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Thornton, CO Weather by Month and Climate Averages
Monthly normals · Rain · Snow
Sunshine · Freeze dates · Records · Best time to visit
What is the weather like in Thornton, CO?
Thornton, CO gets 14.5 in of precipitation a year over about 73 rainy days, and about 44.8 in of snow a season. July is the warmest month (average high 91°F) and January the coldest (average low 19°F).
Humid subtropical climate
Thornton, CO has hot summers and chilly winters. Daytime highs range from about 47°F in December to 91°F in July. May is usually the wettest month, and snow falls in winter. The most comfortable time to visit is typically April and October, when daytime highs sit near 66°F.
| Season | Months | Avg low | Avg high |
|---|---|---|---|
| Winter | Dec–Feb | 20° | 48° |
| Spring | Mar–May | 36° | 65° |
| Summer | Jun–Aug | 56° | 88° |
| Autumn | Sep–Nov | 37° | 68° |
How much rain does Thornton get?
Thornton gets 14.5 in of precipitation in an average year, spread over about 73 days with measurable rain. That is fewer rainy days than 65% of the US.
May is the wettest month, with 2.4 in. January is the driest, with 0.5 in. May has the most rainy days, about 10.
The longest dry spell in the last five years lasted 25 days, to October 18, 2024.
From September 2025 to August 2026 Thornton got 9.0 in of rain, against a normal of 14.5 in for those months. May 2026 had the most, with 2.0 in.
See where Thornton ranks: rainiest cities in the US, US cities with the most rainy days, rainiest cities in Colorado.
Does it snow in Thornton?
Yes. Thornton gets about 44.8 in of snow in an average season, measured at the reporting station.
The snowiest winter on record is 1972–73, with 95.1 in.
The most recent measurable snow at the station fell on May 6, 2026.
From September 2025 to August 2026 the station measured 24.7 in of snow, against a normal of 44.8 in for those months. March 2026 had the most, with 7.0 in.
See where Thornton ranks: snowiest cities in the US.
Thornton weather by month
Thornton weather in January
In January, Thornton averages a high of 47°F and a low of 19°F. It gets 0.5 in of precipitation over about 4 rainy days. Estimated sunshine is 55% of daylight hours, derived from ERA5 cloud cover. The January record high is 77°F (1997) and the record low is -15°F (1985).
Thornton weather in February
In February, Thornton averages a high of 49°F and a low of 21°F. It gets 0.5 in of precipitation over about 4 rainy days. Estimated sunshine is 57% of daylight hours, derived from ERA5 cloud cover. The February record high is 83°F (2017) and the record low is -17°F (1996).
Thornton weather in March
In March, Thornton averages a high of 58°F and a low of 28°F. It gets 1.2 in of precipitation over about 5 rainy days. Estimated sunshine is 52% of daylight hours, derived from ERA5 cloud cover. The March record high is 94°F (2026) and the record low is -5°F (2002).
Thornton weather in April
In April, Thornton averages a high of 64°F and a low of 35°F. It gets 1.9 in of precipitation over about 8 rainy days. Estimated sunshine is 55% of daylight hours, derived from ERA5 cloud cover. The April record high is 90°F (2025) and the record low is 6°F (1997). April is one of the most comfortable months to visit.
Thornton weather in May
In May, Thornton averages a high of 73°F and a low of 44°F. It gets 2.4 in of precipitation over about 10 rainy days. Estimated sunshine is 48% of daylight hours, derived from ERA5 cloud cover. The May record high is 101°F (2003) and the record low is 20°F (2013).
Thornton weather in June
In June, Thornton averages a high of 84°F and a low of 53°F. It gets 1.5 in of precipitation over about 7 rainy days. Estimated sunshine is 53% of daylight hours, derived from ERA5 cloud cover. The June record high is 105°F (2018) and the record low is 34°F (1988).
Thornton weather in July
In July, Thornton averages a high of 91°F and a low of 59°F. It gets 1.7 in of precipitation over about 7 rainy days. Estimated sunshine is 59% of daylight hours, derived from ERA5 cloud cover. The July record high is 108°F (2005) and the record low is 43°F (1987).
Thornton weather in August
In August, Thornton averages a high of 88°F and a low of 57°F. It gets 1.3 in of precipitation over about 8 rainy days. Estimated sunshine is 60% of daylight hours, derived from ERA5 cloud cover. The August record high is 110°F (2008) and the record low is 41°F (1986).
Thornton weather in September
In September, Thornton averages a high of 80°F and a low of 49°F. It gets 1.2 in of precipitation over about 6 rainy days. Estimated sunshine is 70% of daylight hours, derived from ERA5 cloud cover. The September record high is 102°F (2019) and the record low is 18°F (1985).
Thornton weather in October
In October, Thornton averages a high of 67°F and a low of 37°F. It gets 1.1 in of precipitation over about 5 rainy days. Estimated sunshine is 69% of daylight hours, derived from ERA5 cloud cover. The October record high is 93°F (2024) and the record low is 4°F (2019). October is one of the most comfortable months to visit.
Thornton weather in November
In November, Thornton averages a high of 55°F and a low of 27°F. It gets 0.7 in of precipitation over about 5 rainy days. Estimated sunshine is 65% of daylight hours, derived from ERA5 cloud cover. The November record high is 84°F (2025) and the record low is -6°F (1993).
Thornton weather in December
In December, Thornton averages a high of 47°F and a low of 19°F. It gets 0.5 in of precipitation over about 4 rainy days. Estimated sunshine is 62% of daylight hours, derived from ERA5 cloud cover. The December record high is 82°F (2025) and the record low is -24°F (1990).
Sunshine, humidity and wind in Thornton
September is the sunniest month in Thornton, with estimated sunshine of 70% of daylight hours from ERA5 cloud cover. May is the cloudiest, at 48%. The annual cloud-cover estimate is 59% of daylight hours; it is not a measurement of sunshine duration. Thornton is sunnier than 84% of the US.
Humidity peaks in January at 57% and is lowest in September at 37%.
Thornton has about 50 days a year above 90°F. Thornton is hotter than 69% of the US.
Thunderstorms occur on about 12 days a year.
See where Thornton ranks: sunniest cities in the US, cloudiest cities in the US, hottest cities in the US.
First and last freeze in Thornton
The first fall freeze in Thornton typically comes around October 7, and the last spring freeze around May 4. That leaves a frost-free growing season of about 156 days.
Thornton weather records
These records cover NORTHGLENN during 1984–2026. Earlier records or other stations in the city may differ.
The hottest temperature on record at the Thornton station is 110°F, on August 2, 2008. The coldest is -24°F, on December 22, 1990.
The wettest day in the available station history brought 2.5 in of precipitation, on August 24, 1992.
45 all-time records have been set at the station since 1984.
The annual mean temperature has changed by +1.0°F per decade since 1985.
The best time to visit Thornton
The most comfortable time to visit is typically April and October, when daytime highs sit near 66°F.
Winter (December–February) is chilly, with average highs around 48°F and lows near 20°F. Snow is possible.
Spring (March–May) is mild, with average highs around 65°F and lows near 36°F.
Summer (June–August) is hot, with average highs around 88°F and lows near 56°F.
Autumn (September–November) is mild, with average highs around 68°F and lows near 37°F.
Monthly climate
| Month | Average low | Average high | Precip | Rain days | Humidity | Estimated sunshine | Record high | Record low |
|---|---|---|---|---|---|---|---|---|
| January | 19° | 47° | 0.45 in | 4 | 57% | 55% | 77° | -15° |
| February | 21° | 49° | 0.54 in | 4 | 55% | 57% | 83° | -17° |
| March | 28° | 58° | 1.2 in | 5 | 51% | 52% | 94° | -5° |
| April | 35° | 64° | 1.9 in | 8 | 41% | 55% | 90° | 6° |
| May | 44° | 73° | 2.4 in | 10 | 49% | 48% | 101° | 20° |
| June | 53° | 84° | 1.5 in | 7 | 43% | 53% | 105° | 34° |
| July | 59° | 91° | 1.7 in | 7 | 41% | 59% | 108° | 43° |
| August | 57° | 88° | 1.3 in | 8 | 40% | 60% | 110° | 41° |
| September | 49° | 80° | 1.2 in | 6 | 37% | 70% | 102° | 18° |
| October | 37° | 67° | 1.1 in | 5 | 39% | 69% | 93° | 4° |
| November | 27° | 55° | 0.73 in | 5 | 46% | 65% | 84° | -6° |
| December | 19° | 47° | 0.48 in | 4 | 49% | 62% | 82° | -24° |
Station: NORTHGLENN, 5 km from the city. Temperature normal baseline: 1991–2020, calculated from available NOAA GHCN-Daily observations. Available station history: 1984–2026; record values refer to this station and period, not the entire city’s history. Precipitation includes rain and the water equivalent of frozen precipitation; snowfall depth is shown separately when available. Sources and methods
From ERA5 reanalysis. Sunshine is estimated from cloud cover.
Thornton climate questions
How much rain does Thornton get?
Thornton gets 14.5 in of precipitation in an average year, over about 73 rainy days.
What is the wettest month in Thornton?
May is the wettest month in Thornton, with 2.4 in. January is the driest, with 0.5 in.
How many rainy days does Thornton have a year?
Thornton has about 73 days with measurable rain in an average year. May has the most, about 10.
Does it snow in Thornton?
Yes. Thornton gets about 44.8 in of snow in an average season. The snowiest winter on record is 1972–73, with 95.1 in.
What is the hottest month in Thornton?
July is the warmest month in Thornton, with an average high of 91°F.
What is the coldest month in Thornton?
January is the coldest month in Thornton, with an average low of 19°F.
What is the record high temperature in Thornton?
Within the available 1984–2026 station history, the record high at the Thornton station is 110°F, set on August 2, 2008. The record low is -24°F, on December 22, 1990.
What is the sunniest month in Thornton?
September is the sunniest month in Thornton, with estimated sunshine of 70% of daylight hours from ERA5 cloud cover. May is the cloudiest.
When is the first frost in Thornton?
The first fall freeze in Thornton typically comes around October 7. The last spring freeze is around May 4.
What is the best time to visit Thornton?
The most comfortable time to visit is typically April and October, when daytime highs sit near 66°F.