BOZEMAN, Mont., February 9, 2015—Snow, rain and well above average temperatures contributed to January's below average snowpack percentages, according to snow survey data collected by the USDA Natural Resources Conservation Service (NRCS). After a large snowstorm during the first week of the month, January was mostly dry with below normal snowfall. During the last week, well above average temperatures set new daily highs at many SNOTEL sites on Jan. 26 and 27.
Many basins were well above normal on Jan.1, however the lack of snowfall and warm temperatures dropped basin percentages as the month progressed. Statewide, the snowpack percentages dropped from 110 percent on Jan. 1 to 100 percent on Feb. 1. The largest decreases were generally west of the Continental Divide and in the northern half of the state, but southwest basins also saw a drop during the month
A few basins in the state have been below normal snowpack since snow began accumulating in November. West of the Divide, the Kootenai River basin is currently the lowest in the state at 69 percent of normal, and east of the Divide, the Madison River basin is currently 83 percent of normal. The upper reaches of the Jefferson River basin in the Ruby River drainage and Red Rocks Valley currently have well below normal snowpack, though the rest of the basin downstream continues to be above normal.
This gradient in the snowcover exists along the Canadian and Montana/Idaho borders in other river basins. Some headwaters of the major river basins are well below normal, while other parts of the basin are well above average. More information about specific sub-basins can be found in the Feb. 1 Water Supply Outlook Report.
Mountain and valley precipitation was below normal for most basins in Montana during the month of January. Statewide only 88 percent of the average monthly precipitation fell. Even with the lack of precipitation during the last month, most basins are still near to above the water year-to-date average for Feb. 1. Statewide there is 107 percent of the water year-to-date average on Feb. 1. The Madison River Basin is the only major basin that is well below normal for this time of year. It only received 67 percent of the average January precipitation and is 84 percent of normal for Feb. 1. In general, valley locations were favored during the month of January, except for southwest Montana where mountain SNOTEL sites received more than valley weather stations.
Due to the lack of snowfall during January and declining basin percentages of normal snowpack, streamflow forecasts have dropped for the April-July time period. Because of the early season snowfall in November and December, most basins still look to have near average streamflow runoff this spring. Statewide streamflow forecasts indicate 100 percent of average flows, but some individual basins are above and below this value. Currently, the St. Mary-Milk and Madison River Basins have the lowest forecasted runoff at 81 percent and 79 percent, respectively. Basins west of the Divide currently have the highest streamflow forecasts in the state. For a closer look at individual basin streamflow prospects, consult the Feb. 1 Water Supply Outlook Report.
“Carryover storage in the reservoirs across Montana is very good for Feb. 1, due the abundance of snow last winter,” said Lucas Zukiewicz, NRCS water supply specialist for Montana. “Should winter continue the dry pattern experienced in January, the carryover storage will certainly help augment flows in rivers and to irrigators this spring.”
Source: USDA NRCS