THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE
LOWER MISSISSIPPI VALLEY...AND INTO PARTS NORTHEAST TEXAS AND
SOUTHEAST OKLAHOMA...
...SUMMARY...
Widely scattered severe thunderstorms are possible over parts of
Texas and Oklahoma beginning late in the day and into the evening on
Wednesday. A severe threat will also develop overnight over the
lower Mississippi Valley, with tornado risk.
...Synopsis...
An upper trough will become positively tilted as it moves east from
the Four Corners to the Plains through Thursday morning, with an
elongated speed max extending from the base of the trough from the
southern Plains across the lower MO Valley and toward Lake Michigan
late. Ahead of the trough, an upper high will remain over the
Bahamas, with rising heights through 00Z across much of the
Southeast.
At the surface, low pressure will translate east from NM into OK
through 00Z, ahead of a cold front which will surge south into the
OK/TX Panhandles. This low is not forecast to deepen, but will
continue northeastward ahead of the cold front to the Ozarks by 06Z
and lower OH Valley by 12Z Thursday.
Southerly surface winds will aid low-level moisture return during
the day, with mid 60s F dewpoints common by 00Z over eastern TX and
the lower MS Valley. Low 60s F dewpoints are eventually expected to
reach the lower OH River/western KY by 12z Thursday, with the more
substantial moisture from about Memphis south. Strengthening 850 mb
winds over 40 kt will aid moisture transport, with modest
instability and strong shear aiding severe potential from TX to the
lower MS Valley, primarily after 00Z.
...Northeast TX...southeast OK into western AR...
Heating will occur over OK and TX ahead of the cold front and south
of the low, steepening lapse rates. Eventually, persistent southerly
winds will bring low 60s F dewpoints to the Red River, most likely
near or after 00Z. Modestly cool midlevel temperatures and
convergence along the front may then be enough to break the cap,
resulting in a few severe storms. Supercell wind profiles will
exist, favoring large hail. Should the boundary layer moisten
sufficiently, a tornado risk could develop. Much of this area
appears conditional given mixed CAM signals, late moisture return,
relatively late time of day (evening) and potential for capping. In
addition, various forecast soundings indicate subsidence in the
midlevels. However, stronger heating near the boundary coupled with
late moisture return should result in at least isolated storms with
hail.
...LA...MS...eastern AR...western TN...
Rapid moistening of the boundary layer during the day is expected to
lead to clouds and keep temperatures relatively cool. This should
minimize the potential for convection through 00Z as a capping
inversion will exist at or below 700 mb. Rain and thunderstorms are
likely to develop after 03Z over much of AR, northern MS, and
western TN, as dewpoints rise into the mid 60s F beneath a 50 kt
low-level jet core. After about 06Z, a plume of > 1000 J/kg SBCAPE
is forecast to extend from LA into eastern AR, gradually shifting
into northwest MS and perhaps western TN. As such, it is possible
that initially elevated convection transitions to surface based,
which would increase the risk of isolated tornadoes. Better lift
along the cold front could become a more favorable focus for
supercells with tornado threat into Thursday morning. In general,
the lack of a substantial baroclinic zone may mitigate the overall
severe risk for much of the period, given cool boundary-layer
temperatures. However, effective SRH near 300 m2/s2 will
conditionally favor tornadoes with any established supercells that
develop late near the MS River.
