(AP) — Warm temperatures have already accelerated runoff flows in smaller streams and creeks this week and the levels of major central and western rivers are expected to rise quickly as well. The National Weather Service posted a flood watch for the Shoshone, Big Wind, Green and Little Wind rivers effective this (Friday) morning through Sunday night.

“If you know your area is flood prone, you might want to get last-minute preparations made,” National Weather Service hydrologist Jim Fahey said.

The South Fork of the Shoshone River above the Buffalo Bill Reservoir is at 7.6 feet as of Friday afternoon. Flood stage is 9.5 feet. The river is expected to rise slowly and crest at 8.6 feet by Tuesday, according to the National Weather Service.

Foothill communities will see the highest water levels in the late evening and early morning hours, the service said.

“With mountain streams running highest in late afternoon/early evening, stream crossing will be most dangerous during those times of the day,” said the Weather Service in a Friday news release. “Hikers and folks in areas where water is flowing should not cross into the waters!”

Relatively minor flooding occurred in Wyoming during May from melting snow, but water experts caution residents along rivers and streams not to become complacent. They say the mountain snowpack remains exceptionally deep in many places and the main runoff is starting and is expected to be prolonged this year.

Park County Road 3LD, in the Meeteetse area, was closed on Thursday due to high water in the Greybull River and partial road wash outs, the Park County Sheriff's Office said. The closure will remain in effect until further notice. Local traffic will be allowed to “travel at their own risk” on the road beyond the barricade, the Sheriff's Office said in a Facebook post. Contact the Park County Engineers Office at 754-8520 for more information.

Only eastern Wyoming appears free from any flood threat now.

Warm weather at the outset of May melted off snow at the lower elevations — below the 8,500 foot (2,591 meter) altitude — and started melting some high elevation snow above 8,500 feet. However, the last two full weeks of May were wet and cool and left an unusually high snowpack entering June, according to Lee Hackleman, a water supply specialist with the Natural Resources Conservation Service in Riverton.

Statewide, Wyoming’s snowpack this week was more than twice the usual amount as measured by instruments in central and western mountain ranges, according to the NRCS. Wyoming normally sees some flooding from the spring snowmelt but this year is different in that the accumulated snowpack is high in a wide area and in multiple mountain ranges.

“The whole western side of the state is high,” Hackleman said.

Areas of Wyoming, such as Fremont County, with rivers and streams fed by the mountain runoff have been placing sandbags and other barriers to protect homes, businesses and key public infrastructure.

Fahey said the high snowpack this late in May likely will prolong the annual runoff.

“The Green especially could see moderate to high flows through July,” Fahey said.

Runoff in the Green River Basin normally peaks between June 10 and June 20, he said.

While rivers will be running high, a weather pattern of fluctuating temperatures between warm and cool would be ideal for an “efficient” runoff, Fahey said.

The wildcard is whether it rains.

“If we get enough rain on top of the melt, it really brings the rivers up high,” Fahey said.

Managers of reservoirs around the state have been draining water to make room for the high runoff.