30-year climate normals
McHenry County Climate and Weather Averages
Hottest month — July
84.0°average daily high. The coldest month is January, averaging a low of 14.2°F.
McHenry County gets 39.35" of precipitation a year and 35.1" of snow, 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 | Snow |
|---|---|---|---|---|
| January | 31.5° | 14.2° | 1.97" | 10.0" |
| February | 35.2° | 16.3° | 1.84" | 9.0" |
| March | 46.8° | 26.4° | 2.51" | 4.4" |
| April | 59.2° | 36.7° | 3.76" | 1.2" |
| May | 71.3° | 47.9° | 4.98" | 0.0" |
| June | 80.3° | 58.4° | 5.26" | 0.0" |
| July | 84.0° | 62.5° | 3.90" | 0.0" |
| August | 82.0° | 61.2° | 3.81" | 0.0" |
| September | 74.4° | 52.4° | 3.54" | 0.0" |
| October | 61.9° | 42.4° | 3.20" | 0.2" |
| November | 47.5° | 30.5° | 2.48" | 1.6" |
| December | 35.5° | 20.4° | 2.10" | 8.7" |
Rainfall by month
Precipitation is spread fairly evenly through the year here, with 36% falling in the wettest three months (May, Jun, Jul).
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.
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 McHenry County, where electricity is one line of eight.
Common questions
What is the weather like in McHenry County?
McHenry County averages a high of 84.0°F in July and a low of 14.2°F in January. Annual precipitation is 39.35 inches, including 35.1 inches of snow.
When is the rainy season in McHenry 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 McHenry County?
The average daily high in July, the hottest month, is 84.0°F. That drives 771 cooling degree days a year, which is what your air conditioning has to work against.
Does it snow in McHenry County?
Yes. McHenry County averages 35.1 inches of snow a year.
Sources
- Temperature, precipitation and snowfall normals — NOAA National Centers for Environmental Information, 1991–2020 Monthly Climate Normals, station CRYSTAL LAKE 4NW, IL US (USC00112048), 5.2 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, Illinois residential average.
- Wet-season share is the wettest three consecutive months as a percentage of annual precipitation, calculated from the monthly normals.