LANDER - After eight years of drought, an average amount of snow can seem like a windfall.

This winter's mountain snowpack has been generally good, scientists said Monday, but the "make-or-break" months for Wyoming's water supply are just now commencing.

The Cowboy State, historically, has depended on heavy, wet snows between now and the end of May to produce much of the water that soaks the state's river drainages, gets used for irrigation and recharges reservoirs for the summer and ensuing months.

Almost all of Wyoming has received a normal amount of snowfall so far this winter, and compared to last year, most places have seen a 20 to 25 percent increase.

As of Monday, most parts of the state had accumulated between 92 and 97 percent of historically typical levels of snowpack. Three basins - the Upper Yellowstone-Madison, Upper North Platte and Little Snake River - have amassed above-average snowpack so far this winter.

The Upper Green River Basin has been the driest, having accumulated only 84 percent of its normal snow for this time of year.

"So far it has been an average winter," said Steve Gray, Wyoming's state climatologist. "But this is the beginning of the time of year when we start to get a lot of our moisture. From here on up until May is when we make the largest percentage of our snow that is then converted into water. A lot of the water we care about is yet to be determined."

Environment reporter Chris Merrill can be reached at chris.merrill@trib.com or at (307) 267-6722.