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Winter Air Quality Update & Forecast
Friday, January 11, 2019 8:34 AM

Locations and Air Quality Conditions


Current Situation Forecast
Air quality on Friday morning was MODERATE in many western valleys. Winds were generally light and from the west across the region with weak inversions in place in many valleys. These inversions have led to valley fog in many locations. Air quality on Friday is expected to improve in most locations for a brief time in the afternoon, likely reaching GOOD levels. Conditions are expected to change starting Friday night into Saturday. See the Forecast section for more information.

Check Today’s Air for current conditions.
A strong ridge of high pressure is expected to build over Montana starting Friday night. This will bring very light winds both at the surface and aloft. The light winds, combined with clear skies, will promote the formation of strong overnight inversions across western Montana. Beginning Saturday morning, we will likely see widespread MODERATE air quality in the valleys. Some areas may see hourly levels reach UNHEALTHY FOR SENSITIVE GROUPS.

Many valleys will struggle to lift out from under these inversions, due to poor vertical air movement associated with the stable air mass. This will be most prevalent in northwest Montana, although Missoula, Helena, and Butte may also struggle. This will lead to worsening air quality as the weekend progresses and we move into next week. We may see widespread UNHEALTHY FOR SENSITIVE GROUPS air quality in the valleys by Sunday or Monday morning, with hourly readings possibly reaching UNHEALTHY levels. In the larger valleys of southwest Montana, such as Dillon and Bozeman, air quality should reach GOOD levels briefly each afternoon as the inversions lift.

Right now, it looks like we may see some relief beginning Tuesday or Wednesday when more active weather tries to move in. However, history tells us that these types of weather patterns can be stubborn to break. Another update will be posted Monday with any changes.


Check Today’s Air for current conditions.

Air Quality Bureau
Montana Department of Environmental Quality
Phone: (406) 444-3490
Email: DEQMTSmoke@mt.gov




Fog over the Helena Valley this morning, where air quality is currently moderate. 

Fog over the Helena Valley this morning, where air quality is currently moderate.
Source: USFS.

 
Little to no wind is expected in western valleys this weekend due to a stable air mass.

Little to no wind is expected in western valleys this weekend due to a stable air mass.
Source: Weather Underground.

Poor dispersion is expected throughout the weekend.

Poor dispersion is expected throughout the weekend.

Source: University of Washington. 




Real time particulate information is currently available in most of the larger urban areas from MTDEQ's Today's Air website.

Today's particulate report below compares particulate levels received from DEQ's
reporting stations with MTDEQ’s Health Effect Categories.

Locations and severity of PM 2.5 particulate values over the past 24 hours from the time above.
Health Effects Categories City
  Hazardous  
  Very Unhealthy  
  Unhealthy  
  Unhealthy for Sensitive Groups  
  Moderate

 Frenchtown
Helena
Libby
Missoula
 

  Good

 All other reporting locations. 

B1(x) One-hour BAM value (number of values)
B8(x) Eight-hour average BAM
B24 24 hour  average BAM value