SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0624 AM CST Sun Dec 15 2024
Valid 151300Z - 161200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
NORTH TEXAS TO THE OZARKS...
...SUMMARY...
Isolated hail near severe limits is possible tonight from portions
of north Texas to the Ozarks.
...Synopsis...
In mid/upper levels, a low-amplitude longwave pattern will remain in
place over the CONUS, with progressive shortwave to synoptic troughs
traversing the prevailing westerlies. The leading trough --
currently anchored by a closed low near the northern IL/IN border --
should devolve to an open wave and move to the northern Mid-Atlantic
region by 12Z tomorrow. Meanwhile, a series of shortwaves and
vorticity lobes -- occupying broadly cyclonic flow over much of the
western CONUS -- will consolidate/phase somewhat through the period
while shifting eastward. By 00Z, a loosely organized synoptic
trough will extend from the Dakotas across the central High Plains
to AZ. Overnight, a closed 500-mb low should develop over southern
MB, with the trough extending across central NE/KS to southern NM
and northwestern MX by 12Z.
At the surface, 11Z analysis showed a decaying cold to stationary
front from eastern IL across southern AR, north-central and west-
central TX. This boundary will move slowly northward through the
day and continue to weaken. Meanwhile, cold frontogenesis is
forecast today ahead of the mid/upper trough, and over parts of the
central/northern Plains. This Plains front should reach western
parts of MN/IA, northeastern to south-central KS, and the TX
Panhandle by 00Z. By 12Z, the cold front should reach central/
southern IL, the Ozarks, eastern/southern OK, and the TX South
Plains region.
...North TX to the Lower OH Valley...
Episodic, isolated to scattered thunderstorms are expected
throughout the period, embedded in a plume of low-level warm/moist
advection and moisture transport extending from central/east TX to
the lower Ohio Valley. Through the day, this activity will occur in
weak midlevel lapse rates and modest deep shear, with most or all of
it elevated over a relatively stable, near-surface layer, and
accordingly minimal severe potential. Meanwhile, surface dewpoints
in the 60s F will spread northward into and across much of the
outlook area, as the older boundary becomes diffuse ahead of the
Plains cold front.
Concurrent with height falls aloft and increasing deep shear, the
warm conveyor and accompanying isentropic ascent to LFC should
intensify this evening amid mass response to the consolidation/
approach of the mid/upper trough, and related 45-55-kt LLJ.
Greatest thunderstorm coverage in the plume is expected after about
03Z from near the Red River Valley to the Ozarks, spreading into the
lower Ohio Valley from around 09Z onward. During phases when
convection is still relatively discrete, and around the southern
part of denser/later convective coverage, the most vigorous cells
may produce severe hail. Forecast soundings show a nearly
saturated, near-neutral stability profile in the boundary layer over
north TX to eastern OK, and perhaps into some of northwestern AR,
depending on outflow timing/intensity. This renders profiles that
may be effectively surface-based, with MLCAPE in the 1000-1500 J/kg
rage and slightly greater MUCAPE, but still often containing weak,
near-surface static stability. At this time, severe-gust/tornado
potential appears too conditional and low to draw even marginal
categorical probabilities for those hazards, and the previous
outlook area still appears to capture the consensus of most
probable, favorably positioned convection in the plume as well.
..Edwards/Goss.. 12/15/2024
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