BOISE, Idaho (AP) -- Wildfire experts have come across a seeming contradiction this summer: While the number of acres charred across the West is almost double the 10-year average, the blazes haven't been as big or devastating as those in past years.
Experts say that's due to the unusual moisture patterns in the region earlier this year, which favored big grass fires on the open range. Timber in the mountains got more moisture than usual well into the summer, keeping forest fires small.
And fate has played a role.
''It's sort of like Swiss cheese. All the holes have not lined up at the same time,'' said Tom Wordell, a wildland fire analyst for the U.S. Forest Service and leader of the multiagency group of scientists and meteorologists that predicts fire danger around the nation.
''To get a big fire, you need high temperatures, low relative humidity, dry fuels and winds all aligned on the same day,'' said Wordell. ''We haven't seen that much this year, yet our overall acreage burned is much higher than in the past.''
According to the National Interagency Fire Center, over 7.8 million acres -- more than 11,000 square miles -- have burned in the U.S. since May. About half of that was in Alaska, where large fires often are not fought aggressively if they pose no threat to people or structures.
With the 2005 wildfire season two-thirds over, the number of fires is down -- about 46,000 compared to the 10-year average of 63,000 -- and the number of firefighters suppressing the blazes has been lower than in recent years. Yet the total acreage burned is nearly double the 4 million acres that burned on average through late August over the past decade.
Analysts say the primary reason for the higher-than-average fire acreage this year is huge range fires that burned in the Southwest and Great Basin, where a wet winter allowed fine grasses and vegetation to flourish. Those ''flashy'' fuels then dried and cured early in the dry spring, inviting the spread of range fires as summer approached.
''Earlier this season, when we knew we had large fine-fuel loading, one of the sage old firefighters said to me, 'Man, the fires are going to be in the deserts this year and not the mountains.' And that's been the case,'' said Brad Smith, a Texas Forest Service fire behavior analyst.
Many of the range fires have been epic in size and speed. A blaze in late July in southwestern Idaho at one point was burning 500 acres an hour. It eventually blackened an area 35 miles wide and 10 miles across.
Despite their size, though, the range fires have frequently burned in areas far from civilization and have caused relatively little structural damage.
''I'm always cautious to downplay range fires because if it's your ranch building or grazing allotment that got burned up it's pretty important,'' said Wordell, head of the National Predictive Services Group at the Interagency Fire Center.
''But timber fires require a lot more people, equipment, time and money to put out, and so far even when we've had lightning ignition, we didn't get the large fire initiation.''
The primary reason for this year's lack of huge timber fires -- the 100,000-plus-acre blazes that make national headlines _ is the moisture retained by trees and foliage in the higher elevations of the Cascades, the Sierra Nevada and the Northern Rockies, captured during an unusually long, wet spring.
''We're just not seeing significant spread through the alpine zones'' because of the moist fuels, said Jack Cohen, a research physical scientist for the U.S. Forest Service's fire sciences laboratory in Missoula, Mont. ''The fire is abating as it burns in these areas.''
Between the moist timber in the high mountains and the fine dry grasses on the desert range lies the greatest potential for catastrophic blazes in the remainder of this season, fire analysts say.
Mid-elevation woodlands with a heavy buildup of dry, dead material on the forest floor mixed with open areas that have heavy grass and shrubs are yielding higher than average ''energy release components'' -- a measure of the available energy that would be released in the flaming front of a fire.
''In the area that runs from Northern California through central and eastern Oregon on into central Idaho, we are seeing energy release components that are setting records,'' said Wordell.
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