SPC AC 210527

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1227 AM CDT Sat Jul 21 2018

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SUNDAY AFTERNOON
   AND EVENING ACROSS PARTS OF THE SOUTH ATLANTIC COAST REGION AND
   PARTS OF THE NORTHERN PLAINS...

   ...SUMMARY...
   A few severe thunderstorms are possible Sunday afternoon and evening
   across parts of the south Atlantic Coast region and across parts of
   the northern Plains.

   ...Synopsis...
   To the north of a prominent subtropical high, centered near the
   southern Rockies, troughing within the mid-latitude westerlies may
   broaden near/north of the western into central Canadian/U.S. border.
   Within the troughing, it appears that a substantive short wave
   impulse will remain progressive.  Associated stronger mid-level
   height falls are forecast to spread from Saskatchewan into Manitoba
   during the day, before continuing into northwest Ontario and perhaps
   developing south of the international border through the eastern
   Dakotas and Minnesota by 12Z Monday.  Models indicate that the
   primary accompanying surface cyclone will remain well to the north
   of the international border, but a secondary low may develop across
   the mid Missouri Valley, just ahead of a cold front advancing into
   the northern U.S. Plains.

   Downstream, ridging, building to the northwest of the western
   Atlantic subtropical high, is forecast to nose into much of New
   England.  Between the subtropical highs, models continue to suggest
   that large-scale troughing east of the Mississippi Valley may
   undergo considerable deformation, elongating southward through much
   of the remainder of the south Atlantic Coast region.  Seasonably
   high moisture content (characterized by precipitable water of 2+
   inches) likely will linger in plumes on the southern and eastern
   periphery of the troughing.  This may include an inland return
   across coastal portions of the Mid Atlantic, but lapse rates
   supportive of moderate to large CAPE likely will remain focused on
   the southern periphery of the troughing, across parts of the eastern
   Gulf into south Atlantic coast.

   ...South Atlantic Coast region...
   Convective developments today through tonight could still have a
   considerable impact on convective potential for Sunday.  However,
   the latest model output suggests that moderate to large CAPE will
   develop with insolation by midday across much of northern Florida
   and southeastern Alabama/Georgia into the coastal plain and piedmont
   of South Carolina.  This is where forcing for ascent associated with
   a short wave impulse digging through the base of the upper trough
   may contribute to thunderstorm development.  Aided by
   momentum/vertical shear associated with 30+ kt flow in 850-500 mb
   layer, a few supercell structures or organizing clusters of storms
   are possible, posing a risk for hail and potentially damaging wind
   gusts.

   ...Northern Plains...
   Although stronger mid-level forcing for ascent likely will remain
   north of the international border, seasonably strong westerly
   mid/upper flow near the base of the upper troughing may contribute
   to sufficient shear for organized convective development, including
   supercells, ahead of the front across the Dakotas.  This may be
   supported by lift associated with weak low-level warm advection and
   high-level difluent/divergent flow, with model output now suggesting
   sufficient boundary layer moistening to support moderately large
   CAPE within at least a narrow pre-frontal corridor.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:     15%     - Slight
   Hail:     15%     - Slight

   ..Kerr.. 07/21/2018

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

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