Heat dome and high pressure boost southern US solar as polar vortex clouds the north

North America experienced a pronounced divide in solar conditions through March, with the southern half of the continent recording widespread increases in solar resource while the north faced persistent cloud and storm activity.

The strongest gains were centered on northeastern Mexico and southeastern Texas where deviations reached roughly 20–25% above the long-term March average, with much of California also seeing similar increases. Canada, the Great Lakes and the northeastern United States recorded lower-than-normal irradiance as polar air and storm systems dominated conditions. This produced a month in which the usual seasonal contrast between north and south was sharpened, with clearer skies in the south and cloudier conditions in the north compared with the 2007–2025 average.

Much of the southern United States and northern Mexico benefited from a pair of high-pressure systems positioned over the Pacific and Atlantic coasts of North America. These systems stabilised the atmosphere and kept skies clearer than normal across large areas. Southern Mexico and Florida were exceptions to the southern trend, each experiencing slightly below average irradiance where localised cloud cover persisted.

A pronounced heat dome over the southwestern United States further reinforced these conditions, driving temperatures 10–19 C (18-35 F) above seasonal norms and breaking multiple records, as localized areas saw even large increases. These warm conditions, more like summer temperatures than spring, were the result of high atmospheric stability, which also suppressed cloud formation and supported extended periods of clear skies. As a result, California emerged as one of the strongest-performing regions relative to average conditions, with irradiance levels significantly elevated through much of the month. The scale of the heat anomalies was notable, with attribution studies indicating these extremes would be highly unlikely without the influence of climate change.

At the same time, northern parts of the continent experienced a very different pattern as an unstable polar vortex pushed cold polar air into Canada and the northern United States. This brought snowstorms and blizzards across several regions, particularly around the Great Lakes and the Northeast, where irradiance fell far below normal for March. These stormy conditions contributed to the largest percentage drops from average in areas north of the Great Lakes.

The push of polar air extended unusually far south, reaching into Florida and contributing to its slightly below normal irradiance despite the generally sunnier conditions across most of the southern half of North America. Collectively, these factors reinforced the strong contrast between the sunnier southern regions and the cloudier, storm affected conditions across the north.

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