Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1251 AM CDT Fri Apr 23 2021
Valid 231200Z - 241200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON INTO TONIGHT ACROSS PARTS OF EASTERN TEXAS...MUCH OF
CENTRAL AND NORTHERN LOUISIANA...ADJACENT SOUTHERN ARKANSAS AND
SOUTHWESTERN MISSISSIPPI...
...SUMMARY...
Severe thunderstorms are possible today across the southern Great
Plains into the lower Mississippi Valley. This may include the
evolution of large, organized cluster of storms across the Piney
Woods vicinity into the lower Mississippi Valley by this evening,
which could produce a swath or two of damaging wind gusts and
perhaps a couple of tornadoes.
...Synopsis...
Deep mid-level troughing, with a developing embedded low, has
emerged from the Arctic latitudes and is forecast to become
entrenched across much of interior Canada during this period,
downstream of a blocking mid-level high which has become centered
across Alaska. To the southeast of the low, a similar preceding
perturbation, and associated deep surface cyclone, appear likely to
gradually turn northward across and north of the Canadian Maritimes.
As this lead system gradually loses influence on the Northeast,
models indicate that a belt of westerlies emanating from the
mid-latitude Pacific will continue to become a more prominent
influence across much of the remainder of the United States. This
regime includes a significant short wave trough now turning eastward
across parts of the Southwest and northwestern Mexico, as it comes
in phase with a belt of westerlies emanating from the subtropical
eastern Pacific. It appears that this feature will accelerate
east-northeastward, across southern portions of the Great Plains
into the lower Mississippi Valley by late tonight.
In lower levels, while another intrusion of cold air surges south of
the Canadian/U.S. border, to the east of the northern Rockies,
through much of the northern Great Plains, potentially cold air
associated with a preceding intrusion will, at least initially, be
slow to lose influence across much of the Southeast into lower
Mississippi Valley. However, a substantive return flow of moisture
is ongoing off the western Gulf of Mexico into the southern Great
Plains, and this will tend to spread east-northeastward in advance
of the impulse emerging from the Southwest/Mexican Plateau, and
broad surface troughing developing eastward across the southern
Great Plains.
...Southern Great Plains through the central Gulf states...
Beneath steep mid-level lapse rates associated with elevated
mixed-layer air, daytime heating is expected to contribute to
moderately large mixed-layer CAPE, in at least a narrow corridor
along a developing dryline from the eastern Texas Panhandle into the
Hill Country vicinity by this afternoon. Low clouds may slow
destabilization within a developing wedge of returning
boundary-layer moisture across central/southeast Texas into the
north central Gulf coast vicinity, while trajectories emanating from
surface ridging slow boundary-layer moistening across and northeast
of the lower Mississippi Valley.
Further complicating warm sector boundary-layer destabilization,
various model output suggests that thunderstorm activity may
initiate by midday east of the dryline, across parts of central
Texas into the Texas coastal plain. It appears that this may occur
in response to forcing associated with a subtropical perturbation
preceding the primary short wave trough, aided by lower/mid
tropospheric warm advection, and guidance indicates a steady
increase in thunderstorm development while spreading
east-northeastward through the afternoon.