SPC 0830Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0225 AM CST Thu Feb 25 2021

Valid 271200Z - 281200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk of severe thunderstorms currently appears negligible across
the U.S. for Saturday through Saturday night.

...Discussion...
Suppression of an initially prominent blocking high and amplified
mid-level ridging across the eastern Pacific appears likely to
continue during this period, as a significant short wave trough
progresses around its northern periphery, across the northeastern
Pacific.  A more pronounced split in the downstream flow may develop
inland of the Pacific coast, as short wave ridging shifts across
British Columbia and adjacent portions of the U.S. Pacific
Northwest.  By late Saturday night, the leading edge of this regime
may begin to translate to the north of a vigorous short wave impulse
sharply digging across the Great Basin into the lower Colorado River
vicinity of the Southwest.

Across and east-northeast of the Rockies, mid-level flow is forecast
to trend increasingly confluent, between more prominent subtropical
ridging across the Gulf of Mexico into the Southeast and a vigorous
short wave impulse pivoting southeastward out of the Arctic.  As
this perturbation digs across Saskatchewan and Manitoba, an
increasingly sheared short wave impulse is forecast to accelerate
northeast of the Wyoming/Colorado Rockies toward the Upper Midwest,
while a more amplified downstream impulse accelerates east of the
Great Lakes into the Canadian Maritimes.  Each of these latter
features may be accompanied by developing surface cyclones, while
cold surface ridging builds beneath the confluent flow across the
Great Plains, as far south as the Texas/Oklahoma Panhandle region by
12Z Sunday.

The net result of these developments in lower levels is expected to
be the evolution and/or reinforcement of a frontal zone near the
northern periphery of the mid-level subtropical ridging, from near
or south of the Texas Big Bend into the Mid Atlantic Coast vicinity.
South/southwesterly low-level return flow, off a still modifying
boundary layer over the Gulf of Mexico, will contribute to
moistening and destabilization along and north of this front.  This
will become the focus for areas of scattered thunderstorm
development Saturday through Saturday night, with models indicating
that warm layers aloft and subsidence will suppress convective
development to the south of the front.

Models do indicate that southwesterly flow around the 850 mb level
may strengthen to 40-50+ kt across the Arkansas/Kentucky/Tennessee
vicinity late Saturday afternoon and evening.  It might not be out
of the question that this could contribute to a risk for organizing
storms with the potential to producing damaging surface gusts. 
However, much may depend on how close convection forms to the
surface frontal position (and the depth of the near-surface stable
layer below the convection).  With this uncertain, and model output
still indicating only generally weak destabilization, severe
probabilities appear less than 5 percent at the  present time.

..Kerr.. 02/25/2021

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