SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1125 PM CST Mon Jan 11 2021

Valid 121200Z - 131200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for thunderstorms appears negligible across the U.S. today
through tonight.

...Synopsis...
It appears that a perturbation within the persistent strong
mid-latitude Pacific jet will undergo considerable amplification
(near 160 W latitude) during this period.  As it does, downstream
ridging is forecast to build within the mid-latitude westerlies, and
across the subtropical eastern Pacific.  On the northeastern
periphery of this ridging, models indicate that a vigorous short
wave perturbation will accelerate east-northeastward toward the
Pacific Northwest coast today, before turning eastward, inland near
the international border area tonight.  This may be accompanied by a
developing surface frontal wave into coastal areas northwest of
Puget Sound by this evening, and more prominent surface cyclogenesis
to the lee of the Canadian Rockies by 12Z Wednesday.  A plume of
moisture (emanating from the lower latitude western Pacific) on its
southern periphery will probably be shunted southward ahead of the
cold front, becoming focused across northern California by the end
of the period.

Downstream, relatively dry and stable conditions are expected to
generally prevail across much of the remainder of the U.S., with
confluent mid-level flow contributing to the maintenance of cold
surface ridging across much of the Gulf Coast states and
northwestern Gulf of Mexico.  Models suggest that the frontal zone
marking the leading edge of this air mass will stall across southern
portions of the Florida Peninsula and the southern Gulf of Mexico,
along and south of which seasonably high moisture content likely
will remain confined. 

...South Florida/Keys...
Although there may be some further boundary-layer moistening
along/ahead of the initially southward advancing cold front, showers
associated with moistening and forcing for ascent aloft probably
will tend to stabilize lapse rates and minimized boundary-layer
destabilization.  While a brief, weak thunderstorm or two might not
be entirely out of the question, it is not yet clear that
probabilities meet the minimum 10 percent threshold.

...Parts of south central Texas into lower Mississippi Valley...
Within remnant mid-level troughing gradually emerging from the
northern Mexican Plateau and adjacent southwest Texas, a compact
embedded mid-level low is forecast to track near/south of the Hill
Country toward the lower Mississippi Valley today through tonight. 
Although this is well to the cool side of the surface frontal zone, 
forecast soundings indicate that, near the base of steeper mid-level
lapse rates beneath the mid-level cold core, elevated moisture
return may contribute to weak CAPE supportive of scattered
high-based convection.  Much of this is currently forecast to remain
above the freezing level, and probabilities for weak thunderstorms
are being maintained at less than 10 percent.  However, sporadic
lightning with convection may not be entirely out of the question
along the track of the low.

...Pacific Northwest...
Strong mid-level cooling may not spread inland across northwestern
Washington until after 13/06Z this evening, and the extent to which
thermodynamic profiles become conducive to convection capable of
producing lightning remains unclear, based on latest forecast
soundings.  While sporadic lightning appears possible, mainly near
the international border to the west of the Cascades, probabilities
still appear less than 10 percent.

..Kerr.. 01/12/2021

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