SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0630 AM CST Sun Jan 10 2021

Valid 101300Z - 111200Z


Sporadic non-severe thunderstorms are possible over south Texas and
southern Louisiana.

In mid/upper levels, the large-scale pattern will be characterized
by a broad cyclone over the Gulf of Alaska, mean ridging from CA
across the northern Rockies and northwestern Canada, and a complex,
split-flow regime of mean troughing over the central CONUS.  The
principal southern-stream perturbation, around which the flow
splits, is evident in moisture-channel imagery over eastern NM and
far west TX, with a nearly closed cyclone around a 500-mb low
located over southeastern NM.  The low should close fully through
the remainder of this morning and move eastward across west TX,
reaching the area between CDS-ABI by 00Z.  By 12Z, the low should be
near TXK, along a deamplifying shortwave trough, then becoming an
open wave again and weakening across the Mid-South on day 2.

At the surface, a distinct low should develop off Padre Island by
around 18Z, from a trough analyzed at 11Z near a BRO-CRP-SAT axis. 
The low should move east-northeastward from there across the
northwestern Gulf, and remaining south of the mainland through the
rest of the period. By 12Z, the low should be located south of
southeastern LA, with warm front arching to just south of the moth
of the Mississippi River, then southeastward over the east-central
Gulf.  A cold front will trail south-southwestward from the low
across the northwestern Gulf. 

...South TX...
Isolated to widely scattered thunderstorms are possible today across
much of south TX, within a broad plume of elevated, low-level warm
advection and moisture transport wrapping toward the mid/upper low. 
This activity will be supported by elevated MUCAPE in the 200-500
J/kg range, rooted around 750-850 mb in southern areas and 650-750
mb from the Edwards Plateau across south-central TX. 

A main convective swath -- perhaps a southward extension of the zone
of elevated frontogenetic lift now passing the AQO/SAT/COT corridor
-- should evolve through the day just inland from the lower TX Coast
and shift eastward.  This activity should remain elevated and non-
severe over land, behind the developing surface cyclone.  The
convection should increase in coverage and intensify after reaching
the Gulf surface low and encountering a higher-theta-e, more
surface-rooted inflow layer of the warm sector.  Forecast soundings
suggest that deep shear and CAPE may become favorable for a severe
threat affecting offshore interests well south of the upper TX and
LA Coasts, but should not extend inland/north of the warm front, due
to lack of boundary-layer buoyancy.

..Edwards/Mosier.. 01/10/2021

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