The main purpose of this ongoing blog will be to track planetary extreme, or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😉
Main Topic: Changing Precipitation Normals from Climate Central
Dear Diary. As I’ve indicated over the last five years of doing this blog, the United States is drying in the West and getting wetter east of the Rockies. Today Climate Central has released a very detailed report indicating such.
What’s alarming since the start of 2022, highlighting this trend, is that our historic megadrought in the West is getting worse. There have been no big Pacific systems smashing into the West Coast since the start of January, and a dipole pattern preventing such looks like it will hold into early March.
Here is Climate Central’s report on longer term trends:
Changing Precipitation Normals
FEB 16, 2022
We look at the change in precipitation between the 1991-2020 and 1981-2010 periods, and break down the regional and seasonal patterns across the U.S.
- Climate normals are 30-year averages of weather data that provide a baseline for comparing current conditions in each season and region of the country.
- Here, we look at the change in average precipitation between the 1991-2020 and 1981-2010 normal periods.
- Annual average precipitation has increased east of the Rockies and decreased to the west, especially in the Southwestern U.S.
- Seasonal averages show high regional variation, with a strong winter wetting signal in the North Central U.S., and strong summer and fall drying signals throughout the West, Southwest and Northwestern U.S.
- Local changes in precipitation between the old and new normal periods were assessed using station data for 247 locations across the U.S.
U.S. Precipitation Normals
- Rainfall is highly variable day-to-day, month-to-month and year-to-year. Climate normals average 30 years of weather data, including precipitation, to determine typical conditions for a particular location and time of year.
- NOAA releases a new set of U.S. climate normals each decade, and the 1991–2020 period provides the most recent 30-year baseline for comparing current weather.
- We’ve previously covered the change in average temperature between 1991-2020 and the previous 30-year period (1981-2010). Here, we look at the change in average precipitation between these two periods.
Nationwide Change in Precipitation Normals: The percent change in annual average precipitation between the current (1991-2020) and previous (1981-2010) 30-year period is represented here in national maps based on gridded data.
- Annual average precipitation has generally increased east of the Rockies and in the North Central U.S., and decreased in the West (especially the Southwest).
- Comparing seasonal average precipitation between the 1991-2020 and 1981-2010 periods reflects more of the month-to-month and region-to-region variability across the diverse microclimates of the contiguous U.S.
- Average winter precipitation increased for much of the contiguous U.S., especially in the Northern Rockies and Plains and Upper Midwest regions, where some areas were up to 25% wetter during 1991-2020 than during 1981-2010.
- Average spring precipitation increased in the Ohio Valley and much of the Southeast, while the Southwest became drier.
- Average summer precipitation decreased throughout the West and into the Northwest, while the eastern two-thirds of the U.S. showed a mix of wetter and drier zones east of the Rockies.
- Average fall precipitation decreased throughout the Southwest, South Central, and Western regions. Decreases in average fall precipitation between the old and new normal periods exceeded -25% in parts of California.
Local Change in Precipitation Normals: For a closer look within each region, Climate Central charted the change in annual and seasonal average precipitation between the 1991-2020 and 1981-2010 periods for 247 locations across the U.S. based on weather station data.
- Of the 247 stations in our network, 70% experienced an increase in annual average precipitation. Lexington, Ky. and Atlantic City, N.J. both experienced the largest percent increases in annual average precipitation (+10%). Traverse City, Mich. and Eugene, Ore. experienced the largest percent decreases (-12% and -11%, respectively).
- 73% of stations saw wetter winters during 1991-2020 than in 1981-2010. The largest percent increase in average winter precipitation was in Mitchell, S.D. (+25%) and the largest percent decrease was in Traverse City, Mich. (-34%).
- 72% of stations saw wetter springs, with the largest percent increase in Honolulu, Hawaii (+21%) and the largest percent decrease in Tucson, Ariz. (-21%).
- 64% of stations saw wetter summers, with the largest percent increase in San Jose, Calif. (+156%) and the largest percent decrease in Bakersfield, Calif. (-58%).
- Average fall precipitation increased for 45% of stations and decreased for 54%. The largest percent increase in average fall precipitation was in Greenville, N.C. (+17%) and San Jose, Calif. had the largest percent decrease (-33%).
Precipitation Normals and Climate Change:
The two normal periods in this analysis overlap by 20 years and cover a total of just 40 years. Given this limited time window and the highly variable nature of precipitation, it is difficult to link the change in the two most recent precipitation normals to climate change. The seasonal precipitation shifts observed between the two most recent 30-year normals are, however, generally consistent with modeled and theoretical precipitation changes anticipated over the 21st century under climate change. Climate models project a shift toward drier conditions in the southwestern U.S. and wetter winter and spring conditions in the northern U.S.
Comparing precipitation normals since the 1901-1930 period with the 20th century average shows a general shift toward wetter annual conditions overall (despite regional variation including drier conditions in the Southwest), especially during the four most recent normal periods. This general trend toward wetter normals is likely linked in part to warming over the 20th century because warmer temperatures increase evaporation rates over the ocean and land surface, ultimately leading to more precipitation on average.
POTENTIAL LOCAL STORY ANGLES
What do climate normals mean to my community?
Climate normals aren’t just used to describe weather—they’re used to inform decisions across a range of sectors. Consider interviewing professionals from industries that use climate normals, such as: growers, municipal officials, city planners, energy or construction companies, and insurance groups.
Where can I find more information on the new climate normals?
On the NCEI website, NOAA provides national maps for other temperature and precipitation metrics which you can customize by month or season. You can also create local charts, choosing your own parameter and time scale.
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 precipitation and climate change. The American Association of State Climatologists is a professional scientific organization composed of all state climatologists.
- Jared Rennie
Research Meteorologist, NOAA’s NCEI
Expertise: weather and climate monitoring
The change in annual and seasonal precipitation normals (percent change from 1981-2010 to 1991-2020) was calculated for 247 stations using data from the Applied Climate Information System. The national maps showing the change in annual and seasonal precipitation across the contiguous United States were created using data from the NOAA Monthly U.S. Climate Gridded Dataset (NClimGrid).
DEC 1, 2021
To kick off meteorological winter, Climate Central looks at changing seasonal normals, finding that every season—especially winter—was warmer during 1991-2020 than during the previous 30-year period.
MAY 5, 2021
Updated U.S. Climate Normals from NOAA help us put weather in the context of our “normal” climate, but also illustrate how warming is accelerating with climate change.
JAN 19, 2022
Snow keeps our planet cooler, feeds water supplies, and underpins local economies and cultures. We unpack how climate change is affecting snow—and snow-dependent communities—across the U.S.
Here are some “ET” reports from Wednesday:
Here is more climate and weather news from Wednesday:
(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article. The most noteworthy items will be listed first.)
Now here are some of today’s articles and notes on the horrid COVID-19 pandemic:
(If you like these posts and my work please contribute via the PayPal widget, which has recently been added to this site. Thanks in advance for any support.)
Guy Walton “The Climate Guy”