When is the last frost in Alpine, CA?

For ZIP code 91901, the average last spring frost (32°F) is February 12, based on NOAA 1991-2020 climate normals for the Alpine, CA weather station. There is a 1-in-10 chance of a frost after March 20.

When is the first frost in Alpine, CA?

The average first fall frost (32°F) is December 24. 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 91901?

In half of years, the frost-free season (between the last and first 32°F frost) is at least 317 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 91901Alpine, CA

The average last spring frost in Alpine is February 12 and the average first fall frost is December 24, giving a typical growing season of about 317 days. Dates are based on NOAA 1991-2020 climate normals.

Average last spring frost: Feb 12
Average first fall frost: Dec 24
Growing season: 317 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 15 · Mar 17 · Apr 16	Nov 15 · Dec 7 · Dec 23	263 days	100%
Frost / freeze (32°F)	Dec 29 · Feb 12 · Mar 20	Dec 2 · Dec 24 · Feb 3	317 days	90%
Hard freeze (28°F)	Dec 12 · Jan 22 · Feb 23	Dec 10 · Jan 4 · Feb 20	365 days	38%

Where these dates come from

ZIP code 91901 is matched to the NOAA station Alpine, CA, 2.3 km away, at 1,695 ft elevation (366 ft lower than the ZIP code's center). Nearby stations for comparison:

Station	Elevation	Avg last frost	Avg first frost
Alpine, CA (used)	1,695 ft	Feb 12	Dec 24
El Capitan Dam, CA	600 ft	Mar 19	Dec 8
El Cajon, CA	495 ft	Jan 6	Dec 21
Cuyamaca, CA	4,640 ft	Apr 19	Oct 27

Frost dates near Alpine

Alpine, CA 91903 · last Feb 12, first Dec 24
Jamul, CA 91935 · last Feb 12, first Dec 24
Descanso, CA 91916 · last Mar 27, first Dec 1
El Cajon, CA 92021 · last Jan 6, first Dec 21
Lakeside, CA 92040 · last Jan 6, first Dec 21
Guatay, CA 91931 · last Mar 27, first Dec 1
Santee, CA 92072 · last Jan 6, first Dec 21
Spring Valley, CA 91978 · last Jan 6, first Dec 21

Frequently asked questions

When is the last frost in Alpine, CA?: For ZIP code 91901, the average last spring frost (32°F) is February 12, based on NOAA 1991-2020 climate normals for the Alpine, CA weather station. There is a 1-in-10 chance of a frost after March 20.
When is the first frost in Alpine, CA?: The average first fall frost (32°F) is December 24. 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 91901?: In half of years, the frost-free season (between the last and first 32°F frost) is at least 317 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.