Trends point out shifting snow in a warming U.S.

Climate Central -- How snow forms

We may be in a cold spell currently but this winter has proven to be on the warmer side and beautiful here in Florida.

We’re not the only ones feeling this warm up. Winter is the fastest warming season, with those who see numerous days below freezing feeling the impacts most.

When the air warms up it’s able to hold more moisture. For every 1° warmed the air can hold 4% more moisture.

With the number of freezing (32°) days declining it’s slowly impacting the amount of snowfall seen in the U.S.

Trends showing days below 32. (Climate Central)

According to a report from Climate Central between the years of 1970-2019 snowfall has decreased most during the spring and fall seasons.

It’s important to note that we’re seeing a gradual warm up but record snowfall amounts are still possible if the ingredients are there, temperatures below 32° and moisture in the air. Just like we saw in California in December 2020. The Sierra Nevada mountain range saw 70% of their average annual snowfall already. At that point in December they had already seen 264 inches of snowfall.

This is key because snowfall makes up more than 50% of the Western U.S. water supply.

Lets dig a little deeper into our regional snow trends provided by Climate Central.

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 snowpackearlier 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.