U.S. Severe Weather Forecast (Convective Outlook)

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000 
acus01 kwns 230523 
swody1 
Storm Prediction Center ac 230522 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1122 PM CST Fri Feb 22 2019 


Valid 231200z - 241200z 


..there is a moderate risk of severe thunderstorms across parts of 
northern Mississippi...southwest Tennessee and far northwest 
Alabama... 


... 
Scattered severe thunderstorms are expected to develop today from 
the arklatex region and lower to mid Mississippi Valley eastward 
into the Tennessee and Ohio valleys. Tornadoes, wind damage and 
isolated large hail will be possible across much of the area. 


..significant tornado and wind damage event expected across parts 
of the lower to mid Mississippi and Tennessee valleys today... 


..arklatex/lower to mid Mississippi Valley/Tennessee and Ohio 
valleys... 
a well organized negatively-tilted upper-level trough will move 
across the Southern Plains today as a 90 to 100 kt mid-level jet 
moves through the base of the trough. At the surface, a low will 
gradually deepen and move northeastward across the Central Plains 
into the lower Missouri Valley. A surface trough is forecast to 
extend southward into the lower Mississippi Valley with a moist 
airmass located across the region. Surface dewpoints in the upper 
60s and lower 70s f will overspread northern Louisiana, southeast 
Arkansas and most of Mississippi by midday. At the start of the 
period, a cluster of thunderstorms should be ongoing from northern 
Mississippi into western and middle Tennessee. The stronger storms 
embedded in the cluster may have an isolated severe threat. This 
activity is forecast to move northeastward away the moderate risk 
area allowing for the moist sector to warm up late this morning. In 
response, a corridor of moderate instability is expected to be in 
place by midday from northeast Louisiana into far southeast Arkansas 
and western Tennessee. As large-scale ascent increases ahead of the 
Southern Plains upper-level trough, thunderstorms are forecast to 
develop during the morning along the surface trough in the arklatex 
with this convection moving northeastward into southeastern Arkansas 
by midday. More isolated thunderstorms will be possible across the 
moist sector from northern Louisiana into north-central Mississippi. 
During the early to mid afternoon, convective coverage should 
increase with scattered thunderstorms moving east-northeastward 
across the enhanced and moderate risk areas. 


Rap forecast soundings across the moderate risk area from 
north-central Mississippi into southwest Tennessee at 21z show 
moderate instability and impressive kinematic profiles. MLCAPE is 
forecast to be from 1000 to 1200 j/kg with 0-6 km shear in the 50 to 
55 kt range. This will support supercell formation with cells that 
remain discrete. In addition, hodographs are long and looped with 
0-3 km storm relative helicity values in the 350 to 450 m2/s2 range. 
This low-level shear environment will be favorable for tornadoes. A 
potential for long-track significant tornadoes will exist across the 
moderate risk area from late this morning through much of the 
afternoon. Wind damage and isolated large hail will also be possible 
with supercells. A squall-line is also expected to develop and move 
across the enhanced and moderate risk areas during the late 
afternoon and early evening. Wind damage, isolated large hail and a 
few tornadoes will also be possible with the stronger thunderstorms 
embedded in the line. This squall-line with wind damage potential 
should move across middle Tennessee and north-central Alabama during 
the evening. 


Further north across the Ohio Valley, scattered thunderstorms are 
forecast to move northeastward into western Kentucky and southern 
Indiana during the afternoon. Forecast soundings at 21z for Paducah 
show MLCAPE near 800 j/kg with 0-6 km shear of 65 kt. This combined 
with strong low-level shear will be sufficient for severe storms 
capable of producing tornadoes and wind damage. Most of the severe 
convection should remain south of the Ohio River. Due to the weaker 
instability in the Ohio Valley, severe coverage is expected to be 
less. 


.Broyles/Bentley.. 02/23/2019 


$$ 

Mesoscale Discussion


000 
acus11 kwns 222352 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 222352 
msz000-arz000-laz000-230145- 


Mesoscale discussion 0121 
National Weather Service Storm Prediction Center Norman OK 
0552 PM CST Fri Feb 22 2019 


Areas affected...northeast la...southeast Arkansas and western/northern MS 


Concerning...severe potential...watch unlikely 


Valid 222352z - 230145z 


Probability of watch issuance...20 percent 


Summary...thunderstorms will increase across parts of northern 
Louisiana, southeast Arkansas and western/northern Mississippi this 
evening. Severe potential will remain limited and a watch is not 
expected. 


Discussion...widely scattered thunderstorms were developing this 
evening across northern la into west-central MS in a strong warm 
advection regime. A surface warm front was noted across central la 
into central MS/al, and should begin to advance northward with time 
tonight. As this occurs, the warm sector will continue to 
destabilize with northward extent. However, most convection is 
expected to remain elevated on the cool side of the boundary, or to 
quickly become elevated as convection crosses the boundary into 
cooler air. This will tend to limit damaging wind potential despite 
some organized updrafts in strong effective shear environment. 


Because deep layer shear is supportive of organized cells, some 
midlevel rotation may be noted as convection increases tonight. 
However, steeper midlevel lapse rates are not anticipated to spread 
eastward into the region until after 06z tonight when stronger 
height falls commence and the low level jet increases in response. 
As such, any stronger convection will be rather transient through 
the evening hours with limited potential for severe thunderstorms. 
An isolated strong storm may occur south of the mesoscale discussion area across 
southern la/southern MS where better instability exists, but weak 
shear and lack of forcing for ascent also will limit severe 
potential further south. As such, a watch is not anticipated this 
evening. 


.Leitman/Hart.. 02/22/2019 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...Meg...Jan...lzk...lch...shv... 


Latitude...Lon 32748976 31989096 31629174 31449245 31509292 31679315 
31949321 32299319 32649306 33439241 34049125 34369037 
34378993 34328953 34078924 33818916 33528915 33288924 
32748976