle vicinity. 

Preceding the cyclogenesis, considerable thunderstorm activity may 
be ongoing early Friday in association with weak elevated 
destabilization above a warm frontal zone, in a corridor from The 
Ark-la-tex vicinity through the Tennessee Valley. This front may 
remain one focus for continuing convection through much of the 
period, while gradually advancing northward into and through the 
Ozark Plateau and lower Ohio Valley. 

As cyclogenesis commences, additional thunderstorm development is 
likely across parts of the Southern Plains Friday night. 

..lower Mississippi Valley... 
Models indicate that modest boundary-layer destabilization will take 
place in a corridor south of the initial warm frontal convection, 
roughly across parts of central Louisiana through portions of 
western and central Mississippi by late Friday afternoon. Aided by 
daytime heating, cape on the order of 500-1000 j/kg may develop, in 
the presence of strong shear beneath 40-50 kt mid-level flow (around 
500 mb). Although forcing to support the initiation of 
surface-based storms remains unclear, the environment may become 
conducive to the initiation of a few discrete storms capable of 
producing at least marginally severe hail and wind. 

..Southern Plains... 
Guidance generally suggests that any appreciable severe weather 
potential probably will await the onset of strengthening large-scale 
forcing for ascent associated with the developing cyclone. This may 
not begin to interact with increasing Gulf moisture return until 
late Friday night/early Saturday (23/09-12z time frame) across parts 
of northeast Texas into southeastern Oklahoma and adjacent portions 
of Arkansas and Louisiana. But the evolution of thermodynamic 
profiles characterized by increasing convective instability and cape 
on the order of 500-1000 j/kg, even if based above a residual 
near-surface stable layer, may still become conducive to storms at 
least capable of producing severe hail and wind by daybreak 

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

.Kerr.. 02/21/2019