Denver Pavement Climate Data

Last reviewed 2026-07-25. Journalists, researchers, and community groups are welcome to cite any figure on this page with attribution and a link.

This page collects the figures behind the advice elsewhere on the site. Most come from NOAA's 1991-2020 climate normals for Denver International Airport, station USW00003017, where Denver's official snowfall has been measured since the fall of 2007. The normals file publishes counts in tenths; the tables below convert them and show the arithmetic wherever a figure is derived rather than published.

Other figures come from NCEI's comparative climate tables, the NWS Boulder office, the World Health Organization, and city and federal records on streets and soils. Each source is listed at the bottom with the values drawn from it. Nothing here is a forecast. Normals describe an average year, and any single season can run well off them in either direction.

The freeze-thaw arithmetic

NOAA counts how many days a year the low reaches 32 degrees or colder and how many days the high never climbs above 32. Taking the second count away from the first leaves the days when pavement crosses the freezing line and comes back, the cycle that pries cracks open. NOAA leaves the spring all-day-frozen count blank for this station, so the spring figure below is what remains after winter and fall are subtracted from the annual total.

Winter is 85.7 lows at or below 32 minus 15.1 frozen days; fall is 32.6 minus 2.7.

Sun, heat and dry air

Altitude and dry air decide how hard the sun works on a surface. The WHO rule of about 10 percent more UV per 1,000 meters puts pavement a mile up at roughly 16 percent above sea level. NCEI's cloudiness counts and humidity averages show why the dose adds up over a year, and NOAA's heat counts show how often a dark surface bakes.

The sealing and paving calendar

Frost dates set the outer limits for paving, but sealer follows a warmer rule: manufacturers want 50 degrees and rising and no drop below 50 for 24 hours after application. The counts of nights at or below 50 by season are what narrow the Denver sealing window to summer.

Dates are medians, meaning half of years see the event earlier and half later.

Rain, snow and hail

Denver's precipitation is light and lopsided. Summer, the season of afternoon thundershowers on the plains, is the wettest, while winter brings little water despite the snow. Official snowfall has been measured at the airport since the fall of 2007; the older Stapleton and Central Park record carries a 1991-2020 normal of 49.0 inches, and the long-term city average back to 1882 is 56.6.

Hail is the wild card. On May 8, 2017, golf-ball- and egg-sized hail fell on Lakewood and Wheat Ridge, including a 2.75-inch stone at Wheat Ridge at 3:05 p.m., and the storm produced more than 100,000 homeowner claims and 167,000 auto claims, the costliest event in Colorado records. June is the most common month for Colorado hail.

Streets and soils

Two records describe the ground a driveway sits on and the public pavement around it. The city's transportation department publishes network condition and alley counts, and USGS and NRCS describe the clays that make heave a Front Range problem.

• Denver street network condition index: 73.4, with 82% of pavement fair or better (DOTI, September 2026)
• Alleys: about 1,400 asphalt-overlaid, nearly 2,500 concrete, fewer than 150 unimproved (DOTI)
• Bentonite beds under a southwest-metro subdivision: about 62% smectite, 39-43% lab swell (USGS)
• Typical silty claystone in the same study: 2-8% lab swell (USGS)
• Denver soil series: clay loam over clay, slow to very slow permeability (NRCS)

Sources & Methodology

Every figure above was taken from the primary sources below (accessed 2026-07-25). Where a number is derived (arithmetic on published figures) or covers a broader period or area, the text says so.

1. NOAA NCEI, 1991-2020 Climate Normals, Denver International Airport (USW00003017) — Values in tenths: ANN-TMIN-AVGNDS-LSTH032 1569 (156.9 days), ANN-TMAX-AVGNDS-LSTH032 200 (20.0), DJF 857 and 151, SON 326 and 27, LSTH020 652, LSTH000 58, TMIN LSTH050 by season 871, 126 and 768, TMAX GRTH090 396, DUTR 284, precipitation 1430, freeze dates from PRBLST and PRBFST at 50 percent.
2. NWS Boulder, History of Snowfall Observations at Denver — Move of official snowfall to Denver International Airport in fall 2007, the 47.0-inch airport normal, the 49.0-inch Central Park normal and the 56.6-inch long-term average.
3. NCEI Comparative Climatic Data, average relative humidity — Denver afternoon averages of 43 percent annual and 35 percent in July, period 1995-2018; St. Louis annual afternoon 58 percent.
4. NCEI Comparative Climatic Data, mean days clear, partly cloudy and cloudy — Denver annual means of 115 clear, 130 partly cloudy and 120 cloudy days over 61 years.
5. World Health Organization, Radiation: Ultraviolet (UV) radiation — UV levels rise about 10 percent with every 1,000 meters of altitude.
6. AccuWeather, the May 8, 2017 hailstorm — Hail sizes in Lakewood and Wheat Ridge, the 2.75-inch stone at 3:05 p.m., claim counts from the Rocky Mountain Insurance Information Association, and June as the peak hail month.
7. Denver DOTI, 2027 City Council budget hearing presentation — Network pavement condition index of 73.4 weighted by lane miles, 82 percent fair or better, presented September 24, 2026.
8. Denver DOTI, Street Maintenance and Improvement — Alley counts by type and the description of mill and overlay removing about the top 2 inches.
9. USGS, Geologic control of severe expansive clay damage, southwest Denver metro — Bentonite about 62 percent smectite with 39 to 43 percent lab swell; silty claystone about 23 percent smectite with 2 to 8 percent swell.