Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS01 KWNS 170553
SPC AC 170552
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1152 PM CST Mon Jan 16 2017
Valid 171200Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF SOUTH TEXAS...
A few severe thunderstorms may affect portions of south Texas today
An upper cyclone is forecast to track from portions of the Gulf of
California and northwest Mexico to the vicinity of northeastern NM
and the TX Panhandle. A band of enhanced midlevel southwesterly flow
will extend over TX, being reinforced by the progression of a
moderate speed maximum attendant to the cyclone. In response to
these developments, modest low-level warm advection will persist
through the period across a portion of the South-Central States,
while a surface frontal zone extends from the lower MS Valley to
...Portions of south TX...
Persistent low-level warm advection will support thunderstorm
potential on the cool side of the boundary through the day and into
the overnight hours. Sufficient vertical shear beneath the enhanced
midlevel southwesterly flow (effective bulk shear around 35 to 50
kt), amid moderate midlevel lapse rates and ample high-level
venting, will support an isolated, marginally severe hail risk with
elevated convection north of the boundary.
For this evening into tonight, a slight boost in deep ascent
peripheral to the mobile cyclone may offer some near-surface-based
convective potential, near and on the warm side of the frontal
zone -- especially across portions of the TX coast. Relatively rich
low-level moisture was sampled by the Corpus Christi and Brownsville
Monday evening soundings, with mean mixing ratios around 13.2-13.4
g/kg. Similar rich moisture should persist into tonight. Sufficient
deep shear, with curved low-level hodographs, may support organized
convection capable of isolated instances of all severe hazards.
The overall compact nature of stronger mid-level height falls
tracking well to the west/northwest of richer low-level moisture,
and the only modest low-level mass response to the mobile cyclone,
and anticipated cluster-type convective mode, should tend to
marginalize the overall severe risk.