USDA Hardiness Zone 7b
Frost Dates for 19131 — Philadelphia, Pennsylvania
NOAA 1991–2020 normals from Phila Franklin Inst, PA (60 ft), 3 miles southeast.
Updated
In Philadelphia, the last spring frost (32°F) is around March 30 in half of years and has passed by April 12 in nine years out of ten. The first fall frost comes around November 17, as early as November 4 one year in ten, leaving a typical freeze-free season of 232 days (NOAA, Phila Franklin Inst, PA).
- Last spring frost
- March 30
- First fall frost
- November 17
- Growing season
- 232 days
- Hardiness zone
- 7b
50% probability
50% probability
freeze-free, 50%
5 to 10°F (-15.0 to -12.2°C) coldest night
- First snow
- December 20
- Last snow
- March 6
- Winters with snow
- 96%
- Snow per year
- 16.1"
median, 1991–2020
median, 1991–2020
24 of 25 observed
NOAA normal
Frost risk by date in Philadelphia
Half of springs at Phila Franklin Inst, PA see their last 32°F night by March 30; only one in ten is past it by March 15, and one in ten still has one after April 12. Planting tender crops after April 4 leaves a 30% risk of a frost on them, after April 7 20%, and after April 12 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 94% of the 176 Pennsylvania stations behind this site's ZIP pages.
In fall the first 32°F night comes by November 17 in half of years, as early as November 4 one year in ten, and holds off past December 4 one year in ten. A hard freeze of 28°F follows 12 days later, around November 29; in spring the one-in-ten date for 28°F is March 31, 12 days before the 32°F one. The freeze-free season lasts 232 days in a typical year, the longest of the 176 Pennsylvania stations; it reaches 255 days one year in ten and falls short of 214 one year in ten. On average 62 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 9 days longer, to about April 8, and return around November 5. Severe cold of 16°F or below comes in 95% of winters, usually between January 9 and February 9.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Mar 27 | Apr 1 | Apr 3 | Apr 6 | Apr 8 | Apr 11 | Apr 15 | Apr 19 | Apr 23 |
| 32°F | Mar 15 | Mar 20 | Mar 24 | Mar 27 | Mar 30 | Apr 1 | Apr 4 | Apr 7 | Apr 12 |
| 28°F | Mar 1 | Mar 7 | Mar 11 | Mar 15 | Mar 17 | Mar 20 | Mar 23 | Mar 27 | Mar 31 |
| 24°F | Feb 18 | Feb 25 | Mar 1 | Mar 5 | Mar 8 | Mar 11 | Mar 14 | Mar 17 | Mar 22 |
| 20°F | Feb 2 | Feb 8 | Feb 15 | Feb 20 | Feb 25 | Mar 1 | Mar 5 | Mar 8 | Mar 14 |
| 16°F95% of yrs | Jan 16 | Jan 25 | Jan 31 | Feb 4 | Feb 9 | Feb 15 | Feb 21 | Feb 27 | Mar 5 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 23 | Oct 28 | Oct 31 | Nov 3 | Nov 5 | Nov 8 | Nov 11 | Nov 15 | Nov 20 |
| 32°F | Nov 4 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 20 | Nov 23 | Nov 28 | Dec 4 |
| 28°F | Nov 12 | Nov 17 | Nov 21 | Nov 26 | Nov 29 | Dec 2 | Dec 6 | Dec 11 | Dec 18 |
| 24°F | Nov 24 | Dec 1 | Dec 5 | Dec 9 | Dec 14 | Dec 19 | Dec 22 | Dec 27 | Jan 2 |
| 20°F | Dec 7 | Dec 13 | Dec 19 | Dec 23 | Dec 27 | Dec 31 | Jan 4 | Jan 9 | Jan 16 |
| 16°F95% of yrs | Dec 19 | Dec 28 | Jan 1 | Jan 5 | Jan 9 | Jan 13 | Jan 17 | Jan 23 | Feb 1 |
Freeze probabilities 1991–2020 at Phila Franklin Inst, PA, 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 19131 →Compare Philadelphia with another place →
Weather by month in Philadelphia
July is the warmest month at Phila Franklin Inst, PA, averaging 89°F by day and 71°F at night; January is the coldest at 42°F and 28°F. A freezing night is all but certain in every month from December to March (a 90% chance or more). From May to October the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 44% of years.
Warmth for growing adds up to 4,429 growing degree days a year (base 50°F), the most of the 176 Pennsylvania stations. 35% of them (1,552) have built up by the end of June, and July adds the most, 941. Precipitation totals 50.9 inches a year, most in August (5.0") and least in February (3.3"); May to September bring 46% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 42 | 28 | 3.6 | 100% | 20 | 7 |
| Feb | 45 | 30 | 3.3 | 100% | 16 | 10 |
| Mar | 54 | 36 | 4.5 | 98% | 9 | 56 |
| Apr | 66 | 46 | 4.0 | 44% | 1 | 222 |
| May | 76 | 56 | 4.1 | 0% | 0 | 496 |
| Jun | 85 | 66 | 4.8 | 0% | 0 | 762 |
| Jul | 89 | 71 | 4.8 | 0% | 0 | 941 |
| Aug | 87 | 70 | 5.0 | 0% | 0 | 879 |
| Sep | 80 | 63 | 4.9 | 0% | 0 | 645 |
| Oct | 68 | 51 | 4.2 | 3% | <1 | 310 |
| Nov | 56 | 41 | 3.4 | 84% | 3 | 85 |
| Dec | 47 | 33 | 4.3 | 99% | 13 | 17 |
Monthly normals 1991–2020 at Phila Franklin Inst, PA (60 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, Philadelphia International Airport, PA, 8 miles south of Philadelphia, has a last frost 3 days later (April 2), a first frost 7 days earlier (November 10), a season 8 days shorter.
When it snows in Philadelphia, Pennsylvania
The first measurable snow (0.1 inch or more) in Philadelphia usually arrives around December 20, and the last of the season around March 6. Those are the middle dates across the winters of 1991–2020 at Phila Franklin Inst, PA, 3.2 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 24 days after the last snow.
Planting calendar for 19131
| When | What to do |
|---|---|
| January 19 – February 2 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 2 – February 16 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 2 – March 16 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| March 30 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 25 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 3 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 17 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 19131 is 3 miles from Phila Franklin Inst, PA, which stands at 60 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 44 other ZIP codes share the station; its figures are presented in full for 19120 (Philadelphia). The 2023 USDA Plant Hardiness Zone Map lists ZIP 19131 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across Pennsylvania →
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.