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Severe Storm Outlook Narrative (AC)

acus01 kwns 261222
spc ac 261221

day 1 convective outlook
nws storm prediction center norman ok
0621 am cst sun feb 26 2017

valid 261300z - 271200z

... there is a marginal risk of severe thunderstorms this evening
into tonight across parts of north and northeast texas...

... summary...
thunderstorms are expected to develop from central into northeast
texas this evening through tonight. large hail is possible with the
strongest activity.

... north and northeast tx this evening into tonight...
a low - amplitude shortwave trough over southern ca this morning will
move quickly eastward to the red river valley of tx/ok by tonight.
downstream from this trough, weak lee cyclogenesis is expected
across the southern high plains, which will help induce the
northward return of a modifying air mass from the western gulf of
mexico. boundary layer dewpoints in the 60s will spread inland
across the lower and middle tx coastal plain in a warm advection
regime, beneath relatively steep midlevel lapse rates from the west.
a few showers will be possible this afternoon across south central
and central tx (generally east of i - 35). however, the risk for
slightly - elevated thunderstorms will be greater this evening and
tonight farther to the north and northeast where low - level warm
advection and ascent will be stronger in advance of the
low - amplitude shortwave trough.

the increasing low - level moisture and 7 - 8 c/km midlevel lapse rates
could boost mucape values to near 1000 j/kg by this evening and
overnight across central tx. some storm - scale organization is
possible with convection along the northeast extent of the stronger
buoyancy, given effective bulk shear in excess of 50 kt. the
strongest storms could produce marginally - severe hail in tx, with
elevated convection expanding in coverage but weakening in intensity
while spreading eastward overnight across southern ar and northern

... western or today...
a midlevel trough will move southeastward over western or today.
isolated low - topped thunderstorms will be possible as weak buoyancy
develops inland with onshore flow and steep lapse rates associated
with cold midlevel temperatures (-34 c at 500 mb).

.. thompson/kerr.. 02/26/2017