Storm Prediction Center - Day 1 Outlook

Data From the SPC

Day 1 Graphical Outlook

Definition: The probability values represent the chance of severe weather occurring within 25 miles of any point, which is approximately the size of a major metropolitan area.

Day 1 & 2: The outlook contains individual severe probabilities for tornadoes, wind, and hail.
Day 3: Due to greater uncertainty, the outlook only forecasts the combined probability of all three types of severe weather.

Context: Probabilities for severe thunderstorm wind and hail are typically higher than for tornadoes because they are more common. A 15% probability for a tornado means significantly above normal odds of a tornado nearby, which should be taken seriously, even though the number seems low.

Note: The peak daily tornado probabilities in the most tornado prone portions of the country (Plains and Southeast) are slightly above 2%. Therefore, most days with any tornado probabilities are well above climatology.


SPC Category Descriptions (Click image to enlarge)



Issue Times

Day 2 Outlook

Day 1 Outlook Discussion

SPC AC 131957

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0257 PM CDT Sun Sep 13 2026

   Valid 132000Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
   OHIO VALLEY INTO CENTRAL NEW YORK...

   ...SUMMARY...
   Isolated to widely scattered severe thunderstorms will be possible
   across parts of the upper Ohio Valley into the Northeast this
   afternoon and evening. Isolated strong to severe thunderstorms may
   also occur across parts of the central and northern High Plains.

   ...20Z Update...
   Minor changes where made to the ongoing forecast based on recent
   observations and model guidance. The overall forecast reasoning
   remains valid, however. See the previous discussion for additional
   details.

   ..Wendt.. 09/13/2026

   .PREV DISCUSSION... /ISSUED 1139 AM CDT Sun Sep 13 2026/

   ...Northeast and upper/middle Ohio Valley...
   Have upgraded portions of the region to a categorical Slight Risk
   with expectations of a semi-focused regional corridor of wind damage
   later this afternoon through early evening. Within large-scale upper
   troughing over eastern Canada, a strong west-southwesterly mid-level
   jet will overspread the Great Lakes into the Ohio Valley and
   Northeast later today into tonight. A surface cold front will
   likewise track eastward across these regions through tonight. A
   seasonably moist low-level airmass will be in place ahead of the
   cold front, but poor lapse rates aloft (around 6-6.5 C/km) and cloud
   cover should limit the degree of destabilization that can occur this
   afternoon, although cloud cover has tended to thin/abate since early
   this morning across the upper Ohio Valley. While the main influence
   of the upstream upper-level trough will not arrive until this
   evening, strengthening mid-level flow through the day will support
   35-45 kt of deep-layer shear and the potential for organized bands
   of convection.

   At least widely scattered thunderstorms are expected to develop
   along/ahead of the front by mid afternoon (around 19-22Z) from parts
   of Ohio into western New York, and then spread quickly eastward
   across the upper Ohio Valley into the Northeast. The deep-layer
   shear will be strong enough for some supercells initially, with
   perhaps a marginal/isolated hail threat even with the poor lapse
   rates present aloft. But, clusters/bowing segments with an isolated
   damaging wind threat should quickly develop given the linear forcing
   of the front. This convection is forecast to weaken with eastward
   extent this evening with the onset of nocturnal cooling, and as it
   encounters a less unstable airmass.

   ...Wyoming and central/northern High Plains to Missouri Valley...
   A closed mid/upper-level low over the Pacific Northwest this morning
   will move eastward to the northern Rockies/High Plains through the
   period. Diurnal destabilization will generally be limited ahead of
   this low, though a narrow zone of weak instability may develop by
   late afternoon across southern Wyoming, and across northeast
   Colorado into the Nebraska Panhandle in a modest low-level upslope
   flow regime. Isolated thunderstorm development is expected with
   sufficient wind profiles for isolated severe hail/wind potential.

   Elevated thunderstorms should again increase in coverage across
   western/central South Dakota towards the mid Missouri Valley late
   tonight into early Monday morning. Moderate MUCAPE and sufficient
   cloud-layer shear could support an isolated hail threat with the
   initial development across western/southern South Dakota, though
   mergers/interactions and weakening buoyancy will likely limit the
   longevity and eastward extent of this threat into the mid Missouri
   Valley.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z

Issued by the Weather Prediction Center