Frost dates / California / Napa
Frost dates in Napa, CA
The station on this page is NAPA STATE HOSPITAL, CA US (USC00046074), 2.4 miles from the city point. Population in the Census 2024 estimate is 76,921.
Zone 9bUSDA average annual extreme minimum 25°F to 30°F, from ZIP 94559 (3.2 miles from the city point used on this page).
Outside the median season Growing seasonTicks: 10%, 50%, and 90%
Last 32°F in spring
NCEI’s probability is the chance the last spring minimum of 32°F or lower occurs on or after the date.
| Probability | Date | How to read it |
|---|---|---|
| 90% | January 3 | Earlier date. A last 32°F on or after this day is common. |
| 50% | February 12 | Median. |
| 10% | March 13 | Later date. A last 32°F on or after this day is uncommon. |
First 32°F in fall
NCEI’s probability is the chance the first autumn minimum of 32°F or lower occurs on or before the date.
| Probability | Date | How to read it |
|---|---|---|
| 10% | November 15 | Earlier date. A first 32°F on or before this day is uncommon. |
| 50% | December 4 | Median. |
| 90% | January 4 | Later date. A first 32°F on or before this day is common. |
32°F growing-season length
Days between the last spring 32°F and the first autumn 32°F. The figure is a length the season meets or exceeds at that probability, from NCEI, not a subtraction done on this site.
| Probability the season is at least this long | Days |
|---|---|
| 10% | 338 |
| 50% | 299 |
| 90% | 257 |
28°F threshold
| 10% | 50% | 90% | |
|---|---|---|---|
| Last, on or after | February 13 | January 11 | December 16 |
| First, on or before | December 1 | December 19 | January 23 |
| Season at least | 365 days | 348 days | 316 days |
36°F threshold
| 10% | 50% | 90% | |
|---|---|---|---|
| Last, on or after | April 19 | March 27 | February 26 |
| First, on or before | October 31 | November 17 | December 4 |
| Season at least | 272 days | 236 days | 206 days |
Station NAPA STATE HOSPITAL, CA US (USC00046074). Completeness flag S, 28 years used for the 32°F dates. NCEI’s annual probability of at least one day at or below 32°F is 98.4%. Freeze dates are conditional on that threshold occurring. Elevation 10.7 m. The same probability language applies to the 28°F and 36°F rows when those dates passed the same quality checks.
Planting calendar for Napa · Zone 9b
Check a crop against this station
Napa, CA
Zone 9bAverage annual extreme minimum 25°F to 30°F
Outside the median season Growing seasonTicks: 10%, 50%, and 90%
California. Nearest qualified station: NAPA STATE HOSPITAL, CA US (USC00046074), 2.4 miles. Median last 32°F February 12. Median first 32°F December 4. The 50% growing-season length is 299 days.
Open the ZIP page · Crop guides for California
32°F probabilities at this station
| 10% | 50% | 90% | |
|---|---|---|---|
| Last 32°F on or after | March 13 | February 12 | January 3 |
| First 32°F on or before | November 15 | December 4 | January 4 |
Column order matches the NCEI file: for the last freeze, 10% is the later date and 90% is the earlier date. How to read the probabilities.
Planting calendar
Windows below are from UC ANR, UC Master Gardener Program, Time of planting, retrieved 2026-10-10. North and North Coast = Monterey County north; South Coast = San Luis Obispo County south; Interior Valleys = Sacramento, San Joaquin, and similar valleys; Desert Valleys = Imperial and Coachella Valleys. Source line on the page: California Master Gardener Handbook, Table 13.2, Adapted from Vegetable Gardening Illustrated 1994.
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