SPC AC 150559

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Wed Jul 15 2020

   Valid 161200Z - 171200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST
   OH INTO WESTERN PA/NY...

   ...SUMMARY...
   Strong to severe storms are possible on Thursday from the Ozarks
   into the Ohio Valley and western New York. Additional strong storms
   are possible over the central High Plains.

   ...Ozarks/Ohio Valley into western PA/NY...

   A broad upper trough will be centered over the Upper Midwest
   Thursday morning. A shortwave impulse embedded in the broader-scale
   trough will eject northeast from the lower Ohio Valley to western
   PA/NY through 00z, while the main upper trough pivots eastward
   across the upper Great Lakes during the day, to the lower Great
   Lakes by Friday morning. This will result in a band of enhanced
   southwesterly flow from the lower Ohio Valley to western PA/NY. At
   the surface, low pressure near southern Lake MI early Thursday will
   develop east/northeast toward Lake Erie by Thursday night. A
   trailing cold front will push east/southeast across much of the
   Midwest, stretching from west-central NY southwestward to the MO
   Bootheel and then westward near the OK/KS border by Friday morning. 


   A seasonally moist airmass will reside ahead of the front, with
   mid-to-upper 60s F dewpoints in place. Moderate to strong
   instability is expected by mid-afternoon and scattered thunderstorms
   are expected to develop ahead of the surface low and cold front.
   Guidance varies in the strength of vertical shear and this will have
   some impact on how well organized convection becomes. However, given
   expected instability and forcing aloft as well as at the surface in
   relation to the cold front, at least isolated clusters of strong to
   severe storms appear possible. High PW values and steepening low
   level lapse rates will favor a threat mainly for locally damaging
   wind gusts. However, backed southeasterly low level winds ahead of
   the surface front should augment low level shear, and mean mixing
   ratio values near 15-17 g/kg, could support a tornado or two.

   A low level jet is forecast to increase during the evening, and this
   could lead to some upscale development into eastward propagating
   line segments, but instability will wane with eastward extent as
   inhibition increases with the loss of daytime heating. 

   Guidance varies on timing and how widespread additional thunderstorm
   develop will occur over the Ozarks, where the cold front will not be
   a well-defined as further northeast. However, a very unstable and
   moist air mass will reside over this region as well. Additionally,
   an MCV may shift eastward into the region from convection expected
   across parts of the central/southern Plains in the Day 1 period.
   This should result in at least isolated storms by evening, mainly
   posing a locally damaging wind gusts threat. 

   ...Central High Plains...

   Moist upslope flow will transport low 60s dewpoints westward across
   the region. Strong heating and steep midlevel lapse rates will aid
   in moderate to strong destabilization, and a weak shortwave impulse
   ejecting across the central/southern Rockies will support isolated
   to scattered thunderstorm development. High-based supercells are
   possible, posing a threat for locally strong gusts. While deep layer
   flow will be rather weak, west/northwesterlies atop southeasterly
   low level winds will result in effective shear near 35 kt amid very
   steep lapse rates, and isolated large hail also will be possible.

   ..Leitman.. 07/15/2020

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