An analysis of how climate change boosted United States temperatures in April 2026
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 April in cities across the United States. (Dataset downloadable as Excel workbook here.)
1. High-level findings
Overall, the U.S. saw above-average temperatures in April, with an average anomaly — or difference from normal — of 3.4°F across 192 cities.
While the western U.S. remained only slightly above average, the national trend was primarily driven by substantial anomalies across the east.
Sixty-two cities experienced one of their top five warmest April temperatures on record. On average, stations have data dating back to 1893.
Elevated temperature anomalies — or differences from normal — occurred in all nine U.S. Climate Regions: Southwest, West, Northwest, Northern Rockies and Plains, South, Southeast, Upper Midwest, Ohio Valley, and Northeast.
April 2026 was exceptionally warm, mirroring long-term April warming trends, which show that nearly all cities analyzed have warmed since 1970, consistent with findings from Climate Central’s 2025 Winter Package.
Figure 1. Temperature anomalies (differences from normal) for April 2026 relative to 1991-2020 normals. Analysis based on threaded ACIS station-level data.
Figure 2. Statewide average days with a CSI level 2 or higher for April 2026. Analysis based on ERA5 data.
2. Local temperature anomaly analysis
The average temperature anomaly — or difference from normal — across the 192 cities analyzed was 3.4°F.
April temperatures were overwhelmingly warm, with 179 cities recording warmer-than-average conditions, compared to 11 cities that experienced cooler-than-average conditions.
Temperatures were elevated across many areas in the Northwest, Southwest, West, Northern Rockies and Plains, South, Southeast, and Upper Midwest, Ohio Valley, and Northeast. The Ohio Valley stood out as the warmest region, with average temperatures more than 5.8°F above normal.
Twenty-two cities experienced their hottest April on record.
The most unusually warm city in April was Jonesboro, Arkansas, which was 8.2°F warmer than usual.
Of the 192 locations analyzed, most (183) showed long-term warming trends for April, indicating that these cities have warmed on average since 1970.
Reno, Nevada, experienced the greatest increase, with average April temperatures 7.9°F warmer than in 1970.
Table 1. ACIS stations with the highest April 2026 temperature anomaly.
City
State
Temperature anomaly or difference from normal (°F)
Average temperature (°F)
Warming since 1970 (°F)
Jonesboro
AR
8.2°
68.8°
0.2°
Evansville
IN
8.0°
65.1°
2.7°
Huntington
WV
7.8°
64.8°
3.5°
Paducah
KY
7.5°
66.3°
2.4°
Columbus
OH
7.4°
60.3°
4.7°
Indianapolis
IN
7.3°
60.8°
2.9°
Pittsburgh
PA
7.3°
58.7°
4.6°
Cincinnati
OH
7.2°
61.6°
3.2°
Louisville
KY
7.2°
66.1°
4.9°
Parkersburg
WV
7.1°
61.6°
3.1°
Table 2. ACIS stations with the fastest warming April since 1970.
City
State
Warming since 1970 (°F)
Temperature anomaly or difference from normal (°F)
Average temperature (°F)
Reno
NV
7.9°
0.0°
51.4°
Las Vegas
NV
7.2°
1.3°
68.8°
El Paso
TX
7.0°
2.5°
69.1°
Tucson
AZ
6.8°
3.8°
71.8°
Phoenix
AZ
6.5°
4.5°
77.6°
Tampa
FL
5.5°
1.9°
75.7°
Albany
GA
5.1°
2.1°
68.9°
Erie
PA
5.0°
5.6°
52.8°
Louisville
KY
4.9°
7.2°
66.1°
Chattanooga
TN
4.9°
4.9°
66.6°
3. Local Climate Shift Index analysis
San Juan, Puerto Rico, had 19 days at or above CSI 2 in April, indicating that temperatures on those days were made at least two times more likely because of climate change.
Four cities across the country experienced at least a week’s worth of days at or above CSI 2.
On average, cities in the Southwest experienced the highest number of days (10) with a CSI of 2 or above.
Table 3. ACIS stations with the highest number of days at or above CSI 2 during April 2026.
City
State
Days at CSI 2 or higher
Days at CSI 5
Average temperature (°F)
Temperature anomaly or difference from normal (°F)
San Juan
PR
19
12
80.6°
0.5°
Honolulu
HI
19
14
76.2°
-0.3°
Colorado Springs
CO
14
0
50.7°
3.3°
San Diego
CA
14
0
64.0°
1.1°
Tucson
AZ
13
4
71.8°
3.8°
Salt Lake City
UT
11
1
52.5°
0.8°
Grand Junction
CO
10
1
54.7°
2.9°
Odessa
TX
10
0
70.3°
4.3°
San Francisco
CA
10
0
59.1°
1.8°
Phoenix
AZ
10
1
77.6°
4.5°
Victoria
TX
10
5
73.9°
3.7°
METHODOLOGYCalculating 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 192 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 (compared to 1991-2020 normals), and precipitation information, and to derive average monthly warming trends for each city.
Regions
Regions are defined by NOAA’s National Centers for Environmental Information climate regions.