SPC AC 290526

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1226 AM CDT Fri May 29 2020

   Valid 291200Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTHEASTERN UNITED STATES...

   ...SUMMARY...
   Scattered thunderstorms, some severe, are possible across an area
   centered over PA/NY Friday afternoon through Friday evening. A few
   strong storms are also possible across the northern Rockies region.

   ...Northeastern US...

   Early-morning water-vapor imagery depicts a well-defined mid-level
   vort/short-wave trough over the Mid-South lifting northeast in line
   with short-range model guidance. This feature should begin to eject
   quickly over the next 24hr as 500mb flow increases across the
   central Appalachians this morning before translating into New
   England overnight. This increase in mid-high level flow is expected
   to enhance the likelihood for organized convection later today.

   While mid-level lapse rates are not forecast to be particularly
   steep, latest guidance suggests a corridor of strong boundary-layer
   heating should develop across the Appalachians, which should result
   in surface readings breaching convective temperatures around 17-18z.
   Thunderstorms should develop by noon along a corridor from OH into
   Upstate NY ahead of a pronounced cold front. This activity will
   evolve within a strongly sheared southwesterly flow regime. While
   vertical shear seems supportive of supercells, and a few may
   develop, it appears thunderstorm clusters and line segments may be
   the more common storm mode. Damaging winds, some hail, and perhaps a
   tornado or two can be expected with pre-frontal convection as it
   spreads toward New England late this afternoon.

   ...Northern Rockies Region...

   Short-wave ridging will dominate the northern Rockies during the
   day1 period; although, a strong upper low should approach the
   central CA Coast by 30/12z. Prior to this upper low, diurnal heating
   and orographic forcing will be the mechanisms by which scattered
   convection develops across this region. A few high-based
   thunderstorms are expected by late afternoon along an arcing
   corridor from OR-central ID-northwestern WY. Gusty winds and
   marginally severe hail are possible with the strongest convection.

   ..Darrow/Karstens.. 05/29/2020

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