SPC AC 301720

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1220 PM CDT Sat Sep 30 2017

   Valid 011200Z - 021200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL GREAT
   PLAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SOUTHEAST SD TO
   THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Isolated to scattered severe storms are expected across parts of the
   central Great Plains Sunday afternoon and evening.

   ...Synopsis...
   A longwave trough will remain anchored over the West with an
   embedded shortwave impulse amplifying across the northern High
   Plains. This will coincide with strengthening mid-level
   west-southwesterlies across the CO Rockies and into parts of SD to
   KS, Sunday evening/night. Primary surface cyclone over ND should
   gradually deepen as it shifts into southern Saskatchewan. A cold
   front will arc from this cyclone to a low in the lee of the CO
   Rockies.

   ...Central Great Plains...
   Have expanded Marginal and Slight risks with an increasingly
   probable expectation for at least a few severe storms, including
   potential for a long-track supercell.

   A relatively confined plume of modest boundary layer moisture
   characterized by middle 50s to lower 60s should advect north from
   southeast SD to central and southern High Plains. From the central
   High Plains to the east-northeast, an elevated mixed layer will
   overspread this moisture return, yielding sufficient inhibition
   until afternoon amid steep mid-level lapse rates. Weak mid-level
   height falls/DCVA should aid in storm initiation first off the Front
   Range by mid afternoon. The aforementioned strengthening flow aloft
   along with a veering wind profile with height will be favorable for
   supercell formation. Most CAMs suggest a long-track supercell may
   evolve east across northeast CO and southwest NE. Large hail will
   likely be the primary hazard, but the tornado and wind threat may
   increase towards the CO/NE/KS border area near 00Z where
   boundary-layer moisture should be relatively richer.

   Additional storms may form farther northeast along the strengthening
   frontal zone during the evening, as well as to the south near the
   dryline. Dryline storm initiation is more uncertain with southern
   extent given warmer mid-level temperatures/minimal height change.
   Cooler boundary-layer temperatures to the north/east from
   central/eastern NE to southeast SD should spatially confine and tend
   to limit the hazard to mainly severe hail.

   ..Grams.. 09/30/2017

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   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z