Isleworth Threshold Days by Year (USC00084332)

5 fixed thresholds counted per year at Isleworth (USC00084332): hot days, frost, tropical nights and heavy rain, with the most days in a year.

Key Facts for Isleworth Thresholds

Isleworth: days with 10 mm (0.39 in) or more of precipitation in 63 years, most in 1953 with 57.
Isleworth: days with 25 mm (0.98 in) or more of precipitation in 63 years, most in 1953 with 27.
Isleworth: days with 50 mm (1.97 in) or more of precipitation in 63 years, most in 1979 with 9.
Isleworth: days with 100 mm (3.94 in) or more of precipitation in 23 years, most in 1933 with 2.
5 fixed thresholds have at least one qualifying day at Isleworth.

Days with 10 mm (0.39 in) or more of precipitation

63 years with a qualifying day

Days per year at Isleworth with 10 mm (0.39 in) or more of precipitation, with the decade average as a line. The most was 57 in 1953.

Days with 10 mm (0.39 in) or more of precipitation per year at Isleworth
Year	Days	Decade average
1917	34	34.5
1918	35	34.5
1920	45	36.8
1922	47	36.8
1923	32	36.8
1925	35	36.8
1926	43	36.8
1927	30	36.8
1928	31	36.8
1929	31	36.8
1930	56	41.2
1931	38	41.2
1932	35	41.2
1933	36	41.2
1934	47	41.2
1935	42	41.2
1936	44	41.2
1937	46	41.2
1938	26	41.2
1939	42	41.2
1940	37	41.1
1941	52	41.1
1942	39	41.1
1943	41	41.1
1944	47	41.1
1945	39	41.1
1946	44	41.1
1947	43	41.1
1948	37	41.1
1949	32	41.1
1950	33	39.6
1951	33	39.6
1952	35	39.6
1953	57	39.6
1954	33	39.6
1955	36	39.6
1956	27	39.6
1957	46	39.6
1958	43	39.6
1959	53	39.6
1960	42	40.2
1961	40	40.2
1962	37	40.2
1963	43	40.2
1964	39	40.2
1965	37	40.2
1966	43	40.2
1967	32	40.2
1968	42	40.2
1969	47	40.2
1970	38	37.6
1971	40	37.6
1972	35	37.6
1973	40	37.6
1974	43	37.6
1975	40	37.6
1976	38	37.6
1977	30	37.6
1978	34	37.6
1979	38	37.6
1980	32	38
1981	38	38
1982	44	38

For each year, a bar from the first to the last day at Isleworth meeting 10 mm (0.39 in).

First to last qualifying date each year at Isleworth
Year	First date	Last date
1917	1917-01-05	1917-10-16
1918	1918-01-06	1918-12-28
1920	1920-01-17	1920-12-27
1922	1922-01-17	1922-12-19
1923	1923-01-03	1923-12-15
1925	1925-01-12	1925-12-20
1926	1926-01-10	1926-11-15
1927	1927-02-18	1927-12-03
1928	1928-01-28	1928-09-24
1929	1929-01-07	1929-12-22
1930	1930-01-15	1930-12-28
1931	1931-01-05	1931-12-31
1932	1932-01-31	1932-11-23
1933	1933-01-11	1933-11-25
1934	1934-01-08	1934-10-07
1935	1935-01-05	1935-12-22
1936	1936-01-03	1936-12-14
1937	1937-02-09	1937-12-18
1938	1938-03-16	1938-10-24
1939	1939-01-18	1939-12-29
1940	1940-01-07	1940-12-26
1941	1941-01-05	1941-12-12
1942	1942-01-02	1942-12-29
1943	1943-01-27	1943-12-27
1944	1944-01-09	1944-10-19
1945	1945-01-03	1945-12-30
1946	1946-01-15	1946-12-20
1947	1947-02-12	1947-11-18
1948	1948-01-14	1948-12-09
1949	1949-04-03	1949-12-25
1950	1950-03-16	1950-12-30
1951	1951-01-25	1951-12-21
1952	1952-01-28	1952-11-20
1953	1953-01-09	1953-12-23
1954	1954-01-03	1954-12-18
1955	1955-02-08	1955-12-28
1956	1956-01-22	1956-10-16
1957	1957-01-21	1957-12-26
1958	1958-01-07	1958-12-27
1959	1959-01-02	1959-12-24
1960	1960-01-30	1960-12-15
1961	1961-01-13	1961-12-19
1962	1962-02-09	1962-11-12
1963	1963-01-23	1963-12-24
1964	1964-01-07	1964-12-05
1965	1965-01-15	1965-12-20
1966	1966-01-05	1966-10-10
1967	1967-02-09	1967-12-11
1968	1968-01-24	1968-11-19
1969	1969-01-04	1969-12-26
1970	1970-01-03	1970-12-31
1971	1971-01-07	1971-12-03
1972	1972-01-26	1972-12-22
1973	1973-01-11	1973-12-27
1974	1974-02-20	1974-12-17
1975	1975-01-11	1975-11-06
1976	1976-02-22	1976-11-21
1977	1977-01-03	1977-12-21
1978	1978-01-19	1978-12-28
1979	1979-01-02	1979-11-26
1980	1980-01-13	1980-11-28
1981	1981-02-02	1981-12-27
1982	1982-01-13	1982-11-02

Every Fixed Threshold

Fixed thresholds at Isleworth
Threshold	Years with a qualifying day	Most days in a year	Year	Latest year days
10 mm (0.39 in): Days with 10 mm or more rain	63	57	1953	44
25 mm (0.98 in): Days with 25 mm or more rain	63	27	1953	23
50 mm (1.97 in): Days with 50 mm or more rain	63	9	1979	8
100 mm (3.94 in): Days with 100 mm or more rain	23	2	1933	1
200 mm (7.87 in): Days with 200 mm or more rain	2	1	1945	1

Years with under 90 percent of days observed are left out of the most days column. Threshold history at this station starts in 1917.

Download the Data

Data for Isleworth threshold days by year: CSV or JSON. Field meanings are on the data page.

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 2026-10-17 (17 October 2026). Threshold counts are computed by this site.

Data as of 2025-12-31. Last revised 31 December 2025 (2025-12-31).

Isleworth Threshold Days by Year (USC00084332)

Key Facts for Isleworth Thresholds

Days with 10 mm (0.39 in) or more of precipitation

Every Fixed Threshold

Download the Data

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