Zane Grey Estate · Photo: Nathan Simmons · CC BY-SA 3.0Altadena’s winters are milder and less snowy than most of the U.S.
A typical July afternoon reaches 89°, a January night drops to 45°, and snow is almost unheard of.
A year in Altadena at a glance
Each month’s typical high and low, and what it brings.
What stands out about Altadena’s climate
Compared with towns across the U.S., with Altadena’s place in California beside it.
What a year in Altadena feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
Frost is rare
Frost and day counts come from NOAA’s station at Pasadena, CA, 3 miles from the town’s center, 480 ft lower.
The 2023 USDA map puts Altadena’s center in zone 10b: the coldest night of a typical winter, averaged over 1991–2020, reaches about 36°. Plant labels use the zone; frost dates tell you when to plant.
90° days by month
Average days at 90° or more
About 21 inches of rain a year
February is the wettest month and August the driest. Rain falls on about 34 days a year. Snow is rare: about 0.0" in a normal year at Altadena, CA, so most winters see none.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Altadena
44% 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 Pasadena, CA.
Living with Altadena’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
Zone 10b. Frost comes about 1 winter in 8, so tender plants can often stay out through winter.
Months with highs of 62–84° and lows of 40° or more: January, February, March, April, May, June, October, November and December. 14 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Altadena from natural hazards, earthquakes are the largest share (36%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Altadena and its neighbors
Every town next door is within a degree of Altadena in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Altadena’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 |
|---|---|---|---|---|
| Altadena, CA | 45° | 89° | 21" | 0.0" |
| Port Isabel, TX | 52° | 92° | 26" | 0.2" |
| Sierra Vista Southeast, AZ | 32° | 91° | 15" | 0.7" |
| Green, OR | 37° | 86° | 32" | 0.0" |
| Ewa Beach, HI | 62° | 87° | 17" | 0.0" |
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 Altadena averaged 2.6° warmer than the 1900s. The biggest change is in January (+3.5°).
A bigger shift than in all but 32 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 Altadena compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Altadena’s place among California’s.
Altadena weather by month
Highs, lows and precipitation from NOAA’s grid at Altadena’s center; snow, wet days and snow on the ground from Altadena, CA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 67° | 45° | 4.6" | 0.0" | 6 | 0 | 52° – 62° |
| February | 67° | 46° | 5.5" | 0.0" | 6 | 0 | 49° – 65° |
| March | 70° | 48° | 3.1" | 0.0" | 5 | 0 | 52° – 67° |
| April | 74° | 50° | 1.2" | 0.0" | 3 | 0 | 57° – 67° |
| May | 77° | 54° | 0.5" | 0.0" | 2 | 0 | 60° – 72° |
| June | 83° | 59° | 0.1" | 0.0" | 1 | 0 | 67° – 75° |
| July | 89° | 63° | 0.0" | 0.0" | 0 | 0 | 72° – 81° |
| August | 91° | 64° | 0.0" | 0.0" | 0 | 0 | 74° – 81° |
| September | 88° | 62° | 0.2" | 0.0" | 1 | 0 | 71° – 79° |
| October | 80° | 56° | 0.8" | 0.0" | 2 | 0 | 64° – 73° |
| November | 73° | 49° | 1.3" | 0.0" | 2 | 0 | 53° – 65° |
| December | 66° | 44° | 3.1" | 0.0" | 5 | 0 | 50° – 60° |
| Year | 77° | 53° | 20.7" | 0.0" | 34 | 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 65°. August is the most reliable, staying within 6°.
Where Altadena’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 Altadena’s center.
- Snow: Altadena, CA (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Pasadena, CA, 3 miles from the town’s center, 480 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 Altadena’s climate
What is the weather like in Altadena?
A typical July afternoon reaches 89°, a January night drops to 45°, and snow is almost unheard of. Milder January nights than 94% of U.S. towns; hotter July afternoons than 73% of U.S. towns.
How cold does it get in Altadena in winter?
December nights average 44°. A night at 32° or below comes in only some winters (0.1 a year on average). In the coldest December of the last 30 years the month averaged 50°.
How much snow does Altadena get?
About 0.0 inches in a normal winter at Altadena, CA, so most winters see none.
How hot does it get in Altadena?
July, with a typical high of 89° and a low of 63°. About 74 days a year reach 90° and 10 reach 100° (Pasadena, CA).
When is the first and last frost in Altadena?
Most years have no frost at all: a 32° night comes in about 13% of winters at Pasadena, CA, usually in December or January.
What growing zone is Altadena in?
Zone 10b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 36°.
What is the best time of year to visit Altadena?
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 Altadena getting warmer?
Yes: 1991–2020 averaged 2.6° warmer than 1901–2000 on NOAA’s grid. A bigger shift than all but 32 U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Altadena.
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.