Climate Matters•January 19, 2022
Shifting Snow in the Warming U.S.
KEY CONCEPTS
Winter is the fastest warming season for most of the U.S. Warmer air holds more moisture, which can fall as snow when temperatures are below freezing.
Between 1970-2019, snowfall decreased in the spring and fall for most of the U.S. Winter showed a mixed record with more snowfall in some cold northern regions.
Climate change can affect the timing, location, and amount of snowfall—as well as spring snowmelt patterns—in complex ways.
We summarize historical and projected future snow dynamics for the Western, Northeastern, Northern Great Plains and Great Lakes regions, and their impacts on people and ecosystems.
Snow keeps our planet cooler, makes up more than 50 percent of the Western U.S. water supply, and underpins local economies and cultures from coast to coast. So, how is climate change affecting snow across the U.S.?
Snow basics. Two basic conditions are needed to produce snow: both freezing temperatures and moisture in the atmosphere. How are these conditions affected by climate change?
Fewer freezes. Winter is the fastest warming season for most of the U.S., and the number of days with temperatures below 32°F is expected to continue to decline over the coming decades.
More moisture. Our warming atmosphere holds about 4% more moisture per 1°F of temperature rise. But where that moisture falls, and whether it falls as rain or snow, is largely based on the season and region.
Seasonal snow trends. In almost all areas of the U.S., snow is decreasing in the fall and spring, according to a Climate Central analysis of snowfall data from 1970–2019. Over this period:
Fall snowfall (before December 1) decreased in every region of the country with available data.
Spring snowfall (after March 1) decreased in all regions except for the Northeast and the East North Central regions.
Winter showed a mixed record, with increased snow in North Central regions, and decreasing snow in southern regions.
Regional snow trends. Climate change can affect the timing, location, and amount of snowfall, as well as the dynamics of snowmelt. But these changes—and their wide-ranging impacts—vary among regions.
Western U.S.
The amount of mountain snowpack and the timing of snowmelt largely determine the supply of water to rivers and reservoirs in the Western U.S. during the high-demand spring and summer.
But since the mid-20th century, the mountainous Western U.S. has experienced declining snowpack, earlier snowmelt and streamflow, and a shift toward less precipitation falling as snow.
A 2018 study shows that decades of shrinking snowpack has reduced snow-derived freshwater in the West by 15-30% since 1955.
In addition to reducing water supplies available for municipalities, irrigation, industry and ecosystems, reduced mountain snowpack and earlier snowmelt can also increase wildfire risk in Western forests with abundant fuels.
In the Southwestern U.S., declining snowpack, earlier spring snowmelt, and higher rainfall to snowfall ratios all exacerbate the risk of drought in the region.
In the San Joaquin and Colorado River Basins, irrigated agriculture and food production face risks from a mis-match in the timing of (earlier) snowmelt runoff and growing season water demand.
Northeastern U.S.
The Northeast has experienced an increase in the proportion of winter precipitation falling as rain rather than snow. This trend is projected to continue over the 21st century with a northward shift in the snow-rain transition zone.
A 2018 study projects both a decrease in the overall frequency of Northeast snowstorms this century, as well as greater likelihood that the heaviest snowstorms will bring more snow when temperatures are still cold enough.
The multi-billion dollar winter recreation industry is an important part of the regional economy and culture. The industry already takes an economic hit during low snow years, and future emissions scenarios suggest that the winter recreation season is likely to become shorter and smaller throughout much of the Northeast as winters continue to warm.
Great Lakes Region
Although snowfall is often associated with mountains, other features, including large lakes, can also lead to intense local snowfall. In the Great Lakes region, lake effect snow occurs when cold air from the north moves across the relatively milder open water of the Great Lakes.
As the planet has warmed, so have the Great Lakes. Despite year-to-year variability, long-term trends show an average 22% decline in annual maximum ice cover across all of the Great Lakes since 1973.
Longer periods of open water lead to more evaporation and to an increase in lake effect snow. Looking to the future, projections suggest that lake effect snow will still occur in a warming world, but by the late 21st century, we can expect a shortened lake effect snow season.
According to NOAA, the Great Lakes hold 90% of the freshwater in the U.S., and support both recreation and cultural heritage deeply rooted in the surrounding communities.
Northern Great Plains
Warming in the Northern Great Plains has led to shorter snow seasons and a decline in snowpack water storage.
Regional streamflow, especially in late summer, is highly dependent on snowpack. Lower and more variable snow-fed streamflows impact riparian and aquatic ecosystems, as well as the local economies and recreational industries that depend on them.
Mountainous areas of the Northern Great Plains also face snow-dependent economic and ecological risks due to climate change, including shorter skiing and snowmobiling seasons and fewer visitors.
POTENTIAL LOCAL STORY ANGLES
What’s the snow forecast for where you live?
The National Weather Service’s Winter Page provides maps and forecasts for snow and ice in your area. Their Winter Weather Desk provides twice-daily local forecasts for snow and freezing rain.
Regional snowfall resources:
NOAA's Regional Snowfall Index (RSI) ranks snowstorm impacts based on the storm area, amount of snowfall, and affected population. The RSI covers the six easternmost climate regions.
The Snow Telemetry (SNOTEL) Network of over 900 automated data collection sites located mainly in high-elevation watersheds in the western U.S. and in Alaska. The National Weather and Climate Center’s Water and Climate Information System makes this and related data available through charting tools, report generators and interactive maps.
The National Snow and Ice Data Center (NSIDC) is focused on the science of Earth’s changing cryosphere, and manages scientific data on snow, ice, glaciers, frozen ground, and related climate dynamics.
The Rutgers University Global Snow Lab provides maps, graphic products and tabular data on Northern Hemisphere snow cover.
How is climate change impacting winter activities and tourism near you?
Climate Central’s report On Thin Ice covers the impacts of warming winters on America’s cold-weather sports economy.
Tools for reporting on winter weather events near you:
Warmer temperatures can make winter storms more complicated, with sleet and freezing rain. Criteria for winter storm watches, advisories, and warnings can vary by region so check out your local National Weather Service office. The NWS also provides helpful information on how to stay safe in winter conditions, wind chill charts, and an explanation of the polar vortex.
LOCAL EXPERTS
The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on snowfall and climate change. The American Association of State Climatologists is a professional scientific organization composed of all state climatologists.
NATIONAL EXPERTS
Zion Klos, PhD
Assistant Professor, Environmental Science, Marist College
Contact: zion.klos@marist.edu; 920-883-8617
Expertise: adaptation to climate change in the Northeast and Western US; rain-snow transition zones in the Western U.S.Kenneth Kunkel, PhD
Research Professor and Lead Scientist for Assessments
North Carolina Institute for Climate Studies, North Carolina State University
Contact: kekunkel@ncsu.eduAdrienne Marshall, PhD
Assistant Professor
Colorado School of Mines
Contact: adriennemarshall@mines.edu
Expertise: Western U.S. snowpack, water resources, and hydropowerPhilip Mote, PhD
Vice Provost and Dean of the Graduate School, Oregon State University
Contact: philip.mote@oregonstate.edu
Expertise: Regional climate modeling, the influence of climate change on western US snowpackDavid Robinson, PhD
Distinguished Professor and New Jersey State Climatologist
Rutgers University
Contact: david.robinson@rutgers.edu
Expertise: snow cover dynamics at regional and hemispheric scalesColin Zarzycki, PhD
Assistant Professor of Meteorology and Climate Dynamics
The Pennsylvania State University
Contact: czarzycki@psu.edu
Expertise: snowfall in the Eastern U.S.