SPC Apr 15, 2018 2000 UTC Day 1 Convective Outlook

By Newsroom America Feeds at 15 Apr 16:47

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 0340 PM CDT Sun Apr 15 2018 Valid 152040Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF SC...NC INTO VA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK FROM CENTRAL AND SOUTHERN VA TO CENTRAL FL... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK FROM THE UPPER OHIO VALLEY TO MIDDLE-ATLANTIC STATES AND SOUTH TO SOUTH FL... CORRECTED GENERAL THUNDERSTORM GRAPHIC LINES. ...SUMMARY... A line of strong to severe thunderstorms will move northeast across the Southeast and Mid-Atlantic States through tonight. Damaging winds and tornadoes are most likely from eastern South Carolina into Virginia through early evening. ...VA/Carolinas to FL... The ongoing severe-weather threat will persist the rest of this afternoon into the evening across portions of the Carolinas and VA to coastal GA, and across the FL Peninsula. The western portions of the categorical and severe probabilities have been trimmed, given the eastward progression of the squall line. Day 1 forecast reasoning remains valid with this outlook issuance. At mid-late afternoon, mosaic radar imagery showed a nearly continuous squall line extending from southwest VA through western NC to the GA coast into northeast FL. The northeast FL into adjacent southeast GA portion of the line developed along an apparent pre-frontal corridor of ascent. Meanwhile, portions of the long-lived Gulf of Mexico band of storms moved into the coastal areas of the central FL Gulf Coast toward mid afternoon, and will continue to approach south FL and the Keys. Discrete storms had formed in the warm sector across parts of eastern SC and central and eastern NC, with this trend expected to continue as the large upper trough approaching the Day 1 severe risk areas becomes more negatively tilted. ...Parts of northern VA, MD to the Delmarva Peninsula... No changes with the northeast portion of the marginal risk, as strong to severe storms will be possible across these areas as the cold front advances through this region later this evening into the overnight. The backdoor cold front that was analyzed south of the lower Potomac River this afternoon is expected to advance north this evening and tonight as a warm front through at least southern, central and eastern MD, and the Delmarva Peninsula. Modifying environment just ahead of the cold front could prove favorable for strong winds and perhaps a tornado threat. ..Peters.. 04/15/2018 .PREV DISCUSSION... /ISSUED 1148 AM CDT Sun Apr 15 2018/ ...North Florida to the Delmarva vicinity... The base of a prominent upper trough centered over the Midwest will continue to steadily spread northeastward over the Tennessee Valley toward the central/southern Appalachians with ample downstream height falls and a considerable strengthening of south-southwesterly winds through a deep layer. Persistent cloud cover and relatively weak mid-level level lapse rates will hinder robust destabilization, but this will be compensated by an increasingly moist air mass in conjunction with strengthening deep-layer/low-level shear. At midday, a nearly continuous squall line continues to intensify across east Georgia into north Florida while other bands of storms have more recently increased across the western Carolinas. Largely unidirectional/boundary-parallel wind profiles will initially limit the eastward progression of the convective bands, but northeastward-racing bowing segments are likely to evolve over time with some net east/northeastward acceleration. Damaging winds will likely be the most common impact, but some tornadoes can be expected given the degree of low-level SRH coincident with a moist environment. At least some severe risk may develop into the Delmarva vicinity late tonight within a weakly unstable/highly sheared environment. ...Central/South Florida... While the region will be influenced by more modest mid-level height falls and weaker deep-layer shear, an approaching squall line over the Gulf of Mexico will pose some severe risk while additional development could occur via the east-coast sea breeze. Damaging winds will exist along with the possibility of a tornado. ...Ohio Valley... Modest moisture and minimal buoyancy may be sufficient for a few strong updrafts/downdrafts capable of localized severe in relatively close proximity to the surface low track. Read more



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