SPC AC 141956

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0256 PM CDT Tue Jul 14 2020

   Valid 142000Z - 151200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE UPPER MIDWEST/MID MO VALLEY AND SOUTHERN/CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Severe thunderstorms with damaging winds and large hail are expected
   this afternoon into tonight across the Upper Midwest from Iowa into
   Wisconsin, and across the south-central High Plains from southeast
   Colorado into southwest Kansas and the Texas/Oklahoma Panhandles.

   ...20Z Update...
   The Marginal Risk area has been adjusted across the Northeast based
   on current observations and short-term guidance. Mainly an isolated
   strong/gusty wind threat should continue through the remainder of
   the afternoon before diminishing this evening with the loss of
   daytime heating.

   A small westward expansion to the Marginal Risk has been made across
   parts of the lower MS Valley to account for recent convective
   development along a weak surface boundary. Isolated damaging winds
   should be the main threat through the early evening. See Mesoscale
   Discussion 1224 for more information on the near-term severe threat
   across this region.

   Severe potential will continue to increase this afternoon across
   parts of the central/southern High Plains in a post-frontal,
   low-level upslope flow regime. Both large hail and severe wind gusts
   may occur as storms intensify as they move slowly eastward into an
   increasingly unstable airmass this afternoon and evening. For more
   information on the near-term severe threat across this region, see
   Mesoscale Discussion 1223.

   No changes have been made to the Slight Risk across parts of the
   Upper Midwest into the mid MO Valley. Storms are still expected to
   form and subsequently strengthen later this afternoon into the
   evening along/ahead of an eastward-moving cold front. Large hail,
   damaging winds, and perhaps a tornado or two remain possible.

   ..Gleason.. 07/14/2020

   .PREV DISCUSSION... /ISSUED 1147 AM CDT Tue Jul 14 2020/

   ...Eastern Kansas to Wisconsin/southeast Minnesota...
   A general trend of mid-level cooling and strengthening of
   west-southwesterly winds aloft will occur in conjunction with an
   eastward-moving trough over the Upper Midwest. Ahead of an
   eastward-moving cold front, considerable cloud cover/scattered
   convection persist at late morning from southern Minnesota into
   Wisconsin. The degree of destabilization is questionable with
   northeastward extent across Wisconsin, with more robust
   near/pre-frontal destabilization likely across Iowa southwestward
   into southeast Nebraska/northwest Missouri. 

   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. A tornado or two
   could also occur. The southwest extent of diurnal storm development
   toward Kansas still remains uncertain, but 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 Kansas overnight toward parts of this
   region.

   ...Southeast CO/southwest KS and OK/TX Panhandles...
   An upslope flow regime will become increasingly established today
   along and immediately north of a cold front moving southward across
   western Kansas/eastern Colorado. 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 Colorado. This area will be
   south of the stronger mid-level westerlies, but northeasterly
   low-level winds will contribute to sufficient deep-layer shear for a
   few organized storms/supercells within the first few hours after
   initiation. Thereafter, upscale growth into an MCS appears likely as
   storms spread eastward toward southwest Kansas and the
   Oklahoma/northern Texas Panhandles. Large hail will be the main
   threat initially, with a transition to damaging winds (some
   significant-caliber wind gusts possible) expected this evening as
   storms cluster.

   ...Southern New England...
   A closed mid-level low will continue to drift east-southeastward
   over the region today, with modest destabilization evident on its
   southern periphery. Isolated severe thunderstorms capable of
   localized wind damage is the primary hazard, particularly across
   parts of Massachusetts/Connecticut/Rhode Isolated where instability
   is somewhat stronger. Reference Mesoscale Discussion 1222 for
   additional short-term details.

   ...Mississippi...
   A weak/southeastward-moving mid-level wave may influence isolated
   strong/locally severe thunderstorm development within a hot/very
   moist airmass. A few wet microbursts could produce localized damage
   this afternoon.

   ...Northern High Plains...
   A belt of moderately strong cyclonic flow aloft will influence the
   region today, with isolated thunderstorm development expected across
   the region later this afternoon. Instability will be weak,
   particularly by summer standards, but semi-long/straight hodographs
   could support a supercell and a marginally severe storm or two
   presuming adequate destabilization.

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