Report•November 4, 2025
Monthly Attribution Overview – October 2025
An analysis of how climate change boosted United States temperatures in October 2025
Using Climate Central’s Climate Shift Index (CSI) tool to measure the impact of climate change on daily temperatures across the United States, as well as NOAA’s Applied Climate Information System (ACIS) to find daily temperature information, we have compiled a high-level overview of how climate change has affected temperature trends in October in cities across the United States. (Dataset downloadable as Excel workbook here.)
1. High-Level Findings
The U.S. saw elevated temperatures in October with an average anomaly of 2.0°F across 192 cities.
Fifteen cities experienced one of their top five warmest October temperatures on record. On average, stations have data reaching back to 1893.
Elevated temperatures were observed across the U.S. in the Northwest, Southwest, Northern Rockies and Plains, South, Upper Midwest, Ohio Valley, and Northeast (regions defined by the NCEI climate regions).
Honolulu, HI, and San Juan, PR experienced at least two weeks' worth of CSI values of 2 or higher, indicating a strong climate change influence.
Long-term October warming trends show that nearly all cities analyzed have gotten warmer since 1970, consistent with findings from Climate Central’s 2025 Summer Package.
Figure 1. Threaded ACIS temperature anomalies for October 2025 relative to the 1991-2020 standard normal period. Analysis based on ACIS data.
Figure 2. Days with a CSI of 2 or higher for October 2025 for ACIS threaded stations. Analysis based on ERA5 data (10/01 - 10/25) and GFS data (10/26-10/30).
2. Local Temperature Anomaly Analysis
The average temperature anomaly across the 192 cities analyzed was 2.0°F, with a large majority — 150 cities — having hotter-than-average temperatures.
Temperatures were moderately elevated across the country, with nearly every region experiencing positive temperature anomalies, or differences from normal. The region that experienced the most unusual heat was the Ohio Valley (states in this region include Illinois, Indiana, Kentucky, Missouri, Ohio, Tennessee, and West Virginia). The average temperature anomaly was 4.89°F. The region with the smallest difference from normal was the West, where temperature anomalies were 0.5°F cooler than average.
The most unusually warm city this October was Fairbanks, AK, which was 7.1°F warmer than usual.
Of the 191 ACIS stations analyzed, 190 showed positive temperature trends for October, indicating that these cities have been warming on average since 1970.
Wheeling, WV, warmed the most out of all the analyzed cities. The average October in Wheeling is 7.8°F warmer than it was in 1970.
Table 1. Top 10 ACIS stations with the highest October 2025 temperature anomaly.
City | State | Temperature Anomaly (°F) | Average Temperature (°F) | Warming Since 1970 (°F) |
|---|---|---|---|---|
Fairbanks | AK | 7.1 | 33.3 | 6.0 |
Fargo | ND | 6.4 | 52.0 | 2.6 |
Lubbock | ND | 6.4 | 68.2 | 3.2 |
Cedar Rapids | IA | 6.3 | 57.0 | 0.6 |
Kansas City | MO | 6.3 | 62.7 | 1.2 |
Marquette | NV | 6.1 | 0.7 | 71.1 |
Quincy | IL | 6.0 | 61.0 | 1.8 |
Dubuque | IA | 6.0 | 61.0 | 1.8 |
Des Moines | IA | 5.9 | 59.0 | 2.1 |
Sioux City | IA | 5.8 | 56.1 | 0.2 |
Table 2. Top 10 ACIS stations with the fastest warming October since 1970.
City | State | Warming Since 1970 (°F) | Temperature Anomaly (°F) | Average Temperature (°F) |
|---|---|---|---|---|
Wheeling | WV | 7.8 | 0.4 | 54.7 |
El Paso | TX | 7.5 | 5.4 | 72.1 |
Reno | NV | 7.2 | -1.0 | 54.0 |
Burlington | VT | 6.1 | 2.5 | 52.9 |
Tucson | AZ | 6.1 | 1.5 | 74.2 |
Las Vegas | NV | 6.1 | 0.7 | 71.1 |
Fairbanks | AK | 6.0 | 7.1 | 33.4 |
New Orleans | LA | 5.8 | 3.3 | 75.6 |
Anchorage | AK | 5.7 | 4.8 | 41.1 |
Phoenix | AZ | 5.5 | 0.9 | 78.3 |
3. Local Climate Shift Index Analysis
San Juan had 29 days at CSI 5 in October, indicating that temperatures on those days were at least five times more likely because of climate change.
Fifteen cities across the country experienced at least a week of days at, or above, a CSI of 2.
On average, cities in the Southwest experienced the highest number of days — four — with a CSI of 2 or above.
Table 3. Top 10 ACIS stations with the highest number of days at or above a CSI of 2 during October 2025.
City | State | Days at CSI = 2 or higher | Days at CSI = 5 | Average Temperature (°F) | Temperature Anomaly (°F) |
|---|---|---|---|---|---|
San Juan | PR | 31 | 29 | 83.9 | 1.2 |
Honolulu | HI | 26 | 13 | 81.3 | 0.9 |
Anchorage | AK | 12 | 0 | 41.1 | 4.8 |
Corpus Christi | TX | 12 | 2 | 78.5 | 3.4 |
McAllen | TX | 12 | 2 | 82.5 | 3.6 |
Victoria | TX | 12 | 4 | 75.9 | 3.3 |
Tucson | AZ | 9 | 0 | 74.2 | 1.5 |
Colorado Springs | CO | 8 | 0 | 53.6 | 2.9 |
West Palm Beach | FL | 8 | 1 | 79.9 | 1.2 |
El Paso | TX | 8 | 0 | 71.1 | 5.4 |
Sarasota | FL | 7 | 1 | 78.2 | 0.9 |
METHODOLOGY
Calculating the Climate Shift Index
All Climate Shift Index (CSI) levels reported in this brief are based on daily average temperatures and ERA5 data. See the frequently asked questions for details on computing the Climate Shift Index, including a summary of the multi-model approach described in Gilford et al. (2022).
City Analysis
We analyzed 191 Applied Climate Information System (ACIS) stations associated with U.S. cities. For each city, we found the CSI time series from the nearest 0.25° grid cell. We calculated the number of days at CSI levels 2, 3, 4, and 5. We used ACIS data to find the average monthly temperatures, temperature anomalies, and precipitation information, and to derive average monthly warming trends for each city.