Norristown Weather Records (USC00366370)
Record envelope, standing records and threshold days for Norristown (USC00366370), Pennsylvania, United States, with 79 years of record.
Key Facts for Norristown
- Norristown (USC00366370) is a weather station in Pennsylvania, United States at 40.11 latitude and -75.34 longitude, 19 m (62 ft) above sea level.
- The station reports from 1948 to 2026, 79 years of record.
- 1,464 records set at Norristown still stand.
- Records are tracked for tmax, tmin, prcp, snow, snwd: an element needs 30 years of data to be eligible.
- Norristown set a daily record precipitation of 51.6 mm (2.0 in) on 12 October 2026 (provisional).
Provisional Records
Records set in the last 60 days are provisional until they clear the revision window.
About the Station
- Location: Pennsylvania, United States, 40.11 latitude, -75.34 longitude.
- Elevation: 19 m (62 ft).
- Period of record: 1948 to 2026, 79 years.
- Eligible elements: tmax, tmin, prcp, snow, snwd.
Daily Record Envelope and 2026
25 days at or beyond a record| Month | Highest record high | Lowest record low | 2026 highest maximum | 2026 lowest minimum |
|---|---|---|---|---|
| Jan | 24.4 C (75.9 F) | -24.4 C (-11.9 F) | 13.9 C (57.0 F) | -20.0 C (-4.0 F) |
| Feb | 25.6 C (78.1 F) | -20.6 C (-5.1 F) | 10.0 C (50.0 F) | -20.0 C (-4.0 F) |
| Mar | 30.0 C (86.0 F) | -13.3 C (8.1 F) | 27.8 C (82.0 F) | -9.4 C (15.1 F) |
| Apr | 36.7 C (98.1 F) | -9.4 C (15.1 F) | 32.8 C (91.0 F) | -3.3 C (26.1 F) |
| May | 36.7 C (98.1 F) | -1.7 C (28.9 F) | 35.6 C (96.1 F) | 5.0 C (41.0 F) |
| Jun | 37.8 C (100.0 F) | 5.0 C (41.0 F) | 35.0 C (95.0 F) | 8.9 C (48.0 F) |
| Jul | 42.2 C (108.0 F) | 8.9 C (48.0 F) | 38.3 C (100.9 F) | 15.0 C (59.0 F) |
| Aug | 41.1 C (106.0 F) | 4.4 C (39.9 F) | 34.4 C (93.9 F) | 15.0 C (59.0 F) |
| Sep | 38.9 C (102.0 F) | 1.1 C (34.0 F) | 32.8 C (91.0 F) | 10.0 C (50.0 F) |
| Oct | 33.3 C (91.9 F) | -3.3 C (26.1 F) | 31.7 C (89.1 F) | 5.6 C (42.1 F) |
| Nov | 29.4 C (84.9 F) | -10.0 C (14.0 F) | n/a | n/a |
| Dec | 24.4 C (75.9 F) | -23.3 C (-9.9 F) | n/a | n/a |
Which Years Hold Standing Records
1,464 standing records| Year set | Standing records |
|---|---|
| 1951 | 28 |
| 1952 | 23 |
| 1953 | 32 |
| 1954 | 28 |
| 1955 | 21 |
| 1956 | 28 |
| 1957 | 25 |
| 1958 | 20 |
| 1959 | 24 |
| 1960 | 21 |
| 1961 | 16 |
| 1962 | 24 |
| 1963 | 34 |
| 1964 | 31 |
| 1965 | 17 |
| 1966 | 27 |
| 1967 | 31 |
| 1968 | 12 |
| 1969 | 10 |
| 1970 | 21 |
| 1971 | 15 |
| 1972 | 21 |
| 1973 | 11 |
| 1974 | 16 |
| 1975 | 6 |
| 1976 | 37 |
| 1977 | 19 |
| 1978 | 17 |
| 1979 | 61 |
| 1980 | 14 |
| 1981 | 22 |
| 1982 | 34 |
| 1983 | 26 |
| 1984 | 20 |
| 1985 | 19 |
| 1986 | 24 |
| 1987 | 3 |
| 2000 | 35 |
| 2001 | 28 |
| 2002 | 41 |
| 2003 | 15 |
| 2004 | 23 |
| 2005 | 19 |
| 2006 | 21 |
| 2007 | 22 |
| 2008 | 11 |
| 2009 | 15 |
| 2010 | 19 |
| 2011 | 29 |
| 2012 | 33 |
| 2013 | 25 |
| 2014 | 20 |
| 2015 | 35 |
| 2016 | 24 |
| 2017 | 25 |
| 2018 | 31 |
| 2019 | 12 |
| 2020 | 13 |
| 2021 | 14 |
| 2022 | 28 |
| 2023 | 17 |
| 2024 | 14 |
| 2025 | 23 |
| 2026 | 34 |
All-Time Record Progression
10 new records| Date | Kind | Detail |
|---|---|---|
| 1982-01-17 | Record low minimum temperature | Record low minimum temperature -22.2 C (-8.0 F) |
| 1982-01-18 | Record low minimum temperature | Record low minimum temperature -24.4 C (-11.9 F) |
| 2001-07-24 | Record high minimum temperature | Record high minimum temperature 25.6 C (78.1 F) |
| 2001-08-10 | Record high maximum temperature | Record high maximum temperature 41.1 C (106.0 F) |
| 2002-06-27 | Record high minimum temperature | Record high minimum temperature 26.7 C (80.1 F) |
| 2004-09-29 | Record daily precipitation | Record daily precipitation 153.9 mm (6.1 in) |
| 2006-02-12 | Record daily snowfall | Record daily snowfall 45.7 cm (18.0 in) |
| 2006-08-03 | Record high minimum temperature | Record high minimum temperature 27.8 C (82.0 F) |
| 2010-10-01 | Record daily precipitation | Record daily precipitation 177.8 mm (7.0 in) |
| 2011-07-24 | Record high maximum temperature | Record high maximum temperature 42.2 C (108.0 F) |
Wettest Day of Each Month
Oct: 177.8 mm (7.0 in)| Month | Record daily precipitation (mm) | Date |
|---|---|---|
| Jan | 91.4 mm (3.6 in) | 10 January 2024 |
| Feb | 50.8 mm (2.0 in) | 17 February 2003 |
| Mar | 65.5 mm (2.6 in) | 24 March 2024 |
| Apr | 107.2 mm (4.2 in) | 16 April 2007 |
| May | 92.7 mm (3.6 in) | 1 May 2014 |
| Jun | 91.7 mm (3.6 in) | 17 June 2001 |
| Jul | 122.7 mm (4.8 in) | 27 July 1986 |
| Aug | 163.8 mm (6.4 in) | 28 August 2011 |
| Sep | 161.3 mm (6.4 in) | 2 September 2021 |
| Oct | 177.8 mm (7.0 in) | 1 October 2010 |
| Nov | 77.2 mm (3.0 in) | 9 November 1972 |
| Dec | 77.7 mm (3.1 in) | 18 December 2023 |
Period of Record Coverage
1951 to 2026| Year | Days with data | Share of year | Complete |
|---|---|---|---|
| 1951 | 209 | 57% | No |
| 1952 | 366 | 100% | Yes |
| 1953 | 364 | 100% | Yes |
| 1954 | 365 | 100% | Yes |
| 1955 | 365 | 100% | Yes |
| 1956 | 335 | 92% | Yes |
| 1957 | 365 | 100% | Yes |
| 1958 | 364 | 100% | Yes |
| 1959 | 365 | 100% | Yes |
| 1960 | 366 | 100% | Yes |
| 1961 | 364 | 100% | Yes |
| 1962 | 360 | 99% | Yes |
| 1963 | 365 | 100% | Yes |
| 1964 | 365 | 100% | Yes |
| 1965 | 365 | 100% | Yes |
| 1966 | 365 | 100% | Yes |
| 1967 | 363 | 99% | Yes |
| 1968 | 366 | 100% | Yes |
| 1969 | 365 | 100% | Yes |
| 1970 | 365 | 100% | Yes |
| 1971 | 363 | 99% | Yes |
| 1972 | 359 | 98% | Yes |
| 1973 | 212 | 58% | No |
| 1974 | 214 | 59% | No |
| 1975 | 119 | 33% | No |
| 1976 | 213 | 58% | No |
| 1977 | 153 | 42% | No |
| 1978 | 363 | 99% | Yes |
| 1979 | 365 | 100% | Yes |
| 1980 | 366 | 100% | Yes |
| 1981 | 365 | 100% | Yes |
| 1982 | 365 | 100% | Yes |
| 1983 | 363 | 99% | Yes |
| 1984 | 365 | 100% | Yes |
| 1985 | 364 | 100% | Yes |
| 1986 | 333 | 91% | Yes |
| 1987 | 89 | 24% | No |
| 2000 | 266 | 73% | No |
| 2001 | 331 | 91% | Yes |
| 2002 | 357 | 98% | Yes |
| 2003 | 358 | 98% | Yes |
| 2004 | 364 | 99% | Yes |
| 2005 | 332 | 91% | Yes |
| 2006 | 271 | 74% | No |
| 2007 | 299 | 82% | No |
| 2008 | 331 | 90% | Yes |
| 2009 | 332 | 91% | Yes |
| 2010 | 274 | 75% | No |
| 2011 | 330 | 90% | Yes |
| 2012 | 365 | 100% | Yes |
| 2013 | 362 | 99% | Yes |
| 2014 | 356 | 98% | Yes |
| 2015 | 356 | 98% | Yes |
| 2016 | 357 | 98% | Yes |
| 2017 | 363 | 99% | Yes |
| 2018 | 363 | 99% | Yes |
| 2019 | 360 | 99% | Yes |
| 2020 | 366 | 100% | Yes |
| 2021 | 314 | 86% | No |
| 2022 | 365 | 100% | Yes |
| 2023 | 362 | 99% | Yes |
| 2024 | 323 | 88% | No |
| 2025 | 356 | 98% | Yes |
| 2026 | 279 | 76% | No |
Latest Records
20| Date | Station | Record | Value | Beat old record by | Old record stood | Significance |
|---|---|---|---|---|---|---|
| 12 October 2026 | Norristown, US | daily rain (Provisional) | 51.6 mm (2.0 in) | 8.4 mm (0.33 in) | 19 years | 17 of 100 (Routine) |
| 5 July 2026 | Norristown, US | daily high max (Tie) | 37.8 C (100.0 F) | tie | 24 years | 3 of 100 (Routine) |
| 4 July 2026 | Norristown, US | daily high min (Tie) | 24.4 C (75.9 F) | tie | 24 years | 3 of 100 (Routine) |
| 3 July 2026 | Norristown, US | daily high min | 26.7 C (80.1 F) | 1.7 C (3.1 F) | 8 years | 14 of 100 (Routine) |
| 2 July 2026 | Norristown, US | daily high min | 25.6 C (78.1 F) | 2.8 C (5.0 F) | 63 years | 33 of 100 (Routine) |
| 24 June 2026 | Norristown, US | daily low max (Tie) | 21.7 C (71.1 F) | tie | 4 years | 2 of 100 (Routine) |
| 23 June 2026 | Norristown, US | daily rain | 29.5 mm (1.2 in) | 8.4 mm (0.33 in) | 52 years | 28 of 100 (Routine) |
| 12 June 2026 | Norristown, US | daily high min | 21.7 C (71.1 F) | 0.6 C (1.1 F) | 59 years | 25 of 100 (Routine) |
| 6 June 2026 | Norristown, US | daily high max (Tie) | 33.3 C (91.9 F) | tie | 52 years | 5 of 100 (Routine) |
| 24 May 2026 | Norristown, US | daily low max | 11.7 C (53.1 F) | 0.5 C (0.9 F) | 44 years | 20 of 100 (Routine) |
| 21 May 2026 | Norristown, US | daily high max | 33.9 C (93.0 F) | 2.2 C (4.0 F) | 48 years | 25 of 100 (Routine) |
| 20 May 2026 | Norristown, US | daily high min | 22.2 C (72.0 F) | 1.6 C (2.9 F) | 67 years | 30 of 100 (Routine) |
| 20 May 2026 | Norristown, US | daily high max | 35.6 C (96.1 F) | 1.2 C (2.2 F) | 64 years | 28 of 100 (Routine) |
| 19 May 2026 | Norristown, US | daily high min | 22.2 C (72.0 F) | 1.1 C (2.0 F) | 8 years | 11 of 100 (Routine) |
| 12 May 2026 | Norristown, US | daily low min (Tie) | 5.0 C (41.0 F) | tie | 48 years | 5 of 100 (Routine) |
| 6 May 2026 | Norristown, US | daily high min | 17.2 C (63.0 F) | 1.6 C (2.9 F) | 25 years | 17 of 100 (Routine) |
| 22 April 2026 | Norristown, US | daily low min | -1.7 C (28.9 F) | 1.1 C (2.0 F) | 44 years | 22 of 100 (Routine) |
| 21 April 2026 | Norristown, US | daily low min | -2.8 C (27.0 F) | 1.7 C (3.1 F) | 72 years | 32 of 100 (Routine) |
| 17 April 2026 | Norristown, US | daily high min | 18.3 C (64.9 F) | 1.6 C (2.9 F) | 24 years | 17 of 100 (Routine) |
| 16 April 2026 | Norristown, US | daily high max | 31.7 C (89.1 F) | 2.8 C (5.0 F) | 24 years | 18 of 100 (Routine) |
Climate Trend
43 complete years, 1952 to 2025| Year | Annual mean temperature | Difference from the station mean |
|---|---|---|
| 1952 | 12.5 C | +0.15 C |
| 1953 | 12.5 C | +0.19 C |
| 1954 | 12.7 C | +0.38 C |
| 1955 | 12.8 C | +0.45 C |
| 1957 | 12.8 C | +0.49 C |
| 1958 | 11.5 C | -0.87 C |
| 1959 | 13.1 C | +0.74 C |
| 1960 | 12.0 C | -0.37 C |
| 1961 | 12.1 C | -0.21 C |
| 1962 | 11.5 C | -0.82 C |
| 1963 | 11.7 C | -0.61 C |
| 1964 | 12.4 C | +0.07 C |
| 1965 | 12.3 C | -0.07 C |
| 1966 | 12.1 C | -0.23 C |
| 1967 | 11.8 C | -0.60 C |
| 1968 | 12.4 C | +0.08 C |
| 1969 | 12.4 C | +0.03 C |
| 1970 | 12.4 C | +0.04 C |
| 1971 | 12.6 C | +0.21 C |
| 1972 | 11.9 C | -0.44 C |
| 1978 | 11.0 C | -1.34 C |
| 1979 | 10.6 C | -1.71 C |
| 1980 | 11.9 C | -0.47 C |
| 1981 | 11.3 C | -1.08 C |
| 1982 | 11.3 C | -1.09 C |
| 1983 | 12.7 C | +0.30 C |
| 1984 | 12.0 C | -0.32 C |
| 1985 | 11.9 C | -0.44 C |
| 2002 | 13.2 C | +0.89 C |
| 2003 | 11.8 C | -0.52 C |
| 2004 | 12.5 C | +0.15 C |
| 2012 | 14.1 C | +1.76 C |
| 2013 | 12.7 C | +0.32 C |
| 2014 | 11.9 C | -0.41 C |
| 2015 | 13.0 C | +0.64 C |
| 2016 | 13.5 C | +1.18 C |
| 2017 | 13.2 C | +0.82 C |
| 2018 | 12.8 C | +0.46 C |
| 2019 | 13.0 C | +0.67 C |
| 2020 | 13.5 C | +1.18 C |
| 2022 | 12.3 C | -0.09 C |
| 2023 | 13.2 C | +0.86 C |
| 2025 | 12.0 C | -0.32 C |
The annual mean temperature here has risen by 0.11 C (0.03 to 0.20) per decade over 1952 to 2025. In Fahrenheit: 0.20 F (0.05 to 0.35) per decade. The slope is a straight line fitted to 43 complete years; the brackets give its 95 percent interval.
| Measure | Per decade (C) | Per decade (F) | Period | Complete years | Reading |
|---|---|---|---|---|---|
| Annual mean temperature | 0.11 C (0.03 to 0.20) per decade | 0.20 F (0.05 to 0.35) per decade | 1952 to 2025 | 43 | Rise |
| Mean daily maximum | 0.2 C (0.1 to 0.3) per decade | 0.3 F (0.1 to 0.5) per decade | 1952 to 2025 | 43 | Rise |
| Mean daily minimum | 0.06 C (-0.03 to 0.16) per decade | 0.1 F (-0.1 to 0.3) per decade | 1952 to 2025 | 43 | Not clearly different from zero |
A year is complete when all 12 months have at least 20 days of both daily maximum and daily minimum readings. The annual mean is the mean of the monthly means. The trend describes this one station over this period; it does not say what caused the change.
Extremes by Year
1948 to 2026| Measure | Record | Year of the record | Median year | Years with a value |
|---|---|---|---|---|
| Hottest day (TXx) | 42.2 C (108.0 F) | 2011 | 36.7 C (98.1 F) | 64 |
| Coldest night (TNn) | -24.4 C (-11.9 F) | 1982 | -15.6 C (3.9 F) | 64 |
| Wettest day (Rx1day) | 177.8 mm (7.0 in) | 2010 | 68.8 mm (2.7 in) | 67 |
| Wettest five days (Rx5day) | 235.5 mm (9.3 in) | 1973 | 103.1 mm (4.1 in) | 67 |
| Longest dry spell (CDD) | 41 days | 2024 | 18 days | 67 |
Hottest day (TXx)
| Year | Hottest day (TXx) |
|---|---|
| 1948 | n/a |
| 1949 | n/a |
| 1950 | n/a |
| 1951 | 33.3 C (91.9 F) |
| 1952 | 37.8 C (100.0 F) |
| 1953 | 38.9 C (102.0 F) |
| 1954 | 38.3 C (100.9 F) |
| 1955 | 38.9 C (102.0 F) |
| 1956 | 35.6 C (96.1 F) |
| 1957 | 39.4 C (102.9 F) |
| 1958 | 33.9 C (93.0 F) |
| 1959 | 36.1 C (97.0 F) |
| 1960 | 33.9 C (93.0 F) |
| 1961 | 35.0 C (95.0 F) |
| 1962 | 36.7 C (98.1 F) |
| 1963 | 37.2 C (99.0 F) |
| 1964 | 37.8 C (100.0 F) |
| 1965 | 35.6 C (96.1 F) |
| 1966 | 39.4 C (102.9 F) |
| 1967 | 34.4 C (93.9 F) |
| 1968 | 35.6 C (96.1 F) |
| 1969 | 36.1 C (97.0 F) |
| 1970 | 35.6 C (96.1 F) |
| 1971 | 36.1 C (97.0 F) |
| 1972 | 36.7 C (98.1 F) |
| 1973 | 37.2 C (99.0 F) |
| 1974 | 36.1 C (97.0 F) |
| 1975 | 21.7 C (71.1 F) |
| 1976 | 36.7 C (98.1 F) |
| 1977 | 37.8 C (100.0 F) |
| 1978 | 36.1 C (97.0 F) |
| 1979 | 33.3 C (91.9 F) |
| 1980 | 38.3 C (100.9 F) |
| 1981 | 35.6 C (96.1 F) |
| 1982 | 35.0 C (95.0 F) |
| 1983 | 38.3 C (100.9 F) |
| 1984 | 36.1 C (97.0 F) |
| 1985 | 34.4 C (93.9 F) |
| 1986 | 36.1 C (97.0 F) |
| 1987 | 23.3 C (73.9 F) |
| 2000 | 35.6 C (96.1 F) |
| 2001 | 41.1 C (106.0 F) |
| 2002 | 38.9 C (102.0 F) |
| 2003 | 35.6 C (96.1 F) |
| 2004 | 35.6 C (96.1 F) |
| 2005 | 40.0 C (104.0 F) |
| 2006 | 37.8 C (100.0 F) |
| 2007 | 36.7 C (98.1 F) |
| 2008 | 36.7 C (98.1 F) |
| 2009 | 34.4 C (93.9 F) |
| 2010 | 38.3 C (100.9 F) |
| 2011 | 42.2 C (108.0 F) |
| 2012 | 38.9 C (102.0 F) |
| 2013 | 37.8 C (100.0 F) |
| 2014 | 36.7 C (98.1 F) |
| 2015 | 36.7 C (98.1 F) |
| 2016 | 38.9 C (102.0 F) |
| 2017 | 36.7 C (98.1 F) |
| 2018 | 36.1 C (97.0 F) |
| 2019 | 35.6 C (96.1 F) |
| 2020 | 36.1 C (97.0 F) |
| 2021 | 36.1 C (97.0 F) |
| 2022 | 37.8 C (100.0 F) |
| 2023 | 36.1 C (97.0 F) |
| 2024 | 37.2 C (99.0 F) |
| 2025 | 37.2 C (99.0 F) |
| 2026 | 38.3 C (100.9 F) |
Coldest night (TNn)
| Year | Coldest night (TNn) |
|---|---|
| 1948 | n/a |
| 1949 | n/a |
| 1950 | n/a |
| 1951 | -17.2 C (1.0 F) |
| 1952 | -13.9 C (7.0 F) |
| 1953 | -10.6 C (12.9 F) |
| 1954 | -17.2 C (1.0 F) |
| 1955 | -16.7 C (1.9 F) |
| 1956 | -8.9 C (16.0 F) |
| 1957 | -16.7 C (1.9 F) |
| 1958 | -15.0 C (5.0 F) |
| 1959 | -12.8 C (9.0 F) |
| 1960 | -15.6 C (3.9 F) |
| 1961 | -19.4 C (-2.9 F) |
| 1962 | -17.8 C (0.0 F) |
| 1963 | -17.2 C (1.0 F) |
| 1964 | -14.4 C (6.1 F) |
| 1965 | -16.1 C (3.0 F) |
| 1966 | -15.6 C (3.9 F) |
| 1967 | -16.1 C (3.0 F) |
| 1968 | -16.1 C (3.0 F) |
| 1969 | -12.2 C (10.0 F) |
| 1970 | -16.7 C (1.9 F) |
| 1971 | -14.4 C (6.1 F) |
| 1972 | -14.4 C (6.1 F) |
| 1973 | -13.9 C (7.0 F) |
| 1974 | -3.3 C (26.1 F) |
| 1975 | -12.8 C (9.0 F) |
| 1976 | -14.4 C (6.1 F) |
| 1977 | -17.8 C (0.0 F) |
| 1978 | -13.9 C (7.0 F) |
| 1979 | -20.6 C (-5.1 F) |
| 1980 | -18.3 C (-0.9 F) |
| 1981 | -18.3 C (-0.9 F) |
| 1982 | -24.4 C (-11.9 F) |
| 1983 | -23.3 C (-9.9 F) |
| 1984 | -17.8 C (0.0 F) |
| 1985 | -20.6 C (-5.1 F) |
| 1986 | -13.9 C (7.0 F) |
| 1987 | -17.2 C (1.0 F) |
| 2000 | -13.3 C (8.1 F) |
| 2001 | -11.1 C (12.0 F) |
| 2002 | -12.2 C (10.0 F) |
| 2003 | -15.6 C (3.9 F) |
| 2004 | -18.9 C (-2.0 F) |
| 2005 | -16.7 C (1.9 F) |
| 2006 | -12.2 C (10.0 F) |
| 2007 | -14.4 C (6.1 F) |
| 2008 | -12.2 C (10.0 F) |
| 2009 | -14.4 C (6.1 F) |
| 2010 | -10.0 C (14.0 F) |
| 2011 | -15.6 C (3.9 F) |
| 2012 | -12.2 C (10.0 F) |
| 2013 | -13.3 C (8.1 F) |
| 2014 | -17.2 C (1.0 F) |
| 2015 | -18.9 C (-2.0 F) |
| 2016 | -15.6 C (3.9 F) |
| 2017 | -11.7 C (10.9 F) |
| 2018 | -16.1 C (3.0 F) |
| 2019 | -14.4 C (6.1 F) |
| 2020 | -10.0 C (14.0 F) |
| 2021 | -8.3 C (17.1 F) |
| 2022 | -17.8 C (0.0 F) |
| 2023 | -15.0 C (5.0 F) |
| 2024 | -17.2 C (1.0 F) |
| 2025 | -19.4 C (-2.9 F) |
| 2026 | -20.0 C (-4.0 F) |
Wettest day (Rx1day)
| Year | Wettest day (Rx1day) |
|---|---|
| 1948 | 33.0 mm (1.3 in) |
| 1949 | 45.0 mm (1.8 in) |
| 1950 | 50.3 mm (2.0 in) |
| 1951 | 43.2 mm (1.7 in) |
| 1952 | 72.9 mm (2.9 in) |
| 1953 | 56.4 mm (2.2 in) |
| 1954 | 62.2 mm (2.4 in) |
| 1955 | 125.0 mm (4.9 in) |
| 1956 | 50.0 mm (2.0 in) |
| 1957 | 40.6 mm (1.6 in) |
| 1958 | 58.2 mm (2.3 in) |
| 1959 | 56.9 mm (2.2 in) |
| 1960 | 93.5 mm (3.7 in) |
| 1961 | 48.5 mm (1.9 in) |
| 1962 | 41.9 mm (1.6 in) |
| 1963 | 80.5 mm (3.2 in) |
| 1964 | 59.7 mm (2.4 in) |
| 1965 | 52.8 mm (2.1 in) |
| 1966 | 83.8 mm (3.3 in) |
| 1967 | 62.0 mm (2.4 in) |
| 1968 | 83.3 mm (3.3 in) |
| 1969 | 87.9 mm (3.5 in) |
| 1970 | 68.1 mm (2.7 in) |
| 1971 | 142.2 mm (5.6 in) |
| 1972 | 77.2 mm (3.0 in) |
| 1973 | 127.5 mm (5.0 in) |
| 1974 | 53.3 mm (2.1 in) |
| 1975 | 65.0 mm (2.6 in) |
| 1976 | 41.9 mm (1.6 in) |
| 1977 | 49.0 mm (1.9 in) |
| 1978 | 71.4 mm (2.8 in) |
| 1979 | 95.0 mm (3.7 in) |
| 1980 | 56.1 mm (2.2 in) |
| 1981 | 69.6 mm (2.7 in) |
| 1982 | 68.8 mm (2.7 in) |
| 1983 | 59.9 mm (2.4 in) |
| 1984 | 82.8 mm (3.3 in) |
| 1985 | 102.6 mm (4.0 in) |
| 1986 | 122.7 mm (4.8 in) |
| 1987 | 25.9 mm (1.0 in) |
| 2000 | 91.4 mm (3.6 in) |
| 2001 | 91.7 mm (3.6 in) |
| 2002 | 51.1 mm (2.0 in) |
| 2003 | 69.9 mm (2.8 in) |
| 2004 | 153.9 mm (6.1 in) |
| 2005 | 73.4 mm (2.9 in) |
| 2006 | 64.3 mm (2.5 in) |
| 2007 | 113.0 mm (4.4 in) |
| 2008 | 89.2 mm (3.5 in) |
| 2009 | 63.5 mm (2.5 in) |
| 2010 | 177.8 mm (7.0 in) |
| 2011 | 163.8 mm (6.4 in) |
| 2012 | 87.9 mm (3.5 in) |
| 2013 | 95.3 mm (3.8 in) |
| 2014 | 92.7 mm (3.6 in) |
| 2015 | 62.7 mm (2.5 in) |
| 2016 | 40.6 mm (1.6 in) |
| 2017 | 63.5 mm (2.5 in) |
| 2018 | 87.6 mm (3.4 in) |
| 2019 | 57.4 mm (2.3 in) |
| 2020 | 148.6 mm (5.9 in) |
| 2021 | 161.3 mm (6.4 in) |
| 2022 | 57.2 mm (2.3 in) |
| 2023 | 110.2 mm (4.3 in) |
| 2024 | 91.4 mm (3.6 in) |
| 2025 | 49.8 mm (2.0 in) |
| 2026 | 58.9 mm (2.3 in) |
Wettest five days (Rx5day)
| Year | Wettest five days (Rx5day) |
|---|---|
| 1948 | 67.6 mm (2.7 in) |
| 1949 | 68.1 mm (2.7 in) |
| 1950 | 97.6 mm (3.8 in) |
| 1951 | 92.5 mm (3.6 in) |
| 1952 | 131.0 mm (5.2 in) |
| 1953 | 80.8 mm (3.2 in) |
| 1954 | 68.6 mm (2.7 in) |
| 1955 | 155.0 mm (6.1 in) |
| 1956 | 92.5 mm (3.6 in) |
| 1957 | 72.4 mm (2.9 in) |
| 1958 | 91.5 mm (3.6 in) |
| 1959 | 125.4 mm (4.9 in) |
| 1960 | 187.6 mm (7.4 in) |
| 1961 | 97.1 mm (3.8 in) |
| 1962 | 64.3 mm (2.5 in) |
| 1963 | 94.9 mm (3.7 in) |
| 1964 | 93.0 mm (3.7 in) |
| 1965 | 83.3 mm (3.3 in) |
| 1966 | 110.0 mm (4.3 in) |
| 1967 | 86.7 mm (3.4 in) |
| 1968 | 95.8 mm (3.8 in) |
| 1969 | 158.5 mm (6.2 in) |
| 1970 | 117.2 mm (4.6 in) |
| 1971 | 222.3 mm (8.8 in) |
| 1972 | 103.1 mm (4.1 in) |
| 1973 | 235.5 mm (9.3 in) |
| 1974 | 66.6 mm (2.6 in) |
| 1975 | 170.5 mm (6.7 in) |
| 1976 | 61.0 mm (2.4 in) |
| 1977 | 103.1 mm (4.1 in) |
| 1978 | 77.8 mm (3.1 in) |
| 1979 | 119.2 mm (4.7 in) |
| 1980 | 72.7 mm (2.9 in) |
| 1981 | 95.5 mm (3.8 in) |
| 1982 | 102.6 mm (4.0 in) |
| 1983 | 79.8 mm (3.1 in) |
| 1984 | 133.3 mm (5.2 in) |
| 1985 | 141.3 mm (5.6 in) |
| 1986 | 122.7 mm (4.8 in) |
| 1987 | 62.2 mm (2.4 in) |
| 2000 | 93.7 mm (3.7 in) |
| 2001 | 93.0 mm (3.7 in) |
| 2002 | 65.8 mm (2.6 in) |
| 2003 | 122.3 mm (4.8 in) |
| 2004 | 158.2 mm (6.2 in) |
| 2005 | 125.2 mm (4.9 in) |
| 2006 | 146.1 mm (5.8 in) |
| 2007 | 168.4 mm (6.6 in) |
| 2008 | 111.5 mm (4.4 in) |
| 2009 | 88.9 mm (3.5 in) |
| 2010 | 196.4 mm (7.7 in) |
| 2011 | 191.7 mm (7.5 in) |
| 2012 | 98.9 mm (3.9 in) |
| 2013 | 177.8 mm (7.0 in) |
| 2014 | 152.4 mm (6.0 in) |
| 2015 | 124.5 mm (4.9 in) |
| 2016 | 89.7 mm (3.5 in) |
| 2017 | 87.6 mm (3.4 in) |
| 2018 | 142.9 mm (5.6 in) |
| 2019 | 78.6 mm (3.1 in) |
| 2020 | 196.5 mm (7.7 in) |
| 2021 | 187.8 mm (7.4 in) |
| 2022 | 112.1 mm (4.4 in) |
| 2023 | 126.0 mm (5.0 in) |
| 2024 | 120.9 mm (4.8 in) |
| 2025 | 72.6 mm (2.9 in) |
| 2026 | 106.9 mm (4.2 in) |
Longest dry spell (CDD)
| Year | Longest dry spell (CDD) |
|---|---|
| 1948 | 17 days |
| 1949 | 17 days |
| 1950 | 12 days |
| 1951 | 11 days |
| 1952 | 25 days |
| 1953 | 18 days |
| 1954 | 18 days |
| 1955 | 21 days |
| 1956 | 16 days |
| 1957 | 16 days |
| 1958 | 22 days |
| 1959 | 13 days |
| 1960 | 19 days |
| 1961 | 18 days |
| 1962 | 18 days |
| 1963 | 31 days |
| 1964 | 19 days |
| 1965 | 16 days |
| 1966 | 18 days |
| 1967 | 19 days |
| 1968 | 26 days |
| 1969 | 17 days |
| 1970 | 16 days |
| 1971 | 18 days |
| 1972 | 22 days |
| 1973 | 16 days |
| 1974 | 15 days |
| 1975 | 23 days |
| 1976 | 23 days |
| 1977 | 18 days |
| 1978 | 19 days |
| 1979 | 13 days |
| 1980 | 23 days |
| 1981 | 15 days |
| 1982 | 16 days |
| 1983 | 18 days |
| 1984 | 10 days |
| 1985 | 18 days |
| 1986 | 20 days |
| 1987 | 25 days |
| 2000 | 22 days |
| 2001 | 28 days |
| 2002 | 19 days |
| 2003 | 16 days |
| 2004 | 25 days |
| 2005 | 20 days |
| 2006 | 25 days |
| 2007 | 19 days |
| 2008 | 23 days |
| 2009 | 16 days |
| 2010 | 17 days |
| 2011 | 16 days |
| 2012 | 18 days |
| 2013 | 15 days |
| 2014 | 9 days |
| 2015 | 20 days |
| 2016 | 17 days |
| 2017 | 18 days |
| 2018 | 11 days |
| 2019 | 13 days |
| 2020 | 16 days |
| 2021 | 16 days |
| 2022 | 11 days |
| 2023 | 16 days |
| 2024 | 41 days |
| 2025 | 13 days |
| 2026 | 20 days |
Each chart shows one value per year; the dot marks the record year. TXx is the hottest daily maximum, TNn the coldest daily minimum, Rx1day and Rx5day the largest one-day and five-day rain totals, and CDD the longest run of days with less than 1 mm of rain. A year with missing days can understate an extreme.
Frost Dates and Growing Season
43 years with a frostAcross 43 years with a frost, the median last spring frost at Norristown falls on 11 April and the median first autumn frost on 29 October, which leaves a median of 204 days between them.
Fitted over all years, the growing season changes by -0.3 days per decade at this station.
| Measure | Median, all years | Earliest period | Recent period (1966 to 2025) | Recent against earliest | Fitted trend |
|---|---|---|---|---|---|
| Last spring frost | 11 April | n/a | 11 April | n/a | +0.5 days per decade |
| First autumn frost | 29 October | n/a | 30 October | n/a | +0.2 days per decade |
| Growing days | 204 days | n/a | 200 days | n/a | -0.3 days per decade |
A frost day is a day with a daily minimum at or below 0 C (32 F). The last spring frost and the first autumn frost are the last and first such days of the cold season, and growing days are the days between them. A negative trend for the last spring frost means it comes earlier.
Rainfall Return Levels
56 years, 1949 to 2025A day with at least 70.6 mm (2.8 in) of rain is expected about once in 2 years. A day with at least 198.5 mm (7.8 in) of rain is expected about once in 100 years.
| Expected about once in | A day with at least | Note |
|---|---|---|
| 2 years | 70.6 mm (2.8 in) | |
| 5 years | 97.5 mm (3.8 in) | |
| 10 years | 117.9 mm (4.6 in) | |
| 25 years | 147.2 mm (5.8 in) | |
| 50 years | 171.6 mm (6.8 in) | |
| 100 years | 198.5 mm (7.8 in) | Longer than the 56 years of record |
The levels come from a generalised extreme value (GEV) distribution fitted by L-moments to the wettest-day total of each year, 56 years of values from 1949 to 2025.
A return level is an estimate. It is least reliable for the long periods, 50 and 100 years, and for any period longer than the record behind the fit, where the fit has to reach past the largest day actually observed. It is not a forecast.
The largest wettest-day totals in the fit: 163.8 mm (6.4 in) in 2011; 161.3 mm (6.4 in) in 2021; 153.9 mm (6.1 in) in 2004.
Station Changes
1 suspectedOne change was suspected in the annual mean temperature of Norristown, at 2017. Each is measured against neighbouring stations.
- Relative to 5 neighbouring stations, the station's annual mean temperature from 2017 ran 0.4 C (0.7 F) lower than in the years before (possible change).
| Year | Shift (C) | Shift (F) | Strength | Neighbours |
|---|---|---|---|---|
| 2017 | -0.4 | -0.7 | possible | 5 |
Possible change at the station (a move, a new instrument or a new site); the record is kept as measured. A "likely" change has a larger test statistic than a "possible" one. Neither says why the station differs from its neighbours. How changes are found, and the largest ones.
Climate Twins
2002 to 2025 against 1961 to 1990Over 2002 to 2025, Norristown had a mean temperature of 12.9 C (55.1 F) and 1,306.2 mm (51.4 in) of rain a year. The 3 stations whose 1961 to 1990 climate was closest to that are Towson (United States, 133 km away), Ny City Cntrl Park (United States, 138 km away) and Aberdeen Phillips Fld (United States, 100 km away).
| Twin station | Country | Distance away | Mean temperature, 1961-1990 | Rain a year, 1961-1990 | Climate difference |
|---|---|---|---|---|---|
| Towson | United States | 133 km (83 mi) | 12.9 C (55.2 F) | 1,295.9 mm (51.0 in) | 0.57 |
| Ny City Cntrl Park | United States | 138 km (86 mi) | 12.6 C (54.7 F) | 1,215.3 mm (47.8 in) | 0.71 |
| Aberdeen Phillips Fld | United States | 100 km (62 mi) | 12.8 C (55.0 F) | 1,199.9 mm (47.2 in) | 0.77 |
Twins are stations, not cities. A twin is one of the three stations at least 100 km away whose earlier climate is closest to this station's recent one, so a close match does not mean the two places look alike in other ways. A station move or a gap in a record can change that station's averages. The list describes past climate; it is not a forecast and does not say what caused any change. How twins are found, and a search for any station.
Download the Data
Source: NOAA National Centers for Environmental Information, Global Historical Climatology Network Daily (GHCN-Daily). Records are computed by World Extreme Weather Monitor and are not official NOAA products. (US Government open data (NOAA NCEI)) Data as of 2026-10-14 (14 October 2026). Records are computed by this site and are not official.
Data as of . Last revised (2026-10-14).