On Saturday morning a gauge on the Yellowstone River at Corwin Springs picked up the first sign of major snowmelt in the mountains that feed the basin.
From a height of 2.3 feet, the river began to swell as it ran by the equipment set up just outside Yellowstone Park. By Tuesday morning, the river was measuring 4.56 feet.
Later Saturday, the Yellowstone began to surge at Livingston. By Sunday, waters were rising at Billings, and by Tuesday, river graphs were showing signs of a steep rise at Forsyth. It won’t be long before melt water begins to churn the river at Miles City.
Snowpack, even at the highest elevations, is starting to melt, said Tom Frieders, warnings coordination meteorologist at the National Weather Service Office in Billings. And it’s coming out a month early.
No part of the Yellowstone, or any other river in Eastern Montana, is close to flooding, though many are running above average for this time of year.
“It isn’t even on my radar,” Frieders said. “Just be glad it isn’t last year. With the snowpack we had, if we had had this rapid warm-up, things could have been a lot worse than they were.”
Last spring, ample snowpack combined with a wet, cold spring to produce record flooding for many parts of the state.
At Billings on Tuesday afternoon, the Yellowstone was at 4.11 feet, up from 3.2 feet Sunday. Flood stage here is 13.5 feet.
An early melt was set in motion by March temperatures many degrees above normal throughout the state, the meteorologist said. In Montana, it was the third-warmest March on record.
Snowpack, which ranged from slightly below normal to slightly above normal, began to warm, especially in the mountains of Wyoming that feed the lower Yellowstone and its tributaries.
When the pack uniformly hits 32 degrees, it is ready to melt, Frieders said. With warm weather through March and much of April, the mountains heated to above freezing in the daytime.
And when temperatures at lower elevations start hitting the 80s, temperatures in the mountains stay above freezing during the night as well, a critical factor in sending melt water down mountain slopes, he said.
Billings set a record 87 degrees on Monday and tied another record Tuesday with a high of 85.
“In a lot of areas the rivers have jumped two or three feet in the last few days,” Frieders said.
If the warming trend continues, the snow could be melted out by mid-May instead of mid-June, he said.
Temperatures through Thursday are expected to remain in the 70s in Billings. But a system moving in late Thursday could stop or slow the snowmelt. Highs in the 50s through the weekend here will likely mean mountain temperatures during the day will be in the low to mid 30s. They will dip well below freezing at night.
“It may even add a little snowpack,” he said.
Just how much moisture the system will bring is uncertain, he said. Eastern Montana and far northeast Montana could see most of the system’s effect, Frieders said. Even if more snow falls on the mountains, it is likely to melt quickly this late in the year.
Snowpack percentages for this time of year are showing the effects of a warm spring. It’s at 83 percent of average for the upper Yellowstone Basin, the stretch of river from Yellowstone Park to Custer. Snowpack on the lower Yellowstone is at 69 percent of average.