Snow shift in the US

Basic 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 spring and fall for most of the U.S. Winter had 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.

The snow lasts our planet coolerconstitutes more than 50 percent of the water supply in the Western US and supports local economies and cultures from coast to coast. So, how is climate change affecting snow in the US?

Snow Basics. Two basic conditions are required for the production of snow: both low temperatures and moisture in the atmosphere. How are these conditions affected by climate change?

• Fewer frosts. Winter is the fastest warming season for most of the US, and the number of days with temperatures below 32°F is expected to continue to decrease in the coming decades.

• More humidity. Our warm atmosphere prevails 4% more moisture per 1°F of the increase in temperature. But where that moisture falls, and whether it falls as rain or snow, depends largely on the season and region.

Seasonal snow trends. In nearly all regions of the U.S., snow is decreasing in the fall and spring, according to a Climate Central analysis of snowfall data from 1970-2019. During this period:

• Fall snowfall (prior to December 1) decreased in every region of the country with available data.

• Spring snowfall (after March 1) decreased in all regions except the Northeast and East North Central regions.

• The winter saw a mixed record, with increased snow in the north central regions and decreased snow in the 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 far-reaching effects—vary across regions.

Western USA

• The amount of mountain snow and the timing of snowmelt largely determine the supply of water to rivers and reservoirs in the western US during the high-demand spring and summer.

• But since the mid-20th century, the mountainous Western US has experienced descending snowball, earlier snowmelt and stream flow, and a shift to less precipitation falling as snow.

• A 2018 study shows that decades of shrinking snowpack have reduced snow-derived freshwater in the West by 15-30% since 1955.

• In addition to reducing available water supplies for municipalities, irrigation, industry and ecosystems, declining mountain snowpack and early snowmelt may also increase fire hazard in western forests with abundant fuel.

• In the US Southwest, declining snowpack, earlier spring snowmelt, and a higher precipitation-to-snowfall ratio are exacerbating the risk drought in the area.

• In the San Joaquin and Colorado watersheds, irrigated agriculture and food production face risks from timing discrepancy of (past) snow runoff and water demand for the growing season.

Northeastern USA

• The northeast has experienced a increase in the proportion of winter precipitation falling as rain rather than snow. This trend is predicted to continue into the 21st century with a shift to the north in the snow-rain transition zone.

• A 2018 study plots both a reduction in the overall frequency of Northeast blizzards this century, as well as a greater likelihood that more intense blizzards will bring more snow when temperatures are still quite cold.

• The multi-billion dollar winter recreation industry is an important part of the regional economy and culture. The industry is already taking a financial hit in low snow yearsand future emissions scenarios suggest that the winter recreational season is likely to become shorter and smaller across 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 heavy local snowfall. In the Great Lakes region, lake effect snow occurs when cold air from the north moves into the relatively milder open waters 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% decrease in annual maximum ice cover across the Great Lakes since 1973.

• Longer periods of open water lead to more evaporation and an increase in lake-induced snow. Looking to the future, projections suggest that lake-effect snow will still occur in a warming world, but by the end of the 21st century, we can expect a shortened season of lake-effect snow.

• According to NOAA, the Great Lakes are holding 90% of fresh water in the US and support both recreation and cultural heritage that is deeply rooted in the surrounding communities.

Northern Great Plains

• Warming in the Northern Great Plains has led to shorter snow seasons and reducing snow water storage.

• The regional flow of the stream, especially in late summer, is highly snow dependent. Lower and more variable snow-fed flows affect riparian and aquatic ecosystems, as well as the local economies and recreational industries that depend on them.

• Mountain regions 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.

POSSIBLE LOCAL HISTORY CORNERS

What is the snow forecast for where you live?
of the National Meteorological Service Winter page provides maps and forecasts of snow and ice in your area. Theirs Winter Weather Bureau provides twice-daily local forecasts for snow and freezing rain.

Regional sources of snowfall:
of NOAA Regional Snowfall Index (RSI) ranks blizzard impacts based on storm area, amount of snowfall, and population affected. The RSI covers the six easternmost climate zones.

The Snow Telemetry Network (SNOTEL) of over 900 automated data collection sites found primarily in high-elevation watersheds in the western US and Alaska. National Weather and Climate Center Water and Climate Information System makes this and related data available through mapping tools, report generators and interactive maps.

The National Snow and Ice Data Center (NSIDC) focuses on the science of Earth's changing cryosphere and manages scientific data on snow, ice, glaciers, permafrost and related climate dynamics.

The Rutgers University Global Snow Lab provides maps, graphical products and tables for Northern Hemisphere snow cover.

How is climate change affecting winter activities and tourism near you?
Climate Central report On thin ice covers the effects of warming winters on America's cold-weather sports economy.

Tools for reporting winter weather near you:
Warmer temperatures can make winter storms more complicated, with sleet and freezing rain. Criteria for winter storm watches, advisories and warnings may vary by region, so check your region Office of the National Weather Service. The NWS also provides helpful information on how to stay safe in winter conditions, wind chill chartsand an explanation of it polar vortex.

LOCAL SPECIALISTS

The SciLine service, 500 Women Scientists or local university press offices may be able to connect you with local scientists who have expertise in snowfall and climate change. The American Association of State Climatologists is an inclusive professional scientific organization State climatologists.

NATIONAL EXPERTS

• Zion Klos, PhD
  Assistant Professor, Environmental Science, Marist College
  Contact: zion.klos@marist.edu; 920-883-8617
  Expertise: climate change adaptation in the northeastern and western US. transitional zones of rain and snow in the western US

• Kenneth Kunkel, PhD
  Research Professor and Chief Scientist for Evaluations
  North Carolina Institute for Climate Studies, North Carolina State University
  Contact: kekunkel@ncsu.edu

• Adrienne Marshall, PhD
  Assistant Professor
  Colorado School of Mines
  Contact: adriennemarshall@mines.edu
  Expertise: Western US avalanche, water resources and hydropower

• Philip Mote, PhD
  Vice President and Dean of the Graduate School, Oregon State University
  Contact: philip.mote@oregonstate.edu
  Expertise: Regional Climate Modeling, The Impact of Climate Change on the Western US Snowpack

• David Robinson, PhD
  New Jersey State Distinguished Professor and Climatologist
  Rutgers University
  Contact: david.robinson@rutgers.edu
  Specialization: snow cover dynamics at regional and hemispheric scales

• Colin Zarzycki, PhD
  Assistant Professor of Meteorology and Climate Dynamics
  Pennsylvania State University
  Contact: czarzycki@psu.edu
  Expertise: snowfall in the eastern US