USDA Hardiness Zone 10a
Frost Dates for 93402 — Los Osos, California
NOAA 1991–2020 normals from Morro Bay Fire Dept, CA (118 ft), 4 miles north.
Updated
Frost is not a yearly event in Los Osos: a night at or below 32°F came in 15% of the winters of 1991–2020 at Morro Bay Fire Dept, CA, and a 36°F night, cold enough for frost on exposed leaves, in 62%. There is no reliable "last frost date" here; most years have none.
- Winters with a freeze
- 15%
- Winters with 36°F
- 62%
- Coldest month low
- 46°F
- Hardiness zone
- 10a
32°F or below, 1991–2020
frost possible on leaves
average, December
30 to 35°F (-1.1 to 1.7°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 5%
- Snow per year
- 0.1"
median, 1991–2020
median, 1991–2020
1 of 20 observed
NOAA normal
Frost risk by date in Los Osos
At Morro Bay Fire Dept, CA, 4 miles north of Los Osos, 15% of the winters of 1991–2020 had at least one night at or below 32°F, 3% reached 28°F. Nights of 36°F, enough for frost on exposed leaves, are more common (62% of winters) and, when they come, fall between about December 31 and January 21. January is the month most likely to bring one: a 9% chance in a given year. 62 of the 283 other California stations behind this site's ZIP pages freeze in fewer than half of winters too.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F62% of yrs | Dec 18 | Dec 30 | Jan 4 | Jan 11 | Jan 21 | Jan 28 | Feb 3 | Feb 10 | Feb 21 |
| 32°F15% of yrs | too rare for a date | ||||||||
| 28°F3% of yrs | too rare for a date | ||||||||
| 24°F1% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F62% of yrs | Dec 8 | Dec 15 | Dec 20 | Dec 26 | Dec 31 | Jan 3 | Jan 11 | Jan 23 | Feb 4 |
| 32°F15% of yrs | too rare for a date | ||||||||
| 28°F3% of yrs | too rare for a date | ||||||||
| 24°F1% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Morro Bay Fire Dept, CA, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 93402 →Compare Los Osos with another place →
Weather by month in Los Osos
September is the warmest month at Morro Bay Fire Dept, CA, averaging 72°F by day and 56°F at night; December is the coldest at 65°F and 46°F. Every month stays under a 10% chance of a 32°F night; January is the likeliest at 9%.
Warmth for growing adds up to 3,512 growing degree days a year (base 50°F), fewer than at 72% of the 283 California stations. 41% of them (1,440) have built up by the end of June, and October adds the most, 417. Precipitation totals 17.0 inches a year, most in January (3.6") and least in August (0.0"); May to September bring 5% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 65 | 46 | 3.6 | 9% | 1 | 184 |
| Feb | 65 | 48 | 3.6 | 4% | <1 | 188 |
| Mar | 66 | 49 | 3.2 | 0% | 0 | 231 |
| Apr | 67 | 49 | 1.0 | 0% | 0 | 248 |
| May | 67 | 52 | 0.4 | 0% | 0 | 289 |
| Jun | 66 | 54 | 0.2 | 0% | 0 | 300 |
| Jul | 67 | 57 | 0.1 | 0% | 0 | 367 |
| Aug | 70 | 57 | 0.0 | 0% | 0 | 411 |
| Sep | 72 | 56 | 0.1 | 0% | 0 | 413 |
| Oct | 73 | 54 | 0.7 | 0% | 0 | 417 |
| Nov | 69 | 50 | 1.3 | 0% | <1 | 291 |
| Dec | 65 | 46 | 2.8 | 3% | 1 | 175 |
Monthly normals 1991–2020 at Morro Bay Fire Dept, CA (118 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, San Luis Obispo Poly, CA, 10 miles east of Los Osos and 190 feet higher, has a 32°F night in 68% of winters against 15% here, and a coolest-month low 2°F colder (44°F).
When it snows in Los Osos, California
Measurable snow is rare here: only 1 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Morro Bay Fire Dept, CA, 3.8 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 93402 is 4 miles from Morro Bay Fire Dept, CA, which stands at 118 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 93402 in zone 10a, the band where the coldest night of the year averaged 30 to 35°F (-1.1 to 1.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across California →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.