Climateby Month

Thornton, CO climate by month

NOAA 1991-2020 normals · 5,347 ft elevation · also covers Westminster

Summers in Thornton are hot; winters are chilly and snowy. Highs peak at 90°F in July and fall to 46°F in December. The wettest month is May (about 10 wet days) and the driest is December (about 4). Normal snowfall is about 49 in a year. The most comfortable time to visit is May.

Warmest month
90°F
July normal high
Coldest month
18°F
January normal low
Wet days a year
73
14.5 in of precipitation
Snow a year
49.0 in
normal snowfall

How warm is Thornton?

Normal highs range from 46°F in December to 90°F in July.

0°20°40°60°80°100° January: normal high 47°F (8°C), low 18°F (-8°C) February: normal high 48°F (9°C), low 19°F (-7°C) March: normal high 56°F (13°C), low 27°F (-3°C) April: normal high 63°F (17°C), low 34°F (1°C) May: normal high 72°F (22°C), low 43°F (6°C) June: normal high 84°F (29°C), low 53°F (12°C) July: normal high 90°F (32°C), low 59°F (15°C) 90° 59° August: normal high 88°F (31°C), low 57°F (14°C) September: normal high 80°F (27°C), low 48°F (9°C) October: normal high 67°F (19°C), low 36°F (2°C) November: normal high 55°F (13°C), low 26°F (-3°C) December: normal high 46°F (8°C), low 18°F (-8°C) 46° 18° JFMAMJJASOND

Bars run from the normal low to the normal high for each month.

How rainy is Thornton?

May has the most wet days (about 10); the year brings about 15 in of precipitation.

January: 4 wet days February: 4 wet days March: 6 wet days April: 8 wet days May: 10 wet days 10 June: 7 wet days July: 7 wet days August: 8 wet days September: 6 wet days October: 5 wet days November: 5 wet days December: 4 wet days 4 JFMAMJJASOND

Wet day: at least 0.01 in of rain or melted snow, counted from daily records 1991-2020.

How much does it snow?

Normal snowfall is 49.0 in a year, most of it in March.

January: 6.4 in of snow February: 7.6 in of snow March: 8.8 in of snow 8.8 April: 6.2 in of snow May: 1.4 in of snow June: 0.0 in of snow 0.0 July: 0.0 in of snow August: 0.0 in of snow September: 0.8 in of snow October: 3.9 in of snow November: 7.3 in of snow December: 6.6 in of snow JFMAMJJASOND

How humid is Thornton?

Muggy days (dew point 65°F or higher) are rare in any month.

January: 0 muggy days 0 February: 0 muggy days March: 0 muggy days April: 0 muggy days May: 0 muggy days June: 0 muggy days July: 0 muggy days August: 0 muggy days September: 0 muggy days October: 0 muggy days November: 0 muggy days December: 0 muggy days JFMAMJJASOND

Muggy day: daily mean dew point of 65°F or higher, from hourly observations 1991-2020 at Denver International Airport, 17 mi E of the city center (the nearest airport with complete hourly records).

How much daylight?

Daylight ranges from about 9.4 hours in December to 15.0 hours in June.

January: 9.7 hours of daylight February: 10.7 hours of daylight March: 12.0 hours of daylight April: 13.3 hours of daylight May: 14.4 hours of daylight June: 14.9 hours of daylight 14.9 July: 14.7 hours of daylight August: 13.7 hours of daylight September: 12.4 hours of daylight October: 11.1 hours of daylight November: 10.0 hours of daylight December: 9.4 hours of daylight 9.4 JFMAMJJASOND
See all numbers
Monthly climate normals and day counts for Thornton, 1991-2020
MonthHighLowPrecip.Wet daysSnowMuggy daysDaylight
January 47°F18°F 0.5 in4 6.4 in 0 9.7 h
February 48°F19°F 0.5 in4 7.6 in 0 10.7 h
March 56°F27°F 1.2 in6 8.8 in 0 12.0 h
April 63°F34°F 1.9 in8 6.2 in 0 13.3 h
May 72°F43°F 2.4 in10 1.4 in 0 14.4 h
June 84°F53°F 1.5 in7 0.0 in 0 14.9 h
July 90°F59°F 1.7 in7 0.0 in 0 14.7 h
August 88°F57°F 1.3 in8 0.0 in 0 13.7 h
September 80°F48°F 1.2 in6 0.8 in 0 12.4 h
October 67°F36°F 1.1 in5 3.9 in 0 11.1 h
November 55°F26°F 0.7 in5 7.3 in 0 10.0 h
December 46°F18°F 0.5 in4 6.6 in 0 9.4 h

High and low: NOAA 1991-2020 normal daily high and low. Wet days: at least 0.01 in of rain or melted snow. Muggy days: daily mean dew point 65°F or higher.

Best months to visit Thornton

By our comfort score, the best month is May.

Comfort score by month (0-100) and its parts, in days per month
MonthScoreComfortableNotable rainHot or cold
Jan 412210
Feb 45329
Mar 58934
Apr 681352
May 721561
Jun 641048
Jul 493417
Aug 525313
Sep 631134
Oct 651432
Nov 54925
Dec 402211

Score = 40 × share of comfortable days + 25 × share of days without notable rain + 20 × share of days neither hot (90°F+) nor cold (high 40°F or below) + 15 × daylight. How the score works.

Frost dates in Thornton

The last spring frost typically comes around May 2, and the first fall frost around Oct 11, leaving 160 frost-free days in a typical year.

Frost and freeze dates for Thornton
Typical date1 year in 10
Last spring frost (32°F)May 2after May 14
First fall frost (32°F)Oct 11before Sep 26
Last hard freeze (28°F)Apr 20after May 5
First hard freeze (28°F)Oct 21before Oct 7
Frost-free season160 daysunder 142 days

"Typical" is the date with a 50% chance of a later spring frost (or earlier fall frost). Planting after the "1 year in 10" spring date gives a 90% chance of no further frost. The Old Farmer's Almanac publishes 30% dates, which fall between our typical and 1-in-10 dates.

Station: Northglenn (USC00055984), NOAA 1991-2020 freeze probabilities. Frost dates for every city in Colorado.

Hottest and coldest readings, 1991-2020

The highest reading was 104°F (June 29, 2018, and 2 other days); the lowest was -17°F (February 3, 2011, and 1 other day).

From the temperature station's daily records with NOAA quality flags removed. Not an all-time record.

Near Thornton

Similar climates elsewhere

Also covers

Westminster uses the same temperature and rain stations as Thornton, so its monthly numbers are the ones on this page.

Where the numbers come from

  • Temperature, snowfall and snow depth: Denver-Stapleton (USW00023062), 9.1 mi SE of the city center, 5,286 ft (61 ft lower than the city). NOAA normals and daily records, 1991-2020.
  • Rain and frost dates: Northglenn (USC00055984), 3.1 mi NW of the city center, 5,407 ft (60 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Humidity and wind by hour and cloud cover: Aurora Buckley Fld ANGB (USW00023036), 16 mi SE of the city center, 5,663 ft (316 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Daily humidity and wind: Denver International Airport (725650-03017), 17 mi E of the city center, 5,404 ft (57 ft higher than the city). Hourly observations, 1991-2020.

Distances from the city center (USGS). Methodology · Report an error