08/20/2015 Idaho DEQ Smoke Forecast

Updated Noon MDT Thursday, August 20, 2015

Valid through: Noon MDT Friday, August 21, 2015

Smoke Outlook

Air quality is currently ranging from Moderate to Unhealthy across all of Idaho with higher impacts across the Clearwater Basin Drainage, the Treasure Valley, and the Salmon-Challis area.  Air quality is forecast to remain in the Moderate to Unhealthy category for the 24hr standard across central Idaho and Unhealthy for Sensitive Groups across the Treasure Valley.  Impacts are from regional fires burning in Washington State, California, Oregon, and a multitude of local fires in the Clearwater drainage, Central Idaho Mountains, and the Owyhees.

Nez Perce Reservation:  24-hour monitor readings range from Moderate to Unhealthy.  Hourly readings are fluctuating from Moderate to Hazardous, depending on location and wind direction.  The Nez Perce Tribe will continue their Air Quality Advisory.  Please contact the Nez Perce Tribe for more information: airquality@nezperce.org.

The zonal flow pattern over Idaho will provide a consistent northwesterly wind direction both at the surface and aloft as it gives way to an approaching upper level low pressure trough and associated cold front will serve to generate breezy winds with gusty conditions at the surface.  Surface winds will be from the northwest-west across Idaho with south-southwest winds within the Purcell Trench into Boundary County and southwest-west across the Rathdrum Prairie.  Southern Idaho will see northwest winds within the Treasure Valley and west-southwest winds elsewhere.  Surface wind speeds will range from 10-15 mph across all of Idaho with gusts to 30 mph across northern Idaho, particularly along the WA/ID border.  This wind speed will help move smoke out of the area, but also serve to invigorate active fires, potentially leading to increased smoke production.  Mixing heights are expected to be range from 4,000-8,000 ft AGL this afternoon.  On Friday, this cold front will move through Idaho, maintain breezy conditions with gusts up to 40 mph across the southeastern portion of Idaho.  There is high uncertainty as to how the increased winds will impact smoke production and transport.

The strongest smoke impacts are occurring across the Clearwater drainages, Central Idaho Mountains as well as the Treasure Valley and Magic Valley of southern Idaho.  This will continue into the afternoon and especially this evening.  Expect to experience impacts from the Canada border south to the Idaho/Nevada and Idaho/Utah border.  The highest impacts are expected to be within the drainages of the Clearwater, Salmon, Lochsa, down into the Lewiston-Clarkston Valley.  In southern Idaho, impacts will be greatest within the Upper Treasure Valley, north to McCall and Garden Valley and east along the Arco Desert within the Snake River Plain and through the drainages into the Salmon and Challis regions.  Expect impacts within the Weiser, Payette, Brownlee, and Boise drainages this afternoon and evening.  Nocturnal drainage flow will contribute to greater impacts in all of Idaho tonight, especially within the drainages into the Snake River Plain off the Central Idaho Mountains.  Expect widespread smoke coverage across all of Idaho today at both the surface and aloft.  This pattern is likely to persist into Friday given the extreme fire behavior and weather pattern.

DEQ Air Quality Advisories:

Idaho DEQ has issued a state-wide Stage 1 Forecast and Caution for all counties.  This will be re-evaluated tomorrow at 2pm MDT.

Smoke forecasts are dependent on predicted fire growth and weather.  If conditions change unexpectedly, impacts could occur.  When visibility starts to go below 5 miles, sensitive groups should minimize outdoor activities.  Everyone else should minimize prolonged or physical activity outdoors.  Visit the Idaho Smoke Blog for more information at http://idsmoke.blogspot.com/

Your eyes are your best tools to determine if it’s safe to be outside.  Even if you smell smoke, the air quality may still be good. 

AQI Category	Visibility (miles)
Good	11+
Moderate	6-10
Unhealthy for Sensitive Groups	3-5
Unhealthy	1½  -2¾
Very Unhealthy	1-1¼
Hazardous	Less than 1

How to estimate air quality based on visibility for areas without an air quality monitor or airport visibility estimate:

a. Face away from the sun.

b. Determine the limit of your visible range by looking for targets at known distances (miles).

c. Visible range is when an object you can easily see in the distance disappears.

d. Use the visibility values above to determine the local wildfire smoke category.