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.
A frost date is really a percentile from 30 years of records at a nearby weather station: in about half of years a frost still comes after the median date. Both numbers are below, so you can choose the risk yourself.
The odds
Last spring frost
How often a frost still comes on or after each date.
- 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
How often the first freeze comes on or before each date.
- 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 zone nearby
- 9b
- Summer days
- a usual high of about 24 °C76 °F
- Lettuce and spinach run to seed
- July to August, in hot, long days (how we know)
Summer and rain
A growing garden needs about 25 mm1 in of water a week, rain and watering together. Here is what a normal month brings.
- Nearly every drop is yours
- June to September: rain brings less than a quarter of the water a growing garden needs, about 25 mm1 in a week (how we know)
Month by month
- January
- high ~10 °C50 °F · low ~4 °C39 °F · rain ~128 mm5 in
- February
- high ~9 °C49 °F · low ~3 °C38 °F · rain ~122 mm4.8 in
- March
- high ~11 °C51 °F · low ~4 °C39 °F · rain ~112 mm4.4 in
- April
- high ~13 °C55 °F · low ~5 °C41 °F · rain ~56 mm2.2 in
- May
- high ~17 °C62 °F · low ~9 °C47 °F · rain ~33 mm1.3 in
- June
- high ~22 °C71 °F · low ~13 °C56 °F · rain ~7.1 mm0.3 in
- July
- high ~26 °C79 °F · low ~18 °C65 °F · rain ~0 mm0 in
- August
- high ~26 °C78 °F · low ~18 °C65 °F · rain ~1.3 mm0.05 in
- September
- high ~24 °C74 °F · low ~16 °C60 °F · rain ~4.3 mm0.2 in
- October
- high ~19 °C65 °F · low ~11 °C52 °F · rain ~34 mm1.3 in
- November
- high ~13 °C55 °F · low ~6 °C43 °F · rain ~76 mm3 in
- December
- high ~9 °C49 °F · low ~3 °C38 °F · rain ~120 mm4.7 in
Where these numbers come from
NOAA NCEI 1991–2020 Climate Normals, the Mt Hamilton station (listed by NOAA as 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 finds the nearest station to your garden and lowers its confidence with distance, so no number is presented as if it were measured in your garden.
Cold air also pools in low ground on the clear, still nights when frost happens, so a hollow can freeze while a slope a few hundred feet away does not. No table can know that about your garden. A few seasons of your own logged frosts can.
ZIP codes nearest this station
94550, 95013, 95132, 95135, 95138, 95139, 95140.
Nearby stations
The nearest stations and how their last-frost dates compare. Together they show how frost varies across your area.
- Livermore, CA, last frost by February 15
- Skyline Ridge Preserve, CA, last frost by March 21
- Oakland Metro International Airport, CA, last frost by January 7
- Oakland Museum, CA, frost is rare
- San Francisco Oceanside, CA, frost is rare
- Lodi, CA, last frost by February 9
Other stations in California.
- Sacramento 5 ESE, CA, last frost by January 12
- Woodland 1 WNW, CA, last frost by February 7
- Auburn, CA, last frost by February 25
- Fresno 5 NE, CA, last frost by January 30
- Shelter Cove Aviation, CA, frost is rare
- Oxnard, CA, frost is rare
- Woodland Hills Pierce College, CA, last frost by January 24
- Burbank Glendale Pasadena Airport, CA, frost is rare
When do I plant? · Where the dates come from
More ways Milpa can help
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