SPC 0700Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 PM CST Tue Dec 15 2020

Valid 171200Z - 181200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Aside from parts of the Sierra Nevada Thursday morning, the risk for
thunderstorm activity appears negligible across the U.S. the
remainder of Thursday through Thursday night.

...Synopsis...
Much of North America will remain under the general influence of
belts of westerlies branching downstream of a strong mid/upper jet
across the western and central, southern mid-latitude Pacific. 
Models indicate that these will remain largely zonal through this
period, but with a number of modestly amplified and progressive
short wave troughs.

In association with one of these features, a significant surface
cyclone is expected to be in the process of migrating east-north of
the northern Mid Atlantic coast early Thursday, with a trailing cold
front advancing through the remainder of the southeastern Gulf of
Mexico and Florida Peninsula during the day.  In their wake, cool
surface ridging likely will prevail across much of the Gulf of
Mexico, with only modest boundary layer moistening over the
southwestern Gulf.  Thus, despite strengthening southerly low-level
flow forecast through the Great Plains, coincident with deepening
surface troughing to the lee of the Rockies, there appears
negligible potential for appreciable low-level moistening and
destabilization.

...Parts of the northern Sierra Nevada...
Preceded by an influx of moisture, within a narrow plume emanating
from the southern mid-latitude/subtropical Pacific, a vigorous short
wave impulse is forecast to dig inland of the northern California
coast by 12Z Thursday.  It appears that this will be accompanied by
an 80-90 kt cyclonic mid-level jet (around 500 mb), with strong
cooling and forcing for ascent in its left exit region spreading
southeast of the San Francisco Bay area into portions of the
northern Sierra Nevada Thursday morning.  This may contribute to
sufficient destabilization to support low probabilities for
convection capable of producing lightning, particularly where aided
by orographic lift across the Sierra Nevada.

...Southern Florida...
Although weak boundary-layer CAPE may develop ahead of the
southeastward advancing cold front, particularly across southeast
coastal areas, weak low-level convergence and warm layers aloft
(especially near/above 500 mb) appear to preclude an appreciable
risk for thunderstorm Thursday.

..Kerr.. 12/16/2020

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