SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1104 PM CST Thu Dec 03 2020 Valid 041200Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY ACROSS THE COASTAL AREAS OF THE FLORIDA PANHANDLE AND TONIGHT ACROSS COASTAL NORTH CAROLINA... ...SUMMARY... Strong thunderstorms may impact coastal areas of the Florida Panhandle today, and parts of the North Carolina coastal plain tonight, accompanied by at least some risk for severe weather. ...Synopsis... Much of North America will remain under the influence of relatively complex, amplified branching flow, downstream of a strong zonal jet across the southern mid-latitude western and central Pacific. Within this regime, positively tilted large-scale mid-level ridging likely will remain prominent (though with an embedded area of lower heights), across the northwestern U.S. and western Canada. Positively tilted troughing will also linger to its southeast, across the southern Great Plains into the Southwest and Mexican Plateau, although the center of a broadening cyclonic circulation approaching the Texas Big Bend may become its most significant feature. More prominently, one or two vigorous short wave perturbations are forecast to continue digging into and through the base of larger-scale mid-level troughing across the Great Lakes into Ohio Valley region. As this occurs, models indicate that an elongated mid-level circulation emerging from the southern Great Plains will pivot eastward across the Mid South, before becoming increasingly in phase with the larger-scale troughing as it continues across the southern Appalachians into the southern Mid Atlantic coast. It appears that strong large-scale forcing for ascent associated with these developments may contribute to rapid, significant surface cyclogenesis, from the lee of the southern Appalachians by late this evening into areas off the Mid Atlantic coast by daybreak Saturday. This will be accompanied by considerable strengthening of deep-layer wind fields, contributing to sufficiently strong shear to potentially contribute to a risk for severe thunderstorms across a sizable portion of the Southeast and Mid Atlantic, given sufficient low-level moistening and destabilization. However, conditions across much of this region remain generally cool/dry and stable, with the air mass yet to begin to substantively destabilize off the south Atlantic coast, and still in the process of modifying over the north central into northeastern Gulf of Mexico. As a result, it appears that severe weather potential will remain relatively low and confined mostly to coastal areas of the Florida Panhandle and North Carolina, if not the offshore waters. ...Florida Panhandle... NAM/Rapid Refresh forecast soundings suggest that lower/mid 60s surface dew points may advect into immediate coastal areas early today. Despite generally weak lapse rates, it appears that this could contribute to mixed-layer CAPE on the order of 500+ J/kg, in the presence of strengthening westerly mid/upper flow. While deep-layer shear likely will become strong, it appears that low-level wind fields will remain modest in strength, and contribute to generally unidirectional shear profiles. It is possible that scattered thunderstorm development initiating offshore during the day could spread inland and pose a marginally severe hail and wind threat before weakening. ...North Carolina coastal plain vicinity... Considerable spread is evident among the various model output concerning the timing of more rapid surface cyclone deepening. In addition to the potential impacts on possible low-level hodograph structure, this contributes to additional uncertainty concerning inland warm sector boundary-layer moistening and destabilization. A "worst case" scenario for surface cyclone evolution and associated severe weather potential could include a supercell tornado threat across eastern North Carolina and adjacent portions of South Carolina/southeast Virginia. However, based on the bulk of model output, including the convection allowing guidance, appreciable severe weather potential with vigorous thunderstorm development will probably evolve east of the North Carolina coast, but could perhaps impact the Outer and Inner Banks vicinity of North Carolina during the 05/03-09Z time frame. ..Kerr/Lyons.. 12/04/2020
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