SPC AC 171249

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0749 AM CDT Sun May 17 2020

   Valid 171300Z - 181200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS EASTERN IL AND
   WESTERN IN...

   ...SUMMARY...
   A few brief tornadoes are possible between about 3 to 9 PM CDT in
   parts of the Midwest, centered on eastern Illinois and western
   Indiana. Isolated severe hail and/or wind are also possible this
   afternoon into early evening across parts of the Northwest, southern
   Rockies, and Mid to Deep South.

   ...Midwest to MS...
   A pair of shortwave troughs over the central states will slowly move
   east-southeast across the MS Valley through tonight. Occluded
   surface cyclone over north-central IA will hand-off to a developing
   cyclone in southeast IA that should track into the Chicagoland area
   by evening. A warm front will extend east of this low to Lake Erie
   with a cold front south to the tertiary cyclone in the Mid-South.

   Ongoing stratiform rain is pervasive in the warm conveyor and will
   temper destabilization with northern and western extent. Consensus
   of guidance does suggest that the western periphery of greater
   boundary-layer heating east of the extensive cloud/remnant precip
   shield should overlap with a plume of mid to upper 60s surface dew
   points from MS to southeast IL. This should yield a corridor of
   modest buoyancy overlapping semi-enlarged low-level hodographs
   centered on eastern IL/western IN. As convection becomes
   increasingly widespread by mid to late afternoon with strengthening
   convergence along the front, potential will exist for transient
   low-level mesocyclones capable of producing brief tornadoes. 

   Farther south into western TN and MS, low-level hodographs will not
   be as enlarged but a warmer and more moist boundary-layer could
   foster locally damaging winds around peak heating amid 25-35 kt
   850-mb southerlies.

   ...Northwest...
   Fast 500-mb southwesterlies will remain anchored from northern CA to
   the northern Rockies downstream of a longwave trough over the
   northeast Pacific. Favorable mid to upper-level speed shear will
   foster an elongated hodograph supportive of mid-level updraft
   rotation in scattered convection from eastern OR/WA across the ID
   Panhandle into northwest MT. Despite weak buoyancy, a risk for
   isolated severe hail/wind should exist this afternoon into early
   evening.

   ...South-central CO to northeast NM...
   Mid-level height rises will occur today and this should limit
   overall convective coverage compared to recent days. Still, a signal
   exists for isolated thunderstorms forming off the Sangre de Cristos
   and Raton Mesa vicinity at peak heating. Steep lapse rates and
   adequate deep-layer shear should exist for a brief supercell or two
   capable of marginally severe hail and gusty, non-severe winds.

   ..Grams/Goss.. 05/17/2020

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