SPC AC 181256
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0656 AM CST Mon Dec 18 2017
Valid 181300Z - 191200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Isolated to widely scattered thunderstorms are expected from parts
of Texas to southern Georgia through tonight.
...Synopsis...
In mid/upper levels, the pattern will remain characterized
predominantly by split flow over the central/Southern Rockies, then
nearly zonal downstream across the eastern 1/2-1/3 of the nation. A
well-defined cyclone aloft -- now evident in moisture-channel
imagery over southern AZ and northern Sonora -- is forecast to move
eastward to near ELP by 12Z. By then, the accompanying shortwave
trough should extend from southwestern KS through the low to the
west-central MX Pacific coast.
At the surface, a wavy/quasistationary frontal zone was analyzed
from just offshore NC across southern SC and southeastern AL, to a
weak wave low just offshore Padre Island, and into eastern MX. The
boundary is expected to become more diffuse and move northward as a
warm front from about MS westward, while remaining nearly stationary
eastward to the Atlantic coast. This will occur as low-level lee
troughing becomes better-defined over the central/southern High
Plains, aiding in warm advection to its east, and north of the
surface front.
...LA-GA...
A broad fetch of low-level warm advection and moisture transport
will maintain/increase theta-e across the Gulf coastal region today.
Even though lapse rates aloft will remain modest, and anticyclonic
to zonal flow will prevail aloft, sufficient buoyancy should develop
to support sporadic/episodic patches and streamers of convection,
with embedded thunder. This includes ongoing activity noted across
parts of LA/MS, which will shift east-northeastward through the
remainder of this morning. Overall convective coverage should
diminish later this afternoon into tonight as the stronger low-level
lift redevelops farther west.
...South TX...
From late this afternoon through tonight, aforementioned lee
troughing and related theta-e advection should lead to gradually
increasing buoyancy. Isolated thunderstorms should begin within the
associated expanding precip area this evening, with coverage
potentially growing to widely scattered or scattered late tonight
across parts of south-central to east-central TX as the elevated
inflow region continues to warm/moisten. Instability (surface and
aloft) should be too weak to support an organized severe threat.
..Edwards.. 12/18/2017
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