SPC Dec 15, 2024 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0155 PM CST Sun Dec 15 2024

Valid 152000Z - 161200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
NORTH TEXAS TO THE OZARKS...

...SUMMARY...
Isolated severe hail, strong/gusty winds, and perhaps a tornado may
occur tonight through early Monday morning from parts of north Texas
to the Ozarks.

...20Z Update...
The previous forecast (see below) remains on track, and no changes
were needed with this update. The latest guidance indicates some
potential for embedded/loosely organized cells tracking
northeastward across southeast MO during the early morning hours --
mainly capable of producing small hail and/or locally strong gusts.
It is unclear if this activity will be surface-based, and given
marginal midlevel lapse rates/instability, severe potential appears
too low to expand probabilities.

..Weinman.. 12/15/2024

.PREV DISCUSSION... /ISSUED 1030 AM CST Sun Dec 15 2024/

...Synopsis...
Gradual amplification and consolidation of upper troughing will
occur through the period across parts of the northern Plains and
Upper Midwest. The southern fringe of this upper trough will begin
to influence and overspread portions of the central/southern Plains
late this evening and overnight. The primary surface low will
develop towards the international border region of northern
MN/southern Canada, while partially modified Gulf moisture continues
to gradually stream northward over portions of the southern Plains
into the Ozarks ahead of a cold front.

...Eastern Oklahoma into Western Arkansas and Southwest Missouri...
Convective initiation will likely be delayed until 03Z or later this
evening across eastern OK/western AR vicinity, as low-level
warm/moist advection aids in the northward transport of a moist
low-level airmass. Once convection develops as glancing ascent from
the approaching upper trough overspreads the warm sector, convective
mode may quickly become messy, as generally southwesterly
low/mid-level flow encourages updraft interactions and mergers. Even
so, around 1000-2000 J/kg of MUCAPE, aided by modestly steepened
mid-level lapse rates, should support robust updrafts. Coupled with
sufficient (around 30-40 kt) deep-layer shear, some of this initial
development could produce marginally severe hail on an isolated
basis. Based on latest guidance trends showing convective initiation
farther north across parts of northern OK into southwest MO, the
Marginal Risk has been expanded northward to account for this
initial hail threat.

Poor/neutral low-level lapse rates and a generally saturated
boundary-layer shown in various NAM/RAP forecast soundings limit
confidence to some extent in the potential for truly surface-based
thunderstorms tonight across the warm sector. Still, the presence of
a 35-45 kt southwesterly low-level jet, with associated 0-1 km SRH
sufficient for low-level updraft rotation, suggests a non-zero
threat for a tornado along with some potential for occasional
strong/gusty winds as convection spreads eastward across eastern OK
into western AR and the Ozarks through early Monday morning. The
potential for sustained supercells appears limited by a weakness in
the flow/hodograph forecast around 700 mb, with the southward-moving
cold front also encouraging a more linear/cluster mode with time.
Overall, the severe threat with any convection that develops should
remain rather isolated, but within a conditionally somewhat
favorable environment.

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