April storms, warming temperatures heighten flood potential

Tom Gardner

Monday, April 12, 1999 | 3:45 a.m.

RENO, Nev. -- Two weeks of almost steady snow in the Sierra, followed by a forecast for above-normal temperatures, have increased the possibility of springtime flooding along the mountains, water watchers warn.

"The potential for spring snowmelt flooding is high in the eastern Sierra drainages north of the Carson Basin and in northwestern Nevada and northeast California due to continued above average snowpack," National Weather Service hydrologist Gary Barbato said.

Just three weeks ago, Barbato said the likelihood of flooding existed, but would depend on what happens as spring continues.

Now, he said the succession of storms that began at the end of March added several feet of snow in the mountains. And little of the winter's accumulation had a chance to melt in the cool temperatures.

The forecast for the rest of this week calls for highs in the mountains to reach the 60s with readings across western Nevada in the 70s - about 10 degrees above seasonal averages.

"Snowpack ranges from 135 percent of average in the Carson Basin to 171 percent in the Tahoe Basin," Barbato said.

He added that no flood producing flows are forecast or expected at this time and said the actual runoff had a 50 percent chance of being higher and a 50 percent chance of being lower than Monday's outlook.

"The likelihood of flooding depends strictly on weather conditions through the melt period. This period usually extends through May or early June," he said.

"Even in areas with very high flood potential, flooding will occur only if snowmelt is very rapid due to much above normal temperatures or if heavy rain occurs at high elevations."

Barbato said the outlook for April calls for above normal precipitation and average temperatures in the runoff area. The long range expectation is for near normal precipitation and above average temperatures through June.

On a positive note, the end of the storms has also brought an end to the avalanche warning that had been in effect most of this month for the Sierra from Yuba Pass on California 49 to Sonora Pass on California 108, although the U.S. Forest Service in Truckee, Calif., cautioned that slides still are possible as the snow warms up.