Oct 31, 2021 1300 UTC Day 1 Convective Outlook
Updated: Sun Oct 31 12:25:14 UTC 2021 (20211031 1300Z Day 1 shapefile | 20211031 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20211031 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Tornado Graphic
20211031 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
20211031 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Large Hail Graphic
20211031 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
   SPC AC 311225

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0725 AM CDT Sun Oct 31 2021

   Valid 311300Z - 011200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   No severe thunderstorms are expected across the continental United
   States today and tonight.

   ...Synopsis/Discussion...
   In mid/upper levels, largely zonal flow will characterize the
   southern stream from CA across the southern/central Plains to the
   Southeast, with only minor embedded shortwave perturbations.  In the
   northern stream, a synoptic-scale trough is located from western
   Hudson Bay south-southwestward across portions of MN and the
   Dakotas, and is forecast to develop a closed 500-mb cyclone centered
   over northern ON today.  By 12Z tomorrow, the low should reach
   southern James Bay, while a trailing shortwave trough digs south-
   southeastward from SK to eastern MT and the western Dakotas.

   In response to those developments, the longstanding eastern CONUS
   cyclone is devolving into an open-wave trough over the lower Great
   Lakes and northern Mid-Atlantic.  This feature will continue to
   weaken as it accelerates northeastward through New England and
   southern QC, amidst broader-scale height falls that precede the
   northern-stream cyclone.  Any remaining lightning potential with the
   associated, weakening low-level warm-advection plume appears to be
   too isolated and brief over land to warrant continuation of the
   prior day's New England thunder outlook into this period. 

   Meanwhile, as a progressive synoptic trough/cyclone over the open
   northeastern Pacific moves eastward, a smaller cyclone now over
   coastal OR will become an open-wave trough over OR today, shifting/
   extending eastward to southern ID overnight.  The remnant vorticity
   banner should detach from the cyclonic height field preceding the
   northeastern Pacific synoptic wave, and move slowly through a
   larger-scale mean ridge over ID starting near the end of the period
   and through day 2.  To its east, under strongly difluent flow aloft,
   the combination of favorable boundary-layer diurnal heating and
   marginal low/middle-level moisture will enable 100-300 J/kg MLCAPE,
   and MUCAPE around 500 J/kg, with weak inhibition from mid/late
   afternoon into mid-evening.  Isolated weak thunderstorms will be
   possible from portions of southern ID/northern UT to parts of
   southern WY and northwestern CO.

   ..Edwards.. 10/31/2021

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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z