Castle Rock, Colorado climate: Normal weather by month, frost dates and records
Castle Rock's normal year runs from 18°F January nights to 86°F July afternoons, with 17.6 inches of precipitation and 58 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.8°C, January lows of −8°C, July highs of 30°C, 447 mm of precipitation a year.
- NOAA stationCastle Rock
- Station IDUSC00051401
- Location39.41°N 104.91°W
- Elevation6,185 ft (1,885 m)
- Population83,213
On October 23, the normal high in Castle Rock is 62°F and the normal low 32°F, and the chance of measurable rain or snow is 14%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Castle Rock.
- Jan 46° 18°
- Feb 47° 20°
- Mar 54° 27°
- Apr 59° 33°
- May 68° 42°
- Jun 80° 51°
- Jul 86° 56°
- Aug 84° 55°
- Sep 77° 47°
- Oct 65° 35°
- Nov 54° 26°
- Dec 46° 18°
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 Castle Rock each month?
July is the warmest month, with normal highs of 86°F; January the coldest, with normal lows of 18°F. The most precipitation falls in August (2.52 in), the least in January (0.55 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 46°F | 18°F | 31.8°F | 0.55 | 8.0 | 4 | <1 | 30 | 9 h 40 min |
| February | 47°F | 20°F | 33.3°F | 0.70 | 10.7 | 5 | <1 | 26 | 10 h 40 min |
| March | 54°F | 27°F | 40.2°F | 1.54 | 10.7 | 5 | <1 | 24 | 11 h 50 min |
| April | 59°F | 33°F | 45.8°F | 2.08 | 8.3 | 6 | <1 | 17 | 13 h 10 min |
| May | 68°F | 42°F | 55.0°F | 1.97 | 1.1 | 8 | <1 | 4 | 14 h 20 min |
| June | 80°F | 51°F | 65.3°F | 2.20 | 0.0 | 8 | 4 | <1 | 15 h |
| July | 86°F | 56°F | 71.1°F | 2.32 | 0.0 | 8 | 11 | <1 | 14 h 40 min |
| August | 84°F | 55°F | 69.1°F | 2.52 | 0.0 | 10 | 6 | <1 | 13 h 50 min |
| September | 77°F | 47°F | 61.7°F | 1.39 | 0.4 | 6 | 2 | 1 | 12 h 30 min |
| October | 65°F | 35°F | 49.7°F | 0.85 | 2.7 | 4 | <1 | 12 | 11 h 10 min |
| November | 54°F | 26°F | 39.8°F | 0.79 | 6.7 | 4 | <1 | 24 | 10 h |
| December | 46°F | 18°F | 31.8°F | 0.69 | 8.9 | 5 | <1 | 29 | 9 h 20 min |
| Year (annual) | 64°F | 35°F | 49.6°F | 17.60 | 57.5 | 74 | 23 | 167 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 8°C | −8°C | −0.1°C | 14 mm | 20 cm |
| February | 8°C | −7°C | 0.7°C | 18 mm | 27 cm |
| March | 12°C | −3°C | 4.6°C | 39 mm | 27 cm |
| April | 15°C | 0°C | 7.7°C | 53 mm | 21 cm |
| May | 20°C | 5°C | 12.8°C | 50 mm | 3 cm |
| June | 27°C | 10°C | 18.5°C | 56 mm | 0 cm |
| July | 30°C | 14°C | 21.7°C | 59 mm | 0 cm |
| August | 29°C | 13°C | 20.6°C | 64 mm | 0 cm |
| September | 25°C | 8°C | 16.5°C | 35 mm | 1 cm |
| October | 18°C | 1°C | 9.8°C | 22 mm | 7 cm |
| November | 12°C | −4°C | 4.3°C | 20 mm | 17 cm |
| December | 8°C | −8°C | −0.1°C | 18 mm | 23 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00051401; 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 Castle Rock?
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 USC00051401.
When is the last frost in Castle Rock?
In Castle Rock, the last spring frost (32°F) comes after May 9 in half of years and after May 24 in one year in ten; the first autumn frost comes before October 2 in half of years and before September 17 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 91 year in 10 after May 24; 9 in 10 after April 30
- First autumn frost, half of years before
- October 21 year in 10 before September 17; 9 in 10 before October 16
NOAA puts the median frost-free season at 143 days, and the season without a hard freeze (28°F) at 161 days.
A hard freeze (28°F) comes after May 1 in half of springs and before October 12 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Castle Rock in zone 5b across its 3 ZIP code areas (5b in 80104, the largest). By the map's own method, the average of each year's coldest night over 1991-2020, Castle Rock's NOAA station is in zone 5b: the coldest night of a typical year reaches −11°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 USC00051401; 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.
What hardiness zone is each Castle Rock ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Castle Rock's 3 ZIP code areas are all in zone 5b. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Castle Rock?
In a normal year in Castle Rock, 23 days a year reach 90°F, 167 nights fall to 32°F or colder and 74 days bring measurable precipitation.
- Days at 90°F or more
- 23a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 167a normal year
- Days that stay below freezing
- 17high of 32°F or less
- Days with 0.01 inch of precipitation
- 74a normal year
- Days with 1 inch of snow or more
- 17a normal year
The highest temperature in this station's record (since 1893) is 102°F, on July 11, 2022; the lowest is −37°F, on January 6, 1913.
The wettest calendar year on that record is 1965, with 30.39 in; the snowiest season is 1982–83, with 114.8 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00051401; records: ACIS (NOAA Regional Climate Centers), station USC00051401. Records use complete months only; a month missing more than three days is left out.
How sunny is Castle Rock?
Over a year 80% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Castle Rock, 4.8 kWh per square metre a day. September is the sunniest month (85%) and May the cloudiest (76%). Among the 459 U.S. places of 50,000 or more, that ranks tied 125th (with 50 others) in sunshine.
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 79% | 2.6 |
| February | 78% | 3.5 |
| March | 78% | 4.7 |
| April | 76% | 5.8 |
| May | 76% | 6.5 |
| June | 82% | 7.2 |
| July | 83% | 7.0 |
| August | 84% | 6.3 |
| September | 85% | 5.4 |
| October | 82% | 4.0 |
| November | 81% | 2.9 |
| December | 79% | 2.3 |
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 Castle Rock need?
A normal year in Castle Rock brings 6,103 heating degree days, 14% more than the median U.S. place (5,373), and 499 cooling degree days, 45% 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 2,491 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,029 | 0 |
| February | 888 | 0 |
| March | 771 | 0 |
| April | 577 | 1 |
| May | 321 | 11 |
| June | 79 | 89 |
| July | 11 | 198 |
| August | 21 | 149 |
| September | 148 | 47 |
| October | 477 | 2 |
| November | 756 | 0 |
| December | 1,028 | 0 |
| Year (annual) | 6,103 | 499 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00051401. 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 Castle Rock been warmer than normal lately?
2024 averaged 51.6°F, 2.0°F above the 1991-2020 normal of 49.6°F. 2 of the 3 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 56.1°F | +6.5°F | 15.99 | 47.8 |
| 2023 | 49.3°F | −0.4°F | 25.93 | 43.7 |
| 2024 | 51.6°F | +2.0°F | 19.20 | 91.4 |
Over 32 complete years from 1963 to 2024, the station's annual mean temperature rose at a fitted 3.0°F per century (+0.16°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00051401; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Castle Rock's climate compare?
Castle Rock is warmer than 69 of the other 124 places with their own NOAA record in Colorado, and wetter than 89. Across the 7,247 U.S. stations with normals, its annual mean of 49.6°F is warmer than 38%.
In the Köppen classification computed from these normals, Castle Rock 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 Castle Rock share this climate record?
4 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.
- Castle Pines, CO15,162 people · 4 mi NE
- Castle Pines Village, CO4,441 people · 2 mi N
- Perry Park, CO1,801 people · 11 mi S
- Sedalia, CO49 people · 4 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 Castle Rock's climate
What is the coldest month in Castle Rock?
January, with a normal high of 46°F and a normal low of 18°F. The warmest is July (86°F by day, 56°F at night).
Does it snow in Castle Rock?
Yes: 58 inches in a normal year, falling on 23 days with 0.1 inch or more, the most in February (10.7 inches).
What is the rainiest month in Castle Rock?
August, with 2.52 in of precipitation in a normal year; the driest is January with 0.55 in.
What plant hardiness zone is Castle Rock in?
The USDA's 2023 map puts Castle Rock in zone 5b across its 3 ZIP code areas (5b in 80104, the largest). By the same method at Castle Rock's NOAA station, the coldest night of a typical year reaches −11°F (20 years, 1991-2020): zone 5b.
How late can frost come in Castle Rock?
In half of years the last 32°F night comes after May 9; in one year in ten it comes after May 24. Waiting until May 24 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Castle Rock in OctoberThis month day by day, its records and recent years
- Colorado climateThe statewide normals and every place in the state
- Roxborough State Park, CO9 miles from this station, 49.6°F a year
- Parker, CO11 miles from this station, 49.7°F a year
- Centennial, CO11 miles from this station, 50.2°F a year
- Kassler, CO12 miles from this station, 50.2°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made