Executive Overview
NORMAN, OKLA. — On Saturday afternoon, September 5, 2026, the National Weather Service (NWS) Storm Prediction Center (SPC) in Norman, Oklahoma, issued Mesoscale Discussion 2245 at 03:34 PM CDT. The advisory highlights an active, albeit restrained, convective environment unfolding across portions of the western and central Dakotas, stretching down through western and central Nebraska, and clipping eastern Colorado.
While the afternoon heating cycle is actively eroding a persistent capping inversion, the overarching meteorological parameters suggest that any severe weather threat will remain isolated. Consequently, the SPC has pegged the probability of a downstream Tornado or Severe Thunderstorm Watch issuance at a low 20 percent.
The primary atmospheric hazards identified for the late afternoon and evening operational window include marginally severe hail—peaking up to 1.25 inches in diameter—and localized strong to severe wind gusts capable of reaching up to 60 mph. These threats are being driven by a combination of high surface temperatures, steep low-level lapse rates, and significant dry-air entrainment aloft. However, due to weak deep-layer wind shear profiles, storm organization is expected to remain minimal. As a result, storm structures will quickly transition into outflow-dominant regimes, limiting the geographical footprint and temporal continuity of the severe weather threat. Emergency management agencies, local National Weather Service Weather Forecast Offices (WFOs), and public safety officials across the designated target zones have been alerted to monitor localized developments closely, even in the absence of a formal watch product.
Detailed Chronology & Atmospheric Evolution
The Pre-Convective Environment (Early Afternoon)
By early Saturday afternoon, the synoptic stage across the central Plains was dominated by a pronounced surface trough axis stretching from the Dakotas southward into the high plains of eastern Colorado. Ahead of this boundary, unseasonably warm conditions prevailed, with afternoon temperatures soaring into the mid-90s Fahrenheit across western Nebraska and eastern Colorado.
At 18:00 UTC (1:00 PM local daylight time), meteorologists analyzed atmospheric sounding data from North Platte, Nebraska (LBF). The sounding revealed a classic high-Plains convective profile characterized by a substantial capping inversion—quantified as Convective Inhibition (MLCIN)—that had successfully suppressed surface-based updrafts through the morning hours.
However, beneath this capping layer, moderate mixed-layer instability (MLCAPE) had been steadily pooling, fueled by dew point depressions that were beginning to expand rapidly. As solar insolation reached its maximum intensity, surface temperatures climbed, effectively eating away at the remaining MLCIN. By the time the Storm Prediction Center issued Mesoscale Discussion 2245 at 20:34 UTC, isolated towering cumulus clouds were transitioning into bona fide cumulonimbus structures along the surface trough.
[Surface Trough Axis] ---> [Intense Solar Heating] ---> [Cap Erosion] ---> [Isolated Convection]
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+--------------------------------------+
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v
[Weak Deep-Layer Shear (~20-30 kts)]
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v
[Outflow-Dominant Storms / Wind & Hail Threat]Storm Initiation and Updraft Dynamics (Late Afternoon to Early Evening)
The active window defined in the discussion spans from 20:34 UTC to 22:30 UTC. During this two-hour operational bracket, convective initiation is concentrated along the low-level convergence boundary. Because the deep-layer wind shear vector (measured through the lowest six kilometers of the troposphere) remains weak—generally hovering in the 20 to 30 knot range—updrafts lack the kinematic support required for long-lived, rotating supercells.
Instead, the environment is favoring pulse-type storms and transient multi-cell clusters. While the steep lapse rates present in the lower and middle troposphere are allowing individual updrafts to surge rapidly, the lack of organized shear prevents these storms from maintaining steady-state maturity. Consequently, updrafts are prone to pulsing: rapidly intensifying to produce short-lived bursts of hail before collapsing under their own weight or becoming choked by rain-cooled outflow.
Outflow Dominance and Dissipation Phase
As the afternoon progresses into the early evening hours, the combination of high dew point depressions (indicating very dry air in the sub-cloud layer) and falling precipitation is setting the stage for evaporative cooling. When rain droplets fall through this dry mid-tropospheric air, they evaporate rapidly, chilling the surrounding air and creating dense, negatively buoyant parcels that plunge toward the surface.
This process accelerates cold pool formation. The resulting downdrafts spread out rapidly upon hitting the ground, undercutting the updrafts that fed them. This transition to an outflow-dominant storm mode means that while individual cells will pose an immediate threat for brief, strong wind gusts up to 60 mph and marginally severe hail up to 1.25 inches, the storms will struggle to sustain themselves over long distances. The overall convective system is expected to weaken rapidly after sunset with the loss of daytime heating and the stabilization of the boundary layer.
Supporting Context & Operational Metrics
To fully understand why the Storm Prediction Center opted against issuing a formal Severe Thunderstorm Watch, it is necessary to examine the underlying meteorological metrics governing Mesoscale Discussion 2245.
Core Meteorological Parameters
- Valid Time Window: 20:34 UTC – 22:30 UTC (Saturday, September 5, 2026)
- Probability of Watch Issuance: 20% (Unlikely)
- Most Probable Peak Wind Gust: Up to 60 mph (52 knots)
- Most Probable Peak Hail Size: Up to 1.25 inches (quarter to half-dollar scale)
- Deep Layer Shear: 20 – 30 knots (insufficient for widespread organization)
- Primary Forcing Mechanism: Surface trough axis intersecting with diurnal heating and thermal ridge
Spatial Extent and Affected Weather Forecast Offices (WFOs)
The geographic polygon defined in the discussion encompasses a broad swathe of the High Plains, threatening portions of three states:
- South Dakota: Western and central counties.
- Nebraska: Western and central expanses.
- Colorado: Eastern high plains.
To ensure seamless coordination and public safety dissemination, the SPC explicitly alerted multiple National Weather Service Weather Forecast Offices (WFOs). The impacted WFO jurisdictions include:
- ABR (Aberdeen, South Dakota)
- GID (Hastings, Nebraska)
- LBF (North Platte, Nebraska)
- UNR (Rapid City, South Dakota)
- GLD (Goodland, Kansas)
- BOU (Boulder, Colorado)
- CYS (Cheyenne, Wyoming)
Geographic Coordinate Boundary (LAT/LON)
For spatial tracking and automated warning systems, the mesoscale discussion polygon is mapped by the following coordinate pairs:
39410352/-103.5241030377/-103.7742140364/-103.6442920356/-103.5645060320/-103.2045400295/-102.9545640247/-102.4745270123/-101.2344770090/-100.9044140078/-100.7844070082/-100.8243830063/-100.6343330034/-100.3442329983/-99.8341769988/-99.8840510035/-100.3539520239/-102.3939410352/-103.52
Official Statements & Expert Analysis
The meteorological assessment for Mesoscale Discussion 2245 was authored and vetted by SPC forecasters Thornton and Gleason. Their operational analysis emphasizes a nuanced approach to convective forecasting where the presence of instability does not automatically translate to a widespread severe weather outbreak.
"Thunderstorms are developing near the surface trough across the central Plains," noted the forecasters in the official text. "Modifying the 18z sounding from LBF shows MLCIN has weakened but remains. Moderate instability was sampled above the capping layer."
The core challenge for forecasters evaluating this event lies in the delicate balance between thermal energy and kinematic restriction. While the sun has successfully warmed surface temperatures into the mid-90s across western Nebraska and eastern Colorado—slowly eroding the capping inversion—the lack of upper-level support means storms cannot organize into larger, self-sustaining complexes.
Furthermore, the forecasters highlighted the specific thermodynamic mechanisms driving the severe threat:
"Deep layer flow is generally weak, which will likely keep the organized severe potential low. However, deep layer shear around 20-30 kts may support a few stronger cores capable of marginally severe hail. Large dew point depressions and steep lapse rates will favor outflow dominant storms capable of a few instances of strong to severe wind."
Because the spatial coverage of these isolated severe cores is expected to remain limited—falling well below the strict criteria required for a formal county-by-county watch—the SPC concluded that a watch issuance was unwarranted at this juncture. Instead, local forecasters at the regional WFOs will rely on short-fused Special Weather Statements (SPS) and Severe Thunderstorm Warnings to address individual storm cells as they flare up and pose immediate localized threats.
Future Outlook & Public Safety Recommendations
Short-Term Meteorological Trajectory
As evening approaches on this early September weekend, the diurnal cycle will begin to work against convective maintenance. As solar radiation wanes, surface temperatures will drop, removing the primary catalyst for cap erosion and destabilization.
Any storms currently bubbling along the surface trough in western and central South Dakota, western and central Nebraska, and eastern Colorado are expected to peak in intensity over the next one to two hours before steadily weakening. The primary remaining hazard through the remainder of the evening window will be localized, brief wind gusts up to 60 mph driven by collapsing convective cores, alongside isolated, minor accumulations of hail up to 1.25 inches.
Recommendations for Public Safety and Emergency Management
- Monitor Local Forecasts: Residents and travelers across the affected High Plains corridors should stay tuned to local radio broadcasts, NOAA Weather Radio, and official National Weather Service updates (available at www.spc.noaa.gov) for real-time radar tracking.
- Be Prepared for Sudden Gusts: Given the outflow-dominant nature of these storms, high winds can develop rapidly with little advanced warning, posing risks to high-profile vehicles on regional highways (including segments of Interstate 80 and Interstate 76).
- Secure Outdoor Objects: Campers, farmers, and outdoor event organizers should secure loose equipment, awnings, and temporary structures against the possibility of sudden, erratic downburst winds reaching up to 60 mph.
- Stay Alert to Short-Fused Warnings: Because a formal Severe Thunderstorm Watch is unlikely, local WFOs will issue targeted Severe Thunderstorm Warnings if any individual storm core briefly exceeds marginal criteria. Immediate shelter should be sought if a warning is issued for your specific locality.
The Storm Prediction Center will continue to monitor the central Plains mesoscale environment and will issue subsequent updates or additional discussions should atmospheric conditions deviate unexpectedly from the current model projections.
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