SPC AC 080730

   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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