Green County Climate Profile

Green County is located in the south-central part of Wisconsin, along the Illinois border. The land cover of Green County is primarily agricultural, along with woodlands, wetlands, and grassland/pasture. Green County has a humid continental climate, characterized by precipitation year-round and summers that are warm to hot.

Records are computed using all available station data, some of which goes back to 1895 (Source: ACIS).

Averages for freeze dates are computed for the most recent 30 years (1995-2024; Source: ACIS).

Temperatures have been increasing since 1950 in Green County on the annual and seasonal time scales, which is the case for most of Wisconsin. Since 1950, annual average temperatures in Green County have increased at a rate of 0.4°F/decade, which translates to an increase of 1°F every 25 years. This increase in temperature has been most pronounced in the winter months and less pronounced in the summer months. When average winter temperatures are split into daily high and low temperatures, we see that winter minimum temperatures have been increasing by 1°F every 14 years since 1950.

With temperatures warming, this does not mean that every year will be warmer than the last, or that more recent years will all have above-average (1895-2024) temperatures. However, Green County is experiencing more years that are above average than it did in the past. For example, since 2000, Green County has experienced only five years with below-average temperatures. Similarly, if we rank the top ten warmest years in Green County since 1895 (black circles on the above chart), six have occurred since 2000. The top ten coldest years (black squares) are more concentrated in the earlier years of this time period, with nine of the top ten years occurring before 2000.

On the annual timescale, precipitation has been increasing at a rate of 0.92″ per decade since 1950, which translates to an increase of one inch approximately every 11 years. At the seasonal level, precipitation has been increasing across all seasons. Summer is the season of largest increase in precipitation in terms of inches per decade (0.31”/decade), but winter is the season with the largest percentage increase from average annual precipitation in the early 1950’s (35%).

Annual precipitation shows a lot of year-to-year variability, which is normal within a long-term trend. However, there are two notable trends that come from this dataset. First, precipitation is increasing at a rate of 0.53 inches per decade from 1895 to 2024. That’s an increase of one inch approximately every 19 years. Second, if we look at the past 20 years (2005-2024), Green County has had four of its top ten wettest years since 1895 (black circles) and only four years have been drier than the long-term (1895-2024) average. By contrast, of the top ten driest years (black squares), all occurred prior to 2000. These trends are quite similar to what has been observed in Green County with temperatures since 1895.

Green County is no stranger to sweltering summer heat, where daytime temperatures can top 90°F or even 100°F. But when are these hot days most likely to occur in Green County? The State Climatology Office analyzed the likelihood of a “hot day” (daily high temperature ≥ 90°F) or “warm night” (daily low temperature ≥ 70°F) occurring between two calendar dates using historical measured temperature data from NOAA stations in Green County. Based on this analysis, hot days and warm nights have occurred most frequently between July 21 to 31. Over the past 20 years (2005-2024), Green County experienced, on average, 18 hot days per year and seven warm nights per year.

Have Green County summers been getting hotter? It depends on what variable you are looking at. While both summer daytime and nighttime temperatures have been warming since 1950, the increase in nighttime temperatures is slightly higher. Summertime low temperatures have warmed by approximately 2-3°F since 1950.  By comparison, summer high temperatures in Green County have not warmed as much (1-2°F). You can read more about trends in summertime temperatures in Wisconsin in this blog post.

Green County can get quite chilly once winter rolls around! Some of our coldest days of the year in Wisconsin are when the overnight low temperatures dip below 0°F. The State Climatology Office performed an analysis on the likelihood of a “very cold day” (daily high temperature ≤ 10°F) or “very cold night” (daily low temperature ≤ 0°F) occurring between two calendar dates using historical measured temperature data from NOAA stations in Green County. Based on this analysis, very cold days and nights have occurred most frequently between January 21 to 31. Over the past 20 years (2005-2024), Green County experienced, on average, six very cold days per year and 20 very cold nights per year.

Across all four seasons, winter has warmed the most in Green County since 1950, a trend that holds true across most of Wisconsin. Since 1950, average winter temperatures in Green County have warmed by 4-5°F. Over this same time period, low temperatures in winter have warmed a bit more than the average temperatures (5-6°F). The coldest temperature of the year in Green County has shown a slight warming trend since 1950.

Heavy precipitation days, which for this publication refers to a one-day liquid precipitation total of two inches or more, can impact Green County at all times of the year. Extreme precipitation in the winter is measured by the amount of liquid that would be present if you melted down all of the snow that fell that day. The vast majority of these heavy precipitation days (77 percent) have occurred from June through September. June is the month that has historically had the most heavy precipitation days in Green County. In general, summer is the wettest season in Green County, with winter being the driest season. Over the past 20 years (2005-2024), Green County experienced, on average, 18 heavy precipitation days per decade.

Future climate projections from the Wisconsin Initiative on Climate Change Impacts (WICCI) indicate that by mid-century (2041-2060) under a moderate greenhouse gas emissions scenario, average annual temperatures in Green County will continue to increase by approximately 4°F compared to recent averages. Winter is projected to continue to be the season of the largest temperature increase (about 5°F). The number of nights where temperatures drop below 0°F is expected to decrease as winters warm (5 or less per year), and the number of nights in summer with temperatures staying above 70°F is expected to increase. The frequency of days that top 90°F are projected to increase with a warming climate (35 to 40 days per year). Days that top 100°F have been relatively rare in Green County up to 2025, but WICCI projections indicate that temperatures will hit 100°F a few days per year by mid-century.

Annual precipitation is expected to increase by around five percent by mid-century, according to WICCI projections. Winter and spring are projected to be the seasons of greatest precipitation increase in Green County (about 10%), with summers projected to be 5% drier by mid-century. Despite projections for drier summers, the frequency of heavy precipitation days (two inches or more) is projected to increase by mid-century. 

To explore more climate projections from WICCI and learn more about future climate modeling, please visit this website.

The data in this publication are a snapshot of the historical climate data for Green County. If you have questions about this publication or would like more data on a topic, please contact the Wisconsin State Climatology Office. 

For more information about how climate affects your farm, community, health, and livelihood, please check out these resources from the Division of Extension and the Wisconsin Initiative on Climate Change Impacts.