USDA Hardiness Zone 5b
Frost Dates for 80540 — Lyons, Colorado
NOAA 1991–2020 normals from Allenspark 3NW, CO (8,500 ft), 10 miles west.
Updated
In Lyons, the last spring frost (32°F) is around June 14 in half of years and has passed by June 28 in nine years out of ten. The first fall frost comes around September 12, as early as August 25 one year in ten, leaving a typical freeze-free season of 92 days (NOAA, Allenspark 3NW, CO).
- Last spring frost
- June 14
- First fall frost
- September 12
- Growing season
- 92 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 25
- Last snow
- April 29
- Winters with snow
- 100%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
15 of 15 observed
NOAA normal
Frost risk by date in Lyons
Half of springs at Allenspark 3NW, CO see their last 32°F night by June 14; only one in ten is past it by May 24, and one in ten still has one after June 28. Planting tender crops after June 20 leaves a 30% risk of a frost on them, after June 23 20%, and after June 28 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 45% of the 110 Colorado 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 25 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 15, 13 days before the 32°F one. The freeze-free season lasts 92 days in a typical year, shorter than at 88% of the 110 Colorado stations; it reaches 112 days one year in ten and falls short of 69 one year in ten. On average 225 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between October 27 and April 20.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 24 | Jun 1 | Jun 6 | Jun 10 | Jun 14 | Jun 17 | Jun 20 | Jun 23 | Jun 28 |
| 28°F | May 7 | May 13 | May 18 | May 22 | May 27 | May 31 | Jun 4 | Jun 9 | Jun 15 |
| 24°F | Apr 27 | May 1 | May 4 | May 6 | May 9 | May 12 | May 16 | May 21 | May 29 |
| 20°F | Apr 16 | Apr 21 | Apr 24 | Apr 28 | Apr 30 | May 2 | May 5 | May 8 | May 13 |
| 16°F | Mar 31 | Apr 7 | Apr 12 | Apr 16 | Apr 20 | Apr 23 | Apr 26 | Apr 30 | May 4 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 25 | Sep 2 | Sep 6 | Sep 9 | Sep 12 | Sep 15 | Sep 18 | Sep 21 | Sep 25 |
| 28°F | Sep 11 | Sep 16 | Sep 20 | Sep 23 | Sep 25 | Sep 28 | Sep 30 | Oct 3 | Oct 8 |
| 24°F | Sep 18 | Sep 26 | Sep 30 | Oct 2 | Oct 5 | Oct 9 | Oct 12 | Oct 16 | Oct 20 |
| 20°F | Sep 28 | Oct 4 | Oct 8 | Oct 12 | Oct 15 | Oct 18 | Oct 22 | Oct 26 | Oct 31 |
| 16°F | Oct 8 | Oct 14 | Oct 18 | Oct 22 | Oct 27 | Oct 31 | Nov 3 | Nov 6 | Nov 12 |
Freeze probabilities 1991–2020 at Allenspark 3NW, CO, 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 80540 →Compare Lyons with another place →
Weather by month in Lyons
July is the warmest month at Allenspark 3NW, CO, averaging 74°F by day and 44°F at night; January is the coldest at 32°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 81% of years.
Warmth for growing adds up to 831 growing degree days a year (base 50°F), fewer than at 94% of the 110 Colorado stations. 22% of them (180) have built up by the end of June, and July adds the most, 293.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 32 | 14 | 100% | 30 | 0 |
| Feb | 35 | 15 | 100% | 27 | 0 |
| Mar | 42 | 20 | 100% | 29 | 1 |
| Apr | 46 | 23 | 100% | 27 | 1 |
| May | 56 | 32 | 100% | 18 | 34 |
| Jun | 69 | 38 | 81% | 6 | 144 |
| Jul | 74 | 44 | 5% | <1 | 293 |
| Aug | 73 | 43 | 17% | <1 | 242 |
| Sep | 66 | 37 | 96% | 8 | 103 |
| Oct | 52 | 29 | 100% | 22 | 12 |
| Nov | 41 | 20 | 100% | 28 | 1 |
| Dec | 33 | 14 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Allenspark 3NW, CO (8,500 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, Estes Park 3 SSE, CO, 12 miles northwest of Lyons and 688 feet lower, has a last frost 15 days earlier (May 30), a first frost 5 days later (September 17), a season 17 days longer.
When it snows in Lyons, Colorado
The first measurable snow (0.1 inch or more) in Lyons usually arrives around October 25, and the last of the season around April 29. Those are the middle dates across the winters of 1991–2020 at Lyons 1.8 N, CO, 3.9 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 46 days after the last snow.
Planting calendar for 80540
| When | What to do |
|---|---|
| April 5 – April 19 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| April 19 – May 3 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| May 17 – May 31 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| June 14 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 80540 is 10 miles from Allenspark 3NW, CO, which stands at 8,500 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 80540 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.