Ralston Reservoir, Colorado climate: Climate normals at a NOAA weather station
Ralston Reservoir's normal year runs from 23°F December nights to 87°F July afternoons, with 18.7 inches of precipitation and 63 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.8°C, December lows of −5°C, July highs of 31°C, 475 mm of precipitation a year.
- NOAA stationRalston Reservoir
- Station IDUSC00056816
- Location39.83°N 105.24°W
- Elevation5,900 ft (1,798 m)
On October 23, the normal high in Ralston Reservoir is 61°F and the normal low 37°F, and the chance of measurable rain or snow is 17%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Ralston Reservoir.
- Jan 45° 23°
- Feb 46° 22°
- Mar 54° 29°
- Apr 60° 35°
- May 69° 45°
- Jun 81° 55°
- Jul 87° 61°
- Aug 84° 59°
- Sep 76° 51°
- Oct 64° 39°
- Nov 53° 30°
- Dec 45° 23°
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 Ralston Reservoir each month?
July is the warmest month, with normal highs of 87°F; December the coldest, with normal lows of 23°F. The most precipitation falls in May (2.95 in), the least in January (0.70 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 45°F | 23°F | 34.2°F | 0.70 | 8.0 | 4 | <1 | 25 | 9 h 40 min |
| February | 46°F | 22°F | 34.2°F | 0.86 | 9.8 | 5 | <1 | 24 | 10 h 40 min |
| March | 54°F | 29°F | 41.7°F | 1.67 | 11.4 | 6 | <1 | 19 | 11 h 50 min |
| April | 60°F | 35°F | 47.6°F | 2.51 | 9.9 | 8 | <1 | 12 | 13 h 10 min |
| May | 69°F | 45°F | 56.8°F | 2.95 | 1.4 | 9 | <1 | 3 | 14 h 20 min |
| June | 81°F | 55°F | 67.8°F | 1.73 | 0.0 | 7 | 5 | <1 | 15 h |
| July | 87°F | 61°F | 73.8°F | 1.69 | 0.0 | 7 | 13 | <1 | 14 h 40 min |
| August | 84°F | 59°F | 71.6°F | 1.84 | 0.0 | 8 | 7 | <1 | 13 h 50 min |
| September | 76°F | 51°F | 63.7°F | 1.79 | 0.4 | 6 | 1 | <1 | 12 h 30 min |
| October | 64°F | 39°F | 51.6°F | 1.32 | 3.9 | 6 | <1 | 7 | 11 h 10 min |
| November | 53°F | 30°F | 41.3°F | 0.94 | 8.7 | 4 | <1 | 18 | 10 h |
| December | 45°F | 23°F | 33.8°F | 0.72 | 9.0 | 4 | <1 | 25 | 9 h 20 min |
| Year (annual) | 64°F | 39°F | 51.5°F | 18.72 | 62.5 | 75 | 28 | 133 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 7°C | −5°C | 1.2°C | 18 mm | 20 cm |
| February | 8°C | −5°C | 1.2°C | 22 mm | 25 cm |
| March | 12°C | −1°C | 5.4°C | 42 mm | 29 cm |
| April | 16°C | 2°C | 8.7°C | 64 mm | 25 cm |
| May | 21°C | 7°C | 13.8°C | 75 mm | 4 cm |
| June | 27°C | 13°C | 19.9°C | 44 mm | 0 cm |
| July | 31°C | 16°C | 23.2°C | 43 mm | 0 cm |
| August | 29°C | 15°C | 22.0°C | 47 mm | 0 cm |
| September | 25°C | 11°C | 17.6°C | 45 mm | 1 cm |
| October | 18°C | 4°C | 10.9°C | 34 mm | 10 cm |
| November | 11°C | −1°C | 5.2°C | 24 mm | 22 cm |
| December | 7°C | −5°C | 1.0°C | 18 mm | 23 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00056816; 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 Ralston Reservoir?
Normal highs sit between 65°F and 85°F in May, June, August and September. Of those, September has the fewest days with rain (6).
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 USC00056816.
When is the last frost at Ralston Reservoir?
In Ralston Reservoir, the last spring frost (32°F) comes after May 3 in half of years and after May 17 in one year in ten; the first autumn frost comes before October 14 in half of years and before September 30 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 31 year in 10 after May 17; 9 in 10 after April 21
- First autumn frost, half of years before
- October 141 year in 10 before September 30; 9 in 10 before October 28
NOAA puts the median frost-free season at 161 days, and the season without a hard freeze (28°F) at 182 days.
A hard freeze (28°F) comes after April 25 in half of springs and before October 23 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Ralston Reservoir in zone 6a in ZIP code 80007, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, the station is in zone 6a: the coldest night of a typical year reaches −7°F (20 complete years).
Frost dates for every NOAA station in Colorado · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00056816; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. 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 Ralston Reservoir?
In a normal year in Ralston Reservoir, 28 days a year reach 90°F (1 of them 100°F or more), 133 nights fall to 32°F or colder and 75 days bring measurable precipitation.
- Days at 90°F or more
- 28a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 133a normal year
- Days that stay below freezing
- 20high of 32°F or less
- Days with 0.01 inch of precipitation
- 75a normal year
- Days with 1 inch of snow or more
- 22a normal year
Source: NOAA NCEI 1991-2020 annual normals, station USC00056816.
How sunny is it at Ralston Reservoir?
Over a year 77% of the sunlight that would reach the ground under clear skies gets through the clouds at Ralston Reservoir, 4.7 kWh per square metre a day. February is the sunniest month (82%) and May the cloudiest (71%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 81% | 2.7 |
| February | 82% | 3.8 |
| March | 79% | 4.9 |
| April | 73% | 5.6 |
| May | 71% | 6.2 |
| June | 78% | 7.0 |
| July | 75% | 6.4 |
| August | 75% | 5.8 |
| September | 81% | 5.2 |
| October | 80% | 3.9 |
| November | 79% | 2.8 |
| December | 79% | 2.4 |
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 Ralston Reservoir record?
A normal year at Ralston Reservoir brings 5,642 heating degree days, 5% more than the median U.S. place (5,373), and 751 cooling degree days, 17% 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 2,937 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 955 | 0 |
| February | 863 | 0 |
| March | 724 | 0 |
| April | 523 | 2 |
| May | 279 | 25 |
| June | 57 | 140 |
| July | 6 | 277 |
| August | 14 | 220 |
| September | 120 | 81 |
| October | 420 | 6 |
| November | 711 | 0 |
| December | 968 | 0 |
| Year (annual) | 5,642 | 751 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00056816. 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.
Have recent years at Ralston Reservoir been warmer than normal?
2025 averaged 53.5°F, 2.0°F above the 1991-2020 normal of 51.5°F. 3 of the 4 complete years since 2022 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2022 | 52.2°F | +0.7°F | 17.59 | 96.8 |
| 2023 | 51.5°F | at normal | 21.30 | 48.1 |
| 2024 | 54.0°F | +2.5°F | 17.28 | 77.1 |
| 2025 | 53.5°F | +2.0°F | 17.17 | 34.5 |
Source: observed years: ACIS, station USC00056816. A year counts only with all twelve months complete.
How does Ralston Reservoir's climate compare?
Ralston Reservoir is warmer than 101 of the 125 places with their own NOAA record in Colorado, and wetter than 101. Across the 7,247 U.S. stations with normals, its annual mean of 51.5°F is warmer than 47%.
In the Köppen classification computed from these normals, Ralston Reservoir is Cfa: temperate, no dry season, hot summer. 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.
Questions about Ralston Reservoir's climate
What is the coldest month at Ralston Reservoir?
December, with a normal high of 45°F and a normal low of 23°F. The warmest is July (87°F by day, 61°F at night).
Does it snow at Ralston Reservoir?
Yes: 63 inches in a normal year, falling on 24 days with 0.1 inch or more, the most in March (11.4 inches).
What is the rainiest month at Ralston Reservoir?
May, with 2.95 in of precipitation in a normal year; the driest is January with 0.70 in.
What plant hardiness zone is Ralston Reservoir in?
The USDA's 2023 map puts Ralston Reservoir in zone 6a in ZIP code 80007, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches −7°F (20 years, 1991-2020): zone 6a.
How late can frost come at Ralston Reservoir?
In half of years the last 32°F night comes after May 3; in one year in ten it comes after May 17. Waiting until May 17 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Colorado climateThe statewide normals and every place in the state
- Wheat Ridge, CO7 miles from this station, 50.3°F a year
- Lakewood, CO8 miles from this station, 50.4°F a year
- Coal Creek, CO9 miles from this station, 39.9°F a year
- Gross Reservoir, CO9 miles from this station, 43.9°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made