Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 240531
SWODY1
SPC AC 240530

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 AM CDT Fri Mar 24 2017

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING ACROSS PARTS OF THE SOUTHEASTERN PLAINS INTO THE OZARK
PLATEAU AND LOWER MISSISSIPPI VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
SURROUNDING AREAS OF THE CENTRAL AND SOUTHERN PLAINS AND MISSISSIPPI
VALLEY...

...SUMMARY...
Severe thunderstorms are possible today across portions of the
southeastern Plains into the lower Mississippi Valley.  Strongest
activity may impact portions of the Ark-La-Tex late this afternoon
and evening, accompanied by some risk for tornadoes.

...Synopsis...
The mid/upper flow regime appears likely to remain progressive, with
models indicating troughing, within a couple of belts of westerlies
emanating from the mid-latitude Pacific, advancing inland across the
Canadian and U.S. Pacific coast during this period.  As this occurs,
an increasingly vertical stacked downstream southern branch
lower/mid tropospheric cyclone is forecast to continue east of the
central/southern high Plains, toward the mid/lower Mississippi
Valley.  The manner in which this occurs, and the rate of eastward
motion, remain points of at least some variability/spread within the
model output.

At least some weakening/filling of the cyclone appears probable, but
lower/mid tropospheric wind fields above the surface warm sector may
still remain on the order of 50-70 kt.  However, mid-level cooling
to the south and east of the cyclone center appears likely to cut
off the plume of elevated mixed-layer air emanating from the
southern Rockies/Mexican Plateau region.  And, given the state of
the air mass over the Gulf of Mexico, a deep moist return flow off
the Gulf appears unlikely.  Models also suggest that attempts at
low-level moistening may continue to be hampered by downward mixing
of dry lower/mid tropospheric air, particularly near/east of the
lower Mississippi Valley today through tonight.  All of this
contributes to uncertainty concerning the extent of the severe
weather potential,  but scattered thunderstorm activity may impact
much of the lower central and southern Plains into the lower half of
the Mississippi Valley and southern portions of the Great Lakes
region during this period.

...Plains/Mississippi Valley...
A band of remnant cloud cover, from initial convection along the
leading edge of mid-level cooling associated with the cyclone, may
prevent or slow substantive pre-frontal dryline sharpening across
the southeastern Plains today.  This adds to aforementioned
uncertainties, but low-level moistening within an axis of stronger
surface pressure falls forecast across parts of northeast Texas,
northwestern Louisiana and western Arkansas by around 23-00Z this
evening seems to provide the best opportunity/focus for vigorous
convective development.  Destabilization probably will be at least
marginally sufficient for severe storms, in the presence of strong
deep layer wind fields and vertical shear which may include sizable
clockwise curved low-level hodographs by early evening.  The
environment may become conducive to organized convection, including
supercells with at least some risk for tornadoes, in addition to
severe hail and locally strong surface gusts, before activity wanes
across the lower Mississippi Valley overnight.

Other strong storm development may not be out of the question in
closer proximity to the mid-level cold core across parts of
central/eastern Kansas and eastern Oklahoma late this afternoon and
evening, with marginally severe hail and surface gusts possible.

..Kerr.. 03/24/2017

$$


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