Definition

The Clearing Index is an Air Quality/Smoke Dispersion index that combines the affects of the Mixing Height (the maximum height above ground level that smoke will mix to during a designated period) and the Transport Winds (average wind within the Mixing Height). The computation of CI is as follows:

CI = (Mixing Height/100) X Transport Wind

As an example:

Mixing Height = 8000 feet above ground level (AGL)
Transport Winds = 10 knots
CI = (8000/100) X 10 = 800

Therefore, a higher Clearing Index indicates better smoke dispersion.

Purpose

The Clearing Index is currently an experimental graphical forecast product produced by the Missoula Office.This product will be tested by our office and fire weather users this year.

The implementation of this product in western Montana and north central Idaho is an effort to provide burners a more consistent method of using Mixing Height and Transport Wind information in their decision making. The National Oceanographic and Atmospheric Administration's National Weather Service office in Missoula will provide maximum daytime CI forecasts out to three days for this area. The CI will not be provided at night as it will generally be quite low.

Specific Mixing Height and Transport Winds may still be obtained via spot forecasts.

Qualitative Adjectives

A group representing the various land management agencies, the Montana/Idaho Airshed Group, and the Northern Rockies Predictive Service Unit has assigned qualitative smoke dispersion adjectives to CI thresholds as follows:

0 - 400	=	Poor
400 - 650	=	Moderate
650 - 900	=	Good
> 900	=	Excellent

Transport winds (average wind speed and direction through the mixing height) have also been added to the clearing index graphic. Transport wind speed is factored into the clearing index but direction of smoke movement may also be helpful An explanation of how to read wind barbs can be found at:

http://weather.gov/forecasts/graphical/definitions/defineWindSpd.html