30-year climate normals

Lewis and Clark County Climate and Weather Averages

Hottest month — July

81.5°

average daily high. The coldest month is February, averaging a low of 16.2°F.

Lewis and Clark County gets 17.09" of precipitation a year, and 46% of it falls in Apr, May, Jun.

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	35.7°	17.3°	0.64"
February	36.8°	16.2°	0.75"
March	45.3°	23.0°	0.88"
April	53.2°	29.9°	1.77"
May	62.3°	38.4°	2.99"
June	70.6°	45.5°	3.06"
July	81.5°	50.5°	1.23"
August	80.7°	48.9°	1.24"
September	70.1°	40.7°	1.65"
October	55.3°	32.2°	1.37"
November	42.1°	24.6°	0.75"
December	34.4°	17.5°	0.76"

Rainfall by month

Lewis and Clark County has a distinct wet season. 46% of the year's precipitation arrives in Apr, May, Jun.

January 0.64"

February 0.75"

March 0.88"

April 1.77"

May 2.99"

June 3.06"

July 1.23"

August 1.24"

September 1.65"

October 1.37"

November 0.75"

December 0.76"

Annual total 17.09"

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 218

Heating degree days How much heating the climate demands 7,893

Approximate annual cooling cost At 14.67¢/kWh, Montana average $32

Approximate annual electric heating cost Lower where heating is gas rather than electric $405

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 Lewis and Clark County, where electricity is one line of eight.

Common questions

What is the weather like in Lewis and Clark County?

Lewis and Clark County averages a high of 81.5°F in July and a low of 16.2°F in February. Annual precipitation is 17.09 inches, with essentially no snow.

When is the rainy season in Lewis and Clark County?

The wettest stretch is Apr, May, Jun, which accounts for 46% 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 Lewis and Clark County?

The average daily high in July, the hottest month, is 81.5°F. That drives 218 cooling degree days a year, which is what your air conditioning has to work against.

Does it snow in Lewis and Clark County?

Effectively no. Measurable snowfall is rare in Lewis and Clark County.

Sources

Temperature, precipitation and snowfall normals — NOAA National Centers for Environmental Information, 1991–2020 Monthly Climate Normals, station ROGERS PASS 9 NNE, MT US (USC00247159), 6.4 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.