Great Lakes irradiance surges as wet weather weighs on Southwest solar resource
North America’s October solar irradiance was near normal overall, but the Great Lakes and Northeast saw surpluses while the Southwest and northern Mexico faced deficits due to wet weather.
North American irradiance in October remained close to normal overall, with a continental average of 0.8% above normal. However, this average masked significant regional disparities in solar resource availability. The Great Lakes and Northeast experienced substantial irradiance surpluses, averaging 14% above normal, with 95.5% of the region recording above-average levels. Higher atmospheric pressure and reduced precipitation in these areas minimized cloud cover, allowing more solar radiation to reach the surface. Buffalo and Cleveland recorded their strongest October irradiance levels in their respective Solcast records dating back to 2007.
In contrast, the Southwest and northern Mexico faced widespread irradiance deficits, with GHI averaging 9% below normal. A strong low-pressure trough drew Pacific moisture into the Four Corners region, while Tropical Storms Polo and Trudy contributed to heavy rainfall. The San Luis Valley received over four times its usual October rainfall in four days, and the San Juan River at Pagosa Springs reached its second-highest crest since 1911. Elevated atmospheric moisture increased cloud cover across the region, reducing solar radiation.
Phoenix recorded irradiance approximately 10% below its October average, marking October 2026 as the second-lowest October for GHI in the Solcast record. The below-normal conditions extended across the solar-intensive corridor from Southern California into Arizona, impacting a substantial concentration of utility-scale solar assets. The contrast in conditions highlights the sensitivity of solar generation to regional weather patterns and precipitation.
Solcast generates these irradiance figures using satellite data and proprietary AI/ML algorithms to track clouds and aerosols at 1-2km resolution globally. The company’s models achieve typical bias of less than 2% and provide high-resolution irradiance forecasts. Over 350 companies managing more than 350 GW of solar assets worldwide rely on Solcast’s data for operational and planning purposes. The analysis underscores the importance of localized weather data in assessing solar resource variability.