USDA Hardiness Zone 9b
Frost Dates for 95391 — Mountain House, California
NOAA 1991–2020 normals from Tracy Pumping Plt, CA (61 ft), 4 miles northeast.
Updated
In Mountain House, the last spring frost (32°F) is around January 19 in half of years and has passed by February 17 in nine years out of ten. The first fall frost comes around December 10, as early as November 26 one year in ten, leaving a typical freeze-free season of 330 days (NOAA, Tracy Pumping Plt, CA).
- Last spring frost
- January 19
- First fall frost
- December 10
- Growing season
- 330 days
- Hardiness zone
- 9b
50% probability
50% probability
freeze-free, 50%
25 to 30°F (-3.9 to -1.1°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 20 observed
NOAA normal
Frost risk by date in Mountain House
Half of springs at Tracy Pumping Plt, CA see their last 32°F night by January 19; only one in ten is past it by December 25, and one in ten still has one after February 17. Planting tender crops after January 31 leaves a 30% risk of a frost on them, after February 6 20%, and after February 17 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 December 10 in half of years, as early as November 26 one year in ten, and holds off past January 7 one year in ten. A hard freeze of 28°F follows 12 days later, around December 22; in spring the one-in-ten date for 28°F is January 22, 26 days before the 32°F one. The freeze-free season lasts 330 days in a typical year, longer than at 82% of the 219 California stations; it reaches 358 days one year in ten and falls short of 297 one year in ten. On average 10 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 33 days longer, to about February 21, and return around November 29. A 24°F night is unusual: 14% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jan 22 | Jan 31 | Feb 7 | Feb 13 | Feb 21 | Feb 25 | Mar 1 | Mar 9 | Mar 24 |
| 32°F94% of yrs | Dec 25 | Jan 2 | Jan 8 | Jan 13 | Jan 19 | Jan 25 | Jan 31 | Feb 6 | Feb 17 |
| 28°F58% of yrs | Dec 12 | Dec 21 | Dec 26 | Dec 30 | Jan 1 | Jan 5 | Jan 9 | Jan 15 | Jan 22 |
| 24°F14% of yrs | too rare for a date | ||||||||
| 20°F0% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 13 | Nov 19 | Nov 23 | Nov 26 | Nov 29 | Dec 1 | Dec 4 | Dec 8 | Dec 13 |
| 32°F94% of yrs | Nov 26 | Dec 1 | Dec 4 | Dec 7 | Dec 10 | Dec 15 | Dec 20 | Dec 27 | Jan 7 |
| 28°F58% of yrs | Dec 4 | Dec 10 | Dec 14 | Dec 18 | Dec 22 | Dec 26 | Dec 31 | Jan 4 | Jan 10 |
| 24°F14% of yrs | too rare for a date | ||||||||
| 20°F0% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Tracy Pumping Plt, 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 95391 →Compare Mountain House with another place →
Weather by month in Mountain House
July is the warmest month at Tracy Pumping Plt, CA, averaging 93°F by day and 62°F at night; January is the coldest at 56°F and 41°F. From March to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 24% of years.
Warmth for growing adds up to 5,166 growing degree days a year (base 50°F), more than at 69% of the 283 California stations. 38% of them (1,983) have built up by the end of June, and July adds the most, 856. Precipitation totals 12.3 inches a year, most in January (2.5") and least in July (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 | 41 | 2.5 | 69% | 4 | 38 |
| Feb | 62 | 44 | 2.3 | 24% | 1 | 102 |
| Mar | 67 | 47 | 1.6 | 2% | 0 | 229 |
| Apr | 73 | 50 | 0.8 | 1% | 0 | 352 |
| May | 80 | 55 | 0.5 | 0% | 0 | 549 |
| Jun | 88 | 59 | 0.1 | 0% | 0 | 713 |
| Jul | 93 | 62 | 0.0 | 0% | 0 | 856 |
| Aug | 93 | 62 | 0.0 | 0% | 0 | 843 |
| Sep | 89 | 60 | 0.1 | 0% | 0 | 735 |
| Oct | 79 | 55 | 0.7 | 0% | 0 | 521 |
| Nov | 66 | 46 | 1.3 | 17% | <1 | 189 |
| Dec | 57 | 40 | 2.4 | 74% | 4 | 40 |
Monthly normals 1991–2020 at Tracy Pumping Plt, CA (61 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, Livermore, CA, 11 miles southwest of Mountain House and 332 feet higher, has a last frost 27 days later (February 15), a first frost 8 days earlier (December 2), a season 38 days shorter.
When it snows in Mountain House, California
Measurable snow is rare here: only 0 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Tracy Pumping Plt, CA, 3.6 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 95391
| When | What to do |
|---|---|
| November 10 – November 24 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| November 24 – December 8 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| December 22 – January 5 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| January 19 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 17 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 26 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 10 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 95391 is 4 miles from Tracy Pumping Plt, CA, which stands at 61 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 95391 in zone 9b, the band where the coldest night of the year averaged 25 to 30°F (-3.9 to -1.1°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.