USDA Hardiness Zone 5b
Frost Dates for 84017 — Coalville, Utah
NOAA 1991–2020 normals from Coalville, UT (5,550 ft), 3 miles northwest.
Updated
In Coalville, the last spring frost (32°F) is around June 7 in half of years and has passed by June 25 in nine years out of ten. The first fall frost comes around September 12, as early as August 28 one year in ten, leaving a typical freeze-free season of 95 days (NOAA, Coalville, UT).
- Last spring frost
- June 7
- First fall frost
- September 12
- Growing season
- 95 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- October 28
- Last snow
- April 25
- Winters with snow
- 100%
- Snow per year
- 70.1"
median, 1991–2020
median, 1991–2020
20 of 20 observed
NOAA normal
Frost risk by date in Coalville
Half of springs at Coalville, UT see their last 32°F night by June 7; only one in ten is past it by May 21, and one in ten still has one after June 25. Planting tender crops after June 15 leaves a 30% risk of a frost on them, after June 19 20%, and after June 25 10%. The 18 days between the even-odds date and the one-in-ten date is narrower than at 47% of the 66 Utah stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 12 in half of years, as early as August 28 one year in ten, and holds off past September 25 one year in ten. A hard freeze of 28°F follows 13 days later, around September 25; in spring the one-in-ten date for 28°F is June 9, 16 days before the 32°F one. The freeze-free season lasts 95 days in a typical year, shorter than at 94% of the 66 Utah stations; it reaches 118 days one year in ten and falls short of 69 one year in ten. On average 203 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between November 1 and March 30.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 21 | May 28 | May 31 | Jun 4 | Jun 7 | Jun 11 | Jun 15 | Jun 19 | Jun 25 |
| 28°F | May 5 | May 9 | May 13 | May 17 | May 21 | May 24 | May 29 | Jun 2 | Jun 9 |
| 24°F | Apr 19 | Apr 23 | Apr 27 | May 1 | May 3 | May 5 | May 9 | May 13 | May 20 |
| 20°F | Mar 31 | Apr 5 | Apr 10 | Apr 13 | Apr 15 | Apr 19 | Apr 23 | Apr 28 | May 4 |
| 16°F | Mar 6 | Mar 13 | Mar 19 | Mar 26 | Mar 30 | Apr 3 | Apr 6 | Apr 10 | Apr 15 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 28 | Sep 2 | Sep 5 | Sep 9 | Sep 12 | Sep 15 | Sep 18 | Sep 21 | Sep 25 |
| 28°F | Sep 9 | Sep 15 | Sep 19 | Sep 22 | Sep 25 | Sep 27 | Sep 30 | Oct 3 | Oct 6 |
| 24°F | Sep 23 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 8 | Oct 12 | Oct 16 | Oct 23 |
| 20°F | Oct 4 | Oct 9 | Oct 14 | Oct 18 | Oct 21 | Oct 24 | Oct 26 | Oct 30 | Nov 4 |
| 16°F | Oct 18 | Oct 22 | Oct 25 | Oct 28 | Nov 1 | Nov 3 | Nov 6 | Nov 10 | Nov 16 |
Freeze probabilities 1991–2020 at Coalville, UT, 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 84017 →Compare Coalville with another place →
Weather by month in Coalville
July is the warmest month at Coalville, UT, averaging 89°F by day and 48°F at night; December is the coldest at 38°F and 14°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). July is the only month with under a 10% chance of a 32°F night. In spring, June still brings one in 69% of years.
Warmth for growing adds up to 1,939 growing degree days a year (base 50°F), fewer than at 85% of the 66 Utah stations. 27% of them (517) have built up by the end of June, and July adds the most, 572. Precipitation totals 16.4 inches a year, most in May (1.9") and least in August (0.8"); May to September bring 37% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 39 | 13 | 1.5 | 100% | 30 | 0 |
| Feb | 43 | 17 | 1.2 | 100% | 27 | 0 |
| Mar | 55 | 24 | 1.5 | 100% | 27 | 4 |
| Apr | 62 | 29 | 1.7 | 100% | 21 | 28 |
| May | 70 | 35 | 1.9 | 100% | 10 | 137 |
| Jun | 81 | 42 | 1.2 | 69% | 2 | 348 |
| Jul | 89 | 48 | 0.9 | 6% | <1 | 572 |
| Aug | 88 | 47 | 0.8 | 16% | 1 | 539 |
| Sep | 79 | 38 | 1.3 | 96% | 8 | 263 |
| Oct | 66 | 29 | 1.4 | 100% | 22 | 46 |
| Nov | 50 | 21 | 1.4 | 100% | 26 | 3 |
| Dec | 38 | 14 | 1.6 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Coalville, UT (5,550 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, Park City, UT, 17 miles southwest of Coalville and 1,350 feet higher, has a last frost 9 days earlier (May 29), a first frost 13 days later (September 25), a season 22 days longer.
When it snows in Coalville, Utah
The first measurable snow (0.1 inch or more) in Coalville usually arrives around October 28, and the last of the season around April 25. Those are the middle dates across the winters of 1991–2020 at Coalville, UT, 2.5 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 43 days after the last snow.
Planting calendar for 84017
| When | What to do |
|---|---|
| March 29 – April 12 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| April 12 – April 26 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| May 10 – May 24 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| June 7 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 20 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by August 29 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 12 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 84017 is 3 miles from Coalville, UT, which stands at 5,550 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 84017 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°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.