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Will it freeze in Union City in the next 7 nights?
No overnight lows at or below 32°F are forecast in Union City during the next 7 nights in the available NWS frost forecast.
Tonight: forecast low 50°F. Above 36°F.
NWS forecast period: Thu, Nov 5, 6:00 PM PST to Fri, Nov 6, 6:00 AM PST.
No nights at or below 36°F in the National Weather Service forecast for the next 7 nights.
- Tonight 50°F Above 36°F · Mostly Clear
- Fri, Nov 6 49°F Above 36°F · Mostly Clear
- Sat, Nov 7 52°F Above 36°F · Partly Cloudy
- Sun, Nov 8 52°F Above 36°F · Partly Cloudy
- Mon, Nov 9 52°F Above 36°F · Partly Cloudy
- Tue, Nov 10 54°F Above 36°F · Partly Cloudy then Slight Chance Light Rain
- Wed, Nov 11 53°F Above 36°F · Chance Light Rain
Overnight lows from the National Weather Service forecast for this location. This covers the available forecast window, not the first freeze of the whole season. Frost can form above 32°F on clear, calm nights.
Frost and freeze probabilities
Freeze dates shift from year to year. Spring percentages describe the chance of a freeze after the stated date; fall percentages describe the chance of a freeze by that date. The 10% spring date is the cautious one: a later freeze happens about 1 year in 10.
These dates describe historical probabilities, not this year’s forecast or the earliest and latest possible freezes. Different weather stations or probability thresholds can produce different published dates for the same city.
Average first hard freeze in Union City
Most years have no 28°F hard freeze at Fremont, according to NOAA’s 1991–2020 Climate Normals. Check the short-term forecast above during cold snaps.
| Temperature | Last spring date 90% · 50% · 10% chance of a later freeze | First fall date 10% · 50% · 90% chance of an earlier freeze | Season |
|---|---|---|---|
| 36°F frost possible | Jan 3 · Feb 6 · Mar 11 | Nov 17 · Dec 5 · Jan 2 | 301 days |
| 32°F freeze | Dec 14 · Jan 7 · Feb 7 | Dec 2 · Dec 22 · Jan 21 | 353 days |
| 28°F hard freeze | Dec 13 · Dec 31 · Jan 20 | Dec 11 · Dec 29 · Jan 17 | 365 days |
Average high temperature by month
1991–2020 normals at Fremont
Average low temperature by month
Months with lows near or below freezing carry frost risk
Where these frost dates come from
The frost dates for Union City, CA come from the nearest weather station with freeze statistics in NOAA’s 1991–2020 Climate Normals: Fremont (station USC00043244, elevation 38 ft), 4.2 mi from Union City. Local conditions (valleys, hilltops, distance to water, city heat) can shift frost dates by days or weeks. The hardiness zone is from the 2023 USDA Plant Hardiness Zone Map (USDA ARS and Oregon State University PRISM). See our methodology.
Frost dates near Union City
| City | Distance | Last spring frost | First fall frost |
|---|---|---|---|
| Hayward, CA | 5.0 mi | rare | rare |
| Newark, CA | 6.8 mi | rare | rare |
| Fremont, CA | 8.7 mi | rare | rare |
| Pleasanton, CA | 8.7 mi | Feb 15 | Dec 2 |
| Dublin, CA | 11 mi | Feb 15 | Dec 2 |
| San Leandro, CA | 11 mi | Jan 7 | Dec 23 |
| Menlo Park, CA | 11 mi | Feb 1 | Dec 7 |
| East Palo Alto, CA | 11 mi | Feb 1 | Dec 7 |
| San Ramon, CA | 12 mi | Mar 8 | Dec 22 |
| Redwood City, CA | 12 mi | Jan 17 | Dec 12 |
Frequently asked questions
When is the last frost in Union City?
On average, the last spring frost (32°F) in Union City is around January 7. In about 1 year in 10 it comes after February 7, and in 9 years in 10 it comes after December 14.
When is the first frost in Union City?
The first fall frost (32°F) usually arrives around December 22. There’s a 10% chance of a freeze by December 2 and a 90% chance by January 21.
Can it frost in Union City after the last frost date?
Yes. Frost can form on clear, calm nights even when the air stays above 32°F. Temperatures of 36°F or lower, cold enough for frost on exposed plants, have a 50% chance of occurring after February 6.
What growing zone is Union City?
Union City is in USDA Plant Hardiness Zone 9b (average annual extreme minimum temperature 25 to 30°F), based on the 2023 USDA map for ZIP code 94544. See growing zones in California.
More: all California frost dates · California growing zones · UV index today in Union City · frost vs. freeze