Snowpack deficits grow across Montana after a dry, warm January

Well below normal January precipitation and unseasonably warm temperatures stalled Montana’s snowpack accumulation last month.

“Most Montana basins are now reporting below normal snowpack. While some higher elevations are holding onto their snowpack reserves, mid elevation snowpack is falling behind, and low elevation snowpack is noticeably absent,” said Florence Miller, USDA Natural Resources Conservation Service (NRCS) Hydrologist. “As of February 1, most major basins hold 65-90% of median snowpack, a 10-30% decrease from the January 1 medians. Snowpack in the Bears Paw Mountains is currently around 45% of median Snow Water Equivalent (SWE), while the Upper Yellowstone and Bighorn basins are the only basins in the state hovering around 100% of median SWE.”

January precipitation was only 50-75% of median and temperatures remained largely above normal. Many areas across the state lost soil moisture with the dry January and minimal snow cover, causing drought conditions to increase. The snowpack continues to be denser than normal for this time of year due to the above normal temperatures seen in December and January.

Water-year-to-date precipitation remains well above normal (100-150% of median) statewide, thanks to a wet December. Higher elevation SNOTELs, where early precipitation fell as snow, accumulated snowpack surpluses during that period. However, January’s lack of precipitation eroded those surpluses at all but the highest sites. Most SNOTEL and snow course stations across Montana are reporting a one- to five-inch deficit below normal SWE for this time of year, with a couple higher elevation pockets in the Cabinet and Swan Range nearing an eight-inch deficit. A few higher elevation stations have retained up to a five-inch surplus from the early winter precipitation. For example, in the Whitefish Range, the Stahl Peak SNOTEL at 6,040 feet is reporting 24.5 inches of SWE (111% of median). The lower elevation Grave Creek SNOTEL at 4,350 feet has only 4.4 inches of SWE (41% of median).

“Mid- to high-elevation snowpack is the main contributor to summer streamflow. How the lack of low elevation snow coverage will influence snowmelt driven runoff this year is yet to be determined. Official water supply forecasts will be available starting next month after more of the snowpack accumulation season has played out,” explains Miller.

Montana’s mountains typically reach peak snowpack between late March and early May. Conditions at that time will influence summer streamflow far more than this February 1 snapshot. Statewide, most SNOTELs are less than half of the way towards their normal peak snowpack. With two to three months remaining in the snowpack accumulation season, a return of winter and continued snowfall will be crucial to catch up current snowpack deficits. While current snowpack deficits can still be recovered, the larger they grow, and the shorter the time to catch up, the less likely full recovery becomes.