Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 220542
SPC AC 220540

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1140 PM CST Tue Feb 21 2017

Valid 221200Z - 231200Z


The risk for severe thunderstorms appears negligible across the
U.S., today through tonight.

Within one branch of split westerlies emanating from the
mid-latitude Pacific, large-scale troughing is expected to continue
developing inland of the Pacific coast, through much of the
Intermountain West, Rockies and High Plains during this period.  A
series of significant shorter wavelength perturbations embedded
within the base this trough will remain progressive, including one
forecast to pivot across the Great Basin late this evening through
the overnight hours.  Models suggest that this feature could support
the initiation of significant surface cyclogenesis to the lee of the
Colorado Rockies by 12Z Thursday.

A preceding impulse, already emerging from the larger scale
troughing, is currently supporting frontal wave development across
parts of the northern Plains.  This latter feature is expected to
track from parts of the mid Missouri Valley this morning through the
Great Lakes region by late tonight, with the trailing cold front
advancing southeastward across the upper Mississippi Valley and
north central Plains.

Despite these developments, cooling/drying across the Gulf Coast
into the Gulf of Mexico, on northerly flow in the wake of a
lower/mid-tropospheric cyclone now digging into the eastern Gulf,
will preclude a substantive inland return flow of moisture through
this period and beyond.  This cyclonic circulation is forecast to
continue slowly southeastward across parts of southern Florida, the
Keys and the Florida Straits by daybreak Thursday, and may be
accompanied by additional surface cyclogenesis near/south of the
Keys into the Bahamas.  Even in the warm sector of this feature,
however (which may remain south/southeast of the Keys), rather
modest boundary layer moistening seems likely to contribute to
limited convective potential.  One or two rounds of thunderstorm
activity may impact the Florida Keys and portions of the Florida
Peninsula today through tonight, but the potential for severe storms
still appears negligible at this time.

Otherwise, areas of isolated to widely scattered thunderstorm
activity will be possible with the short wave impulses within and
emerging from the large-scale  upper troughing across the West.
However, convective potential, in general, is expected to remain low
across most areas.

..Kerr.. 02/22/2017

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