Potomac Weather Records (USC00246685)
Record envelope, standing records and threshold days for Potomac (USC00246685), Montana, United States, with 63 years of record.
Key Facts for Potomac
- Potomac (USC00246685) is a weather station in Montana, United States at 46.88 latitude and -113.56 longitude, 1,125 m (3,690 ft) above sea level.
- The station reports from 1964 to 2026, 63 years of record.
- 1,464 records set at Potomac still stand.
- Records are tracked for tmax, tmin, prcp, snow, snwd: an element needs 30 years of data to be eligible.
- Potomac set a daily record precipitation of 27.9 mm (1.1 in) on 7 September 2026 (provisional).
Provisional Records
Records set in the last 60 days are provisional until they clear the revision window.
About the Station
- Location: Montana, United States, 46.88 latitude, -113.56 longitude.
- Elevation: 1,125 m (3,690 ft).
- Period of record: 1964 to 2026, 63 years.
- Eligible elements: tmax, tmin, prcp, snow, snwd.
Daily Record Envelope and 2026
15 days at or beyond a record| Month | Highest record high | Lowest record low | 2026 highest maximum | 2026 lowest minimum |
|---|---|---|---|---|
| Jan | 15.6 C (60.1 F) | -43.9 C (-47.0 F) | 11.1 C (52.0 F) | -18.3 C (-0.9 F) |
| Feb | 17.8 C (64.0 F) | -42.8 C (-45.0 F) | 13.9 C (57.0 F) | -14.4 C (6.1 F) |
| Mar | 24.4 C (75.9 F) | -38.3 C (-36.9 F) | 22.8 C (73.0 F) | -16.7 C (1.9 F) |
| Apr | 30.0 C (86.0 F) | -20.0 C (-4.0 F) | 27.2 C (81.0 F) | -10.6 C (12.9 F) |
| May | 36.1 C (97.0 F) | -10.6 C (12.9 F) | 31.1 C (88.0 F) | -6.7 C (19.9 F) |
| Jun | 36.1 C (97.0 F) | -5.0 C (23.0 F) | 28.3 C (82.9 F) | -3.9 C (25.0 F) |
| Jul | 39.4 C (102.9 F) | -4.4 C (24.1 F) | 23.9 C (75.0 F) | 4.4 C (39.9 F) |
| Aug | 38.9 C (102.0 F) | -5.6 C (21.9 F) | n/a | n/a |
| Sep | 36.1 C (97.0 F) | -12.2 C (10.0 F) | 22.8 C (73.0 F) | 7.2 C (45.0 F) |
| Oct | 31.1 C (88.0 F) | -29.4 C (-20.9 F) | n/a | n/a |
| Nov | 22.2 C (72.0 F) | -30.6 C (-23.1 F) | n/a | n/a |
| Dec | 17.8 C (64.0 F) | -45.6 C (-50.1 F) | n/a | n/a |
Which Years Hold Standing Records
1,464 standing records| Year set | Standing records |
|---|---|
| 1964 | 4 |
| 1965 | 45 |
| 1966 | 31 |
| 1967 | 28 |
| 1968 | 27 |
| 1969 | 34 |
| 1970 | 21 |
| 1971 | 37 |
| 1972 | 41 |
| 1973 | 15 |
| 1975 | 11 |
| 1976 | 25 |
| 1977 | 33 |
| 1978 | 32 |
| 1979 | 34 |
| 1980 | 39 |
| 1981 | 27 |
| 1982 | 25 |
| 1983 | 38 |
| 1984 | 42 |
| 1985 | 44 |
| 1986 | 37 |
| 1987 | 29 |
| 1988 | 25 |
| 1989 | 23 |
| 1990 | 26 |
| 1991 | 15 |
| 1992 | 28 |
| 1993 | 40 |
| 1994 | 14 |
| 1995 | 15 |
| 1996 | 33 |
| 1997 | 15 |
| 1998 | 20 |
| 1999 | 23 |
| 2000 | 13 |
| 2001 | 14 |
| 2002 | 38 |
| 2003 | 22 |
| 2004 | 17 |
| 2005 | 22 |
| 2006 | 20 |
| 2007 | 20 |
| 2008 | 30 |
| 2009 | 12 |
| 2010 | 13 |
| 2016 | 1 |
| 2017 | 10 |
| 2018 | 18 |
| 2019 | 40 |
| 2020 | 25 |
| 2021 | 31 |
| 2022 | 34 |
| 2023 | 23 |
| 2024 | 33 |
| 2025 | 32 |
| 2026 | 20 |
All-Time Record Progression
7 new records| Date | Kind | Detail |
|---|---|---|
| 1996-12-24 | Record snow depth | Record snow depth 109.2 cm (43.0 in) |
| 1996-12-26 | Record snow depth | Record snow depth 119.4 cm (47.0 in) |
| 1996-12-28 | Record snow depth | Record snow depth 124.5 cm (49.0 in) |
| 2000-10-01 | Record daily precipitation | Record daily precipitation 39.6 mm (1.6 in) |
| 2001-06-04 | Record daily precipitation | Record daily precipitation 44.7 mm (1.8 in) |
| 2002-07-14 | Record high maximum temperature | Record high maximum temperature 39.4 C (102.9 F) |
| 2020-10-24 | Record daily snowfall | Record daily snowfall 45.7 cm (18.0 in) |
Wettest Day of Each Month
Jun: 44.7 mm (1.8 in)| Month | Record daily precipitation (mm) | Date |
|---|---|---|
| Jan | 28.2 mm (1.1 in) | 23 January 1982 |
| Feb | 22.9 mm (0.9 in) | 27 February 1972 |
| Mar | 36.1 mm (1.4 in) | 14 March 2026 |
| Apr | 30.2 mm (1.2 in) | 10 April 1996 |
| May | 35.6 mm (1.4 in) | 23 May 1980 |
| Jun | 44.7 mm (1.8 in) | 4 June 2001 |
| Jul | 31.2 mm (1.2 in) | 26 July 1989 |
| Aug | 40.6 mm (1.6 in) | 6 August 2009 |
| Sep | 31.2 mm (1.2 in) | 12 September 1972 |
| Oct | 44.7 mm (1.8 in) | 31 October 2005 |
| Nov | 33.5 mm (1.3 in) | 12 November 2008 |
| Dec | 25.1 mm (1.0 in) | 3 December 2007 |
Period of Record Coverage
1964 to 2026| Year | Days with data | Share of year | Complete |
|---|---|---|---|
| 1964 | 30 | 8% | No |
| 1965 | 343 | 94% | Yes |
| 1966 | 346 | 95% | Yes |
| 1967 | 362 | 99% | Yes |
| 1968 | 355 | 97% | Yes |
| 1969 | 333 | 91% | Yes |
| 1970 | 337 | 92% | Yes |
| 1971 | 347 | 95% | Yes |
| 1972 | 261 | 71% | No |
| 1973 | 187 | 51% | No |
| 1975 | 169 | 46% | No |
| 1976 | 356 | 97% | Yes |
| 1977 | 358 | 98% | Yes |
| 1978 | 364 | 100% | Yes |
| 1979 | 361 | 99% | Yes |
| 1980 | 365 | 100% | Yes |
| 1981 | 351 | 96% | Yes |
| 1982 | 365 | 100% | Yes |
| 1983 | 363 | 99% | Yes |
| 1984 | 364 | 99% | Yes |
| 1985 | 330 | 90% | Yes |
| 1986 | 365 | 100% | Yes |
| 1987 | 365 | 100% | Yes |
| 1988 | 363 | 99% | Yes |
| 1989 | 363 | 99% | Yes |
| 1990 | 364 | 100% | Yes |
| 1991 | 365 | 100% | Yes |
| 1992 | 366 | 100% | Yes |
| 1993 | 365 | 100% | Yes |
| 1994 | 303 | 83% | No |
| 1995 | 362 | 99% | Yes |
| 1996 | 336 | 92% | Yes |
| 1997 | 334 | 92% | Yes |
| 1998 | 334 | 92% | Yes |
| 1999 | 363 | 99% | Yes |
| 2000 | 358 | 98% | Yes |
| 2001 | 344 | 94% | Yes |
| 2002 | 345 | 95% | Yes |
| 2003 | 326 | 89% | No |
| 2004 | 330 | 90% | Yes |
| 2005 | 342 | 94% | Yes |
| 2006 | 332 | 91% | Yes |
| 2007 | 338 | 93% | Yes |
| 2008 | 339 | 93% | Yes |
| 2009 | 299 | 82% | No |
| 2010 | 212 | 58% | No |
| 2016 | 44 | 12% | No |
| 2017 | 304 | 83% | No |
| 2018 | 365 | 100% | Yes |
| 2019 | 365 | 100% | Yes |
| 2020 | 365 | 100% | Yes |
| 2021 | 365 | 100% | Yes |
| 2022 | 353 | 97% | Yes |
| 2023 | 364 | 100% | Yes |
| 2024 | 361 | 99% | Yes |
| 2025 | 365 | 100% | Yes |
| 2026 | 183 | 50% | No |
Latest Records
20| Date | Station | Record | Value | Beat old record by | Old record stood | Significance |
|---|---|---|---|---|---|---|
| 7 September 2026 | Potomac, US | daily rain (Provisional) | 27.9 mm (1.1 in) | 4.5 mm (0.18 in) | 24 years | 22 of 100 (Routine) |
| 5 September 2026 | Potomac, US | daily rain (Provisional) | 9.7 mm (0.38 in) | 4.6 mm (0.18 in) | 36 years | 20 of 100 (Routine) |
| 29 June 2026 | Potomac, US | daily low max | 11.1 C (52.0 F) | 1.7 C (3.1 F) | 57 years | 26 of 100 (Routine) |
| 8 June 2026 | Potomac, US | daily low max | 11.7 C (53.1 F) | 1.6 C (2.9 F) | 31 years | 17 of 100 (Routine) |
| 8 June 2026 | Potomac, US | daily low min (Tie) | -3.9 C (25.0 F) | tie | 60 years | 6 of 100 (Routine) |
| 27 May 2026 | Potomac, US | monthly high min (Tie) | 11.1 C (52.0 F) | tie | 46 years | 7 of 100 (Routine) |
| 25 April 2026 | Potomac, US | daily low max (Tie) | 5.6 C (42.1 F) | tie | 32 years | 3 of 100 (Routine) |
| 24 April 2026 | Potomac, US | daily snowfall | 13.0 cm (5.1 in) | 13.0 cm (5.1 in) | 60 years | 50 of 100 (Notable) |
| 24 April 2026 | Potomac, US | daily snow depth | 12.7 cm (5.0 in) | 12.7 cm (5.0 in) | 60 years | 41 of 100 (Notable) |
| 24 April 2026 | Potomac, US | daily rain | 14.2 mm (0.6 in) | 3.3 mm (0.13 in) | 20 years | 19 of 100 (Routine) |
| 22 April 2026 | Potomac, US | daily high max | 27.2 C (81.0 F) | 2.8 C (5.0 F) | 39 years | 21 of 100 (Routine) |
| 2 April 2026 | Potomac, US | daily high min | 1.7 C (35.1 F) | 0.6 C (1.1 F) | 35 years | 17 of 100 (Routine) |
| 30 March 2026 | Potomac, US | daily high min | 2.2 C (36.0 F) | 0.5 C (0.9 F) | 24 years | 13 of 100 (Routine) |
| 21 March 2026 | Potomac, US | daily high min | 3.3 C (37.9 F) | 3.3 C (5.9 F) | 41 years | 23 of 100 (Routine) |
| 21 March 2026 | Potomac, US | daily high max | 22.8 C (73.0 F) | 4.5 C (8.1 F) | 1 year | 14 of 100 (Routine) |
| 20 March 2026 | Potomac, US | daily high max | 21.1 C (70.0 F) | 1.7 C (3.1 F) | 1 year | 9 of 100 (Routine) |
| 16 March 2026 | Potomac, US | daily low min (Tie) | -14.4 C (6.1 F) | tie | 60 years | 6 of 100 (Routine) |
| 14 March 2026 | Potomac, US | monthly rain | 36.1 mm (1.4 in) | 13.0 mm (0.5 in) | 29 years | 64 of 100 (Major) |
| 14 March 2026 | Potomac, US | daily snowfall | 14.0 cm (5.5 in) | 10.2 cm (4.0 in) | 48 years | 40 of 100 (Notable) |
| 13 March 2026 | Potomac, US | daily rain | 15.7 mm (0.6 in) | 3.8 mm (0.15 in) | 20 years | 20 of 100 (Routine) |
Climate Trend
40 complete years, 1965 to 2025| Year | Annual mean temperature | Difference from the station mean |
|---|---|---|
| 1965 | 4.4 C | -0.50 C |
| 1966 | 5.2 C | +0.28 C |
| 1967 | 5.6 C | +0.68 C |
| 1968 | 4.5 C | -0.42 C |
| 1969 | 4.4 C | -0.50 C |
| 1970 | 5.1 C | +0.17 C |
| 1971 | 5.1 C | +0.24 C |
| 1976 | 5.8 C | +0.89 C |
| 1977 | 5.2 C | +0.31 C |
| 1978 | 4.8 C | -0.15 C |
| 1979 | 4.5 C | -0.37 C |
| 1980 | 5.0 C | +0.09 C |
| 1982 | 3.8 C | -1.15 C |
| 1983 | 4.9 C | +0.04 C |
| 1984 | 5.3 C | +0.38 C |
| 1986 | 5.0 C | +0.09 C |
| 1987 | 5.0 C | +0.10 C |
| 1988 | 5.6 C | +0.69 C |
| 1989 | 4.7 C | -0.23 C |
| 1990 | 5.0 C | +0.13 C |
| 1991 | 4.9 C | +0.03 C |
| 1992 | 5.4 C | +0.53 C |
| 1993 | 3.5 C | -1.43 C |
| 1995 | 4.8 C | -0.14 C |
| 1999 | 5.2 C | +0.30 C |
| 2000 | 4.9 C | +0.02 C |
| 2001 | 4.9 C | 0.00 C |
| 2003 | 5.0 C | +0.10 C |
| 2004 | 5.1 C | +0.22 C |
| 2005 | 4.5 C | -0.40 C |
| 2006 | 5.2 C | +0.25 C |
| 2007 | 5.3 C | +0.37 C |
| 2008 | 3.9 C | -0.97 C |
| 2018 | 4.5 C | -0.40 C |
| 2019 | 3.5 C | -1.42 C |
| 2020 | 5.1 C | +0.21 C |
| 2021 | 5.2 C | +0.26 C |
| 2023 | 5.1 C | +0.18 C |
| 2024 | 5.5 C | +0.62 C |
| 2025 | 6.0 C | +1.05 C |
The fitted trend in annual mean temperature here over 1965 to 2025 is 0.01 C (-0.09 to 0.11) per decade. The interval includes zero, so the trend is not clearly different from zero. In Fahrenheit: 0.01 F (-0.17 to 0.20) per decade. The slope is a straight line fitted to 40 complete years; the brackets give its 95 percent interval.
| Measure | Per decade (C) | Per decade (F) | Period | Complete years | Reading |
|---|---|---|---|---|---|
| Annual mean temperature | 0.01 C (-0.09 to 0.11) per decade | 0.01 F (-0.17 to 0.20) per decade | 1965 to 2025 | 40 | Not clearly different from zero |
| Mean daily maximum | 0.1 C (-0.1 to 0.2) per decade | 0.1 F (-0.1 to 0.4) per decade | 1965 to 2025 | 40 | Not clearly different from zero |
| Mean daily minimum | -0.04 C (-0.15 to 0.06) per decade | -0.1 F (-0.3 to 0.1) per decade | 1965 to 2025 | 40 | 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
1964 to 2026| Measure | Record | Year of the record | Median year | Years with a value |
|---|---|---|---|---|
| Hottest day (TXx) | 39.4 C (102.9 F) | 2002 | 35.6 C (96.1 F) | 57 |
| Coldest night (TNn) | -45.6 C (-50.1 F) | 1983 | -34.4 C (-29.9 F) | 57 |
| Wettest day (Rx1day) | 44.7 mm (1.8 in) | 2001 | 24.9 mm (1.0 in) | 57 |
| Wettest five days (Rx5day) | 67.1 mm (2.6 in) | 1980 | 41.2 mm (1.6 in) | 57 |
| Longest dry spell (CDD) | 91 days | 2017 | 29 days | 57 |
Hottest day (TXx)
| Year | Hottest day (TXx) |
|---|---|
| 1964 | 6.7 C (44.1 F) |
| 1965 | 35.0 C (95.0 F) |
| 1966 | 36.7 C (98.1 F) |
| 1967 | 35.6 C (96.1 F) |
| 1968 | 35.0 C (95.0 F) |
| 1969 | 38.9 C (102.0 F) |
| 1970 | 35.0 C (95.0 F) |
| 1971 | 37.2 C (99.0 F) |
| 1972 | 34.4 C (93.9 F) |
| 1973 | 35.0 C (95.0 F) |
| 1975 | 36.7 C (98.1 F) |
| 1976 | 34.4 C (93.9 F) |
| 1977 | 36.1 C (97.0 F) |
| 1978 | 36.1 C (97.0 F) |
| 1979 | 35.6 C (96.1 F) |
| 1980 | 34.4 C (93.9 F) |
| 1981 | 37.2 C (99.0 F) |
| 1982 | 32.2 C (90.0 F) |
| 1983 | 37.8 C (100.0 F) |
| 1984 | 36.1 C (97.0 F) |
| 1985 | 38.3 C (100.9 F) |
| 1986 | 36.1 C (97.0 F) |
| 1987 | 35.6 C (96.1 F) |
| 1988 | 35.6 C (96.1 F) |
| 1989 | 35.6 C (96.1 F) |
| 1990 | 35.6 C (96.1 F) |
| 1991 | 35.6 C (96.1 F) |
| 1992 | 35.0 C (95.0 F) |
| 1993 | 32.8 C (91.0 F) |
| 1994 | 35.0 C (95.0 F) |
| 1995 | 33.3 C (91.9 F) |
| 1996 | 34.4 C (93.9 F) |
| 1997 | 34.4 C (93.9 F) |
| 1998 | 36.1 C (97.0 F) |
| 1999 | 35.6 C (96.1 F) |
| 2000 | 37.8 C (100.0 F) |
| 2001 | 35.6 C (96.1 F) |
| 2002 | 39.4 C (102.9 F) |
| 2003 | 38.3 C (100.9 F) |
| 2004 | 37.8 C (100.0 F) |
| 2005 | 35.0 C (95.0 F) |
| 2006 | 37.8 C (100.0 F) |
| 2007 | 38.9 C (102.0 F) |
| 2008 | 36.1 C (97.0 F) |
| 2009 | 38.3 C (100.9 F) |
| 2010 | 35.6 C (96.1 F) |
| 2016 | 8.3 C (46.9 F) |
| 2017 | 36.7 C (98.1 F) |
| 2018 | 37.8 C (100.0 F) |
| 2019 | 33.9 C (93.0 F) |
| 2020 | 35.0 C (95.0 F) |
| 2021 | 35.6 C (96.1 F) |
| 2022 | 36.1 C (97.0 F) |
| 2023 | 36.7 C (98.1 F) |
| 2024 | 38.9 C (102.0 F) |
| 2025 | 36.1 C (97.0 F) |
| 2026 | 31.1 C (88.0 F) |
Coldest night (TNn)
| Year | Coldest night (TNn) |
|---|---|
| 1964 | -44.4 C (-47.9 F) |
| 1965 | -28.9 C (-20.0 F) |
| 1966 | -29.4 C (-20.9 F) |
| 1967 | -28.3 C (-18.9 F) |
| 1968 | -41.7 C (-43.1 F) |
| 1969 | -35.6 C (-32.1 F) |
| 1970 | -30.6 C (-23.1 F) |
| 1971 | -34.4 C (-29.9 F) |
| 1972 | -40.0 C (-40.0 F) |
| 1973 | -27.8 C (-18.0 F) |
| 1975 | -23.9 C (-11.0 F) |
| 1976 | -33.3 C (-27.9 F) |
| 1977 | -31.1 C (-24.0 F) |
| 1978 | -40.6 C (-41.1 F) |
| 1979 | -41.7 C (-43.1 F) |
| 1980 | -36.7 C (-34.1 F) |
| 1981 | -41.1 C (-42.0 F) |
| 1982 | -41.1 C (-42.0 F) |
| 1983 | -45.6 C (-50.1 F) |
| 1984 | -33.3 C (-27.9 F) |
| 1985 | -35.0 C (-31.0 F) |
| 1986 | -28.9 C (-20.0 F) |
| 1987 | -30.0 C (-22.0 F) |
| 1988 | -30.6 C (-23.1 F) |
| 1989 | -37.2 C (-35.0 F) |
| 1990 | -41.7 C (-43.1 F) |
| 1991 | -31.1 C (-24.0 F) |
| 1992 | -25.6 C (-14.1 F) |
| 1993 | -36.1 C (-33.0 F) |
| 1994 | -31.1 C (-24.0 F) |
| 1995 | -28.3 C (-18.9 F) |
| 1996 | -42.8 C (-45.0 F) |
| 1997 | -25.0 C (-13.0 F) |
| 1998 | -31.7 C (-25.1 F) |
| 1999 | -25.0 C (-13.0 F) |
| 2000 | -30.0 C (-22.0 F) |
| 2001 | -24.4 C (-11.9 F) |
| 2002 | -31.7 C (-25.1 F) |
| 2003 | -30.6 C (-23.1 F) |
| 2004 | -42.2 C (-44.0 F) |
| 2005 | -36.7 C (-34.1 F) |
| 2006 | -35.0 C (-31.0 F) |
| 2007 | -27.2 C (-17.0 F) |
| 2008 | -36.7 C (-34.1 F) |
| 2009 | -33.3 C (-27.9 F) |
| 2010 | -33.9 C (-29.0 F) |
| 2016 | -36.7 C (-34.1 F) |
| 2017 | -38.9 C (-38.0 F) |
| 2018 | -35.6 C (-32.1 F) |
| 2019 | -38.3 C (-36.9 F) |
| 2020 | -29.4 C (-20.9 F) |
| 2021 | -37.2 C (-35.0 F) |
| 2022 | -45.0 C (-49.0 F) |
| 2023 | -38.9 C (-38.0 F) |
| 2024 | -43.9 C (-47.0 F) |
| 2025 | -35.6 C (-32.1 F) |
| 2026 | -18.3 C (-0.9 F) |
Wettest day (Rx1day)
| Year | Wettest day (Rx1day) |
|---|---|
| 1964 | 17.5 mm (0.7 in) |
| 1965 | 19.1 mm (0.8 in) |
| 1966 | 20.6 mm (0.8 in) |
| 1967 | 22.9 mm (0.9 in) |
| 1968 | 21.6 mm (0.9 in) |
| 1969 | 32.5 mm (1.3 in) |
| 1970 | 22.9 mm (0.9 in) |
| 1971 | 25.4 mm (1.0 in) |
| 1972 | 31.2 mm (1.2 in) |
| 1973 | 16.0 mm (0.6 in) |
| 1975 | 31.0 mm (1.2 in) |
| 1976 | 25.4 mm (1.0 in) |
| 1977 | 20.8 mm (0.8 in) |
| 1978 | 26.7 mm (1.1 in) |
| 1979 | 18.0 mm (0.7 in) |
| 1980 | 35.6 mm (1.4 in) |
| 1981 | 20.8 mm (0.8 in) |
| 1982 | 28.2 mm (1.1 in) |
| 1983 | 31.0 mm (1.2 in) |
| 1984 | 24.1 mm (0.9 in) |
| 1985 | 21.8 mm (0.9 in) |
| 1986 | 21.1 mm (0.8 in) |
| 1987 | 15.0 mm (0.6 in) |
| 1988 | 30.5 mm (1.2 in) |
| 1989 | 31.2 mm (1.2 in) |
| 1990 | 24.9 mm (1.0 in) |
| 1991 | 18.8 mm (0.7 in) |
| 1992 | 26.2 mm (1.0 in) |
| 1993 | 22.1 mm (0.9 in) |
| 1994 | 13.7 mm (0.5 in) |
| 1995 | 20.8 mm (0.8 in) |
| 1996 | 30.2 mm (1.2 in) |
| 1997 | 25.7 mm (1.0 in) |
| 1998 | 21.6 mm (0.9 in) |
| 1999 | 30.7 mm (1.2 in) |
| 2000 | 39.6 mm (1.6 in) |
| 2001 | 44.7 mm (1.8 in) |
| 2002 | 27.2 mm (1.1 in) |
| 2003 | 18.8 mm (0.7 in) |
| 2004 | 14.0 mm (0.6 in) |
| 2005 | 44.7 mm (1.8 in) |
| 2006 | 19.3 mm (0.8 in) |
| 2007 | 25.1 mm (1.0 in) |
| 2008 | 33.5 mm (1.3 in) |
| 2009 | 40.6 mm (1.6 in) |
| 2010 | 21.1 mm (0.8 in) |
| 2016 | 10.4 mm (0.4 in) |
| 2017 | 32.5 mm (1.3 in) |
| 2018 | 29.2 mm (1.1 in) |
| 2019 | 27.7 mm (1.1 in) |
| 2020 | 28.7 mm (1.1 in) |
| 2021 | 23.6 mm (0.9 in) |
| 2022 | 16.8 mm (0.7 in) |
| 2023 | 31.8 mm (1.3 in) |
| 2024 | 18.0 mm (0.7 in) |
| 2025 | 18.8 mm (0.7 in) |
| 2026 | 36.1 mm (1.4 in) |
Wettest five days (Rx5day)
| Year | Wettest five days (Rx5day) |
|---|---|
| 1964 | 46.0 mm (1.8 in) |
| 1965 | 36.1 mm (1.4 in) |
| 1966 | 40.4 mm (1.6 in) |
| 1967 | 37.7 mm (1.5 in) |
| 1968 | 40.3 mm (1.6 in) |
| 1969 | 65.7 mm (2.6 in) |
| 1970 | 42.4 mm (1.7 in) |
| 1971 | 34.0 mm (1.3 in) |
| 1972 | 37.1 mm (1.5 in) |
| 1973 | 16.8 mm (0.7 in) |
| 1975 | 40.4 mm (1.6 in) |
| 1976 | 29.2 mm (1.1 in) |
| 1977 | 41.3 mm (1.6 in) |
| 1978 | 33.8 mm (1.3 in) |
| 1979 | 20.1 mm (0.8 in) |
| 1980 | 67.1 mm (2.6 in) |
| 1981 | 40.2 mm (1.6 in) |
| 1982 | 34.0 mm (1.3 in) |
| 1983 | 41.9 mm (1.6 in) |
| 1984 | 38.6 mm (1.5 in) |
| 1985 | 48.7 mm (1.9 in) |
| 1986 | 42.2 mm (1.7 in) |
| 1987 | 26.7 mm (1.1 in) |
| 1988 | 41.4 mm (1.6 in) |
| 1989 | 34.8 mm (1.4 in) |
| 1990 | 36.1 mm (1.4 in) |
| 1991 | 35.9 mm (1.4 in) |
| 1992 | 45.5 mm (1.8 in) |
| 1993 | 36.7 mm (1.4 in) |
| 1994 | 42.2 mm (1.7 in) |
| 1995 | 52.8 mm (2.1 in) |
| 1996 | 54.1 mm (2.1 in) |
| 1997 | 44.5 mm (1.8 in) |
| 1998 | 47.3 mm (1.9 in) |
| 1999 | 52.1 mm (2.1 in) |
| 2000 | 49.0 mm (1.9 in) |
| 2001 | 52.0 mm (2.0 in) |
| 2002 | 41.4 mm (1.6 in) |
| 2003 | 27.9 mm (1.1 in) |
| 2004 | 33.1 mm (1.3 in) |
| 2005 | 47.5 mm (1.9 in) |
| 2006 | 46.7 mm (1.8 in) |
| 2007 | 27.7 mm (1.1 in) |
| 2008 | 36.5 mm (1.4 in) |
| 2009 | 44.2 mm (1.7 in) |
| 2010 | 28.0 mm (1.1 in) |
| 2016 | 14.3 mm (0.6 in) |
| 2017 | 41.7 mm (1.6 in) |
| 2018 | 41.2 mm (1.6 in) |
| 2019 | 36.6 mm (1.4 in) |
| 2020 | 54.6 mm (2.1 in) |
| 2021 | 48.5 mm (1.9 in) |
| 2022 | 28.4 mm (1.1 in) |
| 2023 | 45.1 mm (1.8 in) |
| 2024 | 20.4 mm (0.8 in) |
| 2025 | 51.5 mm (2.0 in) |
| 2026 | 57.8 mm (2.3 in) |
Longest dry spell (CDD)
| Year | Longest dry spell (CDD) |
|---|---|
| 1964 | 4 days |
| 1965 | 27 days |
| 1966 | 21 days |
| 1967 | 36 days |
| 1968 | 32 days |
| 1969 | 39 days |
| 1970 | 39 days |
| 1971 | 25 days |
| 1972 | 27 days |
| 1973 | 31 days |
| 1975 | 15 days |
| 1976 | 27 days |
| 1977 | 37 days |
| 1978 | 36 days |
| 1979 | 64 days |
| 1980 | 35 days |
| 1981 | 53 days |
| 1982 | 27 days |
| 1983 | 15 days |
| 1984 | 35 days |
| 1985 | 53 days |
| 1986 | 26 days |
| 1987 | 50 days |
| 1988 | 33 days |
| 1989 | 12 days |
| 1990 | 25 days |
| 1991 | 29 days |
| 1992 | 21 days |
| 1993 | 22 days |
| 1994 | 25 days |
| 1995 | 21 days |
| 1996 | 21 days |
| 1997 | 18 days |
| 1998 | 20 days |
| 1999 | 36 days |
| 2000 | 58 days |
| 2001 | 35 days |
| 2002 | 28 days |
| 2003 | 28 days |
| 2004 | 28 days |
| 2005 | 34 days |
| 2006 | 32 days |
| 2007 | 69 days |
| 2008 | 19 days |
| 2009 | 24 days |
| 2010 | 20 days |
| 2016 | 13 days |
| 2017 | 91 days |
| 2018 | 35 days |
| 2019 | 31 days |
| 2020 | 38 days |
| 2021 | 32 days |
| 2022 | 30 days |
| 2023 | 40 days |
| 2024 | 28 days |
| 2025 | 30 days |
| 2026 | 29 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
40 years with a frostAcross 40 years with a frost, the median last spring frost at Potomac falls on 24 June and the median first autumn frost on 29 July, which leaves a median of 38 days between them.
Fitted over all years, the growing season changes by +5.4 days per decade at this station.
| Measure | Median, all years | Earliest period | Recent period (1979 to 2025) | Recent against earliest | Fitted trend |
|---|---|---|---|---|---|
| Last spring frost | 24 June | n/a | 23 June | n/a | -0.1 days per decade |
| First autumn frost | 29 July | n/a | 3 August | n/a | +5.3 days per decade |
| Growing days | 38 days | n/a | 41 days | n/a | +5.4 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
44 years, 1965 to 2025A day with at least 24.2 mm (1.0 in) of rain is expected about once in 2 years. A day with at least 48.7 mm (1.9 in) of rain is expected about once in 100 years.
| Expected about once in | A day with at least | Note |
|---|---|---|
| 2 years | 24.2 mm (1.0 in) | |
| 5 years | 30.6 mm (1.2 in) | |
| 10 years | 34.9 mm (1.4 in) | |
| 25 years | 40.4 mm (1.6 in) | |
| 50 years | 44.6 mm (1.8 in) | Longer than the 44 years of record |
| 100 years | 48.7 mm (1.9 in) | Longer than the 44 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, 44 years of values from 1965 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: 44.7 mm (1.8 in) in 2001; 44.7 mm (1.8 in) in 2005; 39.6 mm (1.6 in) in 2000.
Station Changes
1 suspectedOne change was suspected in the annual mean temperature of Potomac, at 1979. Each is measured against neighbouring stations.
- Relative to 5 neighbouring stations, the station's annual mean temperature from 1979 ran 0.6 C (1.1 F) lower than in the years before (likely change).
| Year | Shift (C) | Shift (F) | Strength | Neighbours |
|---|---|---|---|---|
| 1979 | -0.6 | -1.1 | likely | 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.
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 2026-10-12 (12 October 2026). Records are computed by this site and are not official.
Data as of . Last revised (2026-10-13).