SPC AC 050649

   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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