Today | Weather | Saturday, September 19, 2026

Weather in Longmont, Colorado

02:47 AM
Now
Cloudy Night
55° F
Feels Like 55°
Precipitation 13 %
Wind 5 mph
Humidity 90 %
Today
Sunny with a Chance of Thunderstorms
Day 79°
Night 52°
Precipitation 65 %
Wind 7 mph
UV Index (0 - 11+) 5

Longmont Weather Forecast Updated

14 minutes ago
Last updated on
Weather Forecast History
Last Year's Weather on This Day (September 19, 2025)
Cloudy Night

Day

81°

Night

50°

Wind

5 mph

Precipitation

4 %

Air Quality in Longmont

NOW
13 AQI
Good air quality Dominant pollutant: O3

Pollutant Concentrations:

PM2.5 0.61 µg/m³
PM10 0.65 µg/m³
O3 0.014 ppm
NO2 1.6 ppb
SO2 0 ppb
CO 0.10 ppm
NH3 0.94 µg/m³
NO 0 µg/m³
PM2.5 – 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)
PM2.50.61 µg/m³
PM100.65 µg/m³
O326.82 µg/m³
NO23.08 µg/m³
SO20.01 µg/m³
CO110.81 µg/m³
NH30.94 µg/m³
NO0 µg/m³