SPC Day 1 Outlook

   SPC AC 261955

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0255 PM CDT Tue Oct 26 2021

   Valid 262000Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON INTO TONIGHT FROM PARTS OF NORTH TEXAS ACROSS
   WESTERN/CENTRAL OKLAHOMA AND SOUTHWESTERN KANSAS...

   ...SUMMARY...
   Scattered severe thunderstorms capable of producing large hail, wind
   damage, and isolated tornadoes are expected across portions of
   Kansas, Oklahoma, and north/central Texas late this afternoon
   through the evening, and continuing into the overnight hours.

   ...20Z Update...
   No major changes have been made to the ongoing forecast. Pronounced
   ascent associated with an approaching upper trough is evident with
   clouds and low-topped convection that have developed over southern
   CO and NM this afternoon. Clearing of the stratus deck that was
   prevalent this morning has occurred across much of western north TX,
   western OK, and south-central KS ahead of a surface dryline.
   Low-level moisture characterized by generally mid 60s surface
   dewpoints continues to stream northward across the southern Plains
   and into KS. A very strong cap centered around 850 mb and shown in
   12Z observed soundings from AMA, DDC, and LMN should continue to
   inhibit convective development through most of the rest of the
   afternoon. By early evening (23-01Z/6-8 PM CDT), the ascent and
   cooler mid-level temperatures associated with the upper trough are
   expected to aid storm initiation along the dryline. Any supercells
   that form in this environment will initially pose a threat for very
   large hail and isolated tornadoes given the favorable low-level
   shear and very steep mid-level lapse rates that will be present.

   Some recent high-resolution guidance suggests that two areas may be
   favored for initial storm development: northwestern OK into
   south-central KS, and parts of western north TX. Regardless, these
   storms will likely grow upscale into one or more bowing lines this
   evening and tonight in tandem with a strengthening southerly
   low-level jet, while continuing to pose a threat for severe/damaging
   winds and a couple of tornadoes as they spread eastward across
   south-central KS, OK, and north/central TX through early Wednesday
   morning.

   ..Gleason.. 10/26/2021

   .PREV DISCUSSION... /ISSUED 1124 AM CDT Tue Oct 26 2021/

   ...Central/southern Plains late this afternoon into tonight...
   A midlevel shortwave trough near the AZ/NM border will progress
   eastward to the TX Panhandle by late evening, as an associated lee
   cyclone deepens across northeast CO, and a trailing lee
   trough/dryline sharpens across the TX Panhandle into southwest KS. 
   Boundary-layer dewpoints in the mid-upper 60s will spread northward
   today to the east of the developing dryline.  The returning moist
   layer is a bit shallow based on 12z soundings across TX, but is
   sufficient for stratus formation across central/western OK.  The
   stratus could persist during the day from western OK into KS as the
   moisture return replaces a relatively cool air mass, and the clouds
   may tend to restrict the stronger surface heating to a narrow zone
   along the dryline.  The net result will be a narrow corridor of
   moderate buoyancy immediately east of the dryline, with cooler
   temperatures and a stronger cap to the east and northeast.

   The primary band of ascent with the shortwave trough extrapolates to
   the expected dryline location by 00-03z, by which time storm
   initiation is probable.  The questions about moisture depth and
   potentially narrow width of the unstable/relatively uncapped warm
   sector cast some doubt on storm coverage/intensity this evening
   along the dryline, and uncertainty is larger than usual for the
   initiation of dryline storms.  Still, deep-layer vertical shear and
   low-level hodograph curvature will be favorable for a window of
   opportunity for surface-based supercells capable of producing a
   couple of tornadoes, large hail, and damaging winds.  Any dryline
   storms may tend to evolve into clusters/line segments after dark
   while spreading northeastward across KS and northwest OK.

   Later tonight, storm coverage is expected to increase in a band as
   ascent preceding a cold front aloft comes into phase with richer
   moisture profiles across northwest/central TX into central OK,
   likely a little east of the surface Pacific cold front.  Occasional
   damaging gusts and isolated large hail will be the main threats,
   though a tornado or two may also occur with embedded circulations.

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