Average July temperature

Definition

Average July temperature is the long-run mean of daily mean temperatures across the month of July at a place. We compute it as a population-weighted average across the NOAA NCEI climate divisions that intersect each ZCTA, using the 1991–2020 climate normals — the WMO-standard 30-year reference period.

Source data

• NOAA NCEI nClimDiv — Monthly mean temperature by U.S. climate division, 1895–present (1991–2020 climate normals)

Steps

1. Pull monthly mean temperature for July from NCEI nClimDiv for each U.S. climate division, 1991–2020.
2. Average across the 30-year period to produce the climate-normal July mean per division.
3. Attribute each ZCTA to its containing climate division via TIGER polygon intersection.
4. For places spanning multiple ZCTAs, take a population-weighted average of constituent ZCTA values.
5. Buckets: cool (<70°F), warm (70–80°F), hot (80–90°F), very hot (>90°F).

Known limitations

• nClimDiv is the smoothest long-record temperature dataset available; finer spatial variation within a division (e.g., elevation, lake effects, urban heat islands) is not captured.
• Daily extremes are not summarized — a place with mild nights and hot afternoons has the same mean as one with a flatter diurnal range.
• The 1991–2020 normal pre-dates the most recent warming; current-year July averages run hotter than the climate normal.
• Humidity, which dominates perceived warmth in the eastern US, is not captured here. See heat-index methodology when published.

Where this metric appears

Every place page (in the climate section + at-glance row), the Coolest summer towns list, and the Warming velocity methodology references this baseline.

Related methodology

• Warming velocity
• Climate stripes

Cite this methodology

Commerce Institute. (2026). Average July temperature — Methodology. Retrieved from https://commerceinstitute.org/methodology/jul-temp/.