USDA Hardiness Zone 4a
Frost Dates for 59270 — Sidney, Montana
NOAA 1991–2020 normals from Sidney, MT (1,933 ft), 4 miles northeast.
Updated
In Sidney, the last spring frost (32°F) is around May 11 in half of years and has passed by May 25 in nine years out of ten. The first fall frost comes around September 27, as early as September 13 one year in ten, leaving a typical freeze-free season of 137 days (NOAA, Sidney, MT).
- Last spring frost
- May 11
- First fall frost
- September 27
- Growing season
- 137 days
- Hardiness zone
- 4a
50% probability
50% probability
freeze-free, 50%
-30 to -25°F (-34.4 to -31.7°C) coldest night
- First snow
- November 4
- Last snow
- April 7
- Winters with snow
- 100%
- Snow per year
- 30.4"
median, 1991–2020
median, 1991–2020
24 of 24 observed
NOAA normal
Frost risk by date in Sidney
Half of springs at Sidney, MT see their last 32°F night by May 11; only one in ten is past it by April 30, and one in ten still has one after May 25. Planting tender crops after May 17 leaves a 30% risk of a frost on them, after May 20 20%, and after May 25 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 60% of the 68 Montana stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 27 in half of years, as early as September 13 one year in ten, and holds off past October 9 one year in ten. A hard freeze of 28°F follows 9 days later, around October 6; in spring the one-in-ten date for 28°F is May 16, 9 days before the 32°F one. The freeze-free season lasts 137 days in a typical year, longer than at 71% of the 68 Montana stations; it reaches 154 days one year in ten and falls short of 117 one year in ten. On average 178 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 10 days longer, to about May 21, and return around September 18. Severe cold of 16°F or below comes every winter, usually between November 2 and April 2.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 9 | May 13 | May 16 | May 18 | May 21 | May 24 | May 27 | May 30 | Jun 3 |
| 32°F | Apr 30 | May 3 | May 6 | May 8 | May 11 | May 14 | May 17 | May 20 | May 25 |
| 28°F | Apr 18 | Apr 24 | Apr 28 | Apr 30 | May 2 | May 5 | May 7 | May 11 | May 16 |
| 24°F | Apr 7 | Apr 12 | Apr 16 | Apr 19 | Apr 22 | Apr 26 | Apr 29 | May 2 | May 7 |
| 20°F | Mar 25 | Apr 1 | Apr 4 | Apr 8 | Apr 11 | Apr 14 | Apr 17 | Apr 22 | Apr 27 |
| 16°F | Mar 14 | Mar 21 | Mar 26 | Mar 30 | Apr 2 | Apr 5 | Apr 8 | Apr 12 | Apr 17 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 4 | Sep 9 | Sep 13 | Sep 16 | Sep 18 | Sep 21 | Sep 23 | Sep 26 | Sep 30 |
| 32°F | Sep 13 | Sep 18 | Sep 22 | Sep 24 | Sep 27 | Sep 29 | Oct 1 | Oct 5 | Oct 9 |
| 28°F | Sep 22 | Sep 27 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 20 |
| 24°F | Oct 1 | Oct 6 | Oct 11 | Oct 14 | Oct 16 | Oct 19 | Oct 22 | Oct 25 | Oct 30 |
| 20°F | Oct 10 | Oct 15 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 4 | Nov 10 |
| 16°F | Oct 18 | Oct 23 | Oct 28 | Oct 31 | Nov 2 | Nov 6 | Nov 9 | Nov 14 | Nov 19 |
Freeze probabilities 1991–2020 at Sidney, MT, 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 59270 →Compare Sidney with another place →
Weather by month in Sidney
July is the warmest month at Sidney, MT, averaging 87°F by day and 57°F at night; January is the coldest at 27°F and 7°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 89% of years.
Warmth for growing adds up to 2,537 growing degree days a year (base 50°F), more than at 93% of the 68 Montana stations. 31% of them (797) have built up by the end of June, and July adds the most, 680. Precipitation totals 15.7 inches a year, most in June (2.8") and least in February (0.4"); May to September bring 69% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 27 | 7 | 0.5 | 100% | 30 | 0 |
| Feb | 32 | 11 | 0.4 | 100% | 28 | 1 |
| Mar | 46 | 21 | 0.6 | 100% | 27 | 8 |
| Apr | 61 | 32 | 1.2 | 100% | 16 | 67 |
| May | 71 | 43 | 2.4 | 89% | 4 | 249 |
| Jun | 79 | 52 | 2.8 | 2% | <1 | 472 |
| Jul | 87 | 57 | 2.7 | 0% | 0 | 680 |
| Aug | 86 | 55 | 1.3 | 0% | 0 | 643 |
| Sep | 76 | 46 | 1.6 | 67% | 2 | 334 |
| Oct | 59 | 34 | 1.1 | 100% | 14 | 78 |
| Nov | 42 | 21 | 0.6 | 100% | 27 | 4 |
| Dec | 31 | 11 | 0.5 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Sidney, MT (1,933 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
When it snows in Sidney, Montana
The first measurable snow (0.1 inch or more) in Sidney usually arrives around November 4, and the last of the season around April 7. Those are the middle dates across the winters of 1991–2020 at Sidney, MT, 4.1 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 34 days after the last snow.
Planting calendar for 59270
| When | What to do |
|---|---|
| March 2 – March 16 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 16 – March 30 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 13 – April 27 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 11 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 5 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 13 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 27 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 59270 is 4 miles from Sidney, MT, which stands at 1,933 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59270 in zone 4a, the band where the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
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.