Pennsylvania weather and outdoor projects
Pennsylvania has humid summers and cold winters, with Philadelphia milder than Pittsburgh and the central mountains. Pittsburgh and western Pennsylvania are among the cloudiest places in the East, which slows drying in spring and fall.
Late May, June and September are usually the best months for staining and painting. Summer storms and humid nights bring dew on fresh finishes. Winters have many freeze-thaw cycles and road salt, so proper concrete curing and sealing matter, and driveway sealing is best finished by early October.
Frost dates in Pennsylvania
In Philadelphia, the median last spring freeze (32°F) is around April 2 and the median first fall freeze is around November 10, a frost-free season of about 224 days.
In Pittsburgh, the median last spring freeze (32°F) is around April 23 and the median first fall freeze is around October 23, a frost-free season of about 181 days.
How Pennsylvania compares with other states
Philadelphia is tied for the 7th-longest deck staining season of the 50 state main stations (5 good months). Philadelphia is tied for the 13th-least humid summer afternoons of the 47 state main stations (48% humidity at 3 PM, June–August). Philadelphia has the 16th-longest frost-free season of the 50 state main stations (224 days).
| Measure (Philadelphia) | Value | Rank, highest first |
|---|---|---|
| Deck staining season | 5 good months | 7th of 50 |
| Frost-free season | 224 days | 16th of 50 |
| Freezing nights | 77 a year | 30th of 50 |
| Rainy days | 73 a year with 0.1 in or more | 25th of 50 |
| Days at 90°F or hotter | 30 a year | 26th of 50 |
| Summer afternoons | 48% humidity at 3 PM, June–August | 31st of 47 |
Best time to stain a deck in Pennsylvania
In Philadelphia, the most reliable months are May–June and August–October. April, July and November can also work on the right days (average highs Apr 65°F, Jul 88°F, Nov 56°F). December–March is too cold, with average highs around 46°F. In April, nights average about 44°F, so finish early on mild days and check the overnight low. July is hot, with highs near 88°F, so start early and keep out of full afternoon sun. November is cool, with highs around 56°F, so choose the warmest afternoons.
In Pittsburgh, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 62°F, Oct 63°F). November–March is too cold, with average highs around 43°F. In April and October, nights average about 42°F, so finish early on mild days and check the overnight low.
Best time to paint outside in Pennsylvania
In Philadelphia, the most reliable months are May–June and August–October. March–April, July and November can also work on the right days. December–February is too cold, with average highs around 44°F. March and November are cool, with highs around 54°F, so choose the warmest afternoons. In April, nights average about 44°F, so finish early on mild days and check the overnight low. July is hot, with highs near 88°F, so start early and keep out of full afternoon sun.
In Pittsburgh, the most reliable months are May–September. April and October–November can also work on the right days (average highs Apr 62°F, Oct 63°F, Nov 51°F). December–March is too cold, with average highs around 41°F. In April and October, nights average about 42°F, so finish early on mild days and check the overnight low. November is cool, with highs around 51°F, so choose the warmest afternoons.
Best time to pour concrete in Pennsylvania
In Philadelphia, the most reliable months are April–October. November can also work on the right days (average highs Nov 56°F). December–March averages about 18 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. November brings about 5 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
In Pittsburgh, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 62°F, Oct 63°F). November–March averages about 21 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. April and October bring about 4 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
Best time to seal a driveway in Pennsylvania
In Philadelphia, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 65°F, Oct 67°F). November–March is too cold, with average highs around 48°F. April and October are cool, with highs around 66°F, so choose the warmest afternoons.
In Pittsburgh, the most reliable months are June–September. May and October can also work on the right days (average highs May 72°F, Oct 63°F). November–March is too cold, with average highs around 43°F. In April, nights average about 41°F, too cold for the coating to dry and cure overnight. In May, nights average about 51°F, so finish early on mild days and check the overnight low. October is cool, with highs around 63°F, so choose the warmest afternoons.
Best time to fertilize or treat a lawn in Pennsylvania
In Philadelphia, the most reliable months are April–June and August–October. March, July and November can also work on the right days (average highs Mar 53°F, Jul 88°F, Nov 56°F). December–February is too cold, with average highs around 44°F. March and November are cool, with highs around 54°F, so choose the warmest afternoons. July is hot, with highs near 88°F, so start early and keep out of full afternoon sun.
In Pittsburgh, the most reliable months are April–October. November can also work on the right days (average highs Nov 51°F). December–March is too cold, with average highs around 41°F. November is cool, with highs around 51°F, so choose the warmest afternoons.
How the weather differs across Pennsylvania
| Place | Hottest month avg high | Coldest month avg low | Rain per year | Last spring freeze | First fall freeze |
|---|---|---|---|---|---|
| Philadelphia | 88°F | 26°F | 44 in | April 2 | November 10 |
| Pittsburgh | 83°F | 21°F | 40 in | April 23 | October 23 |
Of the places above, Philadelphia has the most good months for staining, painting and concrete combined (17 job-months), and Pittsburgh has the fewest (15).
Monthly weather in Philadelphia
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 41°F | 26°F | 6 | 3.1 in | 51% | 23 |
| February | 44°F | 28°F | 6 | 2.8 in | 46% | 20 |
| March | 53°F | 34°F | 7 | 4.0 in | 43% | 12 |
| April | 65°F | 44°F | 6 | 3.5 in | 41% | 1 |
| May | 74°F | 54°F | 6 | 3.3 in | 45% | 0 |
| June | 83°F | 64°F | 7 | 4.0 in | 47% | 0 |
| July | 88°F | 70°F | 6 | 4.4 in | 47% | 0 |
| August | 86°F | 68°F | 6 | 4.3 in | 49% | 0 |
| September | 79°F | 61°F | 6 | 4.4 in | 50% | 0 |
| October | 67°F | 49°F | 6 | 3.5 in | 50% | 0 |
| November | 56°F | 39°F | 6 | 2.9 in | 49% | 5 |
| December | 46°F | 31°F | 7 | 4.0 in | 53% | 17 |
*Days with 0.1 inch of rain or more; column notes.
Monthly weather in Pittsburgh
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 36°F | 21°F | 7 | 3.0 in | 62% | 25 |
| February | 40°F | 23°F | 7 | 2.6 in | 56% | 23 |
| March | 49°F | 30°F | 8 | 3.1 in | 49% | 19 |
| April | 62°F | 41°F | 9 | 3.3 in | 43% | 6 |
| May | 72°F | 51°F | 8 | 3.8 in | 47% | 1 |
| June | 79°F | 59°F | 8 | 4.1 in | 51% | 0 |
| July | 83°F | 63°F | 7 | 4.3 in | 51% | 0 |
| August | 82°F | 62°F | 6 | 3.5 in | 50% | 0 |
| September | 75°F | 55°F | 6 | 3.3 in | 51% | 0 |
| October | 63°F | 44°F | 7 | 2.8 in | 51% | 2 |
| November | 51°F | 34°F | 7 | 2.9 in | 54% | 14 |
| December | 41°F | 27°F | 7 | 2.8 in | 62% | 23 |
Source: NOAA NCEI U.S. Climate Normals 1991–2020 for PHILADELPHIA INTL AP, PITTSBURGH INTL AP. See how the ratings work and how late in fall you can stain, paint or seal.
Frequently asked questions
When is the best time to stain a deck in Pennsylvania?
In Philadelphia, May–June and August–October. In Pittsburgh, May–September.
When is the last frost in Pennsylvania?
Philadelphia: around April 2; Pittsburgh: around April 23.
Can you pour concrete in winter in Pennsylvania?
Yes, with cold-weather practices: Philadelphia averages about 59 freezing nights from December to February, so fresh concrete needs insulated blankets, a heated enclosure or an accelerated mix, and must not freeze in the first 48 hours. Many homeowners wait for spring.
What months are best for sealing a driveway in Pennsylvania?
In Philadelphia, May–September. In Pittsburgh, June–September.