Apr 9, 2013 - By Eric Blom, Staff WriterHeavy snow blanketed Fremont County on Monday and Tuesday as moisture streaming out of Utah hit a mass of cold air high on the slopes of the Wind River Mountains and froze.
As of 8 a.m. Tuesday, the National Weather Service's heaviest reported snowfall in Fremont County was 21 inches measured 9.5 miles southwest of Lander.
Lander's Hunt Field airport recorded 18.6 inches. Other sites near Lander topped the charts. A site three miles southwest of Lander recorded 20 inches, five miles west-southwest found 17.4 inches, and 15 inches fell on a location nine miles south-southeast of the county seat.
The weather system Monday broke the record for precipitation for that date in Lander. NWS measured 1.31 inches of moisture, surpassing the record of 1.01 inches set in 1900 and trouncing the average value of .05 inches.
The Riverton area saw somewhat less snow. The snowiest official site near Riverton was one in town that saw 12 inches. Another in the city measured 10.1 inches. Unofficial measurements topped 14 inches in several locations.
A site two miles west of Riverton recorded 10 inches of snow.
NWS measured precipitation Monday in Riverton at .32 inch, not enough to beat the 2004 record for that date of .51 inch. Snowfall continued overnight Monday, so some of the storm's moisture will be recorded one day and some on the other.
The whole county saw significant snowfall. A site in Jeffrey City measured 12 inches of snow, Hudson recorded 10 inches, South Pass saw 10 inches, Ethete saw 6 inches, Sweetwater Station saw 3 inches, and Dubois saw 3 inches.
"We had a cold front that moved through the county yesterday morning," said NWS meteorologist Chris Jones. "It hit about sunrise."
Snow started falling at about 9 a.m. April 8 in Riverton and 8 a.m. in Lander, he said.
Jones compared the weather system to "a kid jumping a bicycle off a ramp." The child's goal is to leap high into the air, and the higher the cold front reaches, the more snow falls.
Similar factors contribute to the height of both.
To jump high, Jones said, the kid wants a tall ramp, to ride fast at it, and to hit the ramp at a perpendicular angle. In the case of the weather system, wind provided the speed, its direction was the angle, and the Wind River Mountains were the ramp.
Sustained winds were measured at 20 mph in Riverton, gusting to 30 to 35 mph. It blew southwest out of the northeast, at a right angle to the Wind River range, and pushed the mass of cold air high up the mountain slope.
The frigid air created a dome of frigid air high on the slopes of the Wind River range.
"That's a favorable snowfall pattern across the (Wind River) basin," Jones said.
A low-pressure system was rotating across southern Utah, Jones said, and it pumped moisture across the cold dome. Moisture froze as it crossed the frigid air mass and fell as snow.
More snow fell in locations farther up the slope of the mountains, like Lander, because the cold air reached higher in the atmosphere. Areas such as Riverton were lower on the "ramp" and saw less snow.
"Because it is an upslope flow, it favors locations near the Wind River Mountains," Jones said.
He attributed the duration of snowstorm to the weather in Utah.
"It was such a slow-moving system, we saw the pattern continue for an extensive period of time," Jones said.
He said the heaviest snow had fallen by Tuesday morning.
With the upslope pattern came cold temperatures for local residents. Lows Monday night were in the mid- to upper teens, about 15 degrees below normal. Daytime highs Tuesday were 25-30 degrees below normal.
He said all of the data has not been reviewed, but temperature records may be set.
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