Current SPC Activity Chart

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SPC Activity Chart
Hazard Thu (02/22) Fri (02/23) Sat (02/24) Sun (02/25) Mon (02/26) Tue (02/27) Wed (02/28) Thu (03/01)
Severe No Severe No Severe Slight No Area No Area No Area No Area No Area
Fire No Critical Elevated No Area No Area No Area No Area No Area No Area

Forecast Discussion - Convective Outlook

   SPC AC 220530

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1130 PM CST Wed Feb 21 2018

   Valid 221200Z - 231200Z


   A few strong thunderstorms are possible today through tonight,
   mainly across parts of the southern Plains.  However, the risk for
   severe storms still appears negligible.

   It appears that positively tilted, large-scale mid/upper troughing
   will be maintained across the West today, as another significant
   short wave trough digs southeast of the Pacific Northwest, toward
   the southern Great Basin.  A preceding short wave is already in the
   process of accelerating northeast of the lower Colorado Valley. 
   Models indicate that it will continue across the Four Corners region
   early today, and through the mid Missouri Valley into the Upper
   Midwest by late tonight.

   Forcing for ascent associated with the lead feature is expected to
   remain well to the west and north of a sharp surface frontal zone
   now stalled across the Cumberland Plateau through the lower
   Mississippi Valley and Texas Gulf coast region.  Models are
   suggestive that some erosion of the shallow leading (southeastern)
   edge of the cold surface-based air mass is possible from portions of
   southeast Texas into the lower Ohio Valley, beneath anticyclonic
   mid-level flow on the northwestern periphery of persistent strong
   subtropical ridging centered off the south Atlantic coast.  However,
   generally weak mid-level lapse rates and forcing for ascent are
   expected to limit potential for appreciable boundary layer
   destabilization and vigorous thunderstorm development.

   Highest thunderstorm probabilities seem likely to remain focused
   above the residual cold surface-based air to the north of the
   frontal zone, from portions of the southern Plains northeastward
   toward the Ozark Plateau.  One wave of thunderstorm activity may
   form in association with forcing accompanying the aforementioned
   impulse emerging from the Southwest, spreading across and northeast
   of the Red River Valley this afternoon.  Another wave of
   thunderstorm activity appears possible late tonight, near and
   southeast of the Texas Hill Country into northeast Texas.  This
   latter convection is expected to be supported by low-level warm
   advection downstream of the primary short wave digging into the
   Great Basin, and perhaps forcing associated with an impulse within
   the subtropical stream.  This may occur in the presence of at least
   somewhat more substantive steepening of mid-level lapse rates than
   with the earlier convection.  However, it remains unclear whether
   mid-level destabilization will be sufficient to support an
   appreciable severe hail risk.  Given the late night (end of period)
   timing, less than 5 percent severe probabilities will be maintained
   for now.

   ..Kerr/Leitman.. 02/22/2018