SPC AC 301730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Tue Jun 30 2020

   Valid 011200Z - 021200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS WEDNESDAY INTO
   WEDNESDAY EVENING ACROSS PARTS OF THE LOWER MISSOURI VALLEY INTO MID
   SOUTH AND SOUTHEAST...AS WELL AS ACROSS PARTS OF THE NORTHERN
   ROCKIES AND A SMALL PORTION OF THE UPPER MIDWEST...

   ...SUMMARY...
   Clusters of thunderstorms accompanied by at least some risk for
   severe wind and hail are possible Wednesday across the lower
   Missouri Valley into parts of the Mid South and Southeast.

   ...Synopsis...
   A mid-level high, initially centered near/northeast of the Great
   Lakes, is forecast to weaken during this period, largely in response
   to a short wave trough digging southeast of Hudson Bay, but also as
   the tail end of a negatively tilted short wave trough pivots across
   and north of the central Canadian/U.S. border area.

   As the latter perturbation progresses across the Canadian Prairies,
   another significant short wave trough is forecast to continue
   digging into the northern U.S. intermountain region early Wednesday,
   before turning eastward and northeastward across the northern U.S.
   Rockies late Wednesday through Wednesday night.  Another trailing
   impulse may dig near the British Columbia coast, but models indicate
   that the center of the broader-scale cyclonic flow will shift
   northward away from the international border, across and east of
   southern portions of the Canadian Rockies.  The primary associated
   surface cyclone is expected to migrate northwestward across Alberta,
   while a trailing cold front, initially extending across the northern
   plains Red River Valley into the central plains, becomes
   increasingly diffuse while advancing eastward into parts of the
   Upper Midwest and adjacent Great Lakes region.

   This is expected to occur as prominent mid-level ridging builds
   across much of the lower Rio Grande Valley and southern plains,
   through much of the lower/mid Missouri Valley, Upper Midwest and
   upper Great Lakes region.

   To the east, positively tilted larger-scale troughing appears likely
   to linger across most areas southeast of the lower Great Lakes and
   Ohio Valley, into the western Atlantic, with perhaps some
   southwestward amplification across the eastern Gulf coast and
   northern Florida.

   ...Lower Missouri Valley into Southeast...
   Areas of convective outflow may contribute to a somewhat better
   defined low-level baroclinic zone near the southwestern periphery of
   the large-scale eastern U.S. mid-level troughing.  Seasonably moist
   boundary-layer air along and southwest of this front, beneath
   modestly steep to steep  mid-level lapse rates may contribute to
   moderate to large mixed-layer CAPE with heating during the day
   Wednesday.  Perhaps aided by 20-30 kt northwesterly flow in the
   700-500 mb layer, the environment may become conducive to the
   gradual evolution of organizing clusters of storms capable of
   producing potentially damaging wind gusts and some hail.

   By mid to late Wednesday afternoon, this potential may become more
   conditional beneath the building mid-level ridge across the lower
   Missouri Valley.  However, CAPE likely will be maximized across this
   region (3000-4000+ J/kg), and the intersection of the front/
   convective outflow with the plains surface troughing may provide a
   focus for storm initiation across the northwestern Missouri/
   northeastern Kansas vicinity.

   ...Northern Rockies...
   Beneath relatively cool mid-level temperatures, low-level moisture
   may become sufficient to support mixed-layer CAPE on the order of
   500+ J/kg.  This may be sufficient, in the presence of 30-50 kt
   mid-level flow, to support scattered strong storms capable of
   producing small to marginally severe hail and locally strong surface
   gusts across the higher terrain.  Orographic forcing for convective
   development will be aided by lift associated with the approaching
   short wave during peak late afternoon instability.

   ...Northern Minnesota...
   Some model output (perhaps most notably the NAM) continue to suggest
   that destabilization could become sufficient to support an isolated
   strong to severe storm, aided by forcing for ascent and
   strengthening wind fields associated with the tail end of the
   mid-level troughing, which may pivot across the region during peak
   afternoon heating.

   ..Kerr.. 06/30/2020

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