SPC AC 011729

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1229 PM CDT Wed Jul 01 2020

   Valid 021200Z - 031200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THURSDAY INTO
   THURSDAY NIGHT ACROSS PARTS OF THE WESTERN DAKOTAS...CENTRAL
   PLAINS...OZARK PLATEAU...LOWER MISSISSIPPI VALLEY...NORTHERN NEW
   ENGLAND AND ADJACENT PORTIONS OF UPSTATE NEW YORK...

   ...SUMMARY...
   Clusters of strong thunderstorms may develop across parts of the
   western Dakotas, the central plains and portions of the Ozark
   Plateau into lower Mississippi Valley Thursday into Thursday night,
   posing a risk for strong wind gusts and some hail.  Thunderstorms
   posing some risk for damaging wind gusts and hail are also possible
   across parts of the St. Lawrence Valley into northern New England.

   ...Synopsis...
   A prominent mid-level ridge appears likely to remain centered over
   the south central plains during this period and encompass much of
   northern Mexico, the southern Rockies, central and southern plains,
   upper Mississippi and lower Ohio Valleys and upper Great Lakes.  By
   late Thursday night, models suggest that this ridging will build
   northwestward through the northern high plains,  as one trough axis
   shifts north of the international border through the Canadian
   Prairies.  At the same time, broad, positively-tilted mid-level
   troughing is also forecast to begin pivoting inland of the northern
   Pacific coast.

   Downstream, the mid-level ridging may also begin to build
   east-southeastward toward the central/southern Appalachians, in the
   wake of mid-level troughing slowly turning east of the Mid Atlantic
   coast.  However, it appears that mid-level troughing will linger
   along an axis across the south Atlantic Coast states through the
   northeast/north central Gulf coast vicinity.

   At the same time, it appears that several short waves will progress
   through relatively strong, broadly cyclonic mid-level flow,
   southeast of Hudson Bay through the Canadian Maritimes.  A cold
   front may advance across southern Quebec and the St. Lawrence Valley
   into northern New England, in association with one of these.

   ...Western Dakotas...
   One fairly significant, lingering short wave impulse and associated
   mid-level speed maximum are generally forecast to accelerate
   northeast of the northern U.S. Rockies into southern Saskatchewan by
   mid to late Thursday afternoon.  As this occurs, models indicate
   substantive weakening of initial 30-50 kt south-southwesterly flow
   in the 850-700 mb layer through the day.  Mid-level heights are also
   forecast to continue to generally rise.  However, weak mid-level
   troughing may linger across the western Dakotas through the peak
   late afternoon heating, where CAPE may exceed 2000 J/kg within a
   corridor of stronger heating ahead of a weak cold front.  

   It is possible that mid-level inhibition may remain weak enough to
   allow for late afternoon or early evening storm initiation.  Given
   the presence of steep lower/mid-tropospheric lapse rates, the
   environment probably will be conducive to storms capable of
   producing hail and strong wind gusts.  The extent of this potential
   probably will hinge on the strength of the vertical shear at the
   time of convective development, which remains unclear at the present
   time.

   ...Central Plains into lower Mississippi Valley...
   Although largely beneath the mid-level ridging, and in the presence
   of generally weak wind fields, models indicate a corridor of strong
   differential surface heating developing across the region through
   the day, with a hot, seasonably moist and well mixed boundary layer
   developing on the warm side of this zone.  Beneath modestly steep
   mid-level lapse rates, CAPE of 2000-4000+ J/kg appears likely by
   late afternoon.  Models suggest that mid-level inhibition will not
   be prohibitive to at least scattered areas of thunderstorm
   initiation, some of which may tend to grow upscale and be
   accompanied by a risk for severe hail and wind.

   ...Northern New England/adjacent Upstate New York...
   Modest boundary-layer destabilization appears possible ahead of a
   southward advancing cold front, with CAPE exceeding 1000 J/kg by
   Thursday afternoon.  Northwesterly deep-layer mean flow may remain 
   rather modest, with generally weak shear, but a few vigorous
   thunderstorms are possible during the late afternoon and evening,
   some of which could produce locally strong wind gusts and some hail.

   ..Kerr.. 07/01/2020

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