Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 110946
SPC AC 110945

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CST Sun Dec 11 2016

Valid 141200Z - 191200Z

Latest runs of the GFS and ECMWF are quite similar in their
depiction of synoptic-scale features -- both at the surface and
aloft -- through the Day 4-8 period.  Both depict the upper flow
field to become more progressive with time across the continental
U.S., as a polar vortex shifts across eastern Canada and the
adjacent northeast U.S. Days 4-5 (Wednesday and Thursday), and an
eastern Pacific trough shifts into the western states.

As the western system shifts eastward, lee cyclogenesis over the
high Plains is forecast late Day 5.  This deepening low is then
progged to shift northeast across the central plains toward the
Upper Great Lakes region Day 6, while a strong/trailing cold front
sweeps southeast across the central and southern Plains.  The strong
low pressure system is then progged to advance quickly northeastward
into eastern Canada Day 7 (Saturday), while the trailing cold front
approaches the Atlantic and Gulf Coasts.  Finally, both models shift
the front off the coasts by early in the Day 8 (Sunday) period.

While advance of the front across the south-central and southeast
states from late Day 6 through Day 7 along with associated/strong
flow aloft would imply some increase in convective potential, cold
high pressure which will reside over the eastern U.S. and adjacent
northern Gulf of Mexico suggests that return of more substantial
Gulf moisture will likely be confined to states immediately adjacent
to the Gulf.  Additionally, with the main short-wave energy (and the
associated surface low) progged to eject well to the north, across
the central Plains and upper Midwest, little if any synoptic-scale
deep tropospheric ascent is expected across areas where any
appreciable moisture can return.  As such, potential for a more
substantial severe risk appears unlikely at this point, such that no
outlook areas will be included at this time.

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