Severe Storm Outlook Narrative (AC)
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ACUS03 KWNS 240619
SPC AC 240618

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0118 AM CDT Tue Apr 24 2018

Valid 261200Z - 271200Z


A few thunderstorms are possible from the Sierra Nevada region into
the Pacific Northwest. Isolated thunderstorms might also occur from
a part of the southern and central Plains to the middle Mississippi
Valley as well as over a portion of the Southeast States.


Several vorticity maxima will move through a broad synoptic trough
situated over the eastern two thirds of the U.S. Thursday. Farther
west a closed upper low will move into northern CA and the Pacific
Northwest region. Shortwave trough expected to be over the lower MS
Valley early Thursday will continue through the Southeast States
accompanied by a weak surface low and cold front that will move
through the northern Gulf. Farther west an upstream trough will
advance southeast through the central and southern Plains as well as
the MS valley region accompanied by another frontal surge.

...Southeast States...

With limited moisture return inland and weak lapse rates,
instability will remain very marginal with MUCAPE well below 500
J/kg. However, forcing for ascent accompanying the shortwave trough
and its attendant boundaries will promote shallow and weak
convection advancing through the Gulf Coast states during the day.
Isolated lightning strikes cannot be ruled out with this activity.

...Southern and central Plains through middle Mississippi Valley...

Very limited low-level moisture will reside in pre-frontal warm
sector, but mid-level lapse rates and boundary-layer warming in
conjunction with frontal ascent might be sufficient to initiate
shallow convection. Some of this activity might become deep enough
for a few lightning strikes. Other elevated convection will be
possible into the overnight within band of ascent accompanying the
shortwave trough, and some of this activity might also produce
isolated lightning strikes.

....Northern Sierra Nevada through the Pacific Northwest...

Steep mid-level lapse rates will reside in this region in advance of
the approaching upper trough. Isolated thunderstorms cannot be ruled
out over the Sierra Nevada during the afternoon and early evening.
However, greater thunderstorm chances (with updraft bases rooted
above 700 mb) are expected overnight from northern CA into western
OR when ascent accompanying a vorticity maximum rotates through the
upper low circulation and onshore.

..Dial.. 04/24/2018

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