Day 4-8 Outlook

Day 4-8 Outlook Image

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0325 AM CST Mon Nov 16 2020

Valid 191200Z - 241200Z

The period will begin with a positively tilted trough over the
U.S./Canadian West Coast -- a degraded remnant of the substantial
cyclone now over the northeastern Pacific.  Downstream and in low
levels, a slow-moving cold front will extend from the Great Lakes to
the southern High Plains days 4-5/22nd-23rd, largely parallel to and
south of the faster flow aloft.  Strong low-level ridging over the
Southeast and Gulf Coast will be slow to retreat, precluding robust
moisture return into this regime, with organized severe potential
too low for an outlook area days 4-6. 

Though details differ some at shortwave scales, operational
GFS/ECMWF/CMC, and available ensemble guidance, generally agree that
the positively tilted synoptic trough will cross the western/central
CONUS and amplifying days 5-6, with the front sagging southeastward
through the Appalachians and western Gulf Coast States. 
Considerable spread occurs at mid/upper levels from day 6 onward. 
Still, the general pattern of front-parallel flow aloft suggests
weak lapse rates and abundant clouds/precip near the front that
should keep severe potential generally marginal and conditional.  

One exception may be near the end of the period (days 7-8/23rd-24th)
in the upper Ohio Valley to Mid-Atlantic/Northeast, if a more
intensely amplified northern-stream cyclone, as forecast by
operational ECMWF (but not deterministic GFS/CMC nor several EC
ensemble members), verifies over the southern ON/lower Great Lakes
region.  Such a scenario would strengthen frontal forcing under
intense flow aloft for potential low-topped convective band(s). 
However, at such a long time range, predictability is very low for
such a solution.

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