Walnut Creek, California climate: NOAA's gridded normals for the city, beside the nearest station records
NOAA's gridded 1991-2020 normals put Walnut Creek's center at January lows of 39°F and July highs of 87°F, a yearly mean of 60.0°F and 20.4 inches of precipitation. No NOAA station keeps a record under the city's name. The nearest station record, Concord Wastewater Treatment Plant (6 miles N, 40 ft), has January lows of 42°F and July highs of 88°F.
70,817 people (Census Bureau 2024). Distances and directions are from the city's center.
- Jan 56° 39°
- Feb 61° 42°
- Mar 65° 44°
- Apr 70° 46°
- May 76° 50°
- Jun 83° 54°
- Jul 87° 57°
- Aug 87° 57°
- Sep 84° 55°
- Oct 77° 50°
- Nov 65° 44°
- Dec 56° 39°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
The months above are NOAA's gridded normals at Walnut Creek's center.
What is each month like in Walnut Creek?
NOAA's grid estimates the normals every 5 km or so from the stations around each point, terrain included. It smooths between stations, so night lows at the heart of a large city can run warmer than the grid shows: at five big-city airports we compared, the grid's highs were within about 1°F of the station and its lows 1-6°F cooler. The nearest record's high and low are beside each month.
| Month | High | Low | Mean | Precip. | Concord Wastewater Treatment Plant high | Concord Wastewater Treatment Plant low |
|---|---|---|---|---|---|---|
| January | 56°F | 39°F | 47.6°F | 4.15 | 58°F | 42°F |
| February | 61°F | 42°F | 51.3°F | 3.87 | 63°F | 44°F |
| March | 65°F | 44°F | 54.5°F | 3.09 | 68°F | 47°F |
| April | 70°F | 46°F | 57.6°F | 1.41 | 72°F | 49°F |
| May | 76°F | 50°F | 62.7°F | 0.64 | 78°F | 53°F |
| June | 83°F | 54°F | 68.4°F | 0.12 | 85°F | 57°F |
| July | 87°F | 57°F | 71.6°F | 0.00 | 88°F | 58°F |
| August | 87°F | 57°F | 71.6°F | 0.02 | 88°F | 59°F |
| September | 84°F | 55°F | 69.5°F | 0.08 | 86°F | 58°F |
| October | 77°F | 50°F | 63.5°F | 0.96 | 78°F | 53°F |
| November | 65°F | 44°F | 54.0°F | 1.99 | 67°F | 46°F |
| December | 56°F | 39°F | 47.6°F | 4.11 | 59°F | 41°F |
In metric: a yearly mean of 15.6°C, January lows of 4°C, July highs of 30°C and 519 mm of precipitation a year.
Source: NOAA NCEI U.S. Monthly Gridded Climate Normals 1991-2020 (nClimGrid, accession 0245564); NOAA NCEI 1991-2020 station normals. The grid cell holding the city's Census center point.
What do the station records around Walnut Creek say?
Each row is a NOAA station's own 1991-2020 normals, with the snow and frost dates the grid does not give. A record downhill or nearer the coast than the city can run warmer, one uphill cooler: compare the elevations.
| Record | Where | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Concord Wastewater Treatment Plant | 6 mi N | 40 ft | 62.4°F | 42°F | 88°F | 17.7 | 0 | January 7 |
| Mount Diablo Junction | 6 mi E | 2,170 ft | 58.4°F | 42°F | 83°F | 26.1 | 1 | March 8 |
Source: NOAA NCEI 1991-2020 U.S. Climate Normals; place center and population: Census Bureau 2024. Last frost: the median last spring date of 32°F.
How much snow, how late a frost, what zone and how much sun in Walnut Creek?
NOAA's grid gives no snow, frost dates or records, so these come from the nearest station record, Concord Wastewater Treatment Plant (6 miles N, 40 ft). It gets 0 inches of snow in a normal year. The last spring frost (32°F) comes after January 7 in half of years and the first autumn frost before December 19.
The USDA's 2023 Plant Hardiness Zone Map puts Walnut Creek in zone 9b across its 4 ZIP code areas.
Over a year 80% of the sunlight that would reach the ground under clear skies gets through the clouds in the area (4.7 kWh per square metre a day, NASA POWER 2001-2020); June is the sunniest month (84%) and December the cloudiest (74%).
Concord Wastewater Treatment Plant's page has its months, frost probabilities, records by month and recent years. NOAA's grid has monthly figures only, so there are no day-by-day month pages for Walnut Creek; the nearest record's month pages have them.
Source: NOAA NCEI 1991-2020 normals, station USC00041967; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; sunshine: NASA POWER.
How does the climate vary across Walnut Creek, ZIP code by ZIP code?
4 ZIP code areas lie wholly or partly in Walnut Creek. On NOAA's grid 94597 is the warmest (60.1°F a year) and 94595 the coolest (59.5°F), a spread of 0.6°F. Each row also names the nearest station record and its frost dates.
| ZIP code | Zone | Year | Jan low | Jul high | Precip. | Nearest record | Last frost | First frost |
|---|---|---|---|---|---|---|---|---|
| 94595 | 9b | 59.5°F | 40°F | 84°F | 23.9 | Mount Diablo Junction (8 mi) | March 8 | December 22 |
| 94596 | 9b | 60.0°F | 39°F | 87°F | 20.4 | Mount Diablo Junction (6 mi) | March 8 | December 22 |
| 94597 | 9b | 60.1°F | 39°F | 87°F | 20.5 | Concord Wastewater Treatment Plant (5 mi) | January 7 | December 19 |
| 94598 | 9b | 60.0°F | 39°F | 87°F | 20.4 | Mount Diablo Junction (5 mi) | March 8 | December 22 |
Source: Census Bureau 2020 ZCTA-to-place relationship file and ZCTA centers; NOAA NCEI gridded and station normals, 1991-2020. A ZIP area counts when at least a tenth of its land (and 0.5 km²) is in the city; its figures are the grid cell at its center; frost dates are the nearest record's medians of 32°F.