When is the last frost in Union City, CA?

For ZIP code 94587, the average last spring frost (32°F) is January 7, based on NOAA 1991-2020 climate normals for the Fremont, CA weather station. There is a 1-in-10 chance of a frost after February 7.

When is the first frost in Union City, CA?

The average first fall frost (32°F) is December 22. There is a 1-in-10 chance of frost by December 2, so tender plants are at risk from that point on.

How long is the growing season in 94587?

In half of years, the frost-free season (between the last and first 32°F frost) is at least 353 days long.

Are these frost dates a forecast?

No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.

Frost dates for 94587Union City, CA

The average last spring frost in Union City is January 7 and the average first fall frost is December 22, giving a typical growing season of about 353 days. Dates are based on NOAA 1991-2020 climate normals.

Average last spring frost: Jan 7
Average first fall frost: Dec 22
Growing season: 353 days

Frost risk by date

NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.

Spring dates: chance of a frost AFTER the date. Fall dates: chance of a frost BEFORE the date.
Temperature	Last spring: 90% / 50% / 10% chance	First fall: 10% / 50% / 90% chance	Growing season (50%)	Years with at least one
Light frost (36°F)	Jan 3 · Feb 6 · Mar 11	Nov 17 · Dec 5 · Jan 2	301 days	98%
Frost / freeze (32°F)	Dec 14 · Jan 7 · Feb 7	Dec 2 · Dec 22 · Jan 21	353 days	65%
Hard freeze (28°F)	Dec 13 · Dec 31 · Jan 20	Dec 11 · Dec 29 · Jan 17	365 days	14%

Where these dates come from

ZIP code 94587 is matched to the NOAA station Fremont, CA, 6 km away, at 38 ft elevation (12 ft higher than the ZIP code's center). Nearby stations for comparison:

Station	Elevation	Avg last frost	Avg first frost
Fremont, CA (used)	38 ft	Jan 7	Dec 22
Newark, CA	10 ft	Jan 1	Dec 27
Hayward Air Terminal, CA	43 ft	Jan 2	Dec 25
Palo Alto, CA	25 ft	Feb 1	Dec 7

Frost dates near Union City

Fremont, CA 94555 · last Jan 7, first Dec 22
Hayward, CA 94544 · last Jan 2, first Dec 25
Newark, CA 94560 · last Jan 7, first Dec 22
San Lorenzo, CA 94580 · last Jan 2, first Dec 25
Castro Valley, CA 94546 · last Jan 2, first Dec 25
Sunol, CA 94586 · last Feb 15, first Dec 2
San Leandro, CA 94578 · last Jan 2, first Dec 25
Palo Alto, CA 94303 · last Feb 1, first Dec 7

Frequently asked questions

When is the last frost in Union City, CA?: For ZIP code 94587, the average last spring frost (32°F) is January 7, based on NOAA 1991-2020 climate normals for the Fremont, CA weather station. There is a 1-in-10 chance of a frost after February 7.
When is the first frost in Union City, CA?: The average first fall frost (32°F) is December 22. There is a 1-in-10 chance of frost by December 2, so tender plants are at risk from that point on.
How long is the growing season in 94587?: In half of years, the frost-free season (between the last and first 32°F frost) is at least 353 days long.
Are these frost dates a forecast?: No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.