Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 091001
SPC AC 091001

Day 4-8 Convective Outlook RESENT 1
NWS Storm Prediction Center Norman OK
0401 AM CST Fri Dec 09 2016

Valid 121200Z - 171200Z

The latest GFS and ECMWF runs exhibit a fairly good degree of
model-to-model similarity, with both shifting a large vortex
southeastward across the Canadian Prairie and then eastward across
Quebec and Ontario days 4-6 (Monday through Wednesday).  However,
differences in the amplitude of the surrounding cyclonic flow field
extending into the central and -- eventually -- the eastern U.S. are
noted, with the ECMWF noting more pronounced/amplified cyclonic flow
across the U.S. than the more zonal GFS.  As a result, the ECMWF`s
surface baroclinic zone advances much more quickly southward across
the south central and southeastern U.S. than the GFS`s front.  By
the afternoon of Day 6/Wednesday, the GFS depicts the front from
southeast VA west-southwest across the southern Appalachians and
central Gulf coast states, while the ECMWF places the front across
northern FL and the northern Gulf of Mexico.  While fast flow aloft
would provide ample shear for stronger storms should sufficient CAPE
evolve ahead of the front, the aforementioned model differences
preclude any reasonable attempt to highlight any severe weather risk
areas at this time.

By Day 7 and particularly Day 8, larger-scale differences begin to
emerge between the models, yielding steadily increasing uncertainty
through the end of the period.

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