Oct 20, 2018 1300 UTC Day 1 Convective Outlook
Updated: Sat Oct 20 12:37:27 UTC 2018 (20181020 1300Z Day 1 shapefile | 20181020 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20181020 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
20181020 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
20181020 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
20181020 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 201237

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0737 AM CDT Sat Oct 20 2018

   Valid 201300Z - 211200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   A few thunderstorms will be possible across the lower Great Lakes,
   the Gulf coast, and the Southwest.

   ...Synopsis...
   A pronounced midlevel shortwave trough will dig southeastward today
   over the Great Lakes and upper OH Valley, and reach the Mid Atlantic
   coast by Sunday morning.  An associated cold frontal surge is
   expected to reach the Gulf and Atlantic coasts overnight.  Steep
   low-midlevel lapse rates with cold midlevel temperatures will drive
   at least weak surface-based buoyancy across the lower Great Lakes
   and vicinity.  Scattered clusters/bands of low-topped thunderstorms
   will be possible beginning by midday across southern Lower MI, and
   then spreading east-southeastward across northern OH to western
   PA/NY through early tonight.  Small hail and gusty winds may occur
   with the strongest storms, though limited low-level
   moisture/buoyancy (boundary-layer dewpoints in the upper 30s) and
   rather modest flow below 700 mb (generally 30 kt or less) will tend
   to limit any threat for severe storms.  An isolated waterspout may
   also occur over Lake Erie this afternoon given the steep low-level
   lapse rates and vertical vorticity along the reinforcing cold front.
    
   Otherwise, a few thunderstorms will remain possible from the
   northern Gulf coast to southern GA/SC, where low-level moistening
   should be sufficient for deep convection (mainly this
   afternoon/evening along the cold front).  Gradual low-midlevel
   moistening is also expected from western AZ into extreme southern NV
   and extreme southeastern CA in association with a slow-moving
   midlevel low.  Isolated surface-based storms will be possible with
   afternoon surface heating, but much of the convection that persists
   into tonight should be rooted closer to 700 mb.  Midlevel lapse
   rates will be steep (near 8 C/km) and there will be some deep-layer
   vertical shear, but organized severe storms are unlikely.

   ..Thompson/Peters.. 10/20/2018

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