Midwinter lows in Alta Sierra stay above those of 83% of U.S. towns
High summer brings afternoon highs near 91°. Only 55° separates winter nights from summer afternoons. In July, afternoons here are warmer than in 81% of U.S. towns. The frost-free window for a garden runs roughly April 10 to November 13.
A year in Alta Sierra at a glance
Each month’s typical high and low, and what it brings.
What stands out about Alta Sierra’s climate
Compared with towns across the U.S., with Alta Sierra’s place in California beside it.
What a year in Alta Sierra feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 215 frost-free days a year
In half of years the last 32° night comes by April 10 and the first by November 13. Frost and day counts come from NOAA’s station at Grass Valley #2, CA, 5 miles from the town’s center, 330 ft higher.
The 2023 USDA map puts Alta Sierra’s center in zone 9a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 23°. 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 7 inches of snow a winter
Snow, measured at Colfax, CA, falls mostly in February. Precipitation (rain plus melted snow) adds up to 48 inches a year; December is the wettest month and July the driest. Rain or snow falls on about 76 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Alta Sierra
84% of the work is heating. Months averaging under 55° run from November through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Grass Valley #2, CA.
Living with Alta Sierra’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
215 frost-free days in zone 9a. The last frost comes by Apr 10 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Nov 13.
Months with highs of 62–84° and lows of 40° or more: April, May, June and October. 2.8 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Alta Sierra from natural hazards, river flooding is the largest share (67%); heat waves, cold waves, winter storms and ice storms together are 2%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Alta Sierra and similar climates
TownRatings has no climate map of the towns around Alta Sierra yet.
Climates most like Alta Sierra’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 |
|---|---|---|---|---|
| Alta Sierra, CA | 36° | 91° | 48" | 7.2" |
| Stuttgart, AR | 33° | 91° | 50" | 3.3" |
| Five Forks, SC | 33° | 90° | 49" | 3.9" |
| Garner, NC | 31° | 90° | 49" | 4.5" |
| Portsmouth, VA | 33° | 89° | 48" | 6.2" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Alta Sierra averaged 0.7° warmer than the 1900s. The biggest change is in September (+1.9°).
A smaller shift than in 93% 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 Alta Sierra compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Alta Sierra’s place among California’s.
Alta Sierra weather by month
Highs, lows and precipitation from NOAA’s grid at Alta Sierra’s center; snow, wet days and snow on the ground from Colfax, CA. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 54° | 36° | 8.5" | 0.9" | 11 | 0 | 41° – 52° |
| February | 56° | 38° | 8.3" | 2.6" | 12 | 0 | 40° – 54° |
| March | 60° | 40° | 7.4" | 1.2" | 11 | 0 | 42° – 57° |
| April | 65° | 42° | 4.0" | 0.6" | 8 | 0 | 47° – 58° |
| May | 74° | 49° | 2.3" | 0.0" | 6 | 0 | 52° – 69° |
| June | 83° | 56° | 0.7" | 0.0" | 2 | 0 | 64° – 74° |
| July | 91° | 62° | 0.0" | 0.0" | 0 | 0 | 72° – 80° |
| August | 90° | 61° | 0.1" | 0.0" | 1 | 0 | 72° – 80° |
| September | 85° | 57° | 0.4" | 0.0" | 1 | 0 | 67° – 75° |
| October | 74° | 49° | 2.4" | 0.0" | 4 | 0 | 57° – 68° |
| November | 60° | 41° | 5.1" | 0.4" | 9 | 0 | 43° – 57° |
| December | 53° | 36° | 9.2" | 1.5" | 11 | 0 | 41° – 49° |
| Year | 70° | 47° | 48.2" | 7.2" | 76 | 1 |
How much a month can swing
A normal is an average. May swings the most: from 1991 to 2020 its average ranged from 52° to 69°. August is the most reliable, staying within 7°.
Where Alta Sierra’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 Alta Sierra’s center.
- Snow: Colfax, CA.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Grass Valley #2, CA, 5 miles from the town’s center, 330 ft higher; 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 Alta Sierra’s climate
What is the weather like in Alta Sierra?
A typical July afternoon reaches 91°, a January night drops to 36°, and about 7 inches of snow falls in a normal winter. Milder January nights than 83% of U.S. towns; hotter July afternoons than 81% of U.S. towns.
How cold does it get in Alta Sierra in winter?
December nights average 36°. About 61 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 41°.
How much snow does Alta Sierra get?
About 7.2 inches in a normal winter at Colfax, CA, most of it in February, with snow on the ground about 1 days a year.
How hot does it get in Alta Sierra?
July, with a typical high of 91° and a low of 62°. About 36 days a year reach 90° (Grass Valley #2, CA).
When is the first and last frost in Alta Sierra?
In half of years the last spring frost (32°) comes by April 10 and the first fall frost by November 13, about 215 frost-free days, at Grass Valley #2, CA.
What growing zone is Alta Sierra in?
Zone 9a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 23°.
What is the best time of year to visit Alta Sierra?
By one simple rule (highs of 62–84° and lows of 40° or more), April, May, June and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Alta Sierra getting warmer?
Yes: 1991–2020 averaged 0.7° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 93% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Alta Sierra.
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.