Harrow (Post Office) Threshold Days by Year

4 fixed thresholds counted per year at Harrow (Post Office) (ASN00079021): hot days, frost, tropical nights and heavy rain, with the most days in a year.

Key Facts for Harrow (Post Office) Thresholds

Harrow (Post Office): days with 10 mm (0.39 in) or more of precipitation in 88 years, most in 1951 with 29.
Harrow (Post Office): days with 25 mm (0.98 in) or more of precipitation in 73 years, most in 1933 with 7.
Harrow (Post Office): days with 50 mm (1.97 in) or more of precipitation in 17 years, most in 1946 with 2.
Harrow (Post Office): days with 100 mm (3.94 in) or more of precipitation in 1 years, most in 1946 with 1.
4 fixed thresholds have at least one qualifying day at Harrow (Post Office).

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

88 years with a qualifying day

Days per year at Harrow (Post Office) with 10 mm (0.39 in) or more of precipitation, with the decade average as a line. The most was 29 in 1951.

Days with 10 mm (0.39 in) or more of precipitation per year at Harrow (Post Office)
Year	Days	Decade average
1909	20	20
1910	19	17
1911	15	17
1913	11	17
1915	17	17
1916	19	17
1917	25	17
1918	17	17
1919	13	17
1920	21	17.4
1921	17	17.4
1922	18	17.4
1923	18	17.4
1924	16	17.4
1925	7	17.4
1926	19	17.4
1927	19	17.4
1928	19	17.4
1929	20	17.4
1930	19	16.8
1931	16	16.8
1932	14	16.8
1933	18	16.8
1934	17	16.8
1935	20	16.8
1936	20	16.8
1937	16	16.8
1938	7	16.8
1939	21	16.8
1940	10	16.9
1941	17	16.9
1942	21	16.9
1943	19	16.9
1944	12	16.9
1945	15	16.9
1946	21	16.9
1947	27	16.9
1948	12	16.9
1949	15	16.9
1950	18	19
1951	29	19
1952	27	19
1953	24	19
1954	15	19
1955	22	19
1956	19	19
1957	14	19
1958	15	19
1959	7	19
1960	23	16.3
1961	14	16.3
1962	17	16.3
1963	14	16.3
1964	27	16.3
1965	13	16.3
1966	18	16.3
1967	6	16.3
1968	16	16.3
1969	15	16.3
1970	13	16.8
1971	15	16.8
1972	16	16.8
1973	26	16.8
1974	23	16.8
1975	19	16.8
1976	12	16.8
1978	14	16.8
1979	13	16.8
1980	12	11.5
1982	3	11.5
1983	15	11.5
1986	16	11.5
1991	14	14.4
1993	17	14.4
1994	13	14.4
1997	13	14.4
1999	15	14.4
2000	9	13.1
2001	23	13.1
2002	9	13.1
2003	17	13.1
2004	15	13.1
2005	13	13.1
2006	8	13.1
2007	14	13.1
2008	10	13.1
2024	10	11.5
2025	13	11.5

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

First to last qualifying date each year at Harrow (Post Office)
Year	First date	Last date
1909	1909-02-24	1909-11-19
1910	1910-03-06	1910-12-23
1911	1911-02-05	1911-12-13
1913	1913-02-14	1913-12-22
1915	1915-05-16	1915-09-20
1916	1916-01-06	1916-12-29
1917	1917-02-15	1917-10-20
1918	1918-01-14	1918-10-07
1919	1919-02-03	1919-10-07
1920	1920-03-06	1920-12-17
1921	1921-01-03	1921-11-28
1922	1922-01-07	1922-12-26
1923	1923-05-21	1923-12-14
1924	1924-02-15	1924-11-24
1925	1925-01-22	1925-11-19
1926	1926-04-04	1926-12-06
1927	1927-02-05	1927-12-09
1928	1928-01-20	1928-11-05
1929	1929-01-30	1929-12-28
1930	1930-02-21	1930-12-16
1931	1931-03-13	1931-11-16
1932	1932-02-05	1932-10-12
1933	1933-01-25	1933-12-05
1934	1934-04-03	1934-11-30
1935	1935-01-05	1935-12-02
1936	1936-01-10	1936-12-17
1937	1937-01-02	1937-12-03
1938	1938-01-14	1938-07-24
1939	1939-01-16	1939-12-05
1940	1940-04-15	1940-12-31
1941	1941-01-23	1941-10-26
1942	1942-01-20	1942-12-19
1943	1943-01-22	1943-12-16
1944	1944-02-07	1944-12-23
1945	1945-02-20	1945-12-27
1946	1946-01-17	1946-12-28
1947	1947-02-04	1947-12-23
1948	1948-04-11	1948-12-25
1949	1949-02-20	1949-11-22
1950	1950-02-16	1950-12-20
1951	1951-01-04	1951-12-19
1952	1952-01-25	1952-12-11
1953	1953-01-14	1953-12-07
1954	1954-01-28	1954-12-12
1955	1955-02-10	1955-10-21
1956	1956-03-06	1956-10-17
1957	1957-02-07	1957-12-26
1958	1958-02-19	1958-10-24
1959	1959-01-24	1959-08-12
1960	1960-01-04	1960-11-21
1961	1961-03-28	1961-12-17
1962	1962-02-20	1962-12-30
1963	1963-01-14	1963-10-28
1964	1964-02-06	1964-11-22
1965	1965-05-16	1965-12-07
1966	1966-02-14	1966-12-12
1967	1967-01-15	1967-12-30
1968	1968-02-20	1968-11-02
1969	1969-01-25	1969-12-11
1970	1970-03-20	1970-12-05
1971	1971-02-09	1971-12-10
1972	1972-01-08	1972-11-10
1973	1973-01-31	1973-12-30
1974	1974-01-14	1974-10-16
1975	1975-03-15	1975-11-20
1976	1976-02-09	1976-11-30
1978	1978-04-10	1978-11-19
1979	1979-01-20	1979-11-15
1980	1980-04-19	1980-10-28
1982	1982-01-07	1982-05-06
1983	1983-03-22	1983-11-29
1986	1986-01-16	1986-12-17
1991	1991-01-04	1991-12-20
1993	1993-01-27	1993-12-14
1994	1994-01-06	1994-10-08
1997	1997-01-22	1997-11-01
1999	1999-01-29	1999-12-27
2000	2000-04-30	2000-11-11
2001	2001-01-03	2001-12-03
2002	2002-05-16	2002-12-31
2003	2003-01-30	2003-10-31
2004	2004-03-29	2004-11-13
2005	2005-01-04	2005-11-08
2006	2006-01-02	2006-12-31
2007	2007-01-01	2007-12-22
2008	2008-01-19	2008-12-13
2024	2024-01-07	2024-12-17
2025	2025-03-10	2025-10-22

Every Fixed Threshold

Fixed thresholds at Harrow (Post Office)
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	88	29	1951	13
25 mm (0.98 in): Days with 25 mm or more rain	73	7	1933	2
50 mm (1.97 in): Days with 50 mm or more rain	17	2	1946	1
100 mm (3.94 in): Days with 100 mm or more rain	1	1	1946	1

Years with under 90 percent of days observed are left out of the most days column. Threshold history at this station starts in 1909.

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Data for Harrow (Post Office) 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 2026-10-13 (13 October 2026). Threshold counts are computed by this site.

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

Harrow (Post Office) Threshold Days by Year

Key Facts for Harrow (Post Office) Thresholds

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

Every Fixed Threshold

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