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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