SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1120 PM 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. ...Synopsis... A belt of westerlies emanating from the mid-latitude Pacific will remain a prominent influence across much of the U.S. through this period, with one embedded short wave trough expected to be progressing into/across the southern Appalachians vicinity by 12Z Monday. Models indicate a continued rapid east-northeastward acceleration across the southern Mid Atlantic coast by late Monday afternoon, accompanied by a still modest, but deepening, surface cyclone. This is forecast to occur as a more vigorous short wave trough, on the leading edge of northwesterly flow emanating from the northwestern Canadian Arctic latitudes, accelerates eastward within strengthening cyclonic flow across the upper Great Lakes into the Canadian Maritimes. There may be increased phasing of the two perturbations east of the north Atlantic Seaboard, accompanied by substantive further deepening of the surface cyclone to the southeast of the Canadian Maritimes. In the wake of these features, and in advance of another significant amplifying mid-level trough digging across the southern Rockies and central/southern Great Plains, a confluent mid-level regime is forecast to support building cold surface ridging across and east of the Mississippi Valley into the Atlantic Seaboard. This will tend to suppress surface cyclogenesis to the lee of the southern Rockies, with generally stable conditions being maintained across most areas east of the Rockies, in addition to much of the West. ...Southern Mid Atlantic... Thermodynamic profiles characterized by a stable boundary-layer and generally weak mid-level lapse rates are expected to prevail along the warm frontal zone, ahead of the developing cyclone expected to migrate into the western Carolinas by 12Z Monday. However, at least some forecast soundings (perhaps most notably the NAM) suggest that modest moisture return, in the presence of lift aided by low-level warm advection, may contribute to profiles at least marginally conducive to convection capable of producing lightning. Any such activity probably will be focused just ahead of strong mid-level subsidence warming, which is forecast to accompany a strong cyclonic mid-level jet nosing across the Carolinas by mid afternoon Monday. Low-level and deep-layer shear may become strong by Monday afternoon across the Outer Banks area of North Carolina, where weak boundary-layer destabilization may not be entirely out of the question. However, appreciable potential for strong to severe thunderstorm activity still seems focused offshore, closer to the Gulf stream, late Monday afternoon and evening. ..Kerr.. 12/13/2020
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