Planners behind a September 2009 prescribed burn on the west end of Bethel Ridge, west of Yakima, could not have predicted the changing weather that ended up covering much of the Yakima Valley in a smoky haze, according to an analysis of the event.

A case study released by the Pacific Northwest Research Station in Seattle basically vindicated the Okanogan and Wenatchee National Forest officials who planned and oversaw the controlled fire, which had been dubbed the “Kaboom” fire.

An unexpected inversion and breezeless conditions left smoke from the 6,100-acre fire covering an area from Rimrock to Toppenish. Three weeks after the burn, the Yakima Regional Clean Air Agency fined the Naches Ranger District $12,000; the fine was later rescinded.

In one sense, Kaboom paid off three years later when the burned area became a virtual fire break for the volatile Wild Rose Fire to the east, enabling crews to focus their firefighting efforts elsewhere.

That cut suppression costs for the Wild Rose Fire to less than $9 million, a fraction of what it might otherwise have been.

The analysis by research meteorologists at the Pacific Wildlife Fire Sciences Laboratory and the National Oceanic and Atmospheric Administration, said meteorological models wouldn’t have anticipated the smoky aftermath — certainly not in the areas where it ended up.

The state Department of Natural Resources approved the burn in light of anticipated light winds expected to blow the smoke to the northeast and an approaching cold front ensuring that the smoke would rise and dissipate well before it reached Ellensburg.

Instead, the smoke plume veered east, at elevations low enough to impact air quality and generate numerous complaints to law enforcement, municipal and state agencies in Yakima.

According to the analysis, the smoke intrusion “could not have been easily predicted using the forecasts and models available on the day of the burn, nor could it have been foreseen from enhanced, higher-resolution meteorological models that were not widely available at the time.”

The Kaboom project is still believed to be the largest single-day controlled burn in state history accomplished during the height of fire season, when fire behavior would most closely replicate that of naturally caused fires that were once prevalent across the western landscape.

Naches Ranger District fire-fuels officials had hoped to do a similar large prescribed burn near the Rattlesnake Creek drainage earlier this year, but fire crews were diverted to active uncontrolled wildland fires elsewhere in the state.