SPC AC 060445

   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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