SPC 0600Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1250 AM CDT Wed Sep 16 2020

Valid 171200Z - 181200Z


A threat for tornadoes and damaging wind gusts will accompany
Tropical Cyclone Sally as it migrates across the southeastern U.S.

...Georgia through the Carolinas Coast/Outer Banks...
Models are in a bit better agreement on the forward progression of
Tropical Cyclone Sally, which should accelerate northeastward across
portions of Georgia and the Carolinas under the influence of a
larger-scale trough over southeastern Canada and the northeastern
U.S.  As this process occurs, convection will spread inland along
and just ahead of the cyclone center in tandem with a strongly
sheared airmass favoring development of a few supercells and/or
linear segments.  Buoyancy will not be particularly strong, though a
couple of factors may contribute to pockets of moderate instability,
including 1) areas of insolation, which could locally increase
MUCAPE values around or above 1000 J/kg in the pre-convective
airmass and 2) slightly higher dewpoints/boundary-layer moisture
over South Carolina and vicinity due to maritime influences from the
Gulf Stream, which could also contribute to 1000+ J/kg MUCAPE. 
Either of these regimes would support a threat for surface-based
convection capable of brief tornadoes given the strong shear.  This
is most likely to materialize in the Marginal area - particularly in
South Carolina where convection will occur in a favorable time of
day and location for peak surface-based instability.

...Pacific Northwest...
An approaching mid-level trough over the northeastern Pacific will
spread fast flow aloft over portions of Oregon and Washington State.
Modest mid-level destabilization will also occur, and models are
consistent in developing a few fast-moving thunderstorms during peak
heating hours that may pose a damaging-wind threat.  Limited
low-level buoyancy (as indicated in point forecast soundings) are a
potential mitigating factor however.  Low/Marginal wind
probabilities may be needed in later outlooks - especially if it
becomes apparent that updrafts will root in the boundary layer and
support locally strong downdrafts.

..Cook.. 09/16/2020

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