USDA Hardiness Zone 10a
Frost Dates for 91024 — Sierra Madre, California
NOAA 1991–2020 normals from Mt Wilson Cbs, CA (5,710 ft), 5 miles north.
Updated
In Sierra Madre, the last spring frost (32°F) is around April 28 in half of years and has passed by May 27 in nine years out of ten. The first fall frost comes around November 15, as early as October 18 one year in ten, leaving a typical freeze-free season of 199 days (NOAA, Mt Wilson Cbs, CA).
- Last spring frost
- April 28
- First fall frost
- November 15
- Growing season
- 199 days
- Hardiness zone
- 10a
50% probability
50% probability
freeze-free, 50%
30 to 35°F (-1.1 to 1.7°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 6%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
1 of 18 observed
NOAA normal
Frost risk by date in Sierra Madre
Half of springs at Mt Wilson Cbs, CA see their last 32°F night by April 28; only one in ten is past it by March 31, and one in ten still has one after May 27. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 17 20%, and after May 27 10%. The 29 days between the even-odds date and the one-in-ten date is narrower than at 52% of the 220 California stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by November 15 in half of years, as early as October 18 one year in ten, and holds off past December 9 one year in ten. A hard freeze of 28°F follows 19 days later, around December 4; in spring the one-in-ten date for 28°F is May 10, 17 days before the 32°F one. The freeze-free season lasts 199 days in a typical year, shorter than at 81% of the 219 California stations; it reaches 238 days one year in ten and falls short of 164 one year in ten. On average 50 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 17 days longer, to about May 15, and return around October 30. Nights of 24°F, cold enough to damage hardier plants, come in 96% of winters and 16°F in 12%.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 21 | Apr 29 | May 4 | May 9 | May 15 | May 22 | May 26 | May 31 | Jun 4 |
| 32°F | Mar 31 | Apr 9 | Apr 15 | Apr 22 | Apr 28 | May 2 | May 9 | May 17 | May 27 |
| 28°F | Feb 28 | Mar 15 | Mar 24 | Mar 31 | Apr 8 | Apr 15 | Apr 21 | Apr 30 | May 10 |
| 24°F96% of yrs | Jan 10 | Feb 7 | Feb 20 | Feb 28 | Mar 12 | Mar 21 | Mar 30 | Apr 8 | Apr 18 |
| 20°F57% of yrs | Dec 21 | Jan 1 | Jan 10 | Jan 28 | Feb 11 | Feb 19 | Feb 28 | Mar 13 | Apr 1 |
| 16°F12% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 3 | Oct 13 | Oct 18 | Oct 24 | Oct 30 | Nov 3 | Nov 8 | Nov 13 | Nov 19 |
| 32°F | Oct 18 | Oct 29 | Nov 5 | Nov 10 | Nov 15 | Nov 20 | Nov 26 | Dec 2 | Dec 9 |
| 28°F | Nov 5 | Nov 14 | Nov 23 | Nov 30 | Dec 4 | Dec 8 | Dec 13 | Dec 18 | Dec 29 |
| 24°F96% of yrs | Nov 26 | Dec 3 | Dec 9 | Dec 16 | Dec 22 | Dec 28 | Jan 5 | Jan 25 | Feb 20 |
| 20°F57% of yrs | Dec 6 | Dec 19 | Dec 27 | Jan 1 | Jan 10 | Jan 25 | Feb 7 | Feb 20 | Mar 13 |
| 16°F12% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Mt Wilson Cbs, CA, 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 91024 →Compare Sierra Madre with another place →
Weather by month in Sierra Madre
August is the warmest month at Mt Wilson Cbs, CA, averaging 85°F by day and 64°F at night; February is the coldest at 55°F and 37°F. A freezing night is all but certain in every month from December to March (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 82% of years and May still brings one in 41% of years.
Warmth for growing adds up to 3,992 growing degree days a year (base 50°F), fewer than at 59% of the 283 California stations. 32% of them (1,267) have built up by the end of June, and August adds the most, 759. Precipitation totals 32.2 inches a year, most in February (8.3") and least in August (0.0"); May to September bring 6% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 56 | 38 | 7.7 | 92% | 9 | 73 |
| Feb | 55 | 37 | 8.3 | 93% | 10 | 61 |
| Mar | 59 | 39 | 5.1 | 92% | 8 | 109 |
| Apr | 63 | 42 | 2.1 | 82% | 6 | 162 |
| May | 70 | 48 | 1.1 | 41% | 2 | 318 |
| Jun | 79 | 58 | 0.2 | 4% | <1 | 545 |
| Jul | 85 | 64 | 0.2 | 0% | 0 | 755 |
| Aug | 85 | 64 | 0.0 | 0% | 0 | 759 |
| Sep | 81 | 59 | 0.3 | 0% | 0 | 601 |
| Oct | 72 | 51 | 1.3 | 22% | 1 | 376 |
| Nov | 63 | 43 | 1.9 | 69% | 4 | 172 |
| Dec | 55 | 37 | 4.0 | 97% | 11 | 62 |
Monthly normals 1991–2020 at Mt Wilson Cbs, CA (5,710 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, Pasadena, CA, 5 miles west of Sierra Madre and 4,846 feet lower, has a 32°F night in 13% of winters against 100% here, and a coolest-month low 8°F warmer (45°F).
When it snows in Sierra Madre, California
Measurable snow is rare here: only 1 of 18 winters from 1991 to 2020 recorded 0.1 inch or more at Mt Wilson Cbs, CA, 4.7 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 91024
| When | What to do |
|---|---|
| February 17 – March 3 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 3 – March 17 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 31 – April 14 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 28 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 23 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 1 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 15 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 91024 is 5 miles from Mt Wilson Cbs, CA, which stands at 5,710 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 91024 in zone 10a, the band where the coldest night of the year averaged 30 to 35°F (-1.1 to 1.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across California →
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.