What is Snow Drought?
Snowpack typically acts as a natural reservoir, providing water throughout the drier summer months. Lack of snowpack storage, or a shift in timing of snowmelt from that reservoir, can be a challenge for drought planning. Few drought metrics include storage and release of snow water. Several years of low snowpack, especially across the western U.S., have led to many studies looking into the causes and impacts of reduced snow storage (see Resources) and the creation of a new definition of drought called Snow Drought.
Snow drought is defined as period of abnormally low snowpack for the time of year, reflecting either below-normal cold-season precipitation (dry snow drought) or a lack of snow accumulation despite near-normal precipitation (warm snow drought), caused by warm temperatures and precipitation falling as rain rather than snow or unusually early snowmelt. (AMS Glossary of Meteorology)
Snow-dominated regions face several challenges due to snow drought and its impacts:
- Summer Water Availability: Snow droughts reduce the amount of available water for spring and summer snow melt. This, in turn, reduces streamflow and soil moisture, which can have impacts on water storage, irrigation, fisheries, vegetation, municipal water supplies, and wildfire.
- Winter Water Management: Warmer winter storms lead to rain instead of snow at higher elevations in mountain regions that can create challenges for water management and flood mitigation strategies, particularly when dealing with extreme events.
- Outdoor Tourism and Recreation: Many local economies and industries rely on snowpack and river flows from snowmelt to support their outdoor industries such as skiing, rafting, and fishing.
- Ecosystems: Lack of snow can disrupt ecosystems over shorter and longer timescales.
Current Situation and Impacts in the West
May 30, 2019:
In the Lower 48 snow water equivalent (SWE) is currently below median values for most of western Oregon, Washington, northern Idaho, and western Montana. All other areas in the West are well above normal. Climatologically late May is about the time when many low and mid elevation locations reach melt out. However, large SWE deficits still exist in places like the Washington Cascades where late June melt out dates are more common. Olallie Meadows, Washington at 4,030’ elevation has a current SWE value of 7.5” and 32% of median and will likely melt out well before the median date of June 26. At the larger river basin scale the Upper Columbia, which drains from the Canadian Rockies down to eastern Washington, is currently at 27% of median SWE and the lowest of all the HUC 6 basins. The poor snow conditions will lead to lower mountain runoff this summer and above normal fire potential for June in western Washington spreading to include western Oregon, northern Washington, and northern Idaho by July. In Alaska, with the exception of southern coastal ranges and one station in southeast Alaska, most locations have reached a median value of zero and therefore not reporting percent of median SWE. For southern coastal Alaska all reporting stations are below median (0-79%) with the exception of Independence Mine to the northeast of Anchorage which sits at 238% of median (median SWE for May 27 is 1.9”). In southeast Alaska Long Lake (southeast of Juneau) is currently at 2% of median SWE. This reflects the current D0 (abnormally dry) U.S. Drought Monitor depiction and long-term dryness in the region.
USDA Natural Resources Conservation Service (NRCS) percent of 1981-2010 median snow water equivalent (SWE) over the western U.S. (top) and Alaska (bottom) for May 27, 2019. Only stations with at least 20-years of data are included in the station averages. For an interactive version of this map, including percent of period of station record median SWE, please visit NRCS.
USDA Natural Resources Conservation Service (NRCS) SNOTEL site daily (inches) water year accumulated SWE (red line) plotted with long term median SWE (black line) at Long Lake, Alaska. The current SWE value through May 28 is 0.3 inches which is 2% of the long term median (9.6 inches). Source: NRCS