U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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Storm Prediction Center ac 210822 


Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0222 am CST Thu Feb 21 2019 


Valid 231200z - 241200z 


..there is an enhanced risk of severe thunderstorms Saturday 
through Saturday evening across parts of central/eastern 
Arkansas...the Missouri bootheel...western/central 
Kentucky...western/middle Tennessee...northern Mississippi and 
northwestern Alabama... 


... 
An organized cluster of severe thunderstorms may evolve Saturday in 
a corridor across the Ozark Plateau through the lower Ohio Valley, 
with additional severe storms possible across the lower Mississippi 
into Tennessee valleys. Considerable wind damage may accompany 
these storms along with the risk for tornadoes, some of which could 
be strong. 


... 
In phase with the subtropical westerlies, a vigorous short wave 
impulse of mid-latitude Pacific origins is forecast to accelerate 
northeast of the Southern Plains through the Great Lakes region 
during this period. Strong cyclogenesis may already be underway by 
12z Saturday near the Texas/Oklahoma Panhandle vicinity, and models 
continue to indicate that the rapid evolution of a broad and deep 
cyclone will proceed northeastward into the Great Lakes region by 
the end of the period. 


This likely will include the intensification of a cyclonic mid-level 
jet, including speeds in excess of 100 kt at 500 mb, across the 
Southern Plains Red River valley, through the middle Mississippi and 
Ohio valleys. Across the evolving warm sector, models indicate that 
south/southwesterly winds will strengthen to 50-70+ kt through the 
850-700 mb layer. 


Although the warm frontal zone probably will surge north of the Ohio 
River, and into/through the lower Great Lakes region by late 
Saturday evening, an initial position roughly along the Ohio River 
west-southwestward into the Ozark Plateau may provide the main focus 
for severe thunderstorm potential. Early period convection, 
associated with weak elevated destabilization above the front, may 
inhibit, or at least slow, boundary-layer destabilization to the 
north, while leaving a remnant surface boundary. 


In association with the onset of stronger surface pressure falls, 
surface dew points are expected to increase through the lower/mid 
60s along and south of this boundary. Coupled with strengthening 
large-scale ascent, this is expected to contribute at least weak 
boundary-layer destabilization supportive of an evolving organized 
mesoscale convective system. Cape on the order of 500+ j/kg appears 
possible. Given the strength of the environmental wind fields (and 
shear) within the convective layer, the convective system may be 
accompanied by considerable potential for strong and damaging wind 
gusts. 


It appears that this may initiate over parts of central and eastern 
Arkansas by midday, before progressing east-northeastward through 
the lower Ohio Valley by Saturday evening. A few tornadoes, some 
strong, are also possible, particularly with discrete supercells 
which may form near/just ahead of mainly the southern flank of the 
evolving system. 


More discrete storms, including supercells, may eventually develop 
as far south as the lower Mississippi Valley through portions of the 
southern Appalachians by late Saturday night. 


.Kerr.. 02/21/2019 


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