SPC AC 210557

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CDT Tue May 21 2019

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
   THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY...

   ...SUMMARY...
   Thunderstorms capable of mainly large hail are possible Wednesday
   night into early Thursday morning from the central Plains into the
   middle Mississippi Valley and possibly the southern High Plains. A
   few strong storms with gusty winds and hail will also be possible
   over a portion of the Ohio Valley.

   ...Synopsis...

   In wake of a significant shortwave trough lifting northward through
   the northern Plains and upper MS Valley, an upper ridge over the
   southeast U.S. will build northwestward into the Plains Wednesday.
   Farther upstream an upper trough will amplify across southern CA
   into the Great Basin region. Surface low attending the northern
   stream shortwave trough will occlude over the northern Plains and
   further weaken as it moves into the upper MS Valley. Trailing front
   will extend south into eastern NE and KS then southwestward into the
   southern High Plains. A warm front will extend southeast from the
   low into the OH Valley and reach the southern Great Lakes Wednesday
   night. Dryline will retreat through western TX during the afternoon
   and evening. 

   ...Kansas through northern Missouri...

   Richer low-level moisture with low-mid 60s F dewpoints will return
   through the pre-frontal warm sector, contributing to moderate
   instability (2000-2500 J/kg MUCAPE) in frontal zone by early
   evening. With building upper ridge and presence of a cap, surface
   based storm initiation still appears unlikely. The most probable
   scenario is for storms to develop during the evening within zone of
   increasing isentropic ascent north of the front associated with a
   strengthening low-level jet. These storms will likely be elevated,
   but effective bulk shear will support potential for updraft
   rotation, and the thermodynamic environment with up to 2500 J/kg
   MUCAPE and 7 C/km mid-level lapse rates should promote some risk for
   large hail.  

   ...Southern High Plains...

   Mid-upper 60s F dewpoints will advect rapidly northwestward through
   the southern Plains warm sector beneath modest mid-level lapse
   rates, contributing to moderate to strong instability (2000-3000
   J/kg MLCAPE) during the afternoon. However, significant height rises
   associated with a building upper ridge along with limited forcing
   for ascent should limit thunderstorm development over this region
   most of the period. The dryline will retreat westward with limited
   convergence. While the parameter space will favor severe storms with
   strong instability and 45-50 kt effective bulk shear, confidence is
   low that storms will initiate during the afternoon. Overnight a
   speed max is forecast to rotate through the base of the upper trough
   and approach the southern High Plains late. Forcing for ascent with
   this feature and the strengthening low-level jet might become
   sufficient for thunderstorm initiation very late from eastern NM
   into west TX. However, greater confidence exists that initiation
   will wait until after 12Z. Given the conditional nature of the
   threat in this region will maintain low severe probabilities this
   update.  

   ...Ohio Valley...

   Warm front will retreat northward during the day and likely extend
   from the southern Great lakes into a portion of OH by mid-late
   afternoon. Low-level moisture with 60s dewpoints will return through
   the warm sector resulting in moderate instability, and effective
   shear from 40-45 kt will remain sufficient for a few organized
   storms. However, subsidence associated with building upper ridge
   will result in poor mid-level lapse rates. A few storms may develop
   in vicinity of the warm front during the afternoon and pose some
   risk for gusty winds and hail, but overall threat should remain
   marginal.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:      5%     - Marginal
   Hail:     15%     - Slight

   ..Dial.. 05/21/2019

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