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Will it freeze in Union in the next 7 nights?
The earliest overnight low at or below 32°F in the available NWS frost forecast is Fri, Nov 6: 27°F (Fri, Nov 6, 6:00 PM CST to Sat, Nov 7, 6:00 AM CST).
Tonight: forecast low 39°F. Above 36°F.
NWS forecast period: Thu, Nov 5, 6:00 PM CST to Fri, Nov 6, 6:00 AM CST.
4 of the next 7 nights are forecast at 36°F or colder, cold enough for frost on exposed plants.
- Tonight 39°F Above 36°F · Slight Chance Drizzle then Cloudy
- Fri, Nov 6 27°F Hard freeze · Mostly Clear
- Sat, Nov 7 28°F Hard freeze · Mostly Clear
- Sun, Nov 8 31°F Freeze · Clear
- Mon, Nov 9 35°F Frost possible · Clear
- Tue, Nov 10 37°F Above 36°F · Mostly Clear
- Wed, Nov 11 38°F Above 36°F · Mostly Clear
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
The median first fall hard-freeze date (28°F) is November 3, from NOAA’s 1991–2020 Climate Normals at Union. This is the 50% probability date, not a forecast for this year.
| 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 | Apr 8 · Apr 22 · May 8 | Sep 30 · Oct 13 · Oct 26 | 172 days |
| 32°F freeze | Mar 26 · Apr 11 · Apr 28 | Oct 9 · Oct 23 · Nov 5 | 194 days |
| 28°F hard freeze | Mar 12 · Mar 31 · Apr 15 | Oct 21 · Nov 3 · Nov 18 | 217 days |
Average high temperature by month
1991–2020 normals at Union
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, MO come from the nearest weather station with freeze statistics in NOAA’s 1991–2020 Climate Normals: Union (station USC00238515, elevation 540 ft), 0.6 mi from Union. 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 | Distance | Last spring frost | First fall frost |
|---|---|---|---|
| Washington, MO | 8.1 mi | Apr 8 | Oct 25 |
| Pacific, MO | 14 mi | Apr 8 | Oct 25 |
| Sullivan, MO | 18 mi | Apr 11 | Oct 23 |
| Eureka, MO | 19 mi | Apr 12 | Oct 23 |
| Wildwood, MO | 20 mi | Apr 12 | Oct 23 |
| Ellisville, MO | 24 mi | Apr 12 | Oct 23 |
| Dardenne Prairie, MO | 26 mi | Apr 10 | Oct 26 |
| Lake St. Louis, MO | 26 mi | Apr 10 | Oct 26 |
| Weldon Spring, MO | 26 mi | Apr 10 | Oct 26 |
| Ballwin, MO | 27 mi | Apr 4 | Oct 29 |
Frequently asked questions
When is the last frost in Union?
On average, the last spring frost (32°F) in Union is around April 11. In about 1 year in 10 it comes after April 28, and in 9 years in 10 it comes after March 26.
When is the first frost in Union?
The first fall frost (32°F) usually arrives around October 23. There’s a 10% chance of a freeze by October 9 and a 90% chance by November 5.
Can it frost in Union 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 April 22.
What growing zone is Union?
Union is in USDA Plant Hardiness Zone 6b (average annual extreme minimum temperature −5 to 0°F), based on the 2023 USDA map for ZIP code 63084. See growing zones in Missouri.
More: all Missouri frost dates · Missouri growing zones · frost vs. freeze