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SPC Day 2 Outlook
Day 1 Day 2 Day 3 Day 4-8
SPC Day 2 Outlook Categorical
ACUS02 KWNS 210446
SPC AC 210445

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1145 PM CDT Fri Oct 20 2017

Valid 221200Z - 231200Z


At this time, the risk for severe storms appears negligible across
the U.S., Sunday through Sunday night.

Models continue to indicate that the mid-latitude westerlies will
undergo considerable amplification through this period across the
Pacific into western North America.  This appears likely to include
building upper ridging near the Pacific Northwest/British Columbia
coast, to the north of increasingly prominent subtropical ridging
across the lower latitude eastern Pacific and much of southwestern
North America.

Downstream of the building ridge, larger-scale troughing appears
likely to continue to develop eastward across central Canada and
adjacent portions of the north central United States.  Within this
regime, one significant short wave perturbation may dig through the
international border area and northern U.S. Plains, while another
pivots through the Hudson/James Bay region, accompanied by a deep
surface cyclone.

Much more uncertainty persists with another initially digging short
wave impulse, which is generally forecast to split away from the
northern cyclonic regime, before turning eastward toward the lower
Mississippi Valley.  Rather large spread remains readily evident
among the models and within the ensemble output of the various
models concerning this latter feature.

...South central U.S...
One low-level southward surge of cooler air in the wake of the
Hudson/James Bay cyclone is expected to reach the Ozark Plateau and
southern Plains by 12Z Sunday, before continuing southeastward
through the lower Mississippi Valley and Texas Gulf Coast region.
Of particularly note, seasonably high moisture content air seems
likely to continue to advect inland off the Gulf of Mexico in a
corridor along/ahead the front.  This may provide potential for weak
to moderate boundary layer destabilization by Sunday afternoon,
despite the presence of generally weak mid-level lapse rates ahead
of the mid-level cold core, which is expected to lag to the west of
the front.  Coupled with the potential for modest strengthening of
lower/mid tropospheric wind fields, an environment becoming
conducive to localized pockets of strong/severe storm development
may not be completely out of the question, mainly across parts of
southeast Texas, Louisiana, and perhaps Mississippi.  However, at
least some guidance is suggestive that the front, or pre-frontal
outflow associated with weakening convection, may surge through much
of this region fairly early in the day.  Given this complication, in
conjunction with the previously noted sizable spread within the
model output, the risk for severe storms still appears negligible
through this period (i.e. less than 5 percent).

..Kerr.. 10/21/2017


The Thunderstorm Outlook is created by the Storm Prediction Center in Norman, OK.
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