Precipitation in Alum Rock trails that of 93% of U.S. towns: 15 inches a year
Sunny July days climb to about 86°. The gap between a January night and a July afternoon is 47°. Winters are mild: January nights here are milder than in 87% of U.S. towns. Keep the boiler serviced for the months from December to January, which average under 50°.
A year in Alum Rock at a glance
Each month’s typical high and low, and what it brings.
What stands out about Alum Rock’s climate
Compared with towns across the U.S., with Alum Rock’s place in California beside it.
What a year in Alum Rock feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
A freeze most winters
Frost and day counts come from NOAA’s station at San Jose, CA, 5 miles from the town’s center, 100 ft lower.
The 2023 USDA map puts Alum Rock’s center in zone 9b: the coldest night of a typical winter, averaged over 1991–2020, reaches about 29°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 15 inches of rain a year
February is the wettest month and July the driest. Rain falls on about 56 days a year. Snow is rare: about 0.0" in a normal year at Los Gatos, CA, so most winters see none.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Alum Rock
73% of the work is heating. Months averaging under 55° run from November through February.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at San Jose, CA.
Living with Alum Rock’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
Zone 9b. Frost comes about 6 winters in 10, so tender plants can often stay out through winter.
Months with highs of 62–84° and lows of 40° or more: February, March, April, May, June, September, October and November.
Parks & trails →Of the yearly building losses FEMA expects in Alum Rock from natural hazards, earthquakes are the largest share (81%); heat waves, cold waves, winter storms and ice storms together are 3%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Alum Rock and its neighbors
Every town next door is within a degree of Alum Rock in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Alum Rock’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Alum Rock, CA | 39° | 86° | 15" | 0.0" |
| The Dalles, OR | 31° | 88° | 15" | 5.5" |
| Sierra Vista Southeast, AZ | 32° | 91° | 15" | 0.7" |
| Alpine, TX | 30° | 90° | 15" | 2.2" |
| Kennewick, WA | 29° | 90° | 8" | 2.0" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Alum Rock averaged 1.9° warmer than the 1900s. The biggest change is in August (+2.4°).
A bigger shift than in 85% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Alum Rock compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Alum Rock’s place among California’s.
Alum Rock weather by month
Highs, lows and precipitation from NOAA’s grid at Alum Rock’s center; snow, wet days and snow on the ground from Los Gatos, CA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 59° | 39° | 2.9" | 0.0" | 10 | 0 | 46° – 54° |
| February | 63° | 42° | 2.9" | 0.0" | 9 | 0 | 46° – 58° |
| March | 67° | 44° | 2.5" | 0.0" | 9 | 0 | 50° – 62° |
| April | 71° | 45° | 1.2" | 0.0" | 6 | 0 | 54° – 62° |
| May | 76° | 50° | 0.5" | 0.0" | 2 | 0 | 58° – 69° |
| June | 83° | 54° | 0.1" | 0.0" | 1 | 0 | 64° – 71° |
| July | 86° | 56° | 0.0" | 0.0" | 0 | 0 | 68° – 75° |
| August | 86° | 56° | 0.0" | 0.0" | 0 | 0 | 68° – 74° |
| September | 84° | 54° | 0.1" | 0.0" | 0 | 0 | 65° – 73° |
| October | 77° | 49° | 0.7" | 0.0" | 3 | 0 | 60° – 70° |
| November | 67° | 43° | 1.5" | 0.0" | 6 | 0 | 48° – 59° |
| December | 59° | 39° | 2.6" | 0.0" | 10 | 0 | 45° – 52° |
| Year | 73° | 48° | 15.0" | 0.0" | 56 | 0 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 46° to 58°. August is the most reliable, staying within 6°.
Where Alum Rock’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Alum Rock’s center.
- Snow: Los Gatos, CA.
- Frost, freezing nights, 90° and 100° days, heating and cooling: San Jose, CA, 5 miles from the town’s center, 100 ft lower; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Alum Rock’s climate
What is the weather like in Alum Rock?
A typical July afternoon reaches 86°, a January night drops to 39°, and snow is almost unheard of. Milder January nights than 87% of U.S. towns; hotter July afternoons than 53% of U.S. towns.
How cold does it get in Alum Rock in winter?
December nights average 39°. About 2 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 45°.
How much snow does Alum Rock get?
About 0.0 inches in a normal winter at Los Gatos, CA, so most winters see none.
How hot does it get in Alum Rock?
July, with a typical high of 86° and a low of 56°. About 21 days a year reach 90° and 2 reach 100° (San Jose, CA).
When is the first and last frost in Alum Rock?
There is no reliable frost date: a 32° night comes in about 56% of winters at San Jose, CA, so most years bring a freeze but some pass without one.
What growing zone is Alum Rock in?
Zone 9b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 29°.
What is the best time of year to visit Alum Rock?
By one simple rule (highs of 62–84° and lows of 40° or more), February, March, April, May, June, September, October and November. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Alum Rock getting warmer?
Yes: 1991–2020 averaged 1.9° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 85% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Alum Rock.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.