SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0652 AM CST Tue Jan 26 2021

Valid 261300Z - 271200Z


A few strong to marginally severe thunderstorm gusts are possible
today through tonight over parts of the Southeast, and a tornado
cannot be ruled out.

Mid/upper-level split flow will continue over western/central North
America, now directed largely by a strong trough and embedded/
compact cyclone centered over the Grand Canyon area.  The 500-mb low
will move/redevelop eastward across the southern Rockies to
southeastern CO by 00Z, with trough across southern NM to western
Chihuahua.  By 12Z, the trough (which may still contain a modest
closed low over KS) will extend across southwestern IA, eastern KS,
south-central OK and central TX.  Downstream, a weakening trough was
apparent in moisture-channel imagery over IA to the KS/MO border
area.  This perturbation should accelerate eastward across the
Northeast through the end of the period, while continuing to

At the surface, the 11Z analysis showed a decelerating cold front
arching across eastern TN, central AL, southeastern MS, and
southeastern LA, becoming quasistationary from there southwestward
across the TC shelf waters of the northwestern Gulf.  The rest of
the frontal zone should become quasistationary today -- under nearly
parallel flow aloft -- from the Carolinas across GA and southern AL
to southeastern LA.  A frontal-wave low is expected to develop
tonight over LA and ripple along the front toward southwestern AL by
about 12Z tomorrow. 

Isolated to scattered thunderstorms are possible in multiple
episodes throughout the period, beginning with a band of convection
now along the northern rim of the outlook area of GA/AL.  The main
concern will be isolated damaging gusts, though a tornado could
occur with some mesoscale to storm-scale augmentation of an only 
weakly supportive ambient environment.  

Direct upper support will be lacking, with the weakening northern
trough and stronger/progressive southwestern low/trough each
far-removed from this area.  However, two indirectly related factors
will help to maintain a conditional and marginal severe threat:
1.  A tight height gradient of southwesterly to west-southwesterly
flow will persist, and 
2.  An increase in the LLJ is progged late in the period (after
about 06Z) in the early-stage mass-response/warm-advection field
preceding the approaching southwestern system. 

A favorably rich and deep layer of low-level moisture will remain in
place along and south of the front, with surface dew points
generally in the mid 60s F to isolated low 70s.  This will offset
modest low/middle-level lapse rates to yield fairly persistent
MLCAPE in the 500-1200 J/kg range away from active convection. 
Somewhat veered surface flow will limit convergence and vertical
shear (especially low-level shear).  However, speed shear will
remain favorable (contributing to 45-55-kt effective-shear
magnitudes), given the gradient flow aloft, and some hodograph
enlargement is possible under the LLJ late.

..Edwards/Gleason.. 01/26/2021

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