Arco, Idaho climate: Normal weather by month, frost dates and records
Arco's normal year runs from 7°F January nights to 87°F July afternoons, with 8.8 inches of precipitation and 24 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 6.5°C, January lows of −14°C, July highs of 30°C, 224 mm of precipitation a year.
- NOAA stationArco
- Station IDUSC00100375
- Location43.64°N 113.30°W
- Elevation5,325 ft (1,623 m)
- Population911
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Arco.
- Jan 30° 7°
- Feb 35° 12°
- Mar 46° 23°
- Apr 57° 30°
- May 67° 39°
- Jun 76° 46°
- Jul 87° 52°
- Aug 85° 50°
- Sep 75° 41°
- Oct 60° 31°
- Nov 43° 19°
- Dec 31° 9°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Arco each month?
July is the warmest month, with normal highs of 87°F; January the coldest, with normal lows of 7°F. The most precipitation falls in May (1.20 in), the least in July (0.32 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 30°F | 7°F | 18.6°F | 0.67 | 7.0 | 4 | <1 | 31 | 9 h 20 min |
| February | 35°F | 12°F | 23.2°F | 0.62 | 4.6 | 4 | <1 | 28 | 10 h 30 min |
| March | 46°F | 23°F | 34.4°F | 0.68 | 1.1 | 4 | <1 | 28 | 11 h 50 min |
| April | 57°F | 30°F | 43.8°F | 0.86 | 1.3 | 5 | <1 | 18 | 13 h 20 min |
| May | 67°F | 39°F | 52.8°F | 1.20 | 0.2 | 6 | <1 | 6 | 14 h 40 min |
| June | 76°F | 46°F | 61.0°F | 1.13 | 0.0 | 4 | 1 | 1 | 15 h 20 min |
| July | 87°F | 52°F | 69.1°F | 0.32 | 0.0 | 2 | 10 | <1 | 15 h 10 min |
| August | 85°F | 50°F | 67.2°F | 0.54 | 0.0 | 3 | 7 | <1 | 14 h |
| September | 75°F | 41°F | 57.9°F | 0.66 | 0.0 | 4 | 1 | 3 | 12 h 30 min |
| October | 60°F | 31°F | 45.0°F | 0.71 | 0.3 | 4 | <1 | 18 | 11 h 10 min |
| November | 43°F | 19°F | 30.8°F | 0.55 | 1.2 | 3 | <1 | 28 | 9 h 40 min |
| December | 31°F | 9°F | 20.3°F | 0.86 | 8.1 | 5 | <1 | 31 | 9 h |
| Year (annual) | 58°F | 30°F | 43.7°F | 8.80 | 23.8 | 48 | 19 | 192 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | −1°C | −14°C | −7.4°C | 17 mm | 18 cm |
| February | 2°C | −11°C | −4.9°C | 16 mm | 12 cm |
| March | 8°C | −5°C | 1.3°C | 17 mm | 3 cm |
| April | 14°C | −1°C | 6.6°C | 22 mm | 3 cm |
| May | 19°C | 4°C | 11.6°C | 30 mm | 1 cm |
| June | 25°C | 8°C | 16.1°C | 29 mm | 0 cm |
| July | 30°C | 11°C | 20.6°C | 8 mm | 0 cm |
| August | 29°C | 10°C | 19.6°C | 14 mm | 0 cm |
| September | 24°C | 5°C | 14.4°C | 17 mm | 0 cm |
| October | 15°C | −1°C | 7.2°C | 18 mm | 1 cm |
| November | 6°C | −7°C | −0.7°C | 14 mm | 3 cm |
| December | 0°C | −13°C | −6.5°C | 22 mm | 21 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00100375; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Arco?
Normal highs sit between 65°F and 85°F in May, June, August and September. Of those, August has the fewest days with rain (3).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00100375.
When is the last frost in Arco?
In Arco, the last spring frost (32°F) comes after May 22 in half of years and after June 9 in one year in ten; the first autumn frost comes before September 22 in half of years and before September 4 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- May 221 year in 10 after June 9; 9 in 10 after May 5
- First autumn frost, half of years before
- September 221 year in 10 before September 4; 9 in 10 before October 7
NOAA puts the median frost-free season at 119 days, and the season without a hard freeze (28°F) at 146 days.
A hard freeze (28°F) comes after May 6 in half of springs and before October 3 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Arco in zone 5a in ZIP code 83255, the nearest ZIP area.
Frost dates for every NOAA station in Idaho · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00100375; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Arco?
In a normal year in Arco, 19 days a year reach 90°F, 192 nights fall to 32°F or colder and 48 days bring measurable precipitation.
- Days at 90°F or more
- 19a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 192a normal year
- Days that stay below freezing
- 53high of 32°F or less
- Days with 0.01 inch of precipitation
- 48a normal year
- Days with 1 inch of snow or more
- 7a normal year
The highest temperature in this station's record (since 1914) is 102°F, on July 29, 1934; the lowest is −46°F, on January 21, 1937.
The wettest calendar year on that record is 1968, with 15.33 in; the snowiest season is 1964–65, with 73.4 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00100375; records: ACIS (NOAA Regional Climate Centers), station USC00100375. Records use complete months only; a month missing more than three days is left out.
How sunny is Arco?
Over a year 79% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Arco, 4.5 kWh per square metre a day. July is the sunniest month (89%) and December the cloudiest (64%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 68% | 1.9 |
| February | 70% | 2.8 |
| March | 71% | 4.0 |
| April | 73% | 5.4 |
| May | 77% | 6.5 |
| June | 83% | 7.5 |
| July | 89% | 7.6 |
| August | 88% | 6.5 |
| September | 86% | 5.2 |
| October | 81% | 3.5 |
| November | 73% | 2.2 |
| December | 64% | 1.5 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Arco need?
A normal year in Arco brings 8,053 heating degree days, 50% more than the median U.S. place (5,373), and 313 cooling degree days, 65% fewer than the median (908). Eight months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 1,923 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,437 | 0 |
| February | 1,170 | 0 |
| March | 950 | 0 |
| April | 636 | 0 |
| May | 382 | 4 |
| June | 153 | 35 |
| July | 27 | 154 |
| August | 40 | 106 |
| September | 225 | 14 |
| October | 620 | 0 |
| November | 1,025 | 0 |
| December | 1,387 | 0 |
| Year (annual) | 8,053 | 313 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00100375. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Arco been warmer than normal lately?
2025 averaged 45.9°F, 2.2°F above the 1991-2020 normal of 43.7°F. 2 of the 2 complete years since 2024 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2024 | 45.4°F | +1.7°F | 6.46 | – |
| 2025 | 45.9°F | +2.2°F | 7.25 | – |
Source: observed years: ACIS, station USC00100375. A year counts only with all twelve months complete.
How does Arco's climate compare?
Arco is warmer than 19 of the other 84 places with their own NOAA record in Idaho, and wetter than 3. Across the 7,247 U.S. stations with normals, its annual mean of 43.7°F is warmer than 14%.
In the Köppen classification computed from these normals, Arco is BSk: cold semi-arid steppe. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Arco share this climate record?
2 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Moore, ID175 people · 8 mi NW
- Butte City, ID86 people · 4 mi SE
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Arco's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Arco. This page uses Arco; the other differs by site and elevation:
| Station | From this station | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Arco (17 mi SW) USW00004126 | 18 mi SW | 5,920 ft | 43.0°F | 13°F | 83°F | 15.5 | – | May 24 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Arco's climate
What is the coldest month in Arco?
January, with a normal high of 30°F and a normal low of 7°F. The warmest is July (87°F by day, 52°F at night).
Does it snow in Arco?
Yes: 24 inches in a normal year, falling on 9 days with 0.1 inch or more, the most in December (8.1 inches).
What is the rainiest month in Arco?
May, with 1.20 in of precipitation in a normal year; the driest is July with 0.32 in.
What plant hardiness zone is Arco in?
The USDA's 2023 map puts Arco in zone 5a in ZIP code 83255, the nearest ZIP area.
How late can frost come in Arco?
In half of years the last 32°F night comes after May 22; in one year in ten it comes after June 9. Waiting until June 9 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Idaho climateThe statewide normals and every place in the state
- Craters Of The Moon, ID17 miles from this station, 39.1°F a year
- Howe, ID18 miles from this station, 44.0°F a year
- Idaho Falls (46 mi W), ID19 miles from this station, 42.7°F a year
- Mackay, ID25 miles from this station, 42.2°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made