- 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