SPC AC 141229

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0729 AM CDT Tue Jul 14 2020

   Valid 141300Z - 151200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   INTO EARLY TONIGHT FROM IA TO WI...AND SOUTHEAST CO TO SOUTHWEST
   KS...

   ...SUMMARY...
   Severe storms with damaging winds and large hail are expected this
   afternoon into early tonight from Iowa into Wisconsin, and from
   southeast Colorado into southwest Kansas.

   ...Eastern KS to WI through early tonight...
   A midlevel trough will continue to move slowly eastward from the
   northern Plains toward the upper MS Valley, as embedded speed maxima
   progress east-northeastward around the southern periphery of the
   trough.  An associated surface cold front will move southeastward
   across MN/WI/IA, and southward into the southern High Plains by
   tonight.  This front will provide the primary focus for
   strong/severe thunderstorm development through the period.

   Overnight convection is weakening over eastern KS as the low-level
   jet weakens/veers to southwesterly and warm advection likewise
   diminishes this morning.  A remnant MCV emanating from this MCS will
   move eastward from KS to MO today, though it is not clear that
   additional storms will form with the MCV as it moves east of the
   more unstable surface warm sector.  In the wake of the weakening
   MCS, a corridor of mid-upper 70s boundary-layer dewpoints will
   spread northward from OK into KS and IA by mid-late afternoon,
   beneath the eastern extent of an elevated mixed layer plume.  These
   factors, in combination with surface heating as cloud debris clears,
   will result in strong buoyancy along the front from KS to IA this
   afternoon, with somewhat lesser moisture and weaker lapse
   rates/buoyancy farther northeast into WI.

   The cap will be stronger with southwestward extent toward KS, where
   thunderstorm development is more in question given only weak/shallow
   ascent along the front.  Farther northeast across IA/WI, weaker
   convective inhibition and stronger vertical shear with proximity to
   the midlevel trough will support earlier and more widespread
   thunderstorm development.  A few supercells may occur early in the
   storm evolution, but multicell clusters will be the primary storm
   mode, with an attendant threat for damaging winds and isolated large
   hail.  The southwest extent of diurnal storm development toward KS
   is the primary uncertainty, where a conditional wind/hail threat
   exists in the strongly buoyant environment.  There is also some
   potential for elevated storm development overnight on the cool side
   of the boundary, and/or storms could spread northeastward along the
   boundary from southwest KS overnight.

   ...Southeast CO/southwest KS area this afternoon into tonight...
   An upslope flow regime will become established today along and
   immediately north of a cold front moving southward across western
   KS/eastern CO from NE.  Steep lapse rates and strong surface
   heating/mixing along the front, as well as the richer low-level
   moisture immediately north of the boundary, will result in a narrow
   corridor of 2500-3500 J/kg MLCAPE and weaker convective inhibition
   by mid-late afternoon.  The more probable areas for initiation this
   afternoon will be along/south of the Palmer Divide to the Raton Mesa
   vicinity in southeast CO.  This area will be south of the stronger
   midlevel westerlies, but northeasterly low-level winds will
   contribute to sufficient deep-layer shear for a few
   organized/supercell storms in the first few hours after initiation. 
   Thereafter, upscale growth into an MCS appears probable as storms
   spread eastward toward southwest KS.  Large hail will be the main
   threat initially, with a transition to damaging winds this evening
   as storms cluster.  

   ...Southeast New England today...
   A closed midlevel low will move slowly eastward over southern New
   England today.  Thunderstorm clusters are ongoing in a loose arc
   around the eastern and northern periphery of the low, and additional
   diurnal storm development is expected as cloud breaks allow surface
   heating/destabilization.  Midlevel lapse rates and vertical shear
   will be relatively weak near the midlevel low, but the strongest
   storms could produce isolated strong outflow winds capable of
   producing (mostly minor) damage.

   ..Thompson/Dial.. 07/14/2020

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