SPC 0830Z Day 3 Outlook

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0147 AM CST Sat Dec 12 2020

Valid 141200Z - 151200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms appears negligible across the
U.S., Monday through Monday night.

...Discussion...
Within the belt of westerlies emanating from the mid-latitude
Pacific, models indicate that a lead short wave trough will rapidly
accelerate east-northeast of the southern Appalachians, across the
southern Mid Atlantic coast and into the western Atlantic during
this period.  This is expected to occur to the southeast of a
vigorous short wave trough of Arctic origins, which is forecast to
accelerate eastward within strengthening cyclonic flow, from the
upper Great Lakes into the Canadian Maritimes.

While there may be at least some increase in phasing of these
perturbations, it appears that this will be mostly well east of the
Atlantic Seaboard, supporting a rapidly deepening cyclone over the
Atlantic to the south/southeast of the Canadian Maritimes by 12Z
Tuesday.  Models do suggest that the onset of more rapid
cyclogenesis could occur as early as midday Monday, but generally
just offshore of the Mid Atlantic coast.  Prior to this, it is
possible that low-level moistening and large-scale ascent may
contribute to very weak destabilization across parts of the middle
and south Atlantic Seaboard.  However, forecast thermodynamic
profiles, at best, currently appear only marginally conducive to
convection capable of producing lightning.  Primary thunderstorm
development seems likely to become focused closer to the Gulf
stream, as forcing for ascent spreads offshore Monday afternoon.

Meanwhile, upstream, models indicate considerable amplification of
another short wave trough of mid-latitude Pacific origins, across
the Rockies into the central and southern Great Plains by late
Monday night.  However, preceded by expansive cold surface ridging,
building beneath a strongly confluent mid-level regime across and
east of the Mississippi Valley, models indicate that surface
cyclogenesis to the lee of the southern Rockies will be subdued. 
Generally cold, dry and/or stable conditions likely will prevail
across most areas east of the Rockies, as well as across the West.

..Kerr.. 12/12/2020

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