Severe Storm Outlook Narrative (AC)
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ACUS02 KWNS 200628
SWODY2
SPC AC 200627

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1227 AM CST Tue Feb 20 2018

Valid 211200Z - 221200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Showers and embedded thunderstorms are expected from Texas through
the lower Mississippi valley to the central Appalachians Wednesday.

...Synopsis...

A broad positive-tilt synoptic trough will persist over the western
half of the U.S. Wednesday. Several embedded vorticity maxima will
eject from the Southern Plains through the OH Valley. A cold front
from the Great Lakes through south TX will continue southeast, but
may begin to stall from a portion of the lower MS Valley to Deep
south TX.

...Southern TX through the Lower Mississippi Valley...

A moist boundary layer with upper 60s F dewpoints will reside in
pre-frontal warm sector across south and southeast TX supporting
moderate instability (1000-1500 J/kg MLCAPE). Tendency will be for
low-level jet to shift northeast away from TX warm sector leaving
modest flow in the near-surface to 800 mb layer. In south TX the
east-west orientation of the cold front relative to southwesterly
winds aloft will contribute to an anafrontal regime where storms
initiating along the front will tend to become elevated as they
cross into the cool side of the boundary. Nevertheless MUCAPE from
400-800 J/kg and 45+ kt effective bulk shear could support some
threat for hail. Farther east from southeast TX through the lower MS
valley, stronger winds aloft will reside in post frontal zone with
modest deep layer and low-level shear in warm sector. Any storms
developing along warm conveyor belt should remain in an environment
marginally supportive of storm organization. Due to the potential
limiting factors, will not introduce severe probabilities this
update, but a marginal risk category might be needed for a portion
of these areas in future outlooks.

..Dial.. 02/20/2018

$$



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