Today | Weather | Wednesday, March 18, 2026

Active Weather Warnings

Red Flag Warning

Weather in Thornton, Colorado

04:10 PM

Now

82° F

Feels Like 81°

Precipitation 0 %

Wind 16 mph

UV Index (0 - 11+) 3

Humidity 10 %

Today

Day 82°

Night 46°

Precipitation 1 %

Wind 13 mph

UV Index (0 - 11+) 5

Thornton Weather Forecast Updated

33 minutes ago

Last updated on March 18, 2026 at 3:36 PM

Weather Forecast History

Last Year's Weather on This Day (March 18, 2025)

Day

63°

Night

30°

Wind

16 mph

UV Index

Precipitation

55 %

Air Quality in Thornton

NOW

39 AQI

Good air quality Dominant pollutant: O₃

Pollutant Concentrations:

PM_2.5 0.53 µg/m³

PM₁₀ 0.64 µg/m³

O₃ 0.042 ppm

NO₂ 0.1 ppb

SO₂ 0 ppb

CO 0.07 ppm

NH₃ 0.15 µg/m³

NO 0.05 µg/m³

PM_2.5 – Fine particles <2.5μm

PM₁₀ – Inhalable particles <10μm

O₃ – Ozone

NO₂ – Nitrogen dioxide

SO₂ – Sulfur dioxide

CO – Carbon monoxide

NH₃ – Ammonia

NO – Nitric oxide

Health Recommendations:

Air quality is considered satisfactory, and air pollution poses little or no risk.

Show raw pollutant concentrations (µg/m³)

PM_2.5 – 0.53 µg/m³

PM₁₀ – 0.64 µg/m³

O₃ – 81.66 µg/m³

NO₂ – 0.16 µg/m³

SO₂ – 0.09 µg/m³

CO – 79.27 µg/m³

NH₃ – 0.15 µg/m³

NO – 0.05 µg/m³

View Hourly Air Quality Forecast

Weather Alerts and Warnings for Thornton

Severe Expected Likely

Red Flag Warning

Red Flag Warning issued March 18 at 12:29PM MDT until March 18 at 7:00PM MDT by NWS Denver CO

Mar 18, 12:29 PM → Mar 18, 7:00 PM

* AFFECTED AREA...Fire Weather Zones 239, 240, 243, 244, 245,
248, 249, 250 and 251.

* TIMING...Until 7 PM MDT this evening.

* WINDS...Northwest 10 to 20 mph with gusts around 30 mph.

* RELATIVE HUMIDITY...As low as 9 percent.

IMPACTS: Conditions will be favorable for rapid fire spread.
Avoid outdoor burning and any activity that may produce a
spark and start a wildfire.

+ Read More

A Red Flag Warning means that critical fire weather conditions are either occurring now....or will shortly. A combination of strong winds...low relative humidity...and warm temperatures can contribute to extreme fire behavior.

Updated: Mar 18, 3:36 PM Source: NWS Alert