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Fierce weather whips valley

Sep 18, 2013 - By Katie Roenigk, Staff Writer

Another half inch of rain fell in some areas, adding to an already-wet September.

National Weather Service meteorologist Dave Lipson counted eight distinct thunderstorms that rolled through the Riverton Valley Tuesday to Wednesday morning.

The weather events dropped rain in varying amounts over Fremont County, "depending on where you were," Lipson said. At his house, Lipson measured .56 inch of precipitation over the past 24 hours.

The NWS gauge at the Little Wind River south of Riverton held .7 inch of water, and at Riverton Regional Airport .33 inch fell. Downtown Riverton only saw about .14 inch of rain, by contrast.

Eight storms

Lipson said the first downpour he observed Tuesday morning near Fort Washakie was relatively short-lived.

"There were a few claps of thunder, and we had a sprinkle," he said. "It was just like debris, I guess, from a previous weather system the day before. ... But we knew we had the moisture and instability in place."

The second storm was "a bit more intense," he said, and 55 mile per hour wind gusts were measured near Riverton Regional Airport at about 2:30 p.m.

"(It) blew up," Lipson said. "That's the one that gave the east side of Riverton quite a bit of rain."

Residents called the NWS to report mostly dime-sized hail during the event, though people at the Wyoming Fire Academy on Smith Road said the ice balls were as big as pennies.

Lipson said the second storm track was narrow and didn't cover the NWS rain gauge at the Little Wind River south of Riverton.

"That rain gauge ... only measured .13 (inch)," Lipson said. "It was just south of that main storm track."

Another cluster of storms passed to the north and west of town later in the day. Lipson said he was able to chase that grouping north of town to Sand Mesa Road near Boysen Reservoir.

"That's where the most standing water was," Lipson said. "I don't know how much fell from that. It was quite a bit of rain (but it) mainly missed Riverton."

Round four came Tuesday evening and included an "intense storm" in the Sinks Canyon area above Lander. The weather skirted Riverton, but at about 9:45 p.m. Lipson said he saw "mainly perfectly spherical, really hard" three-quarter inch hail falling from the sky east of town at the intersection of Wyoming highways 135 and 136.

"It was amazing," Lipson said. "One stone in particular was kind of jagged and irregularly shaped and was one inch in diameter."

He said the same storm struck the Wind River Casino and Beaver Creek Housing south of Riverton. This time, the downfall was measured at the rain gauge near the Little Wind River.

"We got quite a bit of water out of that one ... .35 inch from that one cell," Lipson said.

The gauge was too far south and east to catch the brunt of the next storm, which covered an area north of Riverton at about 11 p.m. Another downpour around midnight came closer to town but stayed north and west of the city limits, Lipson said.

The final event took place early Wednesday, at about 4:30 a.m. Lipson said the eighth storm dropped six-hundredths of an inch of rain over his home near Buckhorn Flats.

"Evidently the core of that one at one point was just west of Riverton," he said.

Another meteorologist observed lightning strikes during the early morning storm.

"There were brief period of frequent lightning," Lipson said.

Though more showers were possible Wednesday morning and afternoon, Lipson anticipated dryer weather for the coming days, with clear skies forecast for Wednesday evening.

"By tonight things should be relatively benign," he said. "I think we've seen the brunt of it."

Winds

Lipson said the recent storms grew as they drifted over the mountains along Wyoming's western border.

"A lot of the storms were forming over the mountains one after another after another," he said. "Some of them ... amplified as they went across the basin. Others were already pretty strong over the mountains, like the one over Sinks Canyon at about 9 o'clock."

He said the jet stream's air flowed through "just the right spot," bringing the string of storms directly through the Riverton area.

"We happened to be in the right portion ... where the wind enters that area of maximum wind, where it speeds up," Lipson said. "That tends to be an area where you'd typically get a propensity for real strong thunderstorms under right conditions. And we happened to be right underneath that."

Winds were generally light throughout the day Tuesday, but Lipson said the NWS heard reports of a power pole down and several outbuildings blown over along 8 Mile Road.

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