Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS11 KWNS 262359
SPC MCD 262358
Mesoscale Discussion 0215
NWS Storm Prediction Center Norman OK
0558 PM CST Sun Feb 26 2017
Areas affected...Parts of central TX
Concerning...Severe potential...Watch unlikely
Valid 262358Z - 270200Z
Probability of Watch Issuance...5 percent
SUMMARY...Developing thunderstorms near the Austin/San Antonio metro
may pose a very isolated risk for hail, gusty winds, and perhaps
even a brief tornado over the next several hours. Watch issuance is
not expected at this time.
DISCUSSION...Visible satellite loops from the past few hours have
shown an area of weak low-level confluence and agitated cumulus
field over central TX. Better low-level moisture (surface dewpoints
in the lower to mid 60s) has developed northward from south TX and
the western Gulf through the day, and steep mid-level lapse rates
present on the 12Z DRT sounding have advanced eastward over central
TX. With some diurnal heating, MLCAPE of 500-1000 J/kg is presently
located across the discussion area, decreasing with northward extent
due to more limited moisture.
Large-scale forcing for ascent is also increasing across central TX
with the approach of a low-amplitude shortwave trough from the west.
Strong westerly to southwesterly mid-level winds attendant to this
trough are contributing to 50-55 kt of effective bulk shear, which
is more than sufficient for supercell structures. Indeed, several
low-topped supercells have been observed per the KEWX radar between
Austin and San Antonio over the past hour or two. Main limiting
factor that has suppressed more robust thunderstorm development so
far has been pronounced mid-level capping centered between 850-700
mb. Even so, with continued low-level moistening and mid-level
cooling forecast to occur over the next several hours, these
developing thunderstorms may eventually breach the cap and pose a
very isolated risk for hail approaching severe levels, strong/gusty
winds, and perhaps even a brief tornado given effective SRH of
200-250 m2/s2 across central TX.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 29559826 30869757 30839720 30589689 29859680 29409737