Arrowrock Dam, Idaho climate: Climate normals at a NOAA weather station
Arrowrock Dam's normal year runs from 22°F January nights to 92°F July afternoons. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.6°C, January lows of −5°C, July highs of 33°C.
- NOAA stationArrowrock Dam
- Station IDUSC00100448
- Location43.59°N 115.92°W
- Elevation3,235 ft (986 m)
On October 23, the normal high in Arrowrock Dam is 61°F and the normal low 35°F.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Arrowrock Dam.
- Jan 37° 22°
- Feb 43° 25°
- Mar 53° 32°
- Apr 61° 37°
- May 71° 44°
- Jun 80° 50°
- Jul 92° 59°
- Aug 91° 57°
- Sep 80° 49°
- Oct 65° 38°
- Nov 48° 30°
- Dec 37° 24°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like at Arrowrock Dam each month?
July is the warmest month, with normal highs of 92°F; January the coldest, with normal lows of 22°F.
| Month | High | Low | Mean | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|
| January | 37°F | 22°F | 29.5°F | – | <1 | 29 | 9 h 20 min |
| February | 43°F | 25°F | 33.6°F | – | <1 | 24 | 10 h 30 min |
| March | 53°F | 32°F | 42.1°F | – | <1 | 19 | 11 h 50 min |
| April | 61°F | 37°F | 49.1°F | – | <1 | 7 | 13 h 20 min |
| May | 71°F | 44°F | 57.7°F | – | 1 | 1 | 14 h 40 min |
| June | 80°F | 50°F | 65.1°F | – | 6 | <1 | 15 h 20 min |
| July | 92°F | 59°F | 75.3°F | – | 20 | <1 | 15 h 10 min |
| August | 91°F | 57°F | 74.1°F | – | 18 | <1 | 14 h |
| September | 80°F | 49°F | 64.5°F | – | 5 | <1 | 12 h 30 min |
| October | 65°F | 38°F | 51.2°F | – | <1 | 8 | 11 h 10 min |
| November | 48°F | 30°F | 38.9°F | – | <1 | 20 | 9 h 40 min |
| December | 37°F | 24°F | 30.4°F | – | <1 | 27 | 9 h |
| Year (annual) | 63°F | 39°F | 51.0°F | – | 50 | 134 |
The same normals in °C and millimetres
| Month | High | Low | Mean |
|---|---|---|---|
| January | 3°C | −5°C | −1.4°C |
| February | 6°C | −4°C | 0.9°C |
| March | 12°C | 0°C | 5.6°C |
| April | 16°C | 3°C | 9.5°C |
| May | 22°C | 7°C | 14.3°C |
| June | 27°C | 10°C | 18.4°C |
| July | 33°C | 15°C | 24.1°C |
| August | 33°C | 14°C | 23.4°C |
| September | 27°C | 9°C | 18.1°C |
| October | 18°C | 3°C | 10.7°C |
| November | 9°C | −1°C | 3.8°C |
| December | 3°C | −5°C | −0.9°C |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Boise (16 miles away), gets 18 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00100448; 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.
Which months are mildest at Arrowrock Dam?
Normal highs sit between 65°F and 85°F in May, June and September.
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 USC00100448.
When is the last frost at Arrowrock Dam?
In Arrowrock Dam, the last spring frost (32°F) comes after April 28 in half of years and after May 16 in one year in ten; the first autumn frost comes before October 14 in half of years and before October 1 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
- April 281 year in 10 after May 16; 9 in 10 after April 11
- First autumn frost, half of years before
- October 141 year in 10 before October 1; 9 in 10 before October 29
NOAA puts the median frost-free season at 169 days, and the season without a hard freeze (28°F) at 203 days.
A hard freeze (28°F) comes after April 6 in half of springs and before October 27 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Arrowrock Dam in zone 7a in ZIP code 83712, 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 USC00100448; 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 at Arrowrock Dam?
In a normal year in Arrowrock Dam, 50 days a year reach 90°F (9 of them 100°F or more) and 134 nights fall to 32°F or colder.
- Days at 90°F or more
- 50a normal year
- Days at 100°F or more
- 9a normal year
- Nights at 32°F or colder
- 134a normal year
- Days that stay below freezing
- 21high of 32°F or less
The highest temperature in this station's record (since 1911) is 112°F, on July 29, 1934; the lowest is −32°F, on January 21, 1937.
The wettest calendar year on that record is 1983, with 30.10 in; the snowiest season is 1948–49, with 131.3 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00100448; records: ACIS (NOAA Regional Climate Centers), station USC00100448. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Arrowrock Dam?
Over a year 81% of the sunlight that would reach the ground under clear skies gets through the clouds at Arrowrock Dam, 4.6 kWh per square metre a day. July is the sunniest month (92%) and December the cloudiest (63%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 67% | 1.8 |
| February | 71% | 2.8 |
| March | 70% | 3.9 |
| April | 75% | 5.4 |
| May | 79% | 6.6 |
| June | 85% | 7.6 |
| July | 92% | 7.8 |
| August | 91% | 6.7 |
| September | 87% | 5.2 |
| October | 80% | 3.5 |
| November | 71% | 2.1 |
| December | 63% | 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 many heating and cooling degree days does Arrowrock Dam record?
A normal year at Arrowrock Dam brings 5,914 heating degree days, 10% more than the median U.S. place (5,373), and 827 cooling degree days, 9% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,878 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,100 | 0 |
| February | 878 | 0 |
| March | 708 | 0 |
| April | 478 | 1 |
| May | 250 | 23 |
| June | 92 | 94 |
| July | 10 | 329 |
| August | 12 | 294 |
| September | 98 | 82 |
| October | 432 | 4 |
| November | 781 | 0 |
| December | 1,074 | 0 |
| Year (annual) | 5,914 | 827 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00100448. 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.
How does Arrowrock Dam's climate compare?
Arrowrock Dam is warmer than 72 of the 85 places with their own NOAA record in Idaho. Across the 7,247 U.S. stations with normals, its annual mean of 51.0°F is warmer than 45%.
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers.
Which places near Arrowrock Dam share this climate record?
Robie Creek has no NOAA station with 1991-2020 normals of its 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.
- Robie Creek, ID1,240 people · 7 mi NW
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Arrowrock Dam's climate
What is the coldest month at Arrowrock Dam?
January, with a normal high of 37°F and a normal low of 22°F. The warmest is July (92°F by day, 59°F at night).
Does it snow at Arrowrock Dam?
Yes. NOAA publishes no 1991-2020 snowfall normal for the station; the nearest record that keeps one, Boise (16 miles away), records 18 inches of snow in a normal year.
What plant hardiness zone is Arrowrock Dam in?
The USDA's 2023 map puts Arrowrock Dam in zone 7a in ZIP code 83712, the nearest ZIP area.
How late can frost come at Arrowrock Dam?
In half of years the last 32°F night comes after April 28; in one year in ten it comes after May 16. Waiting until May 16 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Idaho climateThe statewide normals and every place in the state
- Boise Lucky Peak Dam, ID8 miles from this station, 52.8°F a year
- Boise, ID16 miles from this station, 53.2°F a year
- Idaho City, ID17 miles from this station, 43.8°F a year
- Emmett, ID32 miles from this station, 51.5°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made