30-year climate normals

Jefferson County Climate and Weather Averages

Hottest month — July

82.4°

average daily high. The coldest month is January, averaging a low of 11.0°F.

Jefferson County gets 38.74" of precipitation a year, and 36% of it falls in May, Jun, Jul.

Temperature through the year

Each bar spans the average daily low to the average daily high for that month.

Month	Avg high	Avg low	Precip
January	26.8°	11.0°	1.64"
February	31.1°	14.1°	1.58"
March	43.2°	24.6°	2.14"
April	56.3°	35.5°	4.02"
May	68.7°	48.1°	4.45"
June	78.8°	58.1°	4.97"
July	82.4°	62.4°	4.54"
August	80.4°	60.8°	4.30"
September	73.6°	51.8°	3.72"
October	60.3°	40.6°	3.12"
November	45.1°	28.5°	2.37"
December	32.5°	18.2°	1.89"

Rainfall by month

Precipitation is spread fairly evenly through the year here, with 36% falling in the wettest three months (May, Jun, Jul).

January 1.64"

February 1.58"

March 2.14"

April 4.02"

May 4.45"

June 4.97"

July 4.54"

August 4.30"

September 3.72"

October 3.12"

November 2.37"

December 1.89"

Annual total 38.74"

What this climate costs you

Degree days measure how hard a building has to work to stay comfortable. They are the reason two identical houses have very different power bills, and they are the link between the weather here and what you pay every month.

Cooling degree days How much air conditioning the climate demands 678

Heating degree days How much heating the climate demands 7,125

Approximate annual cooling cost At 19.74¢/kWh, Wisconsin average $134

Approximate annual electric heating cost Lower where heating is gas rather than electric $492

These are rough planning figures from degree days and the state electricity price, not a bill estimate. House size, insulation and fuel type move them a lot. See the full cost of owning a home in Jefferson County, where electricity is one line of eight.

Common questions

What is the weather like in Jefferson County?

Jefferson County averages a high of 82.4°F in July and a low of 11.0°F in January. Annual precipitation is 38.74 inches, with essentially no snow.

When is the rainy season in Jefferson County?

The wettest stretch is May, Jun, Jul, which accounts for 36% of the year's precipitation. Precipitation is relatively evenly distributed across the year.

How hot does it get in Jefferson County?

The average daily high in July, the hottest month, is 82.4°F. That drives 678 cooling degree days a year, which is what your air conditioning has to work against.

Does it snow in Jefferson County?

Effectively no. Measurable snowfall is rare in Jefferson County.

Sources

Temperature, precipitation and snowfall normals — NOAA National Centers for Environmental Information, 1991–2020 Monthly Climate Normals, station JEFFERSON WWTP, WI US (USC00474108), 2 miles from the county centroid.
Heating and cooling degree days — NOAA, same station and period.
Electricity price — US Energy Information Administration, Electric Power Monthly Table 5.6.A, Wisconsin residential average.
Wet-season share is the wettest three consecutive months as a percentage of annual precipitation, calculated from the monthly normals.