Meteorological summer (June to August) ended with an intense heatwave. Rainfall varied widely this season, with some experiencing drought and others heavy downpours, and severe weather was relatively limited.
Summer Temperatures
This year’s summer featured temperatures very close to normal throughout Wisconsin. The statewide summer average was 67.3 degrees, a mere 0.1 degree above the 1991-2020 average, in sharp contrast to the fourth hottest summer on record experienced by the nation as a whole. Only in a few scattered places did daily average temperatures stray more than a degree from normal (Figure 1), although slightly larger (positive) anomalies were more common for daily minimum temperatures (Figure 2). These fairly typical average temperatures aligned with the tolerable amount of extreme heat Wisconsin experienced this summer.
Hot weather in 2024 has been brief and–except for the late-August heat wave–not especially intense, a far cry from the near record-breaking heat across much of the U.S. this summer. For example, in a typical year there are 10 days of at least 90 degrees at Wisconsin’s first-order weather stations (Eau Claire, Green Bay, La Crosse, Madison, Milwaukee, and Wausau), a frequency that’s been remarkably consistent for many decades despite the warming climate (Figure 3). By the end of summer this year, only six such hot days have occurred as our window for extreme heat rapidly closes with the arrival of September.
It also appears that Wisconsin will not record a 100-degree temperature in 2024. The absence of triple-digit heat is something that has become surprisingly common in recent years, even though Wisconsin’s annual maximum temperature used to regularly surpass 100 degrees, based on data back to the 1880s (Figure 4).
Late August Heat Wave
For the second year in a row, a late-August heat wave generated the hottest weather of the year and led to the National Weather Service issuing an excessive heat warning. A slew of daily temperature records were set throughout the state during the heatwave from August 26 to 29 (Figure 5). The highest temperature of the year (98 degrees) occurred at three locations: Beloit and Brodhead in the far south and Mondovi in the west. The heat was accompanied by stifling humidity, with widespread dewpoint temperatures in the mid-upper 70s and even a couple of stations (Boscobel and Lone Rock) touching 80 degrees.
This combination of extreme heat and moisture produced dangerously high heat indices of at least 110 degrees in a few places. Although this was a significant heat wave, it was short-lived and considerably less intense than the August 2023 event, when the air temperature alone exceeded the century mark in many places and included a statewide maximum for the year of 105 degrees.
Summer Rainfall Surplus
Much of Wisconsin did not have it easy this summer due to an abundance of precipitation (Figure 6). Intense downpours resulted in rainfall rates of one to two inches per hour and extreme one- and two-day precipitation events the weekend of June 21 across many counties from Sauk to Sheboygan. Heavy rains also caused a new June water level record along the Mississippi River at La Crosse and broke Madison’s one-hour accumulation record on July 14. Impacts were substantial, including the dam that failed in Waupaca County on July 5, as described in the July Climate Summary. The surplus of precipitation even pushed northern and southwestern Wisconsin out of their long-lasting drought in mid June.
However, abnormal dryness reappeared in northern and southwestern Wisconsin by the end of July and end of August, respectively, as a result of below-normal precipitation (Figure 7). Despite the highly varying precipitation pattern (both spatially and temporally), meteorological summer ended with a statewide average of 15.73 inches, a noteworthy 3.09 inches above normal and the sixth wettest summer on record. View the latest Wisconsin drought conditions and precipitation maps
Relatively Limited Severe Weather
Summer was relatively quiet in terms of severe weather. Although this year has appeared active in terms of the number of tornadoes, the 21 confirmed tornadoes for summer 2024 tied 1967 for fifteenth place, well behind the 58 tornadoes that slammed the state in the summer of 2005. Of the 21 tornadoes this summer, half were weak EF0s, underscoring the unexceptional severe weather this summer.
Challenging Conditions for Agriculture
The abundance of rainfall the first half of the summer made for difficult working and growing conditions. In August, nearly six days per week were suitable for fieldwork according to the National Agricultural Statistics Service. Despite the early summer challenges, Wisconsin’s corn and soybeans continued to progress, with a majority of the crops remaining in good to excellent condition and hovering right around the five-year average pace throughout the summer.
Apple quantity and quality were a mixed bag for Wisconsin’s approximately 300 orchards. Oneida Orchard is not opening this year for you-pick apples due to low yield from the false spring when many plants developed prematurely due to the record-warm winter and subsequently froze during a cold snap. However, other orchards are yielding a beautiful crop and have been open for picking as early as mid-July thanks to the warm winter pushing the apple buds to grow a lot sooner than normal.
Unfortunately, cherry growers in Door County had a rough season, as noted by Rebecca Wiepz, the superintendent of the UW–Madison’s Peninsular Agricultural Research Station in Door County. In addition to the pests and disease caused by the mild winter and warm, wet spring, the repetitive rains during June and early July made it nearly impossible to protect crops from pests and the excess moisture promoted bacterial and fungal growth. Many growers were unable to harvest fields that they found to be infested. Amazingly, of the almost 15 million pounds of cherries harvested, only 500,000 pounds were rejected, which is impressive given the conditions.
Climate Corner
The “dog days of summer” is a popular term to describe the hot and sultry weather often occurring in the heart of summer. According to folklore, dogs would tend to become mad (rabies) during that time of the year. However, the term goes back to ancient Egyptian astrology, as the “Dog Star,” or Sirius, would rise over the eastern horizon each day just before sunrise during July and early August. The Greeks noted that when Sirius was above the horizon during the daylight hours, heat, drought and sudden thunderstorms would often occur.
With Sirius being in conjunction with the Sun during July, the ancients reasoned that the extra light given off by Sirius during daylight would enhance the Sun’s heating. Hence, the “dog days of summer” were defined as being the 40 days running from July 3 through August 11, centered upon the alignment of Sirius with the Sun. When Sirius returned as a night star, the highly anticipated annual flooding of the Nile River would soon occur with the monsoon rains.
In Wisconsin, the hottest time of year occurs during the dog days in mid-July, based on statewide daily temperature data since 1893. The highest average daily maximum statewide temperature is approximately 82 degrees, occurring around July 19. Wisconsinites have experienced two significant heat waves in 2024, but they occurred during the third week of June and the last week of August. Thus, this year’s most memorable hot weather occurred before and after the true “dog days of summer.”
Steve Vavrus is the Wisconsin state climatologist. Bridgette Mason and Ed Hopkins are the assistant state climatologists.