Frost dates for Mt Hamilton, California
Half of years have their last spring frost by May 3 — but 1 year in 10 still frosts after June 5.
Every other site gives you one date. A frost date is not a date: it is a percentile from 30 years of records at a nearby weather station, and planting to the median means losing the crop in half of years. Both numbers are below, so you can choose the risk yourself.
The odds
Last spring frost
- Frost this late in 1 year in 10
- June 5
- 1 year in 5
- May 26
- 3 years in 10
- May 16
- 2 years in 5
- May 9
- Half of years (the median)
- May 3
First fall freeze
- Freeze this early in 1 year in 10
- October 22
- 1 year in 5
- November 1
- 3 years in 10
- November 7
- 2 years in 5
- November 13
- Half of years (the median)
- November 18
- Growing season
- about 197 days
- Hardiness zones nearby
- 10a, 9b
Where these numbers come from
NOAA NCEI 1991–2020 Climate Normals, station Mt Hamilton (USC00045933), at 37.34, -121.64. These are that station's own records, unshifted. The further your garden is from it, the less exactly they describe your ground — the planner resolves the nearest station to your own ZIP and lowers its confidence with distance, rather than presenting one number as if it were measured in your yard.
Cold air also pools in low ground on the clear, still nights when frost happens, so a hollow can freeze while a slope a hundred metres away does not. No table can know that about your garden. Your own logged frosts eventually can.
ZIP codes nearest this station
94550, 95003, 95013, 95020, 95035, 95037, 95046, 95110, 95111, 95112, 95113, 95116, 95118, 95119, 95120, 95121, 95122, 95123, 95125, 95127, 95131, 95132, 95133, 95135, 95136, 95138, 95139, 95140, 95148.
What can I plant here, and when? →
Nearby stations
The nearest stations, and how their last-frost dates compare — the frost gradient across your area, which no single station shows.
- Livermore Hcn, CA — last frost by February 15
- Skyline Ridge Preserve, CA — last frost by March 21
- Oakland Metro Intl Ap, CA — last frost by January 7
- San Francisco Oceanside, CA — last frost by December 30
- Lodi Hcn, CA — last frost by February 9
- Woodland 1 Wnw, CA — last frost by February 7
Other stations in California.
- Auburn, CA — last frost by February 25
- Fresno 5 Ne, CA — last frost by January 30
- Woodland Hills Pierce College, CA — last frost by January 24
- Burbank Glendale Pasadena Ap, CA — last frost by December 31
- Wrightwood, CA — last frost by May 16
- Torrance Ap, CA — last frost by January 9
- Lake Arrowhead, CA — last frost by May 5
- Tustin Irvine Rch Hcn, CA — last frost by January 5