SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1119 PM CST Sun Dec 13 2020 Valid 151200Z - 161200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for thunderstorms appears negligible across much of the U.S., Tuesday through Tuesday night. ...Discussion... In the wake of a vigorous short wave impulse of Arctic origins, migrating into the northwestern Atlantic, models continue to indicate that mid/upper flow across much of Canada will begin to trend more zonal during this period. Across the U.S., a belt of westerlies emanating from the mid-latitude Pacific will remain a prominent influence, initially with amplified large-scale troughing digging to the lee of the Rockies by 12Z Tuesday. While it does appear that this trough may begin to undergo considerable shearing, a significant embedded short wave perturbation, perhaps including a transient mid-level closed low, is generally forecast to pivot across the central and southern Great Plains, through the middle and lower Mississippi Valley by the end of the period. This may support slowly deepening, weak surface troughing near/east of the Mississippi Valley Tuesday night. However, it appears that a frontal zone on the leading edge of initially expansive cold surface ridging, off the south Atlantic coast through the central Florida Peninsula and north central Gulf of Mexico, will provide the primary focus for potential surface cyclogenesis. And models continue to indicate that there may be a couple of waves developing along it by late Tuesday night. Particularly over the north central Gulf of Mexico, this may be accompanied by sufficient boundary-layer moistening and destabilization to support increasing thunderstorm development Tuesday night. Within the warm sector of the wave developing off the south Atlantic coast, thunderstorm potential remains more unclear due to weaker mid/upper support. Elevated moisture return may lead to the development of very weak CAPE across parts of the Gulf and south Atlantic coast states. However, the extent to which this becomes supportive of convection capable of producing lightning also remains unclear. Perhaps aided by deep-layer forcing for ascent ahead of the short wave trough, CAPE for elevated moist parcels may extend upward through cold enough layers to contribute to weak thunderstorm activity across the southeastern Mississippi/southern Alabama vicinity by late Tuesday night. ..Kerr.. 12/14/2020
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