SPC AC 180557

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CDT Thu Jul 18 2024

   Valid 191200Z - 201200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
   THE NORTHERN/CENTRAL HIGH PLAINS INTO THE NORTHERN/CENTRAL PLAINS...

   ...SUMMARY...
   Isolated strong to severe thunderstorms are possible across portions
   of the northern/central High Plains into the northern/central Plains
   on Friday.

   ...Synopsis...
   Expansive upper ridging is expected to be in place from the
   Southwest into western Canada early Friday morning, with upper
   troughing anticipated east of this ridging across the central/
   eastern CONUS and much of eastern Canada. A shortwave trough
   embedded within this eastern troughing is forecast to progress
   eastward across Ontario and adjacent portions of the St. Lawrence
   Valley and northern New England. Another shortwave trough is
   forecast to progress through the northeastern periphery of the
   western ridge, moving from eastern MT southeastward across the
   northern High Plains and reaching the central Plains by early
   Saturday.

   Surface pattern early Friday will be dominated by a strong high over
   the OH Valley, with a weak stationary front along its southern
   periphery stretching from SC into the TX Hill Country. Warm and
   moist conditions are expected along this boundary, helping to
   support afternoon thunderstorms amid modest low-level convergence
   along the front as well as in the vicinity of a convectively
   generated vorticity maximum expected to move across the Lower MS
   Valley and MS/AL. Storm severity should be mitigated by weak shear
   and largely disorganized storm mode. 

   ...Northern/Central High Plains into the northern/central Plains...
   Surface lee troughing is anticipated across the High Plains, with
   moderate low-level moisture east of this lee troughing across the
   majority of the Plains. Afternoon thunderstorm development appears
   probable along the lee trough as well as farther east into more of
   SD and NE as the previously mentioned shortwave trough moves into
   the region. Moderate northwesterly flow aloft will support a
   southeasterly storm motion, taking any development into areas with
   more favorable low-level moisture and stronger buoyancy. 

   Additionally, this moderate northwesterly flow aloft atop low-level
   southerlies will help support moderate deep-layer vertical shear.
   This shear could help organize initially high-based,
   outflow-dominant storms into one or more coherent bowing segments
   capable of damaging gusts. While this overall convective evolution
   appears probable, where it occurs is less certain. Furthermore,
   there is uncertainty regarding just how strong the gusts with this
   line (or lines) will be. Uncertainties merit delaying the inclusion
   of higher probabilities to later outlooks when these more mesoscale
   details become predictable.

   ..Mosier.. 07/18/2024

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