Photo: YonderStone · CC BY-SA 4.0San Dimas reaches 100° on about 11 days a year, more than 91% of U.S. towns
A typical July afternoon reaches 90°, a January night drops to 43°, and snow is almost unheard of.
A year in San Dimas at a glance
Each month’s typical high and low, and what it brings.
What stands out about San Dimas’ climate
Compared with towns across the U.S., with San Dimas’ place in California beside it.
What a year in San Dimas feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 11 days a year reach 100°
And 71 days reach 90°. Frost and day counts come from NOAA’s station at Pomona/fairplex, CA, 3 miles from the town’s center, at about the same height.
The 2023 USDA map puts San Dimas’ center in zone 10a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 32°. 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 17 inches of rain a year
February is the wettest month and August the driest. Rain falls on about 31 days a year. Snow is rare: about 0.0" in a normal year at Pomona/fairplex, CA, so most winters see none.
Rain + melted snow by month
Inches of water
Heating and cooling a home in San Dimas
49% of the work is heating, so air conditioning is the bigger bill. Months averaging under 55° run from December.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Pomona/fairplex, CA.
Living with San Dimas’ climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
Zone 10a. Frost comes about 7 winters in 10, so the growing year is set by heat, not cold: 11 days at 100° make midsummer the hard season for gardens.
Months with highs of 62–84° and lows of 40° or more: January, February, March, April, May, June, October, November and December. 44 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in San Dimas from natural hazards, earthquakes are the largest share (47%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →San Dimas and its neighbors
Every town next door is within a degree of San Dimas in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like San Dimas’, 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 |
|---|---|---|---|---|
| San Dimas, CA | 43° | 90° | 17" | 0.0" |
| Sierra Vista Southeast, AZ | 32° | 91° | 15" | 0.7" |
| Port Isabel, TX | 52° | 92° | 26" | 0.2" |
| Ashland, OR | 31° | 91° | 19" | 0.5" |
| College Place, WA | 30° | 91° | 15" | 7.2" |
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 San Dimas averaged 2.8° warmer than the 1900s. The biggest change is in January (+3.7°).
A bigger shift than in all but 5 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 San Dimas compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with San Dimas’ place among California’s.
San Dimas weather by month
Highs, lows and precipitation from NOAA’s grid at San Dimas’ center; snow, wet days and snow on the ground from Pomona/fairplex, CA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 67° | 43° | 4.0" | 0.0" | 5 | 0 | 51° – 61° |
| February | 68° | 44° | 4.7" | 0.0" | 6 | 0 | 49° – 66° |
| March | 71° | 47° | 2.7" | 0.0" | 4 | 0 | 52° – 66° |
| April | 75° | 49° | 1.0" | 0.0" | 2 | 0 | 56° – 66° |
| May | 78° | 53° | 0.3" | 0.0" | 1 | 0 | 60° – 72° |
| June | 84° | 57° | 0.1" | 0.0" | 0 | 0 | 66° – 76° |
| July | 90° | 62° | 0.0" | 0.0" | 0 | 0 | 72° – 81° |
| August | 92° | 62° | 0.0" | 0.0" | 0 | 0 | 74° – 81° |
| September | 89° | 60° | 0.1" | 0.0" | 0 | 0 | 71° – 79° |
| October | 81° | 54° | 0.6" | 0.0" | 3 | 0 | 63° – 72° |
| November | 74° | 47° | 1.2" | 0.0" | 3 | 0 | 53° – 65° |
| December | 67° | 42° | 2.7" | 0.0" | 5 | 0 | 50° – 61° |
| Year | 78° | 52° | 17.4" | 0.0" | 31 | 0 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 49° to 66°. August is the most reliable, staying within 7°.
Where San Dimas’ 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 San Dimas’ center.
- Snow: Pomona/fairplex, CA.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Pomona/fairplex, CA, 3 miles from the town’s center, at about the same height; 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 San Dimas’ climate
What is the weather like in San Dimas?
A typical July afternoon reaches 90°, a January night drops to 43°, and snow is almost unheard of. Milder January nights than 92% of U.S. towns; hotter July afternoons than 79% of U.S. towns.
How cold does it get in San Dimas in winter?
December nights average 42°. About 3 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 50°.
How much snow does San Dimas get?
About 0.0 inches in a normal winter at Pomona/fairplex, CA, so most winters see none.
How hot does it get in San Dimas?
July, with a typical high of 90° and a low of 62°. About 71 days a year reach 90° and 11 reach 100° (Pomona/fairplex, CA).
When is the first and last frost in San Dimas?
There is no reliable frost date: a 32° night comes in about 65% of winters at Pomona/fairplex, CA, so most years bring a freeze but some pass without one.
What growing zone is San Dimas in?
Zone 10a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 32°.
What is the best time of year to visit San Dimas?
By one simple rule (highs of 62–84° and lows of 40° or more), January, February, March, April, May, June, October, November and December. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is San Dimas getting warmer?
Yes: 1991–2020 averaged 2.8° warmer than 1901–2000 on NOAA’s grid. A bigger shift than all but 5 U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in San Dimas.
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.