SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1145 PM CDT Mon Oct 05 2020 Valid 071200Z - 081200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS WEDNESDAY ACROSS MUCH OF UPSTATE NEW YORK...VERMONT...NEW HAMPSHIRE...NORTHERN MASSACHUSETTS...AND SOUTHERN MAINE... ...SUMMARY... Thunderstorms may contribute to a risk for potentially damaging wind gusts across parts of Upstate New York through northern New England Wednesday afternoon and evening. ...Synopsis... One seasonably strong and modestly amplified mid/upper jet appears likely to continue progressing across Canada and the northern tier of the U.S., as a somewhat stronger, more zonal upstream jet noses across the northern mid-latitude Pacific during this period. While broad mid-level ridging shifts east of the Canadian and northern U.S. Rockies, through the Canadian Prairies and northern U.S. Great Plains, similar amplitude downstream troughing is forecast to continue to evolve across the eastern Canadian Provinces and Northeast. Models still indicate that the eastern troughing will include a strong short wave perturbation, with a 100+ kt northwesterly mid-level jet streak digging east-southeast of the lower Great Lakes region and across the northern Mid Atlantic/southern New England coast vicinity Wednesday through Wednesday night. This is forecast to be accompanied by a significant surface cyclone, which may undergo substantial further deepening as it migrates from southeastern Ontario/southwestern Quebec into the Canadian Maritimes by 12Z Thursday. Beneath an increasingly confluent regime, in the wake of the mid-level perturbation, cold surface ridging is forecast to build across and east of the Mississippi Valley, and southward into the Gulf Coast states by late Wednesday night. This is expected to contribute to the maintenance of dry and/or stable conditions across most areas east of the Rockies. In lower latitudes, mid/upper ridging likely will persist across the subtropical western Atlantic into Florida and adjacent portions of the Southeast, with several tropical perturbations within the easterlies on its southern and southwestern periphery. This will include Hurricane Delta migrating northwestward into the south central Gulf of Mexico, within a plume of tropical moisture largely confined to the Gulf of Mexico. ...Upstate New York into northern New England... Thermodynamic profiles supportive of convection capable of producing lightning probably will be confined to areas along and north of the strong, digging cyclonic mid/upper jet streak. This will be aided by forcing for ascent and cooling within its left exit region, with subsidence and warming aloft suppressing deeper convection to the south. Boundary-layer moisture in the warm sector of the surface cyclone will probably be rather marginal for vigorous thunderstorm development, and mixed-layer CAPE may only peak around 250-500 J/kg. However, given cool thermodynamic profiles and strong deep-layer vertical shear, this may be sufficient to contribute to storms with small hail. Melting and evaporative cooling in downdrafts should enhance the downward transfer of higher momentum to the surface. Potentially damaging surface gusts appear possible in stronger convection, particularly where mean ambient west-northwesterly flow in the lowest 5-6 km AGL is forecast on the order of 40-50+ kt, in a rough corridor east-southeast of Lake Ontario through portions of northern New England. ..Kerr.. 10/06/2020
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