SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1118 AM CST Fri Nov 20 2020

Valid 211200Z - 221200Z


The risk for severe thunderstorms appears negligible across the U.S.
Saturday through Saturday night.

Models suggest that the most prominent branch of westerlies
emanating from the Pacific may undergo amplification during this
period.  It appears that this will include a building mid-level
ridge across the Canadian Rockies and northern U.S. intermountain
region/Rockies, and a digging short wave trough across the northern
Great Plains and middle Missouri Valley.

The short wave trough may support weak frontal wave development
along the leading edge of a reinforcing cold intrusion across the
Ozark Plateau/lower Missouri Valley vicinity, where southerly return
flow in the wake of a prior cold intrusion has allowed for weak to
modest low-level moistening.  However, substantive further Gulf
moisture return appears unlikely, with only a very gradual continued
boundary-layer moistening within easterly low-level flow to the
south of remnant surface ridging across the Gulf Coast region.

...Four Corners region through the Ozarks vicinity...
Ahead of the digging short wave trough, at least a couple of short
wave perturbations are forecast to traverse the region within a belt
of westerlies emanating from the southern mid-latitude/subtropical
eastern Pacific.  Associated forcing for ascent probably will
contribute to areas of convective development.  However, based on
model forecast soundings, the extent to which this activity may
become capable of producing lightning remains unclear. 

Low-level moisture return and warm advection are expected to remain
focused across parts of the Ozark Plateau into the lower Missouri
Valley, where relatively warm temperatures aloft/weak lapse rates
may inhibit weak thunderstorm development until perhaps late
Saturday evening/Saturday night.

Upstream, very weak CAPE rooted at higher levels, aided by somewhat
steeper mid-level lapse rates, mainly near/above the 700 mb level
could become supportive of weak thunderstorm activity near the
Oklahoma/Kansas border vicinity into southeastern Colorado. 
Otherwise, orographic forcing might contribute to an isolated weak
thunderstorm or two across the mountains of southwestern Colorado
late Saturday afternoon.

Within gradually moistening easterly low-level flow, models suggest
that areas of scattered showers may overspread the peninsula
Saturday through Saturday night.  As a mid-level high center shifts
east of the south Atlantic Seaboard, weak cooling aloft may allow
for increasing probabilities for thunderstorms by Saturday night,
mainly near southeast coastal areas.

..Kerr.. 11/20/2020

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