SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0632 AM CST Tue Dec 01 2020

Valid 011300Z - 021200Z


Severe thunderstorms are not expected through tonight.

In mid/upper levels, a highly amplified pattern will continue
through the period, but with considerable geometric change.  A large
cyclone -- initially covering much of the eastern CONUS and centered
over western PA -- is forecast to move north-northeastward through
12Z tomorrow, with its 500-mb low reaching southern QC.  The
associated surface occluded front extended at 11Z from the low over
central NY across southern New England, to a warm-frontal triple
point southeast of Long Island, with cold front arching southward
and southwestward over the northern/western Bahamas.  Isolated
thunder may be possible for a few more hours over portions of
eastern ME, where elevated MUCAPE up to about 400 J/kg (rooted near
850 mb, atop a deep stable layer) will be possible within a
precip-laden/warm-advection conveyor.

Farther west, a closely aligned series of shortwave troughs was
evident in moisture-channel imagery over western SK, eastern MT, and
the southern WY/northwestern CO area.  The middle perturbation will
lose definition while the northern and southern ones dig south-
southeastward, forming a large cyclone over the central/southern
Rockies and adjoining High Plains by the end of the period.  By
then, the northern trough will close into a low over eastern MT and
shift southward to eastern WY, while the southern one will develop a
closed low over the TX Panhandle.  Being ensconced within the
broader cyclonic gyre, these two lows may begin a temporary
Fujiwhara interaction late in the period, continuing on day 2. 
Low-level warm advection will occur over the northwestern Gulf
region throughout the period, but without sufficient along-
trajectory marine modification to support potentially lightning-
producing convection until late tonight, after 06Z.  Isolated
thunderstorms may move northward across parts of the middle/upper
Texas Coastal Plain thereafter.

..Edwards.. 12/01/2020

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