Current SPC Activity Chart

Current Severe US Wx Maps

SPC Activity Chart
Hazard Sat (09/26) Sun (09/27) Mon (09/28) Tue (09/29) Wed (09/30) Thu (10/01) Fri (10/02) Sat (10/03)
Severe Slight Marginal No Severe No Area No Area No Area No Area No Area
Fire Critical Critical No Area No Area No Area No Area No Area No Area

Forecast Discussion - Convective Outlook

   SPC AC 261627

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1127 AM CDT Sat Sep 26 2020

   Valid 261630Z - 271200Z

   UPPER MI...

   Scattered large hail from quarter to tennis ball size is the most
   likely hazard, with a conditional risk for a couple tornadoes and
   damaging winds between 5 PM and 1 AM CDT across northern Wisconsin
   into Upper Michigan.

   ...Northern WI to Upper MI...
   A shortwave trough along the MT/ND/Saskatchewan border will amplify
   towards the Lake Superior/northwest Ontario region through early
   morning. 500-mb southwesterlies will intensify late in the period,
   supporting deepening of a surface cyclone over east-central SD as it
   tracks from southeast MN into Lake Superior. The potential for
   severe thunderstorms will be focused this evening into tonight along
   the baroclinic zone to the east of the cyclone.

   Low-level moisture will slowly increase today from eastern KS to WI
   with mid 60s boundary-layer dewpoints expected along and south of
   the warm front by evening. This moistening will occur beneath the
   northern extent of a steep mid-level lapse rate plume from the
   southern High Plains to the Great Lakes. Pervasive mid to
   upper-level cloud coverage will limit boundary-layer heating, likely
   holding MLCAPE to between 1000-1500 J/kg. 

   Low-level shear/hodograph curvature and deep-layer
   shear/hodograph length will increase with the approach of the
   shortwave trough, resulting in an environment conditionally
   favorable for supercells. Storm development in the open warm sector
   is unlikely given the lingering cloud cover and MLCIN.
   Stronger/deeper forcing for ascent should be confined to
   along and north of the warm front, with the severe threat beginning 
   between 22-00Z. Surface-based storms will be possible near and north
   of the warm front, but most of the convection should tend to become
   increasingly elevated farther north away from the boundary. Thus,
   large hail is the most likely hazard type with potential for a
   supercell or two to produce significant severe. A couple of
   tornadoes and damaging wind gusts will also be possible with any
   sustained supercells closer to the warm front, prior to the overall
   severe threat waning overnight.

   ..Grams/Elliott.. 09/26/2020