Photo: davidwilson1949 · CC BY 2.0Hardly any U.S. towns collect less precipitation than Arco: 9 inches a year
On a normal July day the thermometer tops out near 86°. Its January nights bite harder than in 97% of U.S. towns. Warming shows here too: 1.1° more than in 1901–2000, led by March. Warm coats and heating bills mark the months from October to April, when means dip under 50°.
A year in Arco at a glance
Each month’s typical high and low, and what it brings.
What stands out about Arco’s climate
Compared with towns across the U.S., with Arco’s place in Idaho beside it.
What a year in Arco feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 119 frost-free days a year
In half of years the last 32° night comes by May 22 and the first by September 22. Frost and day counts come from NOAA’s station at Arco, ID, 0.2 miles from the town’s center, at about the same height.
The 2023 USDA map puts Arco’s center in zone 5a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −18°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 24 inches of snow a winter
Snow, measured at Arco, ID, falls mostly in December. Precipitation (rain plus melted snow) adds up to 9 inches a year; May is the wettest month and July the driest. Rain or snow falls on about 48 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Arco
96% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through May.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Arco, ID.
Living with Arco’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
119 frost-free days in zone 5a. The last frost comes by May 22 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Sep 22.
Months with highs of 62–84° and lows of 40° or more: June, August and September. 0.8 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Arco from natural hazards, river flooding is the largest share (43%); heat waves, cold waves, winter storms and ice storms together are 28%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Arco and similar climates
TownRatings has no climate map of the towns around Arco yet.
Climates most like Arco’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Arco, ID | 7° | 86° | 9" | 24" |
| Rock Springs, WY | 9° | 87° | 9" | 31" |
| Salida, CO | 10° | 85° | 8" | 37" |
| Sidney, MT | 4° | 85° | 15" | 30" |
| Taos, NM | 11° | 84° | 13" | 28" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Arco averaged 1.1° warmer than the 1900s. The biggest change is in March (+2.8°).
A smaller shift than in 68% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Arco compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Arco’s place among Idaho’s.
Arco weather by month
Highs, lows and precipitation from NOAA’s grid at Arco’s center; snow, wet days and snow on the ground from Arco, ID. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 29° | 7° | 0.8" | 7.0" | 4 | 9° – 26° |
| February | 34° | 11° | 0.7" | 4.6" | 4 | 14° – 34° |
| March | 45° | 22° | 0.7" | 1.1" | 4 | 25° – 41° |
| April | 55° | 29° | 0.9" | 1.3" | 5 | 36° – 47° |
| May | 65° | 38° | 1.3" | 0.2" | 6 | 46° – 58° |
| June | 75° | 44° | 1.0" | 0.0" | 4 | 54° – 66° |
| July | 86° | 51° | 0.4" | 0.0" | 2 | 58° – 74° |
| August | 84° | 49° | 0.5" | 0.0" | 3 | 60° – 70° |
| September | 73° | 40° | 0.7" | 0.0" | 4 | 52° – 62° |
| October | 58° | 29° | 0.8" | 0.3" | 4 | 34° – 50° |
| November | 41° | 18° | 0.6" | 1.2" | 3 | 22° – 36° |
| December | 30° | 8° | 0.9" | 8.1" | 5 | 11° – 25° |
| Year | 56° | 29° | 9.3" | 23.8" | 48 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 14° to 34°. September is the most reliable, staying within 9°.
Where Arco’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Arco’s center.
- Snow: Arco, ID (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Arco, ID, 0.2 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Arco’s climate
What is the weather like in Arco?
A typical July afternoon reaches 86°, a January night drops to 7°, and about 24 inches of snow falls in a normal winter. Colder January nights than 97% of U.S. towns; hotter July afternoons than 54% of U.S. towns.
How cold does it get in Arco in winter?
January nights average 7°. About 192 nights a year reach 32° or below and 21 reach 0° or below. In the coldest January of the last 30 years the month averaged 9°.
How much snow does Arco get?
About 24 inches in a normal winter at Arco, ID, most of it in December.
How hot does it get in Arco?
July, with a typical high of 86° and a low of 51°. About 19 days a year reach 90° (Arco, ID).
When is the first and last frost in Arco?
In half of years the last spring frost (32°) comes by May 22 and the first fall frost by September 22, about 119 frost-free days, at Arco, ID.
What growing zone is Arco in?
Zone 5a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −18°.
What is the best time of year to visit Arco?
By one simple rule (highs of 62–84° and lows of 40° or more), June, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Arco getting warmer?
Yes: 1991–2020 averaged 1.1° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 68% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Arco.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.