SPC AC 140545

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1245 AM CDT Wed Jun 14 2017

   Valid 141200Z - 151200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
   GREAT LAKES TO THE LOWER MISSOURI VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM WEST TEXAS
   TO THE UPPER OHIO VALLEY AND CAROLINAS...

   ...SUMMARY...
   Clusters of strong to severe thunderstorms are expected this
   afternoon and evening across parts of the Upper Great Lakes
   southward to the lower Missouri Valley. The primary threats with
   these storms will be damaging wind gusts and large hail. Elsewhere,
   isolated strong/severe storms will be possible across the southern
   Plains, Ohio Valley, and the Carolinas.

   ...Synopsis...
   A closed mid-level low will lift into southern Saskatchewan/Manitoba
   today, as it becomes more vertically stacked and the attendant
   surface low gradually occludes later in the period. Meanwhile, along
   the southern periphery of broad cyclonic flow, a series of impulses,
   likely convectively augmented, will advance eastward towards the
   Mississippi Valley this afternoon. In their wake, broad/modest
   westerly mid-level flow will establish across much of the western
   US. Farther downstream, several weak perturbations will meander
   slowly across the Appalachians and Southeast US, as they persist
   within a weak-flow environment.

   ...Upper Great Lakes to the Missouri Valley...
   The severe threat today may be tempered some by residual cloud
   cover/stabilization from overnight/early morning lingering
   convection. Nonetheless, pockets of heating (especially with
   southward extent) and a layer of steep mid-level lapse rates will
   promote sufficient destabilization by afternoon, with MLCAPE values
   potentially upwards of 2000-3000 J/kg. Outflow boundaries and/or
   weak MCVs emanating from overnight convection will likely support
   convective re-development by mid-day/early afternoon across parts of
   Wisconsin and Illinois. While deep-layer shear will not be
   particularly impressive, dry mid-level air atop a warm/moist
   boundary layer will favor strong downdraft momentum. In turn,
   convection may grow upscale into small clusters/bowing segments as
   they push east towards Indiana and Michigan, with a primary threat
   of damaging wind. Aided by weak impulses aloft, clusters of
   convection may also organize along remnant outflow across parts of
   the lower Missouri Valley. Initial development may be capable of
   severe hail, with the overall threat transitioning to strong,
   damaging winds through the late afternoon and evening.

   Farther north, instability will be less, but mid-level flow and
   effective shear will be considerably stronger. In turn, more
   vigorous convection that can develop near/ahead of the cold front
   during the afternoon will be capable of occasional mid-level
   rotation, increasing the threat of large hail. Moreover, some
   directional and speed shear in the lowest 1-3 km may support a
   tornado or two. However, complex storm interactions/evolution from
   meridional upper-level flow (in addition to concerns regarding
   boundary-layer destabilization) cast doubt upon a higher tornadic
   potential.

   ...Oklahoma and Texas...
   Large-scale ascent will not be particularly strong through the
   period, but ample heating amidst steep mid-level lapse rates will
   encourage MLCAPE values upwards of 3000 J/kg. Convective inhibition
   will likely keep storms sparse, especially across parts of Oklahoma,
   but adequate westerly mid/upper flow and favorable veering of winds
   with height may sustain a few stronger updrafts. In turn, a few
   instances of large hail and damaging winds appear possible during
   the evening and early overnight hours.

   ...Ohio Valley to the Carolinas...
   Encouraged by weak shortwave troughs meandering across the region,
   diurnal convection will blossom through the early/mid afternoon.
   Mid-level flow will be quite weak, such that storm propagation will
   be driven by cold pools (and enhanced by mergers). A moist,
   well-mixed boundary layer will enable strong, locally damaging gusts
   before storms weaken later in the day.

   ..Picca/Gleason.. 06/14/2017

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