SPC 0830Z Day 3 Outlook

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0154 AM CST Fri Dec 11 2020

Valid 131200Z - 141200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms appears negligible across the
U.S., Sunday through Sunday night.

...Discussion...
A vigorous short wave trough digging out of the Arctic latitudes may
be accompanied by a more substantive cold intrusion into portions of
the northern Great Plains and Upper Midwest.  Otherwise, a belt of
westerlies emanating from the mid-latitude Pacific appears likely to
maintain considerable influence across much of the U.S. through this
period.  

One significant embedded short wave trough, likely digging to the
lee of the southern Rockies by 12Z Sunday, may support renewed
surface wave development along a frontal zone, initially stalling
across the lower Mississippi Valley into southern Great Plains. 
With the latest ECMWF (11/00Z) a bit slower than prior runs (and
other model output) with the eastward progression of this feature
through 12Z Monday, there is meaningful spread among the guidance
that contributes to uncertain convective potential across parts of
the northwestern Gulf coast vicinity into the Southeast.

This mostly appears to impact the placement of the 10 percent
probability of thunderstorm line for Sunday through Sunday night, as
the rather modest amplitude of the surface wave forecast by most
guidance is not particularly suggestive of appreciable severe
weather potential.  Furthermore, it appears that stronger mid/upper
forcing for ascent will remain well inland of coastal areas, as
boundary-layer moistening over the northwestern Gulf of Mexico
becomes more supportive of appreciable destabilization.  However,
given the strengthening lower/mid tropospheric wind fields forecast
across coastal areas, if storms can form within the destabilizing
offshore waters, it might not be out of the question that some could
advect into coastal areas and pose some risk for severe weather.  

Due to the conditional, in addition to apparent marginal, nature of
this potential, severe weather probabilities are currently being
maintained at less than 5 percent, but trends will continue to be
monitored.

..Kerr.. 12/11/2020

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