Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS02 KWNS 161729
SPC AC 161728
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1128 AM CST Mon Jan 16 2017
Valid 171200Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE TX COASTAL PLAIN...
A marginal severe threat may develop Tuesday across parts of the
Texas Coastal Plain.
Positively tilted large-scale upper troughing will extend from the
Upper Midwest to the Southwest Tuesday morning, and an embedded
shortwave trough initially over the OH Valley and lower Great Lakes
region will advance eastward to the Mid-Atlantic and New England. An
upper trough/low will evolve northeastward from northwest Mexico to
the southern and central High Plains through the period. A belt of
enhanced (40-70+ kt) southwesterly/westerly mid-level flow will be
present from TX to the OH Valley in association with both upper
A surface low beneath the shortwave trough over the OH Valley/lower
Great Lakes will also develop eastward to western NY by Tuesday
evening, while a trailing cold front makes only slow southeastward
progress across the OH/TN Valleys into the lower MS Valley and TX
Coastal Plain. Forcing for ascent along the length of the cold front
is forecast to remain weak through at least Tuesday afternoon, and
better low-level moisture characterized by mid to upper 60s
dewpoints will likely be confined to parts of coastal TX/LA.
...TX Coastal Plain to the Lower MS Valley...
Isolated showers and thunderstorms may be ongoing at the start of
the period across the OH Valley into the northern TN Valley. With
modest diurnal heating occurring ahead of the front through Tuesday
afternoon, isolated thunderstorms may develop along the length of
the front from the eastern OH Valley southwestward into the lower MS
Valley. Weak low-level convergence along the front, poor mid-level
lapse rates limiting instability, and shortwave ridging over the TN
Valley into the lower MS Valley suggest the severe risk should be
minimal across these areas.
Across the TX Coastal Plain, surface dewpoints generally in the mid
to upper 60s may allow for surface-based convection to develop
along/south of the front. This appears more probable Tuesday evening
into Tuesday night as the glancing influence of ascent with an upper
trough/low over the Southwest and southern High Plains begins to
overspread the TX coast. There are some indications per NAM forecast
soundings across this region that weak instability (around 500 J/kg
MLCAPE) may be present through early Wednesday morning across the TX
Coastal Plain. Although low-level winds are not forecast to be
overly strong, sufficiently strong mid-level winds and some veering
with height should support effective bulk shear values of 35-45 kt.
Accordingly, any thunderstorms that occur along the TX Coastal Plain
might pose some gusty wind risk if they can become surface-based,
along with perhaps a brief tornado.