SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1045 PM CST Mon Nov 02 2020

Valid 031200Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Aside from southern portions of the Great Basin into parts of the
Colorado Plateau, the risk for thunderstorms appears negligible
across much of the U.S. today through tonight.

...Discussion...
Models indicate that the stronger westerlies will trend more zonal
and increasingly confined to the northern mid-latitudes during this
period.  This is forecast to include the deamplication of
large-scale mid/upper troughing, now east of the Atlantic Seaboard,
across the Canadian Maritimes and adjacent northwestern Atlantic,
leaving broadening anticyclonic flow in its wake, across the British
Columbia coast through the St. Lawrence Valley.  

As this occurs, in lower levels, the center of fairly expansive cold
surface ridging appears likely to shift from the central Gulf Coast
states into areas off the north Atlantic coast, but a trailing ridge
axis (and associated potentially cold/dry air) is expected to be
maintained west-southwestward across much of the Gulf Coast region. 
This will continue to inhibit return flow off the Gulf of Mexico,
where boundary-layer moistening will only very slowly be underway,
in the wake of the recent cold intrusion.

A narrow plume of elevated moisture return, emanating from the
lower-latitude eastern Pacific, will still be ongoing early this
morning across the lower Colorado Valley into the southern Great
Basin, ahead of the increasingly deformed remnants of a broad, weak
mid-level low slowly progressing across the southern Sierra Nevada. 
It appears that the continuing approach of more progressive upstream
short waves will force the eastward acceleration of this
perturbation, and contribute to further suppression of a downstream
ridge emanating from the Mexican Plateau.  As this occurs, veering
lower/mid tropospheric flow across the Southwest will gradually
begin to cut off the moisture return.  However, there may still be
sufficient destabilization to support a continuing risk for
scattered weak thunderstorm activity across parts of the southern
Great Basin into the Colorado Plateau through late this afternoon.

..Kerr.. 11/03/2020

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