SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1139 PM CST Mon Dec 28 2020

Valid 291200Z - 301200Z


Organized severe thunderstorms are not anticipated.

...Southern Plains...

Positive-tilt upper trough is digging southeast across southern CA
late this evening and should settle into northern Mexico during the
latter half of the period. The strongest 500mb flow will not
translate through the base of the trough until later day2 into day3
which will allow this feature to eject toward south TX at that time.
Prior to this trough ejecting northeast, weak mid-level height falls
will overspread the Plains which should encourage a weak lee surface
low to migrate off the CO High Plains into the Edwards Plateau
during the overnight hours.

Strengthening LLJ across TX is expected to aid northward movement of
modified Gulf moisture such that upper 50s surface dew points will
return to northwest TX into extreme southwest OK by 30/00z. While
the latest model guidance suggests the strongest boundary-layer
heating will be noted across this region, convection may struggle to
organize until the cold front surges south during the late evening.
Prior to the frontal forcing, warm advection will be the primary
mechanism for scattered weak convection across the southern Plains.

Forecast soundings across northwest TX after sunset suggest
near-surface based buoyancy is likely, however instability should
remain weak given the modest lapse rates. Even so, organized
convection should ultimately evolve along/immediately behind the
front as it surges south, encouraged by southerly 850mb flow atop
the front. While small hail and perhaps some gusty winds could
accompany the most organized storms, weak instability should limit
the overall severe threat.

..Darrow/Wendt.. 12/29/2020

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