SPC AC 132000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Wed Jun 13 2018

   Valid 132000Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NEW YORK
   AND NORTHERN PENNSYLVANIA...AND PART OF THE CENTRAL GREAT PLAINS...

   ...SUMMARY...
   Scattered severe storms are possible, mainly during the late
   afternoon and evening across New York into northern Pennsylvania and
   parts of the central Great Plains. Large hail, damaging winds, and a
   tornado or two may occur.

   ...New York and Pennsylvania...
   Given guidance shows stronger forcing for ascent will spread east
   with a progressive shortwave trough through mainly New York, and
   perhaps affect northern Pennsylvania too, the higher severe
   probabilities that warrant the Slight risk area have been trimmed
   out of southern Pennsylvania.  Otherwise, the previous forecast
   discussion remains on track for this region.

   ...Lower Michigan...
   A midlevel shortwave trough and associated cold front have advanced
   east of Lower Michigan, shifting greater instability east of this
   region and diminishing any severe-weather threat.  Severe
   probabilities and general thunderstorm potential have been removed
   from Lower Michigan.

   ...Central Great Plains...
   Trends in ongoing convection showing an overall decreasing trend in
   storm coverage has allowed for a reduction in areal extent of severe
   probabilities across much of central portions of KS, NE, and SD.

   ..Peters.. 06/13/2018

   .PREV DISCUSSION... /ISSUED 1135 AM CDT Wed Jun 13 2018/

   ...Northern Appalachians...
   A pronounced shortwave trough over the central Great Lakes will
   progress east towards ME through Thursday morning. An associated
   surface cyclone will track east across southern portions of Ontario
   and Quebec, with a cold front trailing southwest across the Lower
   Great Lakes, reaching the northern Appalachians this evening.
   Ongoing convection near the front across eastern Lower MI should
   intensify as it spreads into far southern Ontario before crossing
   over the international border and developing south across parts of
   NY/PA late this afternoon into the evening. 

   Abundant stratus is prevalent from the Upper OH Valley eastward and
   this will temper diabatic heating over most of the region. However,
   the northeast periphery of mid-level lapse rates near 7 C/km (as
   sampled by 12Z APX/DTX soundings should overspread the warm sector,
   contributing to a modestly buoyant air mass with MLCAPE of 750-1500
   J/kg. Deep-layer shear will become quite strong with increasingly
   elongated hodographs with approach of the shortwave trough, as a
   swath of 50+ kt 500-mb westerlies progresses east. Given substantial
   cross-boundary flow/shear vectors, a few supercells are anticipated
   within a broken band of storms along the front. Damaging winds,
   severe hail, and a tornado are possible, although the widespread
   clouds and late arrival of the cold front relative to peak heating
   should modulate a greater severe risk. 

   ...Central Great Plains...
   A couple storm clusters are ongoing in associated with warm
   advection across northwest KS and near the SD/NE border. The
   southern convection may persist through the afternoon and develop
   eastward north of the stalled front in southern KS, where strong
   buoyancy along and south of the boundary will support a threat for
   isolated strong to severe gusts and marginally severe hail. The
   northern convection should persist through much of the afternoon
   amid continued robust warm advection, yielding a risk for a confined
   area of severe hail. Refer to MCD 721 for additional short-term
   information. 

   Farther west, a few storms should form late afternoon into early
   evening near the dryline/front/outflow intersection in northeast CO
   and vicinity. Here, a veering wind profile with height along with
   very steep mid-level lapse rates near 9 C/km may support a
   conditional risk for a slow-moving supercell or two anchored near
   the boundary capable of large hail, severe wind gusts, and a
   tornado.

   ...Mid-MO Valley/IA...
   Warm advection will increase late tonight across the Mid-MO Valley
   into IA. Scattered to widespread elevated storm development is
   expected early Thursday. This area will be monitored for potential
   of marginally severe hail, but uncertainty is great enough to
   preclude adding any probabilities in this outlook.

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