Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 232054
SPC MCD 232053

Mesoscale Discussion 0312
NWS Storm Prediction Center Norman OK
0353 PM CDT Thu Mar 23 2017

Areas affected...Extreme southeastern Wyoming...portions of the
Nebraska Panhandle...southwestern Nebraska...extreme northwestern

Concerning...Severe potential...Watch likely

Valid 232053Z - 232300Z

Probability of Watch Issuance...80 percent

SUMMARY...Widely scattered thunderstorms will develop in the next
few hours. Severe hail and wind gusts are the main threat, but a
brief tornado or two are possible in a narrow zone near and around
the warm front.  A severe thunderstorm watch will likely be needed.

DISCUSSION...Large-scale forcing for ascent associated with an upper
low is slowly approaching the area and contributing to a broad area
of lowering surface pressures across the central high plains.
Separate low pressure near CYS and the other over
southeastern CO should consolidate into a single low over
northeastern CO this evening.  A dryline stretches from far
southwestern KS to near OGA, where it intersects an E-W warm front
that has been reinforced by persistent low-level clouds and showers
from LBF to points east.

Very steep mid-level lapse rates...from 8.5 to 9 C/km...and a tongue
of mid-to-upper 50s boundary layer dewpoints...are contributing to
MLCAPE of 1000-2000 j/kg in the warm, moist air mass. Deep layer
bulk shear of 50-70 kt oriented at a large angle to the dryline and
warm front will support discrete supercells.  Any storms that
develop along the dryline south of the warm front will move into a
high-LCL environment supportive of severe wind gusts, and steep
lapse rates will support severe hail with any of the storms.  As
storms move northeast and interact with the warm front...local
enhancement of low-level shear and lowered LCLs could support
low-level rotation.  However, given the strong reinforcement of the
cool air north of the warm front and relative fast storm
motions...35-40 kt...oriented at a large angle to the front, only a
brief period will exist where a tornado or two will be possible
before the storms interact with the stable boundary layer.  Severe
hail will still be possible with these storms, however, as they
become elevated above the front.

Although the boundary layer is drier over the Nebraska
panhandle...with dewpoints in the upper 30s to mid 40s...very steep
low and mid-level lapse rates are supporting 250-1000 J/kg of
MUCAPE. Deep inverted-V profiles suggest severe wind gusts and hail
are the primary threats in this area, although severe hail will also
be possible.

Given the above expectation of a severe threat emerging in the next
few hours, a severe thunderstorm watch will likely be needed for
parts of the area.

..Coniglio/Hart.. 03/23/2017

...Please see for graphic product...


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