SPC AC 160455

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1155 PM CDT Fri May 15 2020

   Valid 171200Z - 181200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY AFTERNOON
   AND EVENING ACROSS PARTS OF THE OHIO VALLEY INTO SOUTHERN PORTOINS
   OF THE GREAT LAKES REGION...AND PARTS OF THE NORTHERN INTERMOUNTAIN
   REGION...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the Ohio Valley into
   southern portions of the Great Lakes region, as well as parts of the
   northern intermountain region, on Sunday, accompanied by at least
   some risk for severe weather.

   ...Synopsis...
   Models remain similar concerning the depiction of the evolving
   mid-level flow across the eastern Pacific into western North America
   through this period.  An initially broad and deep mid-level low, off
   the Pacific coast at 12Z Sunday, is forecast to continue to slowly
   approach the coast Sunday through Sunday night.  It may elongate
   along the U.S. Pacific coast, as a significant short wave impulse
   pivots around the western through southern periphery of the
   circulation. 

   Downstream, a mid-level high becoming centered near the Texas Big
   Bend may become increasingly prominent across much of the southern
   Rockies and higher Plains, northward into the Dakotas, with ridging
   also building along an axis northeast of the Dakotas into
   northwestern Ontario.

   Within branching flow farther to the east, developments remain at
   least a bit more uncertain due to more substantial spread evident
   among the various models and within their ensemble output.  However,
   in general, a significant wave in one branch may dig southeast of
   the Upper Midwest into portions of the Great Lakes and Ohio Valley
   region.  It appears that this will be accompanied by a modest and
   perhaps slowly deepening surface cyclone, along an initially stalled
   frontal zone across the southern Great Lakes vicinity, and a
   southward surging cold front in its wake, across much of the lower
   Ohio Valley, Ozark Plateau and central Plains by 12Z Monday.

   Across the southern Plains into northwestern Gulf coastal areas, the
   cold front likely will be preceded by an intrusion of cool air,
   associated with a short wave trough digging within a weaker branch
   of westerlies across parts of eastern Texas and Louisiana.

   Farther downstream, this weaker branch may gradually come in phase
   with the subtropical stream over the southwestern Atlantic, where an
   associated low-level cyclone is expected to turn northeastward, east
   of the Carolina coast.

   ...Ohio Valley into southern Great Lakes region...
   The evolution of boundary-layer destabilization within the warm
   sector of the east-southeastward migrating low remains unclear, due
   to potential for considerable early period convection, associated
   cloud cover and precipitation.  However, even with relatively weak
   mid-level lapse rates forecast, guidance suggests that mid/upper 60s
   F surface dew points may contribute to CAPE of 500-1000 J/kg with
   some insolation.

   The primary focus for potential stronger thunderstorm development
   also remains unclear, and could be with a convectively generated or
   enhanced perturbation spreading within southwesterly flow ahead of
   the primary mid-level troughing.  Regardless, it still appears that
   moderate shear beneath 30-40+ kt flow in the 850-500 mb layer may
   contribute to an environment at least marginally conducive to
   organized thunderstorm development, accompanied by a risk for
   potentially damaging wind gusts and some hail.

   ...Northern intermountain region...
   Modest boundary-layer destabilization appears possible across the
   higher terrain of northeastern Oregon into northern Idaho by Sunday
   afternoon in response to modest daytime heating beneath cold and
   cooling mid-level temperatures.  CAPE may reach 500+ J/kg, as a
   strong southwesterly mid/upper jet contributes to strong deep-layer
   shear.  Aided by forcing for ascent associated with an inland
   migrating short wave impulse, storms may initiate across
   northeastern Oregon and perhaps southeastern Washington by 21Z,
   before spreading northeastward through early evening.  Some this
   activity may become capable of producing small to perhaps marginally
   severe hail, along with potential for strong convective gusts.

   ..Kerr.. 05/16/2020

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