SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook AMEND 1
NWS Storm Prediction Center Norman OK
0243 PM CST Thu Dec 31 2020

Valid 312000Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE SABINE
RIVER VALLEY AREAS EASTWARD/NORTHEASTWARD ACROSS THE CENTRAL GULF
COAST STATES...

AMENDED TO ADD MRGL RISK AREA TO A PORTION OF THE EASTERN CAROLINAS

...SUMMARY...
Thunderstorms -- a few of which will likely be severe, with
tornadoes and damaging winds as the primary hazards -- will continue
from the Sabine River Valley vicinity across southwest Louisiana
through this afternoon, and then will expand across the rest of
Louisiana into Mississippi and Alabama this evening and tonight.

...Discussion...
Thunderstorms continue across portions of east Texas at this time,
and will continue spreading into western Louisiana over the next few
hours.  While severe risk has remained muted thus far, the
environment downstream from the ongoing storms has become steadily
more supportive of severe/rotating storms -- both thermodynamically
and kinematically -- over the past few hours, as shown by changes in
the LCH RAOBs from 12Z to 18Z.  

Thus, the ongoing outlook reasoning and areas appear to remain
representative of the evolving situation, with the only changes
which appear necessary at this time being to trim western fringes of
the areas to account for convective advance.

...Northeastern South Carolina/southeastern North Carolina...
A small cluster of thunderstorms has developed in marginally
unstable air near the northeastern South Carolina coast.  Ample
shear observed across this area suggests limited/local risk for
gusty winds or a brief tornado late this afternoon.  Please refer to
SWOMCD #1896 for additional short-term details.

..Goss.. 12/31/2020

.PREV DISCUSSION... /ISSUED 1028 AM CST Thu Dec 31 2020/

...Upper TX coast to MS/AL...
A mid-level closed low over western Coahuila will amplify as it
advances north into OK by early Friday, in response to an upstream
shortwave trough digging south-southeast from southern CA to Sonora.
At the surface, a 1004 mb cyclone should track north from the
Middle/Upper TX coast to northeast TX. By 06Z, this cyclone will
become increasingly occluded, yielding a T-shaped surface pattern
with the apex of the warm sector across the Ark-La-Miss as a cold
front sweeps east across the western Gulf and a west/east-oriented
warm front advances north across central portions of MS/AL. The warm
sector characterized by boundary-layer dewpoints in the mid-upper
60s will spread inland to the east of the cyclone and contribute to
MLCAPE of 500-1000 J/kg across extreme southeast TX/southern LA
through this afternoon, and into tonight across central/southern
portions of MS and AL.

Thunderstorm development has been focused near and offshore of the
Upper TX coast this morning, with multiple supercells noted
offshore. Convection will spread northeast through tonight along and
just ahead of the surging cold front. An additional swath of
convection will likely develop separately downstream across the
central Gulf coast by early evening and persist north over eastern
MS and AL through tonight within a robust low-level warm advection
regime.

Greater low-level shear and enlarged hodograph curvature will
initially be confined to the TX/LA portion of the outlook region
this afternoon before spatially expanding this evening as flow
fields strengthen downstream of the amplifying low. The combination
of linear forcing for ascent along the cold front and substantial
cross-boundary flow of deep-layer shear vectors will support broken
bands of supercells and line segments, capable of producing
tornadoes and damaging winds. However, the magnitude of the tornado
threat should be tempered some by rather modest low-level lapse
rates inland, and less-than-ideal phasing with the ejecting
mid-level trough and surface cyclone glancing the northwest side of
the warm sector. 12Z HREF and recent HRRR guidance remain subdued
with the intensity and coverage of rotation potential within
simulated cells, lowering confidence for identifying a corridor of
10 percent or greater probability of significant tornadoes.

Read more
There’s more click here.

Comments are closed.