SPC Dec 18, 2023 0600 UTC Day 1 Convective Outlook

[NorthGeorgiaWX]

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1159 PM CST Sun Dec 17 2023

Valid 181200Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
COASTAL SOUTHERN NEW ENGLAND...

...SUMMARY...
A damaging gust or two is possible from the eastern shore of New
Jersey into southern New England this morning and afternoon. A few
isolated lightning flashes are possible along the northern/central
California coast.

...Synopsis...
A broad mid-level trough will amplify across the East Coast as a 500
mb jet max overspreads portions of southern New England today,
supporting the rapid northeastward ejection of a 986 mb surface low
into Quebec by evening. Intense low-level wind fields will be in
place ahead of the surface low, supporting conditional damaging gust
potential with any storms that can root into an unstable boundary
layer. Meanwhile, another trough will impinge on the West Coast,
supporting appreciable rainfall accumulations and at least isolated
thunderstorms.

...Portions of southern New England...
The surface low will overspread southern New England, immediately
preceded by a 70+ kt 850 mb southerly jet. Tropospheric flow will be
unidirectional, supporting straight hodographs. 6 C/km lapse rates
above 850 mb may boost MUCAPE to 500 J/kg, which will support at
least elevated convection. The primary mitigating factor for a
robust severe thunderstorm wind threat is the likelihood for a
stable boundary layer, which should dampen downward momentum
transport in stronger storm cores. Modified forecast soundings
suggest surface temperatures would need to reach the mid 60s F amid
60+ F dewpoints to support 100+ J/kg SBCAPE. However, ensemble
guidance suggests that maximum high surface temperatures will
struggle to reach the lower 60s F, casting doubt on the potential
for organized severe storms. Nonetheless, the intense low-level wind
fields suggest that any downward momentum transport within
thunderstorm cores that can occur may support a damaging gust threat
during the late morning and afternoon hours. A Category 1/Marginal
Risk has been maintained for coastal portions of southern New
England to address the conditional damaging gust threat.

..Squitieri/Darrow.. 12/18/2023

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