SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0230 AM CDT Thu Oct 08 2020 Valid 101200Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY ACROSS MUCH OF NORTHERN AND CENTRAL MISSISSIPPI AND ALABAMA...AND ADJACENT PORTIONS OF SOUTHERN TENNESSEE...AS WELL AS ACROSS MUCH OF UPSTATE NEW YORK INTO NORTHERN NEW ENGLAND... ...SUMMARY... The weakening remnants of Delta may continue to contribute to a risk for a couple of tornadoes and strong wind gusts across parts of the central Gulf Coast states on Saturday. Strong thunderstorms may also impact Upstate New York into portions of northern New England, posing at least some risk for severe wind and hail. ...Synopsis... A belt of westerlies emanating from the mid-latitude Pacific appears likely to become increasingly amplified across Canada and the northern tier of the U.S. through this period. This appears likely to include a digging mid-level trough inland of the Pacific coast and across the northern intermountain region, accompanied by surface cyclogenesis within deepening surface troughing to the lee of the Canadian/northern U.S. Rockies by late Saturday night. Downstream troughing is also forecast to amplify to the east and southeast of Hudson Bay, with a lead embedded short wave trough digging across southern Quebec into the Canadian Maritimes. This is forecast to be accompanied by a deep surface cyclone, with another cold front advancing across New York state and New England by the end of the period. Within a weaker branch of westerlies across the southern tier of the U.S., mid-level troughing, including the remnants of Delta, likely will continue to slowly shift east-northeast of the lower Mississippi Valley. Most guidance indicates substantial rapid weakening of the associated surface cyclone as it migrates northeastward out of northeastern Louisiana through northwestern Mississippi. ...Lower Mississippi to Tennessee Valley vicinity... An initially narrow plume of lower 70s surface dew points, wrapping into the low-level circulation center of Delta, may broaden northeastward across much of Mississippi and Alabama through the day. This is where the strongest southerly 850 mb flow will contribute to large clockwise-curved low-level hodographs most conducive to tornado potential. However, the extent of this potential Saturday remains unclear, as the peak wind fields weaken, and warm mid-levels limit boundary-layer destabilization. Still, there may be a window of opportunity for sufficient warming to destabilize the boundary layer before low-level wind fields weaken and hodographs shrink too much, to allow the environment to become conducive to a few low-topped supercells capable of producing tornadoes and locally strong surface gusts. ...Upstate New York into northern New England... To the south of the digging short wave impulse, models suggest that a narrow plume of warm elevated mixed-layer air may advect into the region by the beginning of the period, as boundary-layer moistening proceeds ahead of a southeastward advancing cold front. The NAM appears most aggressive with this moistening, and it may be too moist. However, there appears potential for sufficient pre-frontal boundary-layer destabilization, with daytime heating, to support at least scattered thunderstorm development by Saturday afternoon. Near the southeastern periphery of the digging mid-level trough, 30-50+ kt flow in the 850-500 mb layer may contribute to the risk for organized storms capable of producing potentially damaging wind gusts and marginally severe hail. ..Kerr.. 10/08/2020
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