US Southwest Climate – August 2026 Update
Top States: Arizona, Colorado, New Mexico, and Utah
Summary
The US Southwest endured exceptional late-summer heat, as intense atmospheric pressure and dry terrain elevated temperatures well above historical averages. The region sits under the influence of a moderate El Niño forecast to peak at Very Strong in August-October, driving shifts in broader atmospheric patterns. A sluggish seasonal monsoon has left major reservoirs across the Intermountain West at low capacity. Winter could eventually offer relief through increased regional precipitation.
This month in numbers
The 1-month average temperature anomaly for US Southwest reached +3.38°C above the 1961-1990 baseline, maintaining a stark warming trend. Over the latest 3-month period, the group averaged +2.79°C, while the 12-month rolling anomaly stands at +3.24°C. In the global context, 6 of the top 10 warmest 12-month anomalies worldwide were recorded across US states, underscoring persistent warmth across North America.
Hottest & coolest US states
Heat was intense across all four member states, led by New Mexico (US New Mexico) with a 1-month anomaly of +3.76°C. Arizona (US Arizona) followed closely with an anomaly of +3.44°C, while Utah (US Utah) registered +3.11°C and Colorado (US Colorado) recorded +3.02°C. With every member state running more than three degrees warmer than average, no cool state outliers occurred within the region.
What's driving change?
Regional weather was dominated by persistent that trapped warm air, while accelerated surface heating as missing soil moisture suppressed evaporative cooling. In the tropical Pacific, ENSO dynamics remain central, where a moderate El Niño is active with a Relative Niño Index value of +1.36°C. All of US Southwest's 1 flood this year has happened in the past month, as tracked at Extreme Weather tracker.
Looking ahead
Seasonal outlooks suggest that developing Pacific conditions could favour above-average winter precipitation across the region over the coming months, which historically offers an opportunity to replenish depleted reservoirs and mountain snowpack.
Generated by Gemini from climate data and web sources
At a Glance
Temperature – Average
Long-Term Trends
Climate Insights – US Southwest
Precipitation, Sunshine, Frost and Snow are converted to standard deviations from their own average so they can share an axis with Temperature anomalies.
NOAA Climate at a Glance - regional tavg / pcp / tmax / tmin
Heatwave Days – US Southwest
Warm Spell Duration Index (WSDI) - days in a 6+ day run above the local 90th-percentile temperature for that time of year.
Data: World Bank Climate Change Knowledge Portal (ERA5-derived), aggregated by 4BYO across member states. Refreshed roughly 1-2x/year, ~7-8 months behind present.
Climate Map – USUnited States
Source: NOAA Climate at a Glance — US states & climate regions (tavg, pcp), plus GPCC (Snow, water-equivalent). Anomalies are vs the 1961–1990 baseline. See methodology.
Hottest & Coolest in US Southwest this Month
1-month anomaly vs 1961–1990 across the 4 members we cover. Click a name to open its profile.
Warmest
- 1.🇺🇸New Mexico+3.76°C
- 2.🇺🇸Arizona+3.44°C
- 3.🇺🇸Utah+3.11°C
- 4.🇺🇸Colorado+3.02°C
Coolest
- 1.🇺🇸Colorado+3.02°C
- 2.🇺🇸Utah+3.11°C
- 3.🇺🇸Arizona+3.44°C
- 4.🇺🇸New Mexico+3.76°C
Year-on-Year Trends
The 4byo Climate Helix – US Southwest
NOAA Climate at a Glance — regional tavg / pcp (monthly absolutes).
Monthly Temperature – US Southwest
Background lines show the last 40 years (plus the record year and its opposite, wherever they fall).
NOAA Climate at a Glance — regional tavg / pcp (monthly absolutes).
Records – US Southwest
NOAA Climate at a Glance - regional tavg / pcp - Anomalies vs 1901-2000 mean
Shifting Seasons
Warm / cold seasonsHow spring and autumn have shifted in US Southwest. Spring is defined as the date monthly temperatures first rise above the long-term annual mean (10.8°C, from 1950–1979); autumn is the date they fall back below it. Temperature swings 23.3°C peak-to-peak across the year - a classic four-seasons rhythm.
Baseline vs recent monthly temperature climatology. Biggest warming: Dec (+2.0°C).
NOAA Climate at a Glance — regional tavg. Baseline: first 30 yrs on record. Recent: last 10 yrs on record.
Climate Systems
Loading ENSO tracker…
Emissions & Energy
Explore
Explore Climate Data
Data Sources
Data Sources for US Southwest
Every figure on this page is sourced from official, openly published climate datasets. Anomalies are calculated against the 1961–1990 baseline (temperature) and 1991–2020 (rainfall, sunshine, frost) - see the Methodology & Sources page for the complete dataset list and update calendar.
US 9-region temperature and precipitation series (1895–present).
US state-level CO₂ emissions and electricity generation mix by fuel source. Energy Information Administration.
Frost Days and Heatwave Days (Warm Spell Duration Index), ERA5-derived. World Bank Climate Change Knowledge Portal.
Monthly snow water-equivalent, Global Precipitation Climatology Centre (DWD).
FAQs
FAQs
How is the climate in US Southwest changing?
US Southwest is warming in line with the rest of the world. The page above shows the latest monthly temperature anomaly versus the 1961-1990 baseline, the long-term annual trend, and the region's rank in the historical record. The headline panel also shows the long-term trend rate per decade and the warmest and coolest years on file.
Where does the climate data for US Southwest come from?
Climate data for US Southwest comes from authoritative climate datasets including national meteorological services and peer-reviewed reanalyses, refreshed every month, when the upstream temperature and rainfall data are refreshed.
What is the climate baseline used on this page?
Anomalies on this page are calculated against the 1961-1990 climatological baseline, which is the standard reference period used by the Met Office, NOAA, IPCC and most national climate services. Some panels also show the source-native 1901-2000 (NOAA) or 1991-2020 (WMO) baselines for verification. See Methodology & Sources for the full reference.
Which areas does the US Southwest climate data cover?
The US Southwest climate profile covers Arizona, Colorado, New Mexico, Utah and surrounding areas. NOAA Southwest - AZ, CO, NM, UT
How often is the US Southwest climate update refreshed?
The US Southwest climate update is refreshed monthly, typically a few days after the previous month closes and the upstream provider (Met Office HadUK-Grid, NOAA Climate at a Glance, Copernicus ERA5 or the Global Carbon Project) publishes its update. See the Climate Rankings for cross-region comparisons.
What counts as a Heatwave Day on the US Southwest climate page?
Heatwave Days use the Warm Spell Duration Index (WSDI) - the WMO/ETCCDI-standard heatwave measure: days that are part of a run of 6 or more consecutive days above the local 90th-percentile temperature for that calendar day. The 90th-percentile threshold varies by time of year (a hot day in January is judged differently to one in July) but is fixed to the 1961-1990 baseline for every year shown - it does not shift as the climate warms, which is why Heatwave Days trend upward over time.
Does the US Southwest climate page include frost and snow data?
Yes. Frost Days (days with a minimum temperature below 0°C, World Bank CCKP) and snow water-equivalent (GPCC) are shown alongside temperature and precipitation, each measured against the 1961-1990 baseline where a like-for-like historical comparison is available.