Climate: Southwest tree rings show historic monsoon droughts

Posted on March 12, 2013 by Bob Berwyn
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Ancient Douglas firs are helping researchers track historic patterns of drought. Bob Berwyn photo.

New technique focuses on late-summer tree ring growth to pinpoint seasonal climate patterns

By Summit Voice

SUMMIT COUNTY — A detailed new study of tree rings in the Southwest shows that  patterns of alternating wet and dry seasons observed since the 1950s is not the norm. Rather, the analysis suggests that, during historic decadal droughts, both winter and summer precipitation was below the long-term average.

The new 470-year-long history (1539 to 2008) of summer precipitation in the Southwest covers most of Arizona, western New Mexico and parts of northern Mexico. It was established by looking at rings from Douglas firs and ponderosa pines, including tree-ring samples stored in the archives of the University of Arizona Laboratory of Tree-Ring Research. (more…)

Filed under: climate and weather, Drought | Tagged: , , , | Leave a Comment »

Climate: New clues for ancient Great Basin lakes

Posted on September 30, 2012 by Bob Berwyn

Nevada’s Walker Lake is a remnant of one of the great inland lakes that covered parts of the Great Basin during the last glacial cooling period. Image courtesy NASA Earth Observatory.

Glacial climate regime may have enhanced Southwest Monsoon

By Summit Voice

SUMMIT COUNTY — Geologists and paleoclimatologists have long known that the great basins of the intermountain West were once filled with water, forming vast inland seas. At the peak of the last glacial cooling period, about 14,000 to 20,000 years ago as much as a quarter of Nevada and Utah were covered with water.

What’s not exactly clear is where and when the water came from, but a new study led by a Texas A&M researcher offers additional clues, suggesting that the additional moisture came from a powerful, enhanced summer monsoon.

First, the scientists set out to test the prevailing hypothesis that the water resulted from a shift in the winter storm track that now generally carries storm to the north of the Great Basin, into northern California, Washington and Oregon. (more…)

Filed under: climate and weather, Drought, global warming | Tagged: , , , , , , | Leave a Comment »

Weather: Almost tropical …

Posted on July 15, 2012 by Bob Berwyn

Colorado monsoon season right on schedule

Early morning dew in the grass near Straight Creek shows there’s moisture available to fuel afternoon thunderstorms.

A steady monsoon flow streaming northward should keep much of western Colorado moist the next few days.

By Summit Voice

SUMMIT COUNTY —Hopes are high that another surge of tropical moisture streaming north from Old Mexico will soak at least parts of the Western Slope and the high country with rain the next few days.

National Weather Service forecasters in Grand Junction described conditions in western Colorado as almost tropical, with dew points in the mid-40s and 50s, which means there’s plenty of moisture available for condensation and formation of rain clouds. (more…)

Filed under: climate and weather, Colorado, seasons, Summit County snow and weather | Tagged: , , , , | Leave a Comment »

Summit County weatherblog: Ready for the monsoon?

Posted on July 5, 2011 by Bob Berwyn

Wilderness Sports sponsors the Summit Voice weatherblog. Click to visit Wilderness Sports online.

Summer rains could be boosted by evaporating snow

A National Weather Service graphic shows what a typical post-La Niña monsoon could look like.

By Bob Berwyn

SUMMIT COUNTY — You might want to get your outdoor yah-yahs out of the way early the next few days, as the National Weather Service is predicting an early onset of the monsoon season, with a good chance for afternoon thunderstorms through the rest of the week. Wednesday could be the wettest day, as a plume of subtropical moisture takes direct aim at the high country, but scattered daily rain can be expected right on through next weekend.

Specifically, the National Weather Service says there is a 40 to 50 percent chance of rain through Friday, with highs in the low 70s each day and overnight lows in the mid-40s, fairly close to seasonal averages. The record high for July 5 is 84 degrees, set in 2001. The record low, a chilly 24 degrees, set way back in 1931. Frisco’s all-time record high for July is 89 degrees, a reading that hasn’t been reached since 1939.

The U.S. southwestern monsoon season occurs when winter and spring’s jet stream-driven westerlies retreat to the north. Instead of being dominated by incoming cyclonic storms off the Pacific, the weather in the Southwest and the Rockies is influenced by the clockwise rotation of air around a big area of high pressure parked in the center of the country, often over Texas. The rotation draws moist air northward from the Gulf of Mexico, the Gulf of California and the eastern Pacific. (more…)

Filed under: climate and weather, Colorado, Environment, La Niña, seasons, Snow and weather, Summit County Colorado, Summit County snow and weather | Tagged: , , , , , , , , , , , , , , | Leave a Comment »

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