When is the last frost in Rialto, CA?

For ZIP code 92377, the average last spring frost (32°F) is January 27, based on NOAA 1991-2020 climate normals for the Redlands, CA weather station. There is a 1-in-10 chance of a frost after February 28.

When is the first frost in Rialto, CA?

The average first fall frost (32°F) is December 19. There is a 1-in-10 chance of frost by December 1, so tender plants are at risk from that point on.

How long is the growing season in 92377?

In half of years, the frost-free season (between the last and first 32°F frost) is at least 329 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 92377Rialto, CA

The average last spring frost in Rialto is January 27 and the average first fall frost is December 19, giving a typical growing season of about 329 days. Dates are based on NOAA 1991-2020 climate normals.

Average last spring frost: Jan 27
Average first fall frost: Dec 19
Growing season: 329 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 31 · Mar 2 · Apr 5	Nov 17 · Dec 2 · Dec 19	272 days	100%
Frost / freeze (32°F)	Dec 21 · Jan 27 · Feb 28	Dec 1 · Dec 19 · Jan 26	329 days	88%
Hard freeze (28°F)	Dec 17 · Jan 7 · Feb 15	Dec 13 · Jan 1 · Feb 13	365 days	26%

Where these dates come from

ZIP code 92377 is matched to the NOAA station Redlands, CA, 23.4 km away, at 1,410 ft elevation (217 ft lower than the ZIP code's center). Nearby stations for comparison:

Station	Elevation	Avg last frost	Avg first frost
Redlands, CA (used)	1,410 ft	Jan 27	Dec 19
Ontario Intl Ap, CA	949 ft	Jan 4	Dec 30
Riverside Citrus Exp, CA	986 ft	Jan 10	Jan 2
Lake Arrowhead, CA	5,205 ft	May 5	Nov 2

Frost dates near Rialto

Fontana, CA 92336 · last Jan 27, first Dec 19
Rialto, CA 92376 · last Jan 27, first Dec 19
San Bernardino, CA 92407 · last Jan 27, first Dec 19
Bloomington, CA 92316 · last Jan 10, first Jan 2
Rancho Cucamonga, CA 91739 · last Jan 8, first Dec 28
Cedarpines Park, CA 92322 · last May 5, first Nov 2
Crestline, CA 92325 · last May 5, first Nov 2
Lytle Creek, CA 92358 · last May 5, first Nov 2

Frequently asked questions

When is the last frost in Rialto, CA?: For ZIP code 92377, the average last spring frost (32°F) is January 27, based on NOAA 1991-2020 climate normals for the Redlands, CA weather station. There is a 1-in-10 chance of a frost after February 28.
When is the first frost in Rialto, CA?: The average first fall frost (32°F) is December 19. There is a 1-in-10 chance of frost by December 1, so tender plants are at risk from that point on.
How long is the growing season in 92377?: In half of years, the frost-free season (between the last and first 32°F frost) is at least 329 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.