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Data as of 2026-10-12
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Built 2026-10-19 (19 October 2026)

Altadena Threshold Days by Year (USC00040144)

13 fixed thresholds counted per year at Altadena (USC00040144): hot days, frost, tropical nights and heavy rain, with the most days in a year.

Key Facts for Altadena Thresholds

  • Altadena: days with 10 mm (0.39 in) or more of precipitation in 88 years, most in 1983 with 36.
  • Altadena: days with 25 mm (0.98 in) or more of precipitation in 88 years, most in 1941 with 17.
  • Altadena: days with 50 mm (1.97 in) or more of precipitation in 68 years, most in 1969 with 7.
  • Altadena: days with 100 mm (3.94 in) or more of precipitation in 25 years, most in 1933 with 3.
  • 13 fixed thresholds have at least one qualifying day at Altadena.
6 years with a qualifying day
Days at or above 30 C (86 F) per year at Altadena Days per year at Altadena with a maximum temperature at or above 30 C (86 F), with the decade average as a line. The most was 89 in 1929. 02550751001922: 321923: 571924: 751927: 721928: 711929: 89192219231924192719281929
Days per year at Altadena with a maximum temperature at or above 30 C (86 F), with the decade average as a line. The most was 89 in 1929.
Days at or above 30 C (86 F) per year at Altadena
YearDaysDecade average
19223266
19235766
19247566
19277266
19287166
19298966
First to last qualifying date each year at Altadena For each year, a bar from the first to the last day at Altadena meeting 30 C (86 F). 1922: 13 May 1922 to 25 September 19221923: 8 January 1923 to 20 October 19231924: 7 May 1924 to 28 November 19241927: 23 March 1927 to 2 December 19271928: 20 March 1928 to 22 October 19281929: 1 May 1929 to 18 November 1929192219231924192719281929JanFebMarAprMayJunJulAugSepOctNovDec
For each year, a bar from the first to the last day at Altadena meeting 30 C (86 F).
First to last qualifying date each year at Altadena
YearFirst dateLast date
19221922-05-131922-09-25
19231923-01-081923-10-20
19241924-05-071924-11-28
19271927-03-231927-12-02
19281928-03-201928-10-22
19291929-05-011929-11-18

Every Fixed Threshold

Fixed thresholds at Altadena
ThresholdYears with a qualifying dayMost days in a yearYearLatest year days
30 C (86 F): Days689192989
35 C (95 F): Days626192926
40 C (104 F): Days3219292
90 F (32.2 C): Days669192969
100 F (37.8 C): Days3919299
0 C (32 F): Frost days (min6919299
20 C (68 F): Tropical nights (min52319228
25 C (77 F): Days with min1319223
10 mm (0.39 in): Days with 10 mm or more rain883619837
25 mm (0.98 in): Days with 25 mm or more rain881719415
50 mm (1.97 in): Days with 50 mm or more rain68719691
100 mm (3.94 in): Days with 100 mm or more rain25319331
200 mm (7.87 in): Days with 200 mm or more rain3119381

Years with under 90 percent of days observed are left out of the most days column. Threshold history at this station starts in 1922.

Download the Data

  • Data for Altadena 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 . Last revised (2026-10-12).