Convective Outlook

U.S. Severe Weather Forecast

acus01 kwns 231952 
Storm Prediction Center ac 231950 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0150 PM CST Sat Feb 23 2019 

Valid 232000z - 241200z 

..there is a moderate risk of severe thunderstorms from central 
through northern Mississippi into southwest and south central 
Tennessee and northwest Alabama... 

Threat for a few strong tornadoes, scattered damaging winds, and 
isolated large hail should persist through this evening across the 
lower Mississippi Valley into the Tennessee Valley. The most likely 
period for strong tornadoes is expected through 8 PM CST across 
northern Mississippi, southwest and far southern middle Tennessee, 
and northwest Alabama. 

..lower Mississippi through Tennessee Valley region... 

Primary change to previous outlook has been to trim from the west 
behind broken line of storms. The warm sector continues to 
destabilize from northeast la and especially central through 
northern MS where pockets of diabatic warming have boosted 
temperatures into the mid-upper 70s. The special 18z radiosonde observation data from 
Jackson MS sampled the warm sector and indicated around 1000 j/kg 
MLCAPE. Scattered pre-frontal showers and thunderstorms have been 
slow to intensify due to an inversion present around 700mb. However, 
as the primary zone of forcing along the warm conveyor belt shifts 
eastward and interacts with the destabilizing boundary layer, some 
storms should evolve into supercells given favorable wind profiles 
with 60+ kt effective bulk shear and 200-400 m2/s2 0-1 km storm 
relative helicity along the strengthening low-level jet. 

.Dial.. 02/23/2019 

Previous discussion... /issued 1018 am CST Sat Feb 23 2019/ 

..lower MS and Tennessee valleys... 
No change made to previous outlook except behind ongoing convection 
in The Ark-la-tex. Overall forecast scenario is anticipated to 
unfold from midday through tonight. 

A surface cyclone over far northwest OK will translate quickly 
northeastward, reaching southern WI around midnight. The cyclone 
will deepen rapidly in conjunction with an ejecting midlevel 
shortwave trough and the left-exit region of a strengthening (100+ 
kt) mid-upper jet streak. The deepening cyclone will draw the moist 
warm sector northward from the central Gulf Coast states into parts 
of the mid-south to perhaps as far north as the lower Ohio Valley 
later this afternoon/evening to the east of a cold front, as a 50-60 
kt low-level jet shifts across the northern part of the warm sector. 
Marginally severe hail could occur with the stronger elevated storms 
across the mid MS valley, but the primary severe threat is expected 
farther to the south in the warm moist sector. 

Ongoing convection across the Sabine valley into southern Arkansas will 
increase in coverage/intensity as large-scale ascent overspreads the 
northwest portion of the rich moist sector characterized by upper 
60s to lower 70s boundary-layer dew points. The most robust 
insolation appears to be underway downstream of this activity across 
northern la into central/northern MS where surface temperatures 
should warm into the upper 70s. This will support afternoon MLCAPE 
of 1000-2000 j/kg, with only weak convective inhibition. 
Semi-discrete storms are expected within the lingering band of 
ongoing convection, and in the open warm sector, given strong 
deep-layer shear and substantial cross-boundary shear vectors. The 
tornado threat will be greatest from about 20-02z across 
central/northern MS into northwest Alabama and southwest Tennessee. A few strong 
tornadoes appear probable given 0-1 km/effective srh of 300-500 
m2/s2 and effective bulk shear near 60 kt in the rich moist 
environment. Thereafter, storms should weaken by 03-06z, though 
isolated tornado/damaging wind potential could persist into the 
early morning across northeast Alabama/northwest Georgia where storms will 
encounter a remnant wedge front. 


Mesoscale Discussion

acus11 kwns 232301 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 232301 

Mesoscale discussion 0128 
National Weather Service Storm Prediction Center Norman OK 
0501 PM CST Sat Feb 23 2019 

Areas affected...far eastern MS into west-central and northwest Alabama 
and south-central Tennessee 

Concerning...Tornado Watch 5...6... 

Valid 232301z - 240100z 

The severe weather threat for Tornado Watch 5, 6 continues. 

Summary...corridor of greatest tornado potential the next few hours 
will extend from far east-central MS into northwest/west-central Alabama 
and far south-central Tennessee. 

Discussion...radar trends over the last 30 minutes or so have 
indicated some strengthening in mid and low level storm rotation 
both in semi-discrete convection to the northwest of Meridian MS and 
further north associated with bowing line segment in Monroe County 
MS. Additional semi-discrete storms moving into far south-central Tennessee 
also continue to show signs of rotation. Overall, storms appear to 
be struggling due to a weakness in storm relative flow in the low to 
mid levels. Additionally, stronger forcing for ascent remains well 
west/northwest of the region and height falls have generally been 
rather weak. All of these factors have impacted organization and 
longevity of intense convection. 

Convection currently moving out of eastern MS into western Alabama and 
south-central Tennessee will encounter the best environment of the day, 
with regional vwp data indicating increased flow through the lowest 
3km over over the last 30-60 min. Weak backed low level flow has 
also been noted in this narrow corridor as well. This should help to 
maximize low level shear in axis of greatest heating and 
instability. As such, the greatest severe threat, and tornado 
potential, will exit the next few hours, mainly across west-central 
into northwest Alabama and adjacent south-central Tennessee. In fact, recent 
lsr from mem confirmed a tornado had been sighted in Alcorn County. 

.Leitman.. 02/23/2019 

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


Latitude...Lon 33198866 34158835 35378802 35618778 35668748 35578708 
35358686 34768679 33238704 32818728 32618765 32558832 
32668864 32808881 33198866 

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