SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0647 AM CST Wed Feb 10 2021

Valid 101300Z - 111200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not forecast through tonight across the
contiguous United States.

...Synopsis...
An elongated, binary and very cold mid/upper cyclone will pivot over
central Canada through this period.  A Fujiwhara-style interaction
on day 1 is progged to lead to consolidation of the vortex over MB
late day 2.  To its south, a broad belt of intense mid/upper
westerlies -- with gently cyclonic curvature -- will cover much of
the central and northern CONUS.  

A southern-stream split-flow pattern will exist over the Southwest
and northern/western MX, related to a trough now extending near an
axis from LAS-SAN and south-southwestward across the Pacific west of
Baja.  By 12Z tomorrow, the trough should maintain similarly
positive tilt with some amplification, from near SAF-DMN and across
northwestern mainland MX and southern Baja. 

At the surface, 11Z analysis depicted a quasistationary front across
central FL and the extreme northern Gulf, to deep south TX.  Very
slow northward drift of this boundary as a warm front should occur
in most sections, with western portions merging into the more-
intense Arctic baroclinic zone slowly sagging equatorward across
south TX.  The latter front should reach the lower Rio Grande Valley
late in the period. 

...South-central/southeastern CONUS...
Multiple rounds of isolated to scattered convection, with sporadic
thunderstorms, are possible through the period across the lengthy
outlook area, mainly north of the Gulf frontal zone.  Any surface-
based storms over coastal areas generally should occur amidst weak
CINH, but also, weak low-level shear and a lack of substantial
mid/upper support.  

Very late in the period (likely around 09-12Z), convection may
develop over parts of the TX Rio Grande Valley and vicinity, upriver
from LRD and northward toward the southern Hill Country.  A
combination of frontal lift above the surface and increasing inflow-
layer moisture/theta-e will erode EML-related MUCINH, ahead of the
northwest Mexico perturbation.  MLCAPE locally exceeding 1000 J/kg
may develop, and with forecast soundings exhibiting 40-50-kt
effective-shear vectors, isolated hail approaching severe limits
cannot be ruled out.  Accordingly, the thunder area has been
expanded westward across south TX.  The other change of note is
minor eastward extension in more of the Tennessee Valley region,
also to account for late-overnight thunder potential shortly before
12Z.  There, the fringe of favorable, elevated low-level warm
advection and moistening should support development of 300-500 J/kg
MLCAPE extending into suitable icing layers for isolated lightning.

..Edwards.. 02/10/2021

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