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Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1300Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

  
000
ACUS01 KWNS 031245
SWODY1
SPC AC 031243

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0743 AM CDT Fri Apr 03 2020

Valid 031300Z - 041200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTH TEXAS...

...SUMMARY...
Severe hail and gusts are most probable through tonight across parts
of south Texas.

...Synopsis...
The mid/upper-level pattern will remain highly amplified and blocky
over most of North America, north of a subtropical jet extending
over northwestern MX, central TX and the northern Gulf Coast.  The
center of one cyclone, that has been retrograding off New England,
should pivot southward/southeastward before reaching the coast. 
Meanwhile, a very broad, distorted cyclonic gyre, with multiple
embedded vorticity/circulation centers and orbiting shortwaves, will
persist over western Canada and the northern Rockies region.

At the surface, 11Z analysis showed a strong cold front, from a low
over ON near Lake of the Woods, across eastern IA, central MO,
eastern OK, north-central TX to the lower Pecos Valley,
northwestward to central NM.  By 00Z this front should be located
over central IL, central AR, east TX, and northern Coahuila.  By the
end of the period, the front should reach western Lower MI, western
KY, northern LA, and deep south TX. 

...South through east TX...
Episodic, scattered to numerous thunderstorm development is expected
from late morning or midday through tonight, in a swath across the
corridor from the foothills of the Serranias del Burro in northern
Coahuila, across the middle/lower Rio Grande Valley, southern Hill
Country, and parts of south-central/southeast TX.  Damaging gusts
and severe hail are the main concerns, though a tornado cannot be
ruled out.  More-isolated, less-organized thunderstorms may produce
isolated/marginal severe over parts of east TX.  Northern parts of
the outlook areas have been suppressed southward due largely to
current/anticipated frontal motion.

While weak capping may support initiation in the free warm sector,
the most likely foci for convection will be the cold front and
heating of higher terrain in MX.  The decidedly anafrontal
baroclinic regime -- characterized by strong and deepening post-
frontal cold advection, will result in only brief windows for severe
with near-frontal convection.  Potential for more-sustained,
persistently organized activity will be greater within 2-3 hours of
frontal motion to its south, especially with activity forming near
and west of the Rio Grande.  

Warm-sector kinematic and thermodynamic parameters will be more
favorable with southwestward extent.  Rich low-level moisture will
occupy the warm sector outlook-wide, with surface dew points
commonly in the upper 60s to low 70s F, and 1.3-1.8-inch PW. 
Greater midtropospheric lapse rates (residual EML) and low-level
lapse rates (diabatic heating, behind ongoing mesoscale cloud area)
are likely over south-central TX and the Rio Grande Valley,
resulting in peak MLCAPE of 2000-3000 J/kg.  In the absence of a DRT
sounding, objective analyses reasonably indicate MLCINH already is
weak across roughly a SAT-DRT-LRD triangle westward into Coahuila. 
This suggests potential early initiation of the first prefrontal
convective episode -- perhaps before noon.

A limiting element will be weak low-level winds -- generally less
than 10 kt through most of the surface-700-mb layer -- keeping
hodographs small and SRH minimized.  Regardless, strong deep shear
is forecast under the mid/upper-level subtropical jet, with 50-60-kt
effective-shear magnitudes.  Given those factors and the weak CINH,
a messy array of variably organized multicell clusters and heavy-
precip supercells is possible.  Significant hail cannot be ruled out
with any relatively discrete supercells, especially near the Rio
Grande and over adjoining south-central TX.  However, uncertainties
regarding timing, location and persistence of favorable mode
precludes a focused 10%/hatched area at this time.  Deep, strongly
water-loaded downdrafts will support at least localized severe-wind
potential, with upscale organization possible.

..Edwards/Gleason.. 04/03/2020

$$