30-year climate normals

Washtenaw County Climate and Weather Averages

Hottest month — July

83.8°

average daily high. The coldest month is January, averaging a low of 15.2°F.

Washtenaw County gets 29.78" of precipitation a year, and 34% 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	31.8°	15.2°	1.68"
February	34.6°	16.0°	1.51"
March	45.4°	25.3°	1.95"
April	58.7°	35.3°	3.03"
May	70.1°	45.6°	3.35"
June	79.2°	53.7°	3.61"
July	83.8°	57.2°	3.20"
August	81.4°	56.9°	2.69"
September	74.2°	48.4°	2.76"
October	61.5°	38.3°	2.22"
November	47.9°	29.5°	2.09"
December	36.4°	21.5°	1.69"

Rainfall by month

Precipitation is spread fairly evenly through the year here, with 34% falling in the wettest three months (May, Jun, Jul).

January 1.68"

February 1.51"

March 1.95"

April 3.03"

May 3.35"

June 3.61"

July 3.20"

August 2.69"

September 2.76"

October 2.22"

November 2.09"

December 1.69"

Annual total 29.78"

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 520

Heating degree days How much heating the climate demands 6,742

Approximate annual cooling cost At 22.01¢/kWh, Michigan average $114

Approximate annual electric heating cost Lower where heating is gas rather than electric $519

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 Washtenaw County, where electricity is one line of eight.

Common questions

What is the weather like in Washtenaw County?

Washtenaw County averages a high of 83.8°F in July and a low of 15.2°F in January. Annual precipitation is 29.78 inches, with essentially no snow.

When is the rainy season in Washtenaw County?

The wettest stretch is May, Jun, Jul, which accounts for 34% of the year's precipitation. Precipitation is relatively evenly distributed across the year.

How hot does it get in Washtenaw County?

The average daily high in July, the hottest month, is 83.8°F. That drives 520 cooling degree days a year, which is what your air conditioning has to work against.

Does it snow in Washtenaw County?

Effectively no. Measurable snowfall is rare in Washtenaw County.

Sources

Temperature, precipitation and snowfall normals — NOAA National Centers for Environmental Information, 1991–2020 Monthly Climate Normals, station ANN ARBOR MUNI AP, MI US (USW00094889), 5.5 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, Michigan residential average.
Wet-season share is the wettest three consecutive months as a percentage of annual precipitation, calculated from the monthly normals.