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Fire danger up in Calif., down in N.W.

 Posted: 12:45 PM July 28, 2009

GRANTS PASS — A new wildfire forecast based on climate models shows the risk of big fires eased for the Northwest in the past month, thanks to June rains, but increased a bit for California and the Southwest.

The map produced by researchers for the U.S. Forest Service and Oregon State University shows a high potential for fires larger than 10,000 acres in Oregon's Siskiyou Mountains, California's Trinity Alps and western Sierras, eastern Arizona and western Texas. The map shows a scattering of high potential areas in central and eastern New Mexico.

Nationwide, the forecast for July through September calls for 3.7 million acres burning in the lower 48 states, slightly above the 10-year average of 3.2 million acres. About half of that — 1.8 million acres — has burned already, according to the National Interagency Fire Center.

The forecasts showed nearly all of the potential for moderate to big fires west of the Rockies, where a ridge of high pressure has bottled up hot and dry weather lately.

Forest Service bioclimatologist Ron Neilson said the extremely hot and dry weather in the last half of July for much of the West will not show up in the forecast until next month.

"If this kind of weather continues, my guess is next month we will come back to high (potential for big) fires again," Nielson said from Corvallis.

The driver behind the current state of wildfire danger is warming sea surface temperatures in the Pacific Ocean, connected to the El Nino and Pacific Decadal Oscillation climate cycles, he said. El Nino has just begun to build, and the Pacific Decadal Oscillation has tentatively switched to a positive mode. Both conditions can be expected to warm the Pacific.

The models lay weather expectations over the vegetation on the landscape, from grass to forests, and come up with a potential for fires. They cannot predict actual fires, because that requires an ignition source, whether lightning or a person with a match.

For example, the models predicted the 2002 Biscuit fire in southwestern Oregon — the nation's biggest that year — a year early, when there was no lighting, Neilson said. Conditions had not changed by 2002, when a large lightning storm struck, starting multiple fires that merged to burn through 500,000 acres before they were out.

Neilson said he was worried about the future, if hot and dry weather continues, because drought models show a much larger area that is moderately to extremely dry — nearly all of California, the Oregon Coast Range, western and north-central Washington, and south-central Texas.


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