Shocking July 2024: Unprecedented U.S. Heatwave Exposes Alarming Climate Realities

Unprecedented Heatwaves in July 2024

July 2024 witnessed a dramatic rise in temperatures across the United States, with notable spikes in the eastern and western regions. This month’s analysis reveals that the hottest July on record was observed in 15 cities, and 44 cities experienced temperatures in the top five hottest Julys recorded.

California’s west coast stood out with its severe heat, averaging 3.3°F above normal. Notably, five out of ten cities in California recorded temperatures that were at least 5°F hotter than usual, underscoring the critical impact of climate change.

The Climate Shift Index (CSI) also mirrored these trends, with the eastern and western thirds experiencing the most days with temperatures three times more likely due to climate change. The Southwest reported over 14 days with CSI values of three or higher.

Our data, derived from Climate Central’s CSI tool and NOAA’s ACIS, provide a detailed look at how climate change is reshaping temperature patterns across the country. This analysis will be updated monthly to track ongoing trends.

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Temperature Anomalies Across the Nation

Out of 191 analyzed ACIS stations, 134 showed positive temperature anomalies in July 2024, indicating a warmer month than usual. This was the hottest July on record for 15 cities, with 44 cities ranking in the top five hottest.

The United States saw elevated temperatures in the eastern and western thirds, while the middle regions, from Illinois to Texas, experienced unusually cool temperatures. The West Coast, in particular, had an average of 3.3°F above normal temperatures.

Spokane, Washington emerged as the most unusually hot city, recording 7.24°F above normal. Spokane’s Julys have warmed by 5.9°F since 1970, demonstrating a significant long-term trend.

Key observations include:

• 10 cities with anomalies greater than 5°F, half of which are in California.
• Reno, NV recorded a 4.96°F anomaly and is the fastest warming city since 1970, with a 12.7°F increase.
• Boise, ID, the second fastest warming city, saw a 5.20°F increase this July.

Analyzing the Climate Shift Index (CSI)

CSI analysis revealed that 40 out of 191 stations experienced at least one week with daily CSI values of three or higher, indicating a significant climate change influence. San Juan, Puerto Rico, reported 29 days at CSI 5, highlighting the extreme impacts of climate change.

Florida’s cities, including Miami and Tampa, featured prominently, with more than two weeks of temperatures at CSI values of five. These findings underscore the heightened climate vulnerability in these regions.

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The Southwest exhibited the strongest climate signal, with eight analyzed cities averaging over two weeks of CSI values at or above three. This trend is critical for understanding regional climate impacts.

Overall, the CSI data provide compelling evidence of climate change’s role in shaping extreme temperature events, offering a critical tool for future climate assessments.

Methods and Data Sources

Calculating the Climate Shift Index involved using daily average temperatures and ERA5 data from July 1 to July 31, 2024. For a thorough understanding of the CSI computation, refer to Gilford et al. (2022).

City Analysis included 191 ACIS stations across U.S. cities. Each city’s CSI time series was derived from the nearest 0.25° grid cell. This process helped determine the number of days with CSI levels 2-5.

ACIS data was utilized to assess average monthly temperatures, anomalies, and precipitation, and to calculate warming trends. This comprehensive analysis provides crucial insights into urban temperature dynamics.

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