SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1155 PM CST Wed Feb 24 2021

Valid 261200Z - 271200Z


A few strong thunderstorms are possible in a corridor across parts
of the northwestern Mississippi Delta region and adjacent
southeastern Arkansas into parts of middle Tennessee Friday evening,
accompanied by at least some risk for severe weather.

The southern mid-latitude eastern Pacific blocking ridge may undergo
some suppression during this period, as the first in a series of
significant short wave troughs progresses into/around its
northwestern periphery.  However, ridging will remain a prominent
influence across much of the eastern Pacific.  At mid-levels, models
indicate that the broad ridge axis within the westerlies may take on
more of a positive tilt across the northeastern Pacific, with
ridging building into the British Columbia and adjacent Pacific
Northwest coast by 12Z Saturday.

Downstream flow will take on an increasingly northerly component
across the interior West, with a significant embedded digging short
wave trough contributing to larger-scale trough amplification across
the Intermountain West and Rockies.  As this occurs, one preceding
short wave impulse is forecast to accelerate east of the northern
Rockies, toward the Great Lakes region.  

At least broadly cyclonic mid-level flow is expected to prevail
across much of the interior of the U.S., but models indicate that
subtropical ridging will begin to build northeastward across the
Gulf of Mexico into portions of the Southeast.  And mid-level
ridging in the westerlies will shift ahead of the lead short wave
trough, across much of the Northeast.  It appears that an initially
vigorous short wave impulse progressing through the Ozark Plateau by
12Z Friday, may undergo considerable deformation while accelerating
northeastward toward the northern Mid Atlantic coast region.

In lower levels, the leading edge of southward advancing Arctic air
may spread across the central Canadian/U.S. border area by late
Friday night.  Otherwise, a warming south-southwesterly to
west-southwesterly return flow appears likely to continue to develop
east of the Rockies, in the wake of expansive cold surface ridging
shifting east of the Atlantic Seaboard.  It does appear that one
remnant frontal zone, initially extending across the Gulf into south
Atlantic coast states, may tend to surge north-northeastward,
beneath a 40-70 kt southerly 850 mb jet axis across the Tennessee
Valley toward the Cumberland Plateau.

...Ark-La-Tex into Cumberland Plateau...
Supported by forcing associated with the impulse progressing across
the Ozark Plateau, thunderstorm activity may be ongoing along the
frontal zone in a corridor across the Ark-La-Tex into parts of
northern Alabama early Friday.  This activity is expected to
gradually diminish/decrease in coverage through the day, but some
thunderstorm development may persist and spread with the mid-level
impulse toward the Cumberland Plateau, before diminishing further.

In the wake of this activity, forcing associated with the short wave
emerging from the northern Rockies may contribute to renewed
thunderstorm development to the west and northwest later Friday
through Friday night.  Stronger storms may tend to focus along a
developing area of enhanced lower/mid tropospheric warm advection
near the northwestern Mississippi Delta region by early Friday
evening.  This probably will be on the leading edge of better
low-level moisture return, in the presence of modestly steep
mid-level lapse rates, which may contribute to CAPE of 250-500 J/kg.
 Coupled with the strong low-level shear, it is possible that this
environment could become conducive to the evolution of supercell
structures while developing northeastward with low-level jet, toward
middle Tennessee later Friday night.  Latest NAM forecast soundings
suggest that this will be rooted above a residual near-surface
stable layer, but this may be shallow enough to allow for some risk
for potentially damaging surface gusts, in addition to potential for
small to marginally severe hail.

...Columbia Plateau/Snake River Basin vicinity...
Insolation beneath a 500 mb cold pocket to -35 C may contribute to
weak boundary-layer destabilization and convective development
across a sizable portion of the northern intermountain region
Friday.  While thermodynamic profiles may be largely below freezing,
it appears that they could still become conducive to some lightning
production, mainly where the boundary layer is able to warm above
freezing in the lower elevations.

..Kerr.. 02/25/2021

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