Diablo, CA climate
Diablo has warm winters and pleasant summers. A typical July afternoon reaches 84°, a January night drops to 42°, and snow is almost unheard of.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Diablo feels like
Winter
Spring
Summer
Fall
Diablo 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 | 54° | 42° | 5.1" | 0.1" | 12 | 0 | 44° – 55° |
| February | 56° | 42° | 4.7" | 0.5" | 11 | 0 | 43° – 55° |
| March | 60° | 43° | 3.9" | 0.1" | 10 | 0 | 45° – 59° |
| April | 64° | 45° | 1.8" | 0 | 7 | 0 | 49° – 59° |
| May | 71° | 49° | 0.9" | 0 | 4 | 0 | 53° – 68° |
| June | 78° | 55° | 0.2" | 0 | 1 | 0 | 61° – 70° |
| July | 84° | 60° | 0.0" | 0 | 0 | 0 | 68° – 77° |
| August | 84° | 60° | 0.0" | 0 | 0 | 0 | 68° – 76° |
| September | 82° | 59° | 0.1" | 0 | 1 | 0 | 66° – 74° |
| October | 73° | 54° | 1.2" | 0 | 3 | 0 | 60° – 71° |
| November | 61° | 46° | 2.6" | 0 | 7 | 0 | 47° – 58° |
| December | 54° | 41° | 5.1" | 0 | 11 | 0 | 44° – 51° |
| Year | 68° | 50° | 25.5" | 0.7" | 68 | 0 |
“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 Diablo
Diablo gets 26 inches of rain and melted snow a year. January is the wettest month and July the driest. Rain or snow falls on about 68 days a year.
About 282 frost-free days a year
In half of years the last 32° night comes by March 8 and the first one by December 22. That leaves about 282 frost-free days for gardens, longer than 94% of U.S. towns.
Heating and cooling a home in Diablo
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Diablo, 78% of that work is heating and 22% is cooling.
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.
Diablo and its neighbors
Diablo borders 3 towns with climate data. January nights across them vary by 2.8°. Alamo has the coldest January nights (39°) and Danville the hottest July afternoons (86°). Diablo’s January low is 42° and its July high 84°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Diablo 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 Diablo averaged 1.6° warmer than the 1900s. The biggest change is in January (+2.2°). The shift is larger than in 76% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Diablo’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. May swings the most: between 1991 and 2020 its average temperature ranged from 53° to 68°. December is the most reliable, staying within 7°.
Common questions about Diablo’s climate
What is the coldest month in Diablo?
December, with a typical high of 54° and a low of 41°.
What is the hottest month in Diablo?
August, with a typical high of 84° and a low of 60°. About 27 days a year reach 90°.
How much snow does Diablo get?
Almost none. A normal year brings 0.7 inches.
When is the first frost in Diablo?
In half of years the first 32° night comes by December 22, and the last spring frost by March 8.
What is the rainiest month in Diablo?
January, with 5.1 inches of rain and melted snow. The year totals 26 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Diablo itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Mt Diablo Junction, CA (3 mi) away. Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.