SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1158 PM CST Tue Dec 01 2020

Valid 021200Z - 031200Z


A couple of severe thunderstorms are possible over the middle/upper
Texas Coast and far southwest Louisiana today.

A large upper cyclone over the northeastern U.S. is forecast to
shift northward into Quebec today, as a second evolves/lingers over
the southern Rockies/southern Plains.  Meanwhile, sharp ridging will
remain over the West, though a short-wave trough is expected to
approach the West Coast late in the period.

At the surface, high pressure will prevail over much of the country,
as the main surface low retrogrades across northern Quebec.  A much
weaker surface low is forecast to shift northeastward along the
western Gulf Coast through the period.

...Middle and Upper Texas Coast to southwestern Louisiana...
Showers and embedded thunderstorms are expected to evolve early this
morning, prior to the start of the period -- largely over the
western Gulf, but with elevated convection spreading northward
across portions of East Texas by the start of the period.  As a weak
surface low shifts northeastward near or just offshore during the
day, southeasterly/easterly low-level flow should permit some inland
advance of a partially modified Gulf boundary layer.  Combined with
very limited heating, mixed-layer CAPE of 500 J/kg could evolve
across portions of the Upper Texas Coast and eventually coastal
southwestern Louisiana, with perhaps 1000 J/kg along the Middle
Texas Coast.  This will support an increase in convection during the
late morning and into the afternoon, particularly over the immediate
coastal counties.  While relatively weak lapse rates aloft will
likely limit hail risk, a couple of stronger storms will be capable
of producing gusty/possibly damaging winds.  

Additionally, veering of the low-level flow with height near the low
and attendant warm front, beneath strengthening mid-level
west-southwesterlies will result in shear profiles supportive of
updraft rotation -- including low-level circulations and possibly an
inland tornado with one or two sustained storms.  

Limited severe risk may spread eastward across coastal southern
Louisiana into the evening/overnight while gradually diminishing
over coastal Texas, though more widespread/intense storms should
remain largely offshore through the end of the period.

..Goss/Moore.. 12/02/2020

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