Thornton, Colorado Weather
Thunder retreats as the monsoon dies. Day 93 of summer. Read this microseason across nine climate regions →
Thornton weather forecast — hour by hour, 7-day outlook, NOAA radar
Conditions updated 1:00 AM MDT · Open-Meteo
- TodaySep 21Overcast later——74°52°—
- TuesdaySep 22Overcast37%0.10″83°51°+9°
- WednesdaySep 23Overcast37%—75°65°-8°
- ThursdaySep 24Light Drizzle17%—78°63°+3°
- FridaySep 25Light Drizzle17%—81°63°+3°
- SaturdaySep 26Overcast13%—84°64°+3°
- SundaySep 27Overcast17%—86°64°+2°
Air quality now AQI 51 · Moderate
AQI 51 (Moderate), driven by PM2.5. AQI flat over the last 6 hours (within ±3 points). PM2.5 at 13.1 µg/m³ (AQI 58) with a 0.97 fine-to-coarse ratio and 4 mph wind — combustion smoke trapped in stagnant air, not road dust.
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
PM × Wind × Precip
PM2.5 at 13.1 µg/m³ (AQI 58) with a 0.97 fine-to-coarse ratio and 4 mph wind — combustion smoke trapped in stagnant air, not road dust.
- PM2.5/PM10
- 0.97
- Wind
- calm
- Recent rain
- 0h in last 6h
- Pattern
- stagnant smoke
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
September dries up ditches or breaks down bridges.
- Moonrise
- 4:34 PM
- Moonset
- 1:23 AM
- In sign
- ♑︎ Capricorn
Thunder retreats as the monsoon dies
Read this microseason across nine climate regions →
All 72 microseasons on the year wheel →
Thornton at a glance
- Today vs. normal: Today averages 63°F (high 74°F, low 52°F), about the 63°F normal for Sep 21
- Last frost: May 2 (1991–2020 median, NOAA station 6 km away)
- Microseason: Sep 21–25
- Planting calendar: September — plant garlic (overwinter); harvest tomatoes, peppers, beans, summer squash, winter squash
15-Day Forecast — Thornton
- Mon74°52°7%
- Tue83°51°37%
- Wed75°65°37%
- Thu78°63°17%
- Fri81°63°17%
- Sat84°64°13%
- Sun86°64°17%
- Mon84°67°25%
- Tue83°64°25%
- Wed87°65°15%
- Thu89°73°15%
- Fri75°69°13%
- Sat87°66°16%
- Sun81°64°19%
- Mon80°55°13%
Forecast data from Open-Meteo (CC BY 4.0).
Live wind & temperature near Thornton
Interactive wind and temperature map centered on Thornton — it loads in your browser. Open the full weather map.
Right now in the garden
Fall planting + final harvests
As of September 21, the season's first frost (typically October 11) is approaching. Pick what frost-tender plants still carry before the next cold front. This city's planting calendar for September: plant garlic (overwinter); harvest tomatoes, peppers, beans, summer squash, and winter squash.
SPC Convective Outlook
Storm Prediction Center — Thornton
SPC includes Thornton in the general thunderstorm area tomorrow — no severe risk, but storms are possible.
- TODAYNONENo severe risk
- TOMORROWTSTMGeneral Thunderstorms
- DAY 3TSTMGeneral Thunderstorms
Thunderstorms possible. Not severe, but capable of producing lightning and brief heavy rain.
Source: NOAA / NWS Storm Prediction Center categorical convective outlook.
Sun & seasons in Thornton
Thornton sits in Adams County, where the year’s longest day runs 15h 0m of daylight and its shortest just 9h 20m — a swing of +5h 40m between the June and December solstices. Clocks spring forward on Sunday, March 8, 2026 and fall back on Sunday, November 1, 2026.
Denver, the state’s largest city, lies about 11 miles to the SSE. The nearest town Thornton tracks is Denver, roughly 11 miles to the SSE.
Air quality in Thornton
Air quality in Thornton’s county has trended dirtier since 2020; its cleanest year on record was 2020 (median AQI 49). See the full air-quality history for Thornton.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| April | lettuce, peas, spinach, radishes | — |
| May | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, spinach, radishes |
| June | tomatoes, peppers, beans, squash | lettuce, peas, spinach, radishes |
| July | tomatoes, peppers, beans, squash, fall brassicas, carrots | lettuce, peas, spinach, beans, summer squash, garlic |
| August | — | tomatoes, peppers, beans, summer squash, garlic |
| September | garlic (overwinter) | tomatoes, peppers, beans, summer squash, winter squash |
| October | — | tomatoes, peppers, beans, summer squash, winter squash, fall brassicas, carrots |
| November | — | fall brassicas, carrots |
A year in weather
The year in Thornton tops out in July (~75°F) and dips lowest in December (~33°F), with May wettest at 2.4 inches and January driest at 0.5 inches.
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 34° | 0.5″ | 4 |
| February | 35° | 0.5″ | 5 |
| March | 43° | 1.2″ | 6 |
| April | 50° | 1.9″ | 8 |
| May | 58° | 2.4″ | 10 |
| June | 69° | 1.5″ | 7 |
| July | 75° | 1.7″ | 7 |
| August | 73° | 1.3″ | 8 |
| September | 65° | 1.2″ | 6 |
| October | 52° | 1.1″ | 5 |
| November | 41° | 0.7″ | 5 |
| December | 33° | 0.5″ | 4 |
Regional context
Similar climates Northglenn, CO, Federal Heights, CO, Todd Creek, CO
Per NOAA NCEI 1991-2020 normals, Thornton runs from a 34°F January mean to 75°F in July, a 42°F seasonal spread, with near 14.5 inches of precipitation across about 73 wet days.
Thornton's rain peaks in summer: May brings 2.4 inches over 10.0 thunderstorm-fed days, while January sees just 0.5 inches across 3.9 days under cooler, drier air. That summer-storm rhythm groups Thornton with places like Northglenn, CO, Federal Heights, CO and Todd Creek, CO.
Thornton reaches its last hard frost near May 2; that is the cue for peas, lettuce, spinach, and radishes. Tomatoes and peppers do best set out two weeks later in Thornton, once nights clear the mid-40s°F. Frost returns to Thornton near October 11, ending the tender-crop season. That date is a median: Thornton freezes sooner in half of years.
Similar climates: Northglenn, CO, Federal Heights, CO, Todd Creek, CO, Welby, CO, Derby, CO.
Frequently asked
- When does it freeze in Thornton?
- Frost typically leaves Thornton by May 2 and returns to Thornton near October 11.
- What is the rainy season in Thornton?
- May is the wettest month in Thornton, about 2.4 inches on average; the year totals roughly 15 inches.
- What is the warmest month in Thornton?
- July is Thornton's warmest month, averaging about 75°F.
- What is the coldest month in Thornton?
- Thornton bottoms out in December, with a mean near 33°F.
- When can I start a vegetable garden in Thornton?
- Thornton's last frost (May 2) cues hardy greens; in Thornton, hold heat-lovers two weeks past.
- How many rainy days does Thornton get?
- Thornton records around 73 days of measurable precipitation annually.
- What hardiness zone is Thornton?
- Thornton's hardiness zone tracks its winter low; with December near 33°F, check the USDA ZIP map for the exact zone.
- What is the 10-day forecast for Thornton?
- Thornton's extended outlook — daily high and low temperatures and precipitation chances for each upcoming day — is in the daily forecast above.
- Will it rain this week in Thornton?
- See this week's day-by-day rain chances for Thornton in the daily forecast above, and the next 24 hours in the hourly chart.
- What is the weather like right now in Thornton?
- Current conditions for Thornton and the next 24 hours — temperature, precipitation chance, and wind by the hour — are in the hourly forecast chart above.
- How often is the Thornton forecast updated?
- The Thornton forecast on this page is built from Open-Meteo weather-model data and refreshes regularly through the day.
- When are sunrise and sunset in Thornton?
- Today's sunrise and sunset times for Thornton are in the Almanac section above, along with civil dawn, civil dusk, and day length. Day length is longest near the summer solstice and shortest near the winter solstice.
- How accurate is the weather forecast for Thornton?
- The next few days in Thornton's forecast are the most reliable; accuracy declines beyond about a week as weather-model uncertainty grows.
Thornton sits at 39.9°N; its climate zone is hot desert (Köppen approximation).
ZIP codes in Thornton
- 80023
- 80229
- 80233
- 80241
- 80260
- 80602
- 80614
- 80640