U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 181729 
Storm Prediction Center ac 181728 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1128 am CST Mon Feb 18 2019 

Valid 191200z - 201200z 

..there is a marginal risk of severe thunderstorms across parts of 
East Texas into the lower MS valley... 

Strong thunderstorms may impact parts of East Texas into the the 
lower Mississippi Valley Tuesday evening and overnight, accompanied 
by at least some risk for severe weather. 

Large-scale troughing over the western Continental U.S. Will progress eastward 
over the plains on Tuesday. An embedded shortwave trough is forecast 
to move northeastward from the southwest to the southern/Central 
Plains by Tuesday evening, with shortwave ridging likewise building 
over the upper Midwest and Great Lakes. At the surface, a broad area 
of high pressure over the central/eastern Continental U.S. Will gradually shift 
eastward to the vicinity of New England through the period. 
Low-level moisture return will likely occur across parts of East Texas 
into the lower MS valley as a weak surface low/trough forms across 
this region late Tuesday evening into the overnight. 

..East Texas into the lower MS valley... 
Elevated thunderstorms will likely be ongoing Tuesday morning from 
parts of northeast Texas into Arkansas/MS in a zone of low-level warm air 
advection and related isentropic ascent. With only weak instability 
expected across this region, the severe potential appears quite low 
through the morning. Weak mid-level height falls and large-scale 
ascent should begin to overspread East Texas and the lower MS valley by 
late Tuesday evening, and pronounced warm and moist air advection 
associated with a 40-50+ kt southerly low-level jet should Foster an 
increase in thunderstorm coverage. Modestly steep mid-level lapse 
rates coupled with the increased low-level moisture will likely 
support MUCAPE around 1000-1500 j/kg across this region. A strongly 
veering and strengthening wind profile is also forecast to be 
present through mid levels. Effective bulk shear values of 40-50 kt 
will support organized updrafts, potentially including some 
supercells. Marginally severe hail should be the main severe threat 
with initial development over parts of East Texas into western la 
beginning Tuesday evening, as thunderstorms will likely be rooted 
above a shallow near-surface stable layer. 

Increasing low-level moisture return across southern and central 
la/MS during the overnight hours suggests some potential for 
near-surface-based thunderstorms. There is still considerable 
uncertainty with the northward extent of low to mid 60s surface 
dewpoints due to differences in the track and strength of a weak 
surface low forecast to develop northeastward over this area. This 
uncertainty impacts the potential for severe thunderstorms late 
Tuesday night into early Wednesday morning. Strong to locally 
damaging straight-line winds could occur with any thunderstorms 
forming along the surface trough/front. A tornado could also occur 
given the strong low-level shear present. With large-scale forcing 
remaining generally north of this region, and the low-level jet also 
shifting northward into the mid MS, TN, and lower Ohio Valley late in 
the period, the overall severe threat should remain isolated. Have 
opted to maintain marginal risk with some expansion given these 
uncertainties and limiting factors. 

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

.Gleason.. 02/18/2019