SPC AC 070756
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0156 AM CST Thu Dec 07 2023
Valid 091200Z - 101200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EAST TX
ACROSS THE LOWER MS VALLEY...
Scattered severe thunderstorms will be possible from east Texas
across the Lower Mississippi Valley, mainly on Saturday afternoon
into the early evening.
The broader synoptic trends noted in D2 persist into D3 with a
leading shortwave impulse and attendant cyclogenetic surface low
rapidly progressing across the central Great Lakes towards James
Bay. The trailing cold front from the Midwest to east TX will
continue to push southeast, aided by a seasonably tight surface
pressure gradient between it and a stout anticyclone over the
northern Great Basin. Much weaker secondary cyclogenesis is
generally progged from the Ark-La-Tex on Saturday morning to at
least the TN Valley by Saturday night, as an upstream basal
shortwave impulse shifts from the Four Corners across the southern
Great Plains. Model spread in placement of the surface cyclone/front
increases late in the period.
...East TX to the Mid/Deep South...
Slower timing of appreciable mid-level height falls over the warm
sector on Saturday suggests that more than isolated thunderstorm
development should hold off until midday through the afternoon. This
would likely allow for a plume of moderate buoyancy characterized by
MLCAPE of 1000-1500 J/kg to become established from the Upper TX
Gulf Coast towards the Ark-La-Tex amid surface dew points into the
mid to upper 60s. Deep-layer southwesterly shear vectors should be
nearly parallel to the orientation of the cold front, supporting a
predominant clustered to linear convective mode. As such, convection
will likely become widespread by late afternoon into the evening
with favorable effective bulk shear for organized updrafts.
Low-level shear will be modest with southwest extent where the
larger buoyancy is expected, suggesting a predominant severe
wind/hail threat. Enlarged low-level hodographs should generally be
confined from the Ark-La-Miss to the northeast and east, where
surface-based instability should be diminishing with spatial extent.
Given the overall model trends for only weak secondary cyclogenesis
through 12Z Sunday, the eastern extent of the 15 percent probability
area has been held as-is. Confidence is low in just how far east the
extent of low-probability wind/tornado threats exist overnight.
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NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0830Z