When is the last frost in Saint Helena, CA?

For ZIP code 94574, the average last spring frost (32°F) is February 3, based on NOAA 1991-2020 climate normals for the Saint Helena, CA weather station. There is a 1-in-10 chance of a frost after March 13.

When is the first frost in Saint Helena, CA?

The average first fall frost (32°F) is December 4. There is a 1-in-10 chance of frost by November 14, so tender plants are at risk from that point on.

How long is the growing season in 94574?

In half of years, the frost-free season (between the last and first 32°F frost) is at least 306 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 94574Saint Helena, CA

The average last spring frost in Saint Helena is February 3 and the average first fall frost is December 4, giving a typical growing season of about 306 days. Dates are based on NOAA 1991-2020 climate normals.

Average last spring frost: Feb 3
Average first fall frost: Dec 4
Growing season: 306 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)	Feb 14 · Mar 19 · Apr 17	Oct 31 · Nov 18 · Dec 5	243 days	100%
Frost / freeze (32°F)	Dec 28 · Feb 3 · Mar 13	Nov 14 · Dec 4 · Jan 1	306 days	97%
Hard freeze (28°F)	Dec 11 · Jan 5 · Feb 9	Nov 27 · Dec 17 · Jan 18	349 days	65%

Where these dates come from

ZIP code 94574 is matched to the NOAA station Saint Helena, CA, 1.1 km away, at 225 ft elevation (2 ft higher than the ZIP code's center). Nearby stations for comparison:

Station	Elevation	Avg last frost	Avg first frost
Saint Helena, CA (used)	225 ft	Feb 3	Dec 4
Angwin Pacific Union College, CA	1,715 ft	Apr 7	Dec 5
Calistoga, CA	400 ft	Mar 2	Nov 23
Santa Rosa, CA	166 ft	Feb 25	Dec 1

Frost dates near Saint Helena

Deer Park, CA 94576 · last Mar 2, first Nov 23
Rutherford, CA 94573 · last Feb 3, first Dec 4
Angwin, CA 94508 · last Apr 7, first Dec 5
Oakville, CA 94562 · last Feb 3, first Dec 4
Pope Valley, CA 94567 · last Mar 2, first Nov 23
Calistoga, CA 94515 · last Mar 2, first Nov 23
Kenwood, CA 95452 · last Feb 3, first Dec 4
Yountville, CA 94599 · last Mar 2, first Nov 27

Frequently asked questions

When is the last frost in Saint Helena, CA?: For ZIP code 94574, the average last spring frost (32°F) is February 3, based on NOAA 1991-2020 climate normals for the Saint Helena, CA weather station. There is a 1-in-10 chance of a frost after March 13.
When is the first frost in Saint Helena, CA?: The average first fall frost (32°F) is December 4. There is a 1-in-10 chance of frost by November 14, so tender plants are at risk from that point on.
How long is the growing season in 94574?: In half of years, the frost-free season (between the last and first 32°F frost) is at least 306 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.