SPC Dec 9, 2024 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1150 PM CST Sun Dec 08 2024

Valid 091200Z - 101200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorms are possible from the Lower Mississippi Valley into
much of the Southeast States today through early Tuesday. The
probability for severe thunderstorms appears low.

...Synopsis...
A weakening shortwave trough will quickly progress eastward across
the lower OH river valley early this morning, and is forecast to
exit off the East Coast by afternoon. In its wake, a more amplified
upper wave over the Rockies will continue to shift east, resulting
in broad surface pressure falls across the Plains along and ahead of
a southeastward migrating cold front. This low-level mass response,
while weak, will be sufficient to maintain a southerly flow regime
across the lower MS river valley that will continue to advect a
warm/moist air mass inland through the next 24 hours. The persistent
warm advection regime over the central Gulf coast will maintain
isolated thunderstorm chances through the day. Despite 40-50 knot
mid-level flow, weak low to mid-level lapse rates, sampled well by
00 UTC soundings, will modulate updraft intensities and the
propensity for organized convection for much of the day. 

The southeastward-moving cold front is forecast to reach the lower
MS river valley during the overnight hours tonight. Thunderstorm
chances will likely increase between 06-12 UTC as this boundary
impinges on a higher theta-e air mass overspreading southeast LA
into southern MS. By this time, low-level moisture advection should
be sufficient to mitigate the deleterious effects of nocturnal
cooling to some degree and support surface-based convection.
However, the overall weak synoptic ascent over the region, combined
with limited lapse-rate advection, may not provide sufficient
destabilization for robust deep convection despite improving
low-level thermodynamics. Nonetheless, veering in the lowest 1-2 km
may support weakly rotating shallow convection. Consideration was
given for low-end tornado probabilities to address this nocturnal
concern; however, latest CAM ensemble guidance generally shows a
very weak convective signal (aside from the typically bullish FV3
members), which limits confidence in the overall threat.

..Moore.. 12/09/2024

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