20 September 2026 Supercells and Large Hail

Overview

Through the late afternoon and evening hours of September 20th, 2026, an environment supportive of supercells and large hail would set up across the eastern plains of Colorado. A subtle shortwave atop moist southeasterly flow post cold front, brought an environment of strong shear, high moisture, and instability to the region. Effective shear across the plains ranged around 45-50 knots, with MLCAPE ranging around 1500-2000 J/kg. While not unheard of in September, these conditions are uncommon this late into the month, especially so late in the day. This moist upslope surface flow would go on to produce 5 individual supercells across the area, with 4 of those developing within the NWS Pueblo County Warning Area. With the the aforementioned conditions in place, several of these storms would go on to become long track supercells, some of which had confirmed large hail of 3-4 inches in diameter.

Image of 1 of 5 supercells that developed across the eastern plains of Colorado on September 20th, 2026. This supercell developed across Kiowa County and produced 4 inch hail. Image By: Jake Thompson

Hail
Photos & Video
Radar
Storm Reports
Environment

Hail:

Hail

Multiple supercells developed across the eastern plains this day. While only two supercells had confirmed large hail, one from Limon, CO down to Eads, CO, and another just to the southeast of Eads, CO., based on MRMS MESH data and the environment in place, confidence is very high that the other supercells also had very large hail 2+ inches.


Measured 3.1 inch hail about 9 miles south of Brandon, CO in Kiowa County. Image By: Dan Fitts	Measured 4 inch hail about 3 miles south of Chivington, CO in Kiowa County. Image By: Michael Charnick	Measured 3 inch hail about 3 miles south of Chivington, CO in Kiowa County. Image By: Michael Charnick	MRMS MESH hail swaths from September 20th, 2026. For reference 50 mm = 2 inches and 75 mm = 3 inches. Based on reports MESH was slightly underestimating hail size.

Photos & Video


Image of the second supercell that developed in Kiowa County southeast of Eads, CO. This storm would go on to produce 3-4 inch hail. Image By: Jake Thompson	Image of the second supercell that developed in Kiowa County southeast of Eads, CO. This storm would go on to produce 3-4 inch hail. Image By: Jake Thompson	Image of the second supercell that developed in Kiowa County southeast of Eads, CO. This storm would go on to produce 3-4 inch hail. Image By: Andrew Rodriguez

Radar

Header


Supercell #1 as it crossed into Kiowa County. This supercell tracked from Limon, CO down to the southeast right to Eads, CO. This supercell developed off the cold front/boundary as it drifted to the southwest.	Supercell #2. This supercell developed just to the southeast of Eads, CO right in the forward flank of supercell #1. This is the supercell that produced measured 3-4 inch hail. This supercell developed off the cold front/boundary as it drifted to the southwest.	Supercell #3. This supercell quickly blossomed across far eastern El Paso County late in the day, around 03z, or 9:00 PM MDT. It tracked to the southeast and finally dissipated across northern Otero County. This supercell developed from upslope flow from behind the cold front/boundary.	Supercell #4. This supercell also quickly bloomed across far southern El Paso County late in the day, around 0315z, or 9:15 PM MDT. This storm tracked down into central Pueblo County, This supercell developed from upslope flow from behind the cold front/boundary.


Supercell #5. This supercell developed in NWS Boulder's CWA in Elbert County, just north of El Paso County, late in the day, around 0350z, or 9:50 PM MDT. This storm tracked down into far western Lincoln County. This supercell developed from upslope flow from behind the cold front/boundary.

Storm Reports


Figure 1: Map of storm reports from September 20th, 2026. The swath of hail from Supercells #1 and #2 can be easily seen across Lincoln County down into Kiowa County.

Environment

Synoptic Environment:


Figure 1: 300mb pattern at 8 PM MDT September 20th. Shortwave with weak difluence is evident passing over the region.	Figure 2: 500mb pattern at 8 PM MDT September 20th. Subtle shortwave within the flow is evident passing over the region.	Figure 3: 700mb pattern at 8 PM MDT September 20th.

Near-storm Environment:


Figure 4: Surface analysis at 730 PM MDT September 20th. A cold front pushing across the eastern plains and up into the terrain is evident. Lift along the boundary was initiated supercells #1 and #2. Upslope behind the boundary as it ran into the terrain initiated supercells #3, #4, and #5.	Figure 5: Effective bulk shear at 8 PM MDT September 20th. With westerly-northwesterly flow aloft and southeasterly flow at the surface, effective shear was around 45-50 knots. These values are supportive of organized storms, including supercells.	Figure 6: Mixed-Layer (ML) CAPE across the eastern plains at 8 PM MDT was around 1500 J/kg, with pockets of 2000 J.kg. Instability of this magnitude could easily support deep and intense convection.


Figure 7: Supercell Composite Parameter (SCP) across the plains at 8 PM MDT September 20th. Values hovered around 4 SCP, showing an environment supportive of organized and rotating thunderstorms.	Figure 8: The Significant Hail Parameter (SHIP) across the plains at 8 PM MDT September 20th. Values for SHIP hovered around 1-1.5. Values greater than 1 highlight areas supportive of significant hail development, or hail 2 inches or larger.	Figure 9: RAP model reanalysis sounding around the time of supercells #1 and #2.


Figure 10: RAP model reanalysis sounding around the time of supercells #3 and #4.

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