SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1150 PM CST Sun Nov 29 2020

Valid 301200Z - 011200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN
CAROLINAS INTO SOUTHERN NEW ENGLAND...

...SUMMARY...
Isolated strong to severe thunderstorms capable of producing
damaging winds and a couple of tornadoes will be possible today from
parts of Florida into the Carolinas, Mid-Atlantic and southern New
England.

...Synopsis...
Remnants of an upper low crossing the southern Appalachians region
early in the period will continue to be absorbed by a sharp
northern-stream trough, progged to be crossing the upper Great
Lakes/Mississippi Valley at the start of the period.  As this trough
advances, and fully ingests the remnant upper low, the trough is
expected to gradually close off and become its own large upper
cyclone -- which will reach the central Appalachians area by the end
of the period.

As the upper flow field evolves, a deepening surface low crossing
western North Carolina/Virginia early in the period will move
quickly northward, reaching central New York by 01/00Z where it will
then begin to occlude.  The trailing cold front associated with the
low will move across the Atlantic Coast states through the day,
likely clearing the coast from the Mid Atlantic region to Florida
through the evening, while a warm sector lingers onshore over
southern New England into the overnight hours.

...Eastern Carolinas to southern New England...
Widespread showers and embedded thunderstorms are forecast to be
ongoing at the start of the period over the eastern U.S., with the
main band of frontal convection stretching from West
Virginia/western Virginia to the Florida Peninsula early. 
Limited/local severe potential will be ongoing, with a gradual,
modest increase in threat expected through late morning/early
afternoon from eastern North Carolina northward into the Mid
Atlantic region as at least 500 J/kg mixed-layer CAPE spreads
northward across the coastal Mid-Atlantic/Chesapeake Bay region.  

Very strong flow through a deep layer suggests potential for
damaging winds, where stronger storms can transport momentum
downward.  Meanwhile, favorably increasing/veering flow with height
through the lower troposphere will also support potential for
low-level rotation -- and thus a couple of tornadoes appear possible
where sustained supercell storms can evolve.  

By mid evening, convection will have largely moved off the Mid
Atlantic Coast, while some severe risk lingers over southern New
England -- possibly into the overnight hours.

...Central Florida...
As the cold front shifts southeastward across Florida through the
day, a band of showers and thunderstorms is likewise forecast to
cross the Peninsula.  Storms will likely be ongoing within this
frontal band at the start of the period, but modest CAPE expected
ahead of the front suggests that most of the convection should
remain sub-severe.  Still, with amply strong (around 50 kt)
mid-level westerly flow atop the frontal zone, gusty/locally
damaging winds may occur with one or two of the strongest storms,
before convection weakens into the afternoon hours in the wake of
the passage of a weak vort max.

..Goss/Moore.. 11/30/2020

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