| 8/31/2006 9:04:00 AM | Email this article • Print this article | Monsoon may have been fueled by dry conditions
by Jason Starr
Mail Staff Writer
Heavy monsoon moisture in July and August may have been triggered in part by the dryness preceding it, scientists at the National Center for Atmospheric Research in Boulder believe.
Storms this summer caused localized washouts, Arkansas River beach erosion, hay crop deterioration and muddy river episodes dampening fishing conditions.
They also raised precipitation in Salida from 67 percent of average at the end of June to 125 percent of average by the end of August.
Atmospheric research hydrometeorologist David Gochis said extremely dry conditions last winter and into the spring - especially in New Mexico and Arizona - likely contributed to the strong turnaround.
"It is thought the dry ground preceding the monsoon added heat to the system which is key to building the monsoon pattern," Gochis said.
Dry conditions "helped enforce a ridge in the western United States and aided monsoon development."
A dry winter and spring does not directly cause a heavy summer rain season, but it sets the right conditions, Gochis said.
Dryness contributes to creation of a high pressure ridge over the western United States that opens the door to monsoonal moisture from the south.
"It's not a perfect correlation, but it's a favorable condition," he said.
The biggest turnaround occurred in New Mexico and Arizona where winter snowpack was dismal. Beginning in early July, the southwest began receiving consistent rain that persisted through August.
As a result, precipitation totals that were less than 25 percent of average during the winter have approached - and in some cases surpassed - 100 percent of average this month, National Resources Conservation Service information reports.
By contrast, the ridge of high pressure that opened the door to the monsoon blocked moisture into the northern Rockies. As a result, areas of Idaho, Montana and Wyoming that had decent snow years have had drought conditions increase sharply, according to the conservation service drought monitor.
Meanwhile, drought conditions across the Southwest have improved dramatically since June.
Rainfall has been a "curveball" for fishing enthusiasts along the Arkansas River, local fishing outfitter Rod Patch said. With washouts carrying sediment and muddying some sections of the river, fishermen have been forced into quick itinerary changes.
"We've just been trying to get upstream of the mud," Patch said.
That means switching trips to the Buena Vista area, because many of the washouts have flowed into the Big Bend area or lower. Patch said Bighorn Sheep Canyon east of Salida has seen a lot less fishing activity than during a drier summer.
"From Salida to Coaldale it just hasn't been good fishing because of the dirty water," Patch said, explaining that fish can't find a fisherman's offering when water is brown.
A silver lining is fish will be especially ready to eat during the fall season, Patch said.
"This year, the fish haven't been fished over," he said. "(They are) very hungry and aggressive."
The rain has also affected local hay production as ranchers have had to be extra cautious about where they put their crop and when they bale to avoid weather exposure.
Some of the local hay crop has been compromised because the B12 vitamin in hay can seep out if the crop gets wet after cutting, Kurt Jones of the Colorado State University Chaffee County Cooperative Extension said.
"The rain started July 1, which had an effect on some of the first cutting," he said. "When it's cut and gets weathered, it can lose vitamins and nutrients."
Jones said more local ranchers have tested their hay before selling it to determine its quality. Ranchers have also seen larger yield and increased moisture for grazing because of the rain, Jones said.
"Most of our ranchers were happy about having the rain," he said.
The conservation service reported reservoir storage in the upper Arkansas River basin varied at the end of July.
Twin Lakes and Turquoise Lake near Leadville had storage at 116 percent and 107 percent of average respectively as of July 30, while Pueblo Reservoir was at 82 percent.
Arkansas River basin water commissioner Bruce Smith of the Colorado Division of Water Resources said he has been able to keep Chaffee County reservoirs such as Cottonwood Lake, O'Haver Lake and Boss Lake full this summer.
But, Smith said, more than reservoir storage, the rain has effected the water right call on the river. The call was up to 1896 Monday, which is unusually junior for this time of year.
The call is similar this week to where it was during spring runoff, Smith said. That means more water rights are being fulfilled this summer than in years past.
"The rain water we see is not available for storage because it needs to be delivered to a downstream water right," Smith said. "We are over-appropriated."
The monsoon pattern usually begins to break in late August and early September, Gochis said.
More rain is forecast to move into Colorado tonight and Friday, but it is not a monsoonal scenario.
The storm is coming from the west rather than the south, and it could drop the first snow of the year in the northern Colorado mountains, Gochis said.
"I would say this is the first sign of a fall pattern," he said. "This next system will really cool us down. It's not what we would call a monsoon-type system at all."
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