SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0149 AM 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...PARTS OF NORTHERN MASSACHUSETTS AND SOUTHERN MAINE... ...SUMMARY... Thunderstorms may overspread parts of Upstate New York through northern New England Wednesday afternoon and evening, accompanied by a risk for potentially damaging wind gusts. ...Synopsis... A seasonably strong mid/upper jet across the northern mid-latitude Pacific appears likely to become more zonal while nosing into the northeastern Pacific during this period. As this occurs, within branching downstream flow across North America, another modestly amplified, strong mid/upper jet is forecast to progress eastward across Canada and the northern tier of the U.S. This will include broad ridging gradually shifting east of the Canadian Rockies, through the Canadian Prairies, and broad troughing shifting across eastern Canada and the Northeast. In lower latitudes, mid/upper ridging will persist across the subtropical western Atlantic into Florida and adjacent portions of the Southeast, with several tropical perturbations progressing around its southern/southwestern periphery. It appears that this will include a hurricane (currently Tropical Depression Twenty-Six) migrating slowly northwestward across the central Gulf of Mexico, within a plume of tropical moisture largely confined to the Gulf of Mexico. Within the westerlies, a strong short wave perturbation, including a 100 kt northwesterly mid-level (around 500 mb) jet streak, is forecast to dig east-southeast of the lower Great Lakes region, before turning eastward across New England by Wednesday night. It appears that this will be accompanied by substantial further deepening of a surface cyclone, across southern Quebec through the Canadian Maritimes. 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 will contribute to the maintenance of dry and/or stable conditions across most areas east of the Rockies. ...Upstate New York into northern New England... Boundary-layer moisture within the warm sector of the surface cyclone likely will be rather marginal for vigorous convective development. However, thermodynamic profiles probably will become conducive to convection capable of producing lightning, aided by forcing for ascent and cooling to the north of the strong cyclonic mid-level jet. Even with mixed-layer CAPE on the order of 250-500 J/kg, storms may become sufficiently strong to aid the downward transfer of higher momentum to the surface. With model forecast soundings indicating 40-50+ kt mean ambient flow in the lowest 5-6 km AGL, at least a few gusts exceeding severe limits appear possible. This may commence on the nose of a developing mid-level dry slot east of Lake Ontario Wednesday afternoon, before spreading eastward across parts of northern New England by Wednesday evening. ..Kerr.. 10/05/2020
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