SPC AC 031255

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Thu Aug 03 2017

   Valid 031300Z - 041200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MIDWEST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   MIDWEST AND LOWER MO RIVER VALLEY TO GREAT LAKES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   MID-ATLANTIC/NORTHEAST STATES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   SOUTH-CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Severe thunderstorms are possible this afternoon and evening across
   far eastern Iowa, southeast Minnesota into central and southern
   Wisconsin and northern Illinois, including the potential for a
   tornado or two. Other strong to severe storms are possible across
   other parts of the Midwest, Northeast states, and over the
   south-central High Plains.

   ...Portions of IA/MN/IL/WI...
   A shortwave trough over the eastern Dakotas and western MN early
   this morning will continue to amplify and eventually close off as it
   digs east-southeastward toward the upper MS River Valley through
   tonight, with downstream height falls overspreading much of the
   Midwest and Great Lake region. In response, a surface low will
   steadily deepen as it shifts east-northeastward from IA/southern MN
   into WI ahead of an east/southeastward-moving cold front.

   Scattered showers/thunderstorms and semi-prevalent cloud cover early
   today casts uncertainty regarding the overall degree of
   destabilization within the warm sector ahead of the cold front and
   near/south of a northward-shifting warm front. Even so, it appears
   that a semi-focused supercell risk, including the potential for a
   couple of tornadoes, could materialize especially across
   south-central WI later this afternoon into early evening ahead of
   the deepening surface low and the preceding northward-shifting warm
   front. Within this corridor, low-level shear/SRH will be maximized
   with moderately long/curved low-level hodographs with 0-1 km SRH as
   high as 150-200 m2/s2. Bouts of severe hail and damaging winds will
   otherwise be possible.

   Otherwise, isolated thunderstorms are expected to develop along the
   trailing cold front across eastern IA into northeast MO. This
   activity should propagate into IL ahead of strengthening mid-level
   jet. Large hail and damaging winds are possible with this convection
   as it spreads into a pre-frontal instability axis with fairly steep
   low-level lapse rates.

   ...South-central High Plains...
   Strong boundary-layer heating across the southern High Plains should
   remove convective inhibition along a southward-surging cold front
   near the NM/CO border with low-level upslope trajectories also
   increasing near the front range. Isolated convection is expected to
   develop over the higher terrain then drift southeast within a
   northwesterly flow regime. Gusty winds and hail are the primary
   threats with this activity as it spreads toward the TX Panhandle.

   ...Mid-Atlantic/Northeast States...
   Upper heights will weakly rise today with only weak tropospheric
   winds and somewhat warmer mid-level temperatures (-9 to -10C at 500
   mb) as compared to yesterday. That said, as thunderstorms increase
   in coverage this afternoon, relatively steep low-level lapse rates
   and areas of moderate buoyancy could allow for some stronger
   pulse-type storms capable of localized tree damage.

   ..Guyer/Smith.. 08/03/2017

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