SPC AC 240459

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1159 PM CDT Thu Jul 23 2020

   Valid 251200Z - 261200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY INTO
   SATURDAY NIGHT ACROSS PARTS OF THE UPPER MIDWEST...NORTHERN GREAT
   PLAINS...AND PARTS OF SOUTHERN TEXAS...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the Upper Midwest and
   northern Great Plains Saturday into Saturday night, accompanied by
   at least some risk for severe weather.  Meanwhile, developing
   Tropical Storm Hanna may be accompanied by potential for a couple of
   tornadoes as it makes landfall across parts of the middle and lower
   Texas coast.

   ...Synopsis...
   The stronger westerlies appear likely to remain confined to
   latitudes near and north of the Canadian/U.S. border vicinity, with
   modest amplification possible by late Saturday night across the
   northeastern Pacific into the Canadian Rockies.  To the south of one
   significant downstream short wave trough, progressing across the
   Canadian Prairies and adjacent international border area, it appears
   that mid-level ridging will remain prominent along a major axis
   extending from the southern Rockies through much of the Ohio Valley.
    Within the tropical easterlies, to the south, developing Tropical
   Storm Hanna is currently forecast to make landfall across lower
   Texas coastal areas, to the south of Corpus Christi.

   ...Northern Great Plains into Upper Midwest/Great Lakes...
   Models indicate broad surface troughing across much of the northern
   Great Plains at the outset of the period, before a cold front
   associated with the significant short wave trough advances across
   much of the Dakotas and northwestern Minnesota by 12Z Sunday.  It
   appears that there will be little coinciding eastward development of
   the surface troughing, but the northwestern periphery of surface
   ridging, extending west-northwestward from the Atlantic, may begin
   to weaken across the Upper Midwest into the upper Great Lakes
   region.  This probably will commence as a less pronounced mid-level
   impulse preceding the primary wave accelerates east-northeast of the
   Red River Valley early in the period.  

   There may be considerable remnant convection at the outset of the
   period associated with this lead wave, and it appears that stronger
   southerly/southwesterly 850 mb flow (30-40 kt) will be maintained
   across parts of the middle Missouri Valley toward the Upper Midwest
   through the period.

   Low-level moistening and daytime heating along the southern
   periphery of the mid-level impulse/associated convection may
   contribute to moderately large mixed-layer CAPE by Saturday
   afternoon.  This probably will contribute to an environment
   conducive to vigorous convective development, with the potential for
   one or two upscale growing thunderstorm clusters through Saturday
   evening, particularly across parts of eastern Minnesota and northern
   Wisconsin into the upper peninsula of Michigan.  It is possible that
   this could be accompanied by an organized severe wind threat. 
   However, due to sizable spread still evident within the various
   model output, severe weather probabilities are being maintained at 5
   percent.

   Otherwise, within the surface troughing to the west, ahead of the
   eastward advancing cold front, widely scattered to scattered strong
   thunderstorms are expected Saturday afternoon and evening.  Modest
   westerly mid-level flow may contribute to sufficient shear to
   contribute to storm organization, but low-level wind fields appear
   likely to be rather weak.  And some model output, including the
   latest NAM, suggest that CAPE, where lift is able to overcome
   mid-level inhibition, may be rather modest (around 1000-1500 J/kg).

   ...Middle/lower Texas coast...
   Tropical Storm Hanna may pose a risk for a couple of tornadoes as it
   makes landfall.  However, this risk is still largely conditional as
   mesoscale developments which could impact this potential remain
   highly uncertain at this time.

   ..Kerr.. 07/24/2020

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z