Our forecast is hot and dry | AspenTimes.com

Our forecast is hot and dry

Jeremy Heiman

What appears to be a never-ending dry and hot summer in the Rocky Mountains – and all of Colorado, for that matter – doesn’t look like it will end anytime soon.

The weather that has been predominant recently is caused by a massive dome of high pressure parked over Nevada and Utah, directing moisture away from the Central Rockies, say weather experts. The same high pressure dome has trapped the smoke from 50 or more wildfires burning in the West, resulting in poor visibility and spectacular sunsets.

Chris Cuoco, senior forecaster for the National Weather Service in Grand Junction, said the high pressure centered over the Great Basin will probably stick around for awhile. Why the stalled weather pattern moved in and set up housekeeping, however, is more of a mystery. “It happens in some years,” Cuoco said.

Often in July, monsoon conditions set in, bringing moisture to the Rockies from the south. But the Great Basin high prevents much of the moisture from reaching Colorado.

The flow around the high pressure area is clockwise, he said, driving southern moisture toward the West Coast. Storms from the Pacific Northwest, meanwhile, are deflected into the Upper Midwest by the circular flow.

“This high isn’t going to go anywhere any time soon,” Cuoco said. He said perhaps next week a front from the north would push down the Front Range and bring some cool air and precipitation into the Central Rockies, with the Aspen area catching the tail end of it.

“This may persist even into September,” Cuoco said.

Precipitation in Western Colorado is about a half-inch behind the average for July, Cuoco said. Figures for July are not available yet, but it’s nowhere near the record low moisture of July 1958, when .14 of an inch of rain fell.

“We’re not really classifying this as a drought,” Cuoco said. “We’re not really that far below normal for the year.”

The smoke from the wildfires, Cuoco said, is trapped with stagnant air beneath the dome of high pressure. Especially large fires, such as a 40,000-acre blaze in Idaho and an 80,000-acre fire in Montana, contribute to the haze here in Colorado.

“Until we get a good cold front to blow this out, we’ll have beautiful sunsets,” he said. The smoke isn’t dense enough to present any health danger in rural areas, he said, but it might team with local pollution in larger cities to trigger pollution alerts.

Visibility is seriously affected, though. Normally, visibility in Western Colorado may be as much as 80 or 90 miles from a high vantage point. The current haze has reduced visibility to between 10 and 20 miles, and less than 10 in some areas.

Aspen’s visibility metering system was reporting greater than 10 miles yesterday, he said.

The recent gorgeous sunsets are created when the sun, as it approaches the horizon, passes through a much more smoky atmosphere than when it’s high in the sky. Smoke particles refract and filter the sun’s light, so that we see more of the red and orange light than the other colors in the sunlight.

The high-country snowpack has diminished far beyond the usual summer levels, said Mike Gillespie, snow survey supervisor for U.S. Natural Resources Conservation Service.

The June 1 snowpack was 13 percent of average. All the agency’s automatic snow-measuring sites melted out three to four weeks earlier than average, Gillespie said.

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