Wildfires and Storms Curb Solar in West, Eastern U.S. Sees Gains
Published · 4 min read
In September, North America saw very mixed solar performance. In much of the Western and Midwestern states, solar outputs fell short. But in the Eastern U.S. and parts of Canada, solar energy had a strong month. According to research by Solcast, three main forces shaped this split: wildfire aerosols, storms and frontal systems, and an omega block high-pressure pattern.
Why the West Struggled
From California to the central plains, irradiance levels—essentially sunlight energy reaching panels—were between 10% and 20% below normal. That is a big drop. Usually, late summer brings dry, clear skies in many western states.
But this September was different. Recurring fronts brought extra clouds. Tropical Storm Mario added moisture and instability, suppressing sunshine further. Wildfire smoke, especially drifting from Canada, made things worse. In places like the Pacific Northwest, smoke and particles cut clear-sky irradiance by up to 10%. Along the coast, sea spray and storm debris added further haze and scattering.
- Storms and frontal systems added cloud cover.
- Smoke and aerosols reduced clear sunlight.
- Coastal moisture and debris blurred sky clarity.
Not All the West Was Down
Interestingly, some western parts bucked the trend. The zone east of Vancouver into Alberta, Saskatchewan, and Montana saw irradiance about 10% above average. How? A blocking high-pressure system (omega block) settled in. It stabilized the air and limited cloud formation.
Smoke was still present, but dry, descending air under the high pressure reduced new cloud build-up. Thus, these areas got more sunshine than many expected.
East & Canada: A Sunny Surprise
The contrast was stark in the East. From the Great Lakes through the Southeastern U.S. and up into Quebec, irradiance anomalies hit up to 30% above normal. Storm systems were less disruptive there. The omega block pushed moisture offshore and made skies more stable and dry.
In effect, large parts of the U.S. from Texas to New England saw better solar conditions than usual. Even in parts of Canada, certain provinces recorded strong solar months.
Forecast Into Late 2025
Looking ahead, seasonal forecasts suggest this split may hold through autumn. Solcast’s models point to 15%–20% above average irradiance along much of the eastern seaboard. In contrast, western regions like Washington, California, Utah, and Oklahoma are forecast to stay 10%–15% below average. Meanwhile, a corridor from western Canada into the Mountain West may still see ~10% above average output.
These projections match broader Solcast forecasts for North America, which expect relatively strong solar conditions later this year.
How Solcast Does It
Solcast’s team uses satellite data and AI/ML models to track clouds and aerosols at 1–2 km resolution. Their irradiance models have a bias under 2%. Over 350 firms, managing more than 300 GW of solar assets, depend on these forecasts to make decisions.
They integrate aerosol data too. That lets them account for smoky skies and particulate matter, not just clouds. In earlier seasons, researchers have shown how smoke from wildfires can suppress irradiance even under clear skies.
Table: Performance by Region in September
| Region | Irradiance Anomaly | Main Factors |
| Western & Midwest U.S. | –10% to –20% | Storms, smoke, clouds |
| Pacific Northwest (some zones) | Up to +10% | High pressure, limited cloud |
| Eastern U.S. & Quebec | Up to +30% | Stable skies, moisture offshore |
| Western Canada / Mountain West | ~ +10% | Blocking high, dry air |
Why It Matters
Solar power is very sensitive to weather and atmospheric effects. When wildfires grow, smoke can ride on winds and darken skies far away. Even without clouds, aerosols scatter sunlight and reduce panel output. Scientists have found this effect in past fire seasons.
Also, blocking high pressure systems (like omega blocks) can cause stagnation. They limit cloud formation and hold weather patterns in place. This can make long stretches of unusually dry or sunny days. For the East this was helpful, but for the West it prevented clearing after storms.
For solar developers, grid operators, and households relying on PV power, knowing these regional trends is critical. They help in planning, storage sizing, power trading, and maintenance scheduling.
Final Thoughts
September revealed a tale of two Americas: the West, held back by stormy skies and smoke; the East, lifted by stable high pressure and clear sunlight. As forecasts suggest this pattern may carry through autumn, solar stakeholders will watch closely. Reliable forecasting, like that from Solcast, gives a vital edge.
