U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 211729 
Storm Prediction Center ac 211728 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1128 am CST Thu Feb 21 2019 

Valid 221200z - 231200z 

..there is a marginal risk of severe thunderstorms from the 
arklatex to the lower Mississippi Valley... 

Strong thunderstorms may impact portions of the lower Mississippi 
Valley Friday afternoon, into the arklatex vicinity by late Friday 
night or early Saturday morning, accompanied by at least some risk 
for severe weather. 


A large-scale upper ridge will remain positioned across the eastern 
U.S. On Friday. Further upstream, an intense shortwave trough over 
the southwestern states during the morning will shift east and 
progressively become negatively tilted as it emerges over the 
southern rockies and Southern Plains by 12z Saturday. As this 
occurs, Gulf moisture will stream northward through the lower 
Mississippi Valley, with 60s dewpoints spreading as far north as 
eastern Texas into western Tennessee. As the mid/upper trough approaches the 
southern rockies, rapid Lee cyclogenesis is expected to ensue during 
the evening and overnight hours from far southeast Colorado into the OK/Texas 
Panhandle vicinity. Falling heights will beginning to overspread the 
Southern Plains and Ozark Plateau late in the period, as a 
strengthening south/southwesterly low level jet develops from East 
Texas into the Ozark Plateau. 

..eastern portions of the Southern Plains into the lower MS 

A warm front will be draped southwest-northeast from near the Upper 
Texas coast to central MS/al/SC during the morning. Showers and 
thunderstorms will likely be ongoing in the vicinity of this 
boundary in a warm advection regime. Widespread cloud cover will 
limit stronger destabilization in the warm sector, with forecast 
MLCAPE values generally less than 750 j/kg during peak heating. 
Additionally, forcing for ascent will remain limited for much of the 
period, with the warm front being the main focus for stronger storm 
development. Furthermore, given the orientation of shear vectors to 
the frontal boundary, storms will tend to track toward the cool side 
of the boundary. All of these factors will limit stronger, 
surface-based convection. However, given favorable effective shear 
greater than 40 kt and steepening midlevel lapse rates, should any 
pockets of stronger heating occur, or a storm become tied to the 
warm front, strong wind gusts and perhaps some marginal hail would 
be possible across parts of northern la into southeast Arkansas and 
western MS. 

Further west toward east TX, far southeast OK and southwest AR, 
severe concerns will remain low for most of the period. After 06z, 
increasing forcing for ascent will accompany the arrival of the 
mid/upper trough. Stronger height falls and the intensifying low 
level jet will result in more favorable conditions for convective 
development in the last 3-6 hours of the period. This convection may 
remain elevated given the nighttime boundary layer inversion, but 
strong deep layer shear will support rotating updrafts and hail 
toward Saturday morning. Should any storm become surface based 
before then, strong winds also are possible. At this time, despite 
improving low level kinematic fields, the tornado threat appears 
limited during overnight period given time of day and the elevated 
nature of expected convection. 

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

.Leitman.. 02/21/2019