Hourly Weather Forecast for Longmont, Colorado

Hourly Weather | Today › Wednesday, March 18, 2026

Active Weather Warnings

Red Flag Warning

Longmont, Colorado

11 AM

73°

Feels Like 77°

Humidity: 16%

UV Index: 4

Wind: 8 mph

12 PM

75°

Feels Like 79°

Humidity: 14%

UV Index: 5

Wind: 9 mph

1 PM

79°

Feels Like 81°

Humidity: 12%

UV Index: 5

Wind: 10 mph

2 PM

81°

Feels Like 81°

Humidity: 11%

UV Index: 5

Wind: 12 mph

3 PM

81°

Feels Like 82°

Humidity: 11%

UV Index: 4

Wind: 13 mph

4 PM

82°

Feels Like 82°

Humidity: 10%

UV Index: 3

Wind: 13 mph

5 PM

81°

Feels Like 79°

Humidity: 11%

UV Index: 2

Wind: 12 mph

6 PM

77°

Feels Like 73°

Humidity: 13%

UV Index: 1

Wind: 12 mph

7 PM

73°

Feels Like 70°

Humidity: 15%

UV Index: 0

Wind: 10 mph

8 PM

70°

Feels Like 66°

Humidity: 18%

UV Index: 0

Wind: 10 mph

9 PM

64°

Feels Like 63°

Humidity: 21%

UV Index: 0

Wind: 9 mph

10 PM

63°

Feels Like 59°

Humidity: 24%

UV Index: 0

Wind: 9 mph

11 PM

61°

Feels Like 55°

Humidity: 26%

UV Index: 0

Wind: 8 mph

Hourly Air Quality Forecast - AQI (US EPA)

11 AM

33 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.74 µg/m³
PM₁₀: 1.16 µg/m³
O₃: 0.036 ppm
NO₂: 0.4 ppb
SO₂: 0.1 ppb
CO: 0.08 ppm

Health Recommendations:

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

12 PM

34 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.83 µg/m³
PM₁₀: 1.21 µg/m³
O₃: 0.037 ppm
NO₂: 0.3 ppb
SO₂: 0.1 ppb
CO: 0.08 ppm

Health Recommendations:

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

1 PM

37 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.75 µg/m³
PM₁₀: 1.04 µg/m³
O₃: 0.040 ppm
NO₂: 0.2 ppb
SO₂: 0.1 ppb
CO: 0.07 ppm

Health Recommendations:

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

2 PM

38 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.73 µg/m³
PM₁₀: 1 µg/m³
O₃: 0.041 ppm
NO₂: 0.1 ppb
SO₂: 0.1 ppb
CO: 0.07 ppm

Health Recommendations:

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

3 PM

38 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.76 µg/m³
PM₁₀: 1.02 µg/m³
O₃: 0.041 ppm
NO₂: 0.1 ppb
SO₂: 0.1 ppb
CO: 0.07 ppm

Health Recommendations:

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

4 PM

38 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.73 µg/m³
PM₁₀: 0.97 µg/m³
O₃: 0.041 ppm
NO₂: 0.1 ppb
SO₂: 0 ppb
CO: 0.07 ppm

Health Recommendations:

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

5 PM

38 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.74 µg/m³
PM₁₀: 0.99 µg/m³
O₃: 0.041 ppm
NO₂: 0.1 ppb
SO₂: 0 ppb
CO: 0.07 ppm

Health Recommendations:

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

6 PM

38 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.75 µg/m³
PM₁₀: 1 µg/m³
O₃: 0.041 ppm
NO₂: 0.2 ppb
SO₂: 0 ppb
CO: 0.07 ppm

Health Recommendations:

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

7 PM

35 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.79 µg/m³
PM₁₀: 1.03 µg/m³
O₃: 0.038 ppm
NO₂: 0.6 ppb
SO₂: 0 ppb
CO: 0.08 ppm

Health Recommendations:

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

8 PM

32 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.88 µg/m³
PM₁₀: 1.11 µg/m³
O₃: 0.034 ppm
NO₂: 1.3 ppb
SO₂: 0 ppb
CO: 0.08 ppm

Health Recommendations:

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

9 PM

29 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.95 µg/m³
PM₁₀: 1.19 µg/m³
O₃: 0.031 ppm
NO₂: 1.7 ppb
SO₂: 0 ppb
CO: 0.09 ppm

Health Recommendations:

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

10 PM

26 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 0.98 µg/m³
PM₁₀: 1.22 µg/m³
O₃: 0.028 ppm
NO₂: 1.8 ppb
SO₂: 0 ppb
CO: 0.09 ppm

Health Recommendations:

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

11 PM

24 AQI

Good air quality Dominant pollutant: O₃

Details

Pollutant Concentrations:

PM_2.5: 1 µg/m³
PM₁₀: 1.25 µg/m³
O₃: 0.026 ppm
NO₂: 1.9 ppb
SO₂: 0 ppb
CO: 0.09 ppm

Health Recommendations:

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

Current Real-Time Air Quality Report

Weather Alerts and Warnings for Longmont

Severe Expected Likely

Red Flag Warning

Red Flag Warning issued March 18 at 3:36AM MDT until March 18 at 7:00PM MDT by NWS Denver CO

Mar 18, 11:00 AM → Mar 18, 7:00 PM

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

* TIMING...From 11 AM this morning to 7 PM MDT this evening.

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

* RELATIVE HUMIDITY...As low as 8 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, 10:19 AM Source: NWS Alert

Hourly Air Quality Forecast - AQI (US EPA)

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Weather Alerts and Warnings for Longmont

Red Flag Warning

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