Heavy rainPhiladelphia International AirportDaily gauge record since 1941
Philadelphia's airport had 29 days with 2 inches of rain from 2011 to 2020, the most of any decade since 1941
The airport logged 29 days with 2 inches of rain or more from 2011 through 2020, against 14 to 23 in each earlier decade since 1941.
- Days with 2 inches or more, 2011 to 2020
- 292.9 a year
- Each earlier decade since 1941
- 14 to 23Most: 1971 to 1980
- Days with an inch or more, 2011 to 2020
- 122Also the most of any decade
- 2021 to 2025
- 7Days with 2 inches in five years
Figure 1. Heavy-rain days per decade
2011 to 2020 brought 29 days with 2 inches or more, and no earlier decade passed 23
Philadelphia International Airport recorded 29 days with 2 inches of rain or more from 2011 through 2020, the most of any decade in its record. Each of the seven earlier decades since 1941 had between 14 and 23 such days. The same decade also had the most days with an inch or more, 122, according to the airport's daily precipitation record in the Applied Climate Information System (ACIS), a database of NOAA station data. Precipitation counts rain plus the water in melted snow. From 2021 through 2025 the pace fell back, with 7 days of 2 inches or more in five years.
The airport's record starts on July 1, 1940, and has no missing days from 1941 on, so each decade below is a full count. A day here is one calendar day of readings at the airport gauge.
01Sixteen of the 85 years had no 2-inch day, and 2011 had 7
The count varies widely from one year to the next. 2011 had 7 days with 2 inches or more, the most of any year since 1941, and 64.33 inches of precipitation in all. 1983 had the most days with an inch or more, 21, but only one of them reached 2 inches. Sixteen of the 85 years from 1941 through 2025 had no 2-inch day at all, including 2022 and 2025.
Figure 2. Every year since 1941
2011 brought 7 days with 2 inches of rain, the most in a year at the airport
02The 2011 to 2020 decade averaged 2.9 days a year with 2 inches or more
The 2011 to 2020 decade averaged 2.9 days a year with 2 inches or more. The 1940s and 1950s averaged 1.5 and 1.4. The 1970s came closest to the recent decade, with 23 days. Days with 3 inches or more show the same pattern at a smaller scale: 13 in the 2011 to 2020 decade, against 2 to 8 in each earlier one.
Table 1. Heavy-rain days by decade
13 days of 3 inches or more from 2011 to 2020, against 2 to 8 in each earlier decade
| Decade | 1 in. or more | Per year | 2 in. or more | Bar, 2 inches and 3 inches or more | Per year | 3 in. or more | Inches a year |
|---|---|---|---|---|---|---|---|
| 1941 to 1950 | 94 | 9.4 | 15 | 1.5 | 2 | 41.4 | |
| 1951 to 1960 | 96 | 9.6 | 14 | 1.4 | 2 | 40.8 | |
| 1961 to 1970 | 105 | 10.5 | 19 | 1.9 | 5 | 38.1 | |
| 1971 to 1980 | 117 | 11.7 | 23 | 2.3 | 8 | 45.4 | |
| 1981 to 1990 | 109 | 10.9 | 14 | 1.4 | 3 | 40.8 | |
| 1991 to 2000 | 96 | 9.6 | 15 | 1.5 | 2 | 39.9 | |
| 2001 to 2010 | 113 | 11.3 | 21 | 2.1 | 5 | 43.7 | |
| 2011 to 2020 | 122 | 12.2 | 29 | 2.9 | 13 | 48.6 | |
| 2021 to 2025 (5 years) | 56 | 11.2 | 7 | 1.4 | 2 | 40.7 |
03By October 24, 2026 already had 12 days with an inch or more
From 1991 through 2020 the airport averaged 11.0 days a year with an inch or more and 2.2 days with 2 inches or more. By October 24, 2026 had already passed the first figure: the airport had recorded 12 days with an inch or more and 2 days with 2 inches or more: 2.70 inches on July 9 and 2.33 inches on August 27.
Figure 3. 2026 through October 24
12 days with an inch or more
1991 to 2020 average: 11.0 a year
2 days with 2 inches or more
1991 to 2020 average: 2.2 a year. July 9 brought 2.70 inches and August 27 brought 2.33.
0484 of the 157 days with 2 inches or more fell in July, August or September
Most of the heaviest days come in summer. Of the 157 days with 2 inches or more from 1941 through 2025, 84 fell in July, August or September, and another 21 in June. February had none. July alone had 11 of the 42 days with 3 inches or more.
Figure 4. Heavy-rain days by calendar month
July had 30 days with 2 inches or more, and 11 of the 42 with 3 inches
Days with an inch or more are spread more evenly. August had the most, 112, and February the fewest, 42. December had 74 days with an inch or more but only 7 with 2 inches.
| Month | 1 in.+ | 2 in.+ | 3 in.+ |
|---|---|---|---|
| January | 58 | 4 | 0 |
| February | 42 | 0 | 0 |
| March | 79 | 4 | 1 |
| April | 70 | 10 | 4 |
| May | 72 | 7 | 0 |
| June | 85 | 21 | 3 |
| July | 107 | 30 | 11 |
| August | 112 | 27 | 7 |
| September | 87 | 27 | 9 |
| October | 61 | 12 | 4 |
| November | 61 | 8 | 3 |
| December | 74 | 7 | 0 |
05The wettest day since 1941 brought 8.02 inches, on July 28, 2013
The wettest day in the airport's record since 1941 brought 8.02 inches, on July 28, 2013. Nine of the ten wettest days fell between June 29 and September 16 on the calendar, and six of the ten came in 1999 or later.
Figure 5. The ten wettest days
The ten wettest days brought 4.60 to 8.02 inches. 2026's wettest so far brought 2.70.
06Norristown averaged 14.1 days a year with an inch or more, against 11.5 at the airport
The Norristown station reports once a day, at 7 a.m. in its recent readings. Its record is shorter than the airport's and has long gaps, including no data from 1988 through 1999. In the 12 years from 2012 through 2025 when Norristown missed no more than five days, it counted an average of 14.1 days a year with an inch or more and 3.0 days with 2 inches or more. The airport averaged 11.5 and 2.1 in the same years. In 2018 Norristown had 23 days with an inch or more, against 15 at the airport.
Figure 6. Two gauges, the same years
In 2018 Norristown had 23 days with an inch or more, against 15 at the airport
| Year | 1 inch or more | 2 inches or more | ||
|---|---|---|---|---|
| Norristown | Airport | Norristown | Airport | |
| 2012 | 15 | 7 | 5 | 2 |
| 2013 | 15 | 15 | 4 | 5 |
| 2014 | 13 | 13 | 3 | 2 |
| 2016 | 11 | 8 | 0 | 0 |
| 2017 | 7 | 11 | 2 | 4 |
| 2018 | 23 | 15 | 4 | 3 |
| 2019 | 18 | 12 | 2 | 2 |
| 2020 | 13 | 13 | 4 | 2 |
| 2021 | 15 | 10 | 4 | 4 |
| 2022 | 14 | 11 | 3 | 0 |
| 2023 | 14 | 14 | 5 | 1 |
| 2025 | 11 | 9 | 0 | 0 |
Over all 45 years since 1952 in which Norristown missed no more than five days, the station averaged 12.8 days a year with an inch or more, against 11.0 at the airport in the same years. The background on how freeze-thaw cycles, rain and wind wear a roof here is in the guide to how the weather here wears a roof.
What this means for gutters and valleys
Heavy rain puts the most water through the parts of a roof that carry it off: the valleys where two slopes meet, the gutters and downspouts, the flashing where a roof meets a wall or chimney, and the scuppers and drains on the low-slope rear roofs of many rowhomes. Since two thirds of the airport's 2-inch days came from June through September, clear gutters, downspouts and scuppers in late spring, before the months that bring most of them.
After a day with 2 inches or more, look at the attic and the top-floor ceilings under valleys, chimneys and the rear roof that day or the next, while a stain is fresh. Photograph any stain with the date. If you file a claim, the guide to storm damage and roof insurance claims covers what to keep.
When you get a quote for a new roof, ask what the roofer will install in the valleys and whether the gutters and downspouts are part of the job. The roof inspection checklist lists what to look at between storms.
Caveats
These counts come from one gauge at the airport, and a single thunderstorm can drop 2 inches on one neighborhood and a fraction of that a few miles away. The Norristown comparison shows how much two stations in the same region can differ. Norristown's daily total ends at its 7 a.m. reading, so a storm that falls overnight lands on a different day there than at the airport, and either station can split one storm across two days that each fall below a threshold.
A decade is a short window for a count that ranges from 0 to 7 days a year. One wet year such as 2011 moves a decade's total by several days. The 2026 figures run through October 24 and cover a year still under way, and the latest daily readings can still change.