Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 200522
SPC AC 200520

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1220 AM CDT Fri Apr 20 2018

Valid 201200Z - 211200Z


A few strong to severe thunderstorms with a threat for hail and
downburst winds are possible over the southern High Plains, mainly
later this afternoon into early evening.

...Southern High Plains...

Upper low now approaching the Four Corners region will move through
the Southwest States today, the southern High Plains this evening
and the southern Plains tonight accompanied by a Pacific cold front.
Farther east, a large area of continental-polar high pressure will
advance through the eastern states, maintaining offshore flow over
most of the Gulf coast during the day. As a result richer low-level
moisture will remain south of a quasi-stationary front located over
the northern Gulf into deep south Texas. However, the establishment
of a southerly low-level jet will transport dewpoints in the 40s F
through the High Plains beneath steeper mid-level lapse rates
resulting in a corridor of marginal instability with 400-800 J/kg
MLCAPE. Elevated thunderstorms are likely later this morning over
northeast NM into the southern and central High Plains as forcing
for ascent now evident on water vapor imagery over northern NM
intercepts evolving corridor of moist advection and destabilization.
Upstream of the morning storms, deeper mixing over the High Plains
of New Mexico along with frontal convergence should contribute to
thunderstorm initiation across eastern New Mexico as the boundary
layer destabilizes during the afternoon. Forcing for ascent
attending the upper trough will be weaker with southward extent, but
at least isolated storms may develop over the mountains of southwest
TX. Vertical wind profiles accompanying the upper trough with strong
effective bulk shear and large low-level hodographs will be more
than adequate for organized storms including some supercell
structures capable of mainly a few instances of large hail and
downburst winds. However, the primary limiting factor for a more
robust severe threat is expected to be limited moisture return and
resulting instability. Will therefore maintain a marginal risk this

..Dial/Gleason.. 04/20/2018

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