SPC 0830Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0220 AM CST Tue Feb 23 2021

Valid 251200Z - 261200Z


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

Models indicate that a large, blocking ridge, centered at mid-levels
over the southern mid-latitude eastern Pacific (between 140-160 W),
may reach peak prominence during this period.  It appears likely to
remain in phase with large-scale ridging within the westerlies,
which may continue to build north of the Aleutians and through the
Gulf of Alaska.  Intensifying mid-level flow on the northeastern
periphery of this feature will take on an increasing northwesterly
component near the British Columbia coast into the northern U.S.
intermountain region, with a broad area of stronger mid-level height
falls on the leading edge of this regime.

In response to these developments, models indicate that a vigorous
short wave impulse, initially near the southern Rockies, within the
southern branch of split westerlies, will accelerate
east-northeastward across the southern Great Plains and Ozark
Plateau vicinity by 12Z Friday.  However, this will be preceded east
of the Rockies by the development of fairly expansive cold surface
ridging across much of the Great Plains through the Ohio and
Tennessee Valleys.  And models indicate that any associated wave
development, along the front demarcating the leading edge of this
air mass across southeast Texas through the lower Mississippi
Valley, will be weak.

A continuing southerly return flow in advance of this wave may
support a weak to modest influx of moisture off the northwestern
Gulf of Mexico.  In the wake of the wave, it appears that the
shallow leading edge of the cold air will nose south of the Texas
Rio Grande River vicinity, and into the western Gulf of Mexico, by
the end of the period.

...Gulf States...
Models suggest that stronger mid/upper forcing for ascent will be
focused above/well to the cool side of the initially stalling
low-level frontal zone.  This is expected to overspread parts of
north central and northeast Texas late Thursday afternoon, before
developing east-northeastward into the vicinity of the southern
Appalachians by late Thursday night, with warm layers aloft capping
moisture return to the south.  Associated destabilization is
forecast to remain weak, but sufficient to contribute to
thermodynamic profiles supportive of thunderstorm development.  This
may coincide with a strengthening west-southwesterly jet to 40-50 kt
in the 850-700 mb layer, but with the core of this feature also
focused above a substantive surface-based stable layer, the risk for
severe weather appears negligible (particularly given the weak CAPE
evident in the forecast soundings).

...Columbia Plateau vicinity...
Large-scale ascent and strong mid-level cooling (500 mb temps to -30
to -35 C) accompanying the vigorous digging short wave may
contribute to thermodynamic profiles supportive of convection
capable of producing lightning, mainly Thursday afternoon.

..Kerr.. 02/23/2021

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