30-year climate normals

Jefferson County Climate and Weather Averages

Hottest month — July

82.5°

average daily high. The coldest month is December, averaging a low of 11.5°F.

Jefferson County gets 10.8" of precipitation a year, and 51% 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	35.0°	11.9°	0.28"
February	37.8°	14.0°	0.19"
March	46.8°	20.8°	0.40"
April	54.5°	27.0°	0.78"
May	63.6°	35.3°	1.86"
June	72.0°	42.5°	2.30"
July	82.5°	48.3°	1.38"
August	82.0°	46.2°	1.12"
September	71.9°	38.1°	1.10"
October	57.4°	27.7°	0.64"
November	42.4°	18.6°	0.48"
December	33.6°	11.5°	0.27"

Rainfall by month

Jefferson County has a distinct wet season. 51% of the year's precipitation arrives in May, Jun, Jul.

January 0.28"

February 0.19"

March 0.40"

April 0.78"

May 1.86"

June 2.30"

July 1.38"

August 1.12"

September 1.10"

October 0.64"

November 0.48"

December 0.27"

Annual total 10.8"

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 157

Heating degree days How much heating the climate demands 8,312

Approximate annual cooling cost At 14.67¢/kWh, Montana average $23

Approximate annual electric heating cost Lower where heating is gas rather than electric $427

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 82.5°F in July and a low of 11.5°F in December. Annual precipitation is 10.8 inches, with essentially no snow.

When is the rainy season in Jefferson County?

The wettest stretch is May, Jun, Jul, which accounts for 51% of the year's precipitation. That is a pronounced wet season rather than rain spread evenly through the year.

How hot does it get in Jefferson County?

The average daily high in July, the hottest month, is 82.5°F. That drives 157 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 BOULDER, MT US (USC00241008), 7.8 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, Montana residential average.
Wet-season share is the wettest three consecutive months as a percentage of annual precipitation, calculated from the monthly normals.