SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1121 AM CST Mon Jan 25 2021

Valid 261200Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE TUESDAY
AFTERNOON OR EVENING ACROSS PARTS OF SOUTHEASTERN ALABAMA...THE
WESTERN FLORIDA PANHANDLE AND SOUTHWESTERN GEORGIA...

...SUMMARY...
A couple of strong thunderstorms may impact parts of the eastern
Gulf Coast region late Tuesday afternoon or evening, accompanied by
at least some risk for severe weather.

...Synopsis...
Models indicate that there will be considerable amplification within
the mid/upper flow regime across the mid-latitude Pacific through
this period, including the development of sharpening ridging along
an axis near 160 W longitude.  To the east of this ridge axis, a
vigorous digging short wave trough is forecast to contribute to
deepening large-scale troughing across the eastern Pacific, and into
the Pacific coast vicinity by 12Z Wednesday.  It appears that this
will be accompanied by a deep occluding surface cyclone, with the
occluding front advancing inland across the Oregon and northern
California coast late Tuesday afternoon through Tuesday night.  The
front may be preceded by generally modest moisture return, mostly
across northern California coastal areas late Tuesday afternoon and
evening, and the leading edge of the mid-level cold core associated
with the short wave trough may overspread areas to the west of the
Cascades late Tuesday night.  However, forecast soundings remain
suggestive that potential for thunderstorm activity is negligible
through at least this period.

Meanwhile, with the approach of the upstream perturbation, a
significant short wave impulse currently digging into the Southwest
is forecast to remain progressive.  Models indicate that this
feature will accelerate across the southern Rockies through south
central portions of the Great Plains by late Tuesday night.  At the
same time, a downstream perturbation, becoming sheared within an
increasingly confluent regime, is expected to be forced
eastward/east-southeastward across southern portions of the Great
Lakes region through southern New England.  

In response to these developments, in lower-levels, it appears that
an initial surface cyclone will weaken over the upper Ohio Valley,
while secondary surface cyclogenesis takes place along a warm
frontal zone off the Mid Atlantic coast.  As this occurs, a trailing
cold front likely will advance southeast of southern Appalachians
and become quasi-stationary west-southwestward across north central
Gulf coastal areas by late Tuesday night.  The front appears likely
to stall generally near the northern periphery of subtropical
ridging (centered over the Caribbean), which may maintain strength
through this period, with a continuing return flow of moisture
around it, along and south of the frontal zone.

...Southeast...
Elevated moisture return above the frontal zone will contribute to
weak destabilization and thermodynamic profiles marginally
supportive of occasional weak thunderstorm activity, largely aided
by forcing for ascent supported by the progressive short wave
impulses.

Warm mid-levels beneath the subtropical ridging, to the south of the
frontal zone, seem likely to minimize thunderstorm development. 
However, models do suggest a window of opportunity for
boundary-layer based storm development in a narrow corridor
along/ahead of the surface front across parts of the western Florida
Panhandle, southeastern Alabama and southwestern Georgia late
Tuesday afternoon and evening.  In the wake of the lead short wave
impulse, and in advance of the perturbation emerging from the
Southwest, models suggest that mid-levels may remain sufficiently
cool, as large-scale ascent associated with low-level warm advection
begins to increase, to allow for scattered thunderstorm development.
 In the presence of  30-50+ kt west-southwesterly flow in the
850-500 mb layer, mixed-layer CAPE on the order of 500-1000 J/kg
appears possible and may contribute to strong to severe thunderstorm
development capable of producing potential damaging wind gusts
before diminishing Tuesday evening.

,,,Southern Rockies into adjacent portions of Great Plains...
Models suggest that weak destabilization is possible across the
higher terrain, and at mid-levels across adjacent portions of the
high plains, beneath the mid-level cold pool associated with the
impulse emerging from the Southwest.  It appears that thermodynamic
profiles may become at least marginally conducive to convection
capable of producing lightning, but any such activity probably will
be fairly sparse, with probabilities generally near the minimum
threshold for a categorical thunderstorm outlook.

..Kerr.. 01/25/2021

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