SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1129 AM CST Fri Jan 29 2021

Valid 301200Z - 311200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY
AFTERNOON INTO SATURDAY EVENING ACROSS PARTS OF EASTERN OKLAHOMA
THROUGH NORTHERN ARKANSAS AND SOUTHERN MISSOURI...

...SUMMARY...
An isolated strong thunderstorm or two may impact a narrow corridor
across parts of eastern Oklahoma through northern Arkansas and
southern Missouri Saturday afternoon and evening, accompanied by at
least some risk for severe weather.

...Synopsis...
Ongoing amplification within the westerlies across the central into
eastern mid-latitude Pacific appears likely to begin translating
inland across western North America during this period.  This is
forecast to include the continuing evolution of deep large-scale
mid-level troughing across the eastern Pacific (generally just west
of the Pacific coast), and building large-scale ridging across the
U.S. Intermountain West and Rockies.

As this occurs, an initially vigorous short wave impulse, to the lee
of the southern Rockies by 12Z Saturday, is forecast to continue an
east-northeastward acceleration. However, models indicate at least
some weakening is possible as it progresses into a broadly confluent
regime between low amplitude downstream ridging overspreading the
south Atlantic coast and the western flank of remnant large-scale
troughing shifting east of the Atlantic Seaboard.

It does appear that the perturbation will be accompanied by a
significant surface cyclone emerging from the high plains of
southeastern Colorado.  And guidance indicates that this may include
a period with at least some further deepening as it migrates across
the Kansas/Oklahoma border vicinity into the lower Missouri Valley.

In the wake of a recent cold intrusion, boundary-layer moistening
may be underway across much of the southwestern Gulf of Mexico by
early Saturday, and continue through the period across much of the
remainder of the Gulf.  However, this may still be fairly modest,
with deepest inland boundary-layer moistening confined to southeast
Texas through the lower Mississippi Valley, with surface dew points
in the mid 50s to around 60F.

...Southern Great Plains into Ohio Valley...
Potential for thunderstorm activity is expected to initially be in
association with elevated moisture return (of lower latitude eastern
Pacific origin) and destabilization, supported by strong large-scale
forcing for ascent downstream of the progressive short wave trough. 
Lower/mid tropospheric warm advection, beneath divergent high-level
flow, may be contributing to this early, across Oklahoma and
adjacent portions of the Great Plains/Ozark Plateau.  It appears
that this may diminish during the day, with probabilities for
renewed thunderstorm development becoming focused near the compact
mid-level cold core (including 500 mb temps of -20 to -25 C).  This
is expected to spread across parts of the lower Missouri Valley and
Ozark Plateau by Saturday evening.  It might not be out of the
question that convection capable of producing lightning could
continue east-northeastward in a corridor along the Ohio River
Saturday night, but this potential becomes more unclear due to model
spread.

The stronger mid-level cooling, to the  north of an initially
intense mid-level jet (around 100 kt at 500 mb), appears likely to
spread to the north of the better warm sector boundary-layer
moistening, with warm mid-levels to the south of the jet capping
convective development.  However, early day precipitation will
contribute to boundary-layer moistening in advance of the cold pool,
and forecast soundings suggest potential for weak boundary-layer
destabilization with some insolation beneath a developing dry slot.
Current model output suggests this is most probable along a corridor
across east central Oklahoma through north central Arkansas/south
central Missouri Saturday afternoon into early Saturday evening. 
However, given spread evident among the model output, this axis
could be displaced at least somewhat to the north or south.

Regardless, given the potential for a developing narrow corridor of
at least weak boundary-layer destabilization, vigorous thunderstorm
development appears possible in the presence of strong deep-layer
mean wind fields and vertical shear.  It appears that this will
include 50-70 kt southwesterly to westerly flow in the 850-700 mb
layer, which could support a small organized cluster and/or isolated
supercell structure or two, accompanied by the risk for damaging
wind gusts and perhaps an isolated tornado.

..Kerr.. 01/29/2021

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