Castle Rock, WA climate
Castle Rock has mild winters and pleasant summers, with plenty of rain. A typical July afternoon reaches 79°, a January night drops to 35°, and about 2 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Castle Rock feels like
Winter
Spring
Summer
Fall
Castle Rock weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 47° | 35° | 6.6" | 0.5" | 22 | 1 | 34° – 45° |
| February | 51° | 35° | 4.7" | 0.7" | 19 | 0 | 36° – 49° |
| March | 56° | 37° | 5.0" | 0.2" | 22 | 0 | 43° – 51° |
| April | 61° | 40° | 4.1" | 0 | 20 | 0 | 46° – 55° |
| May | 68° | 45° | 2.9" | 0 | 14 | 0 | 52° – 60° |
| June | 72° | 49° | 2.0" | 0 | 12 | 0 | 58° – 66° |
| July | 79° | 53° | 0.6" | 0 | 6 | 0 | 62° – 69° |
| August | 80° | 52° | 0.9" | 0 | 5 | 0 | 63° – 69° |
| September | 74° | 48° | 2.1" | 0 | 9 | 0 | 58° – 64° |
| October | 62° | 43° | 4.4" | 0 | 18 | 0 | 48° – 57° |
| November | 52° | 38° | 7.2" | 0.1" | 23 | 0 | 40° – 49° |
| December | 45° | 34° | 7.4" | 0.8" | 23 | 1 | 35° – 43° |
| Year | 62° | 42° | 47.8" | 2.3" | 192 | 2 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Castle Rock
Castle Rock gets 48 inches of rain and melted snow a year. December is the wettest month and July the driest. Rain or snow falls on about 192 days a year.
About 210 frost-free days a year
In half of years the last 32° night comes by April 8 and the first one by November 5. That leaves about 210 frost-free days for gardens, longer than 78% of U.S. towns.
Heating and cooling a home in Castle Rock
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Castle Rock, 95% of that work is heating and 5% is cooling, so the furnace matters far more than the air conditioner.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
How Castle Rock compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in Castle Rock averaged 1.3° warmer than the 1900s. The biggest change is in January (+2.8°). The shift is larger than in 60% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Castle Rock’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. February swings the most: between 1991 and 2020 its average temperature ranged from 36° to 49°. August is the most reliable, staying within 6°.
Common questions about Castle Rock’s climate
What is the coldest month in Castle Rock?
December, with a typical high of 45° and a low of 34°.
What is the hottest month in Castle Rock?
August, with a typical high of 80° and a low of 52°. About 10 days a year reach 90°.
How much snow does Castle Rock get?
About 2 inches in a normal winter, most of it in December.
When is the first frost in Castle Rock?
In half of years the first 32° night comes by November 5, and the last spring frost by April 8.
What is the rainiest month in Castle Rock?
December, with 7.4 inches of rain and melted snow. The year totals 48 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Castle Rock itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Clatskanie, OR (18 mi, snow) and Longview, WA (8 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.