Record envelope, standing records and threshold days for Alton (USC00130181), Iowa, United States, with 105 years of record.
Key Facts for Alton
Alton (USC00130181) is a weather station in Iowa, United States at 43.00 latitude and -96.02 longitude, 413 m (1,355 ft) above sea level.
The station reports from 1905 to 2009, 105 years of record.
1,464 records set at Alton still stand.
Records are tracked for tmax, tmin, prcp, snow, snwd: an element needs 30 years of data to be eligible.
Alton tied a monthly record snow depth of 38.1 cm (15.0 in) on 31 December 2009.
About the Station
Location: Iowa, United States, 43.00 latitude, -96.02 longitude.
Elevation: 413 m (1,355 ft).
Period of record: 1905 to 2009, 105 years.
Eligible elements: tmax, tmin, prcp, snow, snwd.
Daily Record Envelope and 2026
0 days at or beyond a record
Record highRecord low2026 daily maximum2026 daily minimum
The band shows the record high and record low for each calendar day at Alton. The lines show the 2026 daily maximum and minimum. 0 days in 2026 matched or passed a record. Temperatures are in degrees Celsius.
Daily record high and record low at Alton, with 2026 drawn through them
Month
Highest record high
Lowest record low
2026 highest maximum
2026 lowest minimum
Jan
18.9 C (66.0 F)
-41.1 C (-42.0 F)
n/a
n/a
Feb
18.3 C (64.9 F)
-36.7 C (-34.1 F)
n/a
n/a
Mar
30.6 C (87.1 F)
-30.0 C (-22.0 F)
n/a
n/a
Apr
35.0 C (95.0 F)
-18.3 C (-0.9 F)
n/a
n/a
May
41.1 C (106.0 F)
-6.1 C (21.0 F)
n/a
n/a
Jun
40.0 C (104.0 F)
0.0 C (32.0 F)
n/a
n/a
Jul
43.3 C (109.9 F)
4.4 C (39.9 F)
n/a
n/a
Aug
41.7 C (107.1 F)
0.6 C (33.1 F)
n/a
n/a
Sep
37.8 C (100.0 F)
-6.7 C (19.9 F)
n/a
n/a
Oct
33.9 C (93.0 F)
-23.3 C (-9.9 F)
n/a
n/a
Nov
25.6 C (78.1 F)
-24.4 C (-11.9 F)
n/a
n/a
Dec
17.2 C (63.0 F)
-36.7 C (-34.1 F)
n/a
n/a
Which Years Hold Standing Records
1,464 standing records
Year with most
1,464 records at Alton still stand. 1936 holds the most, with 63.
Standing records at Alton by the year they were set
Year set
Standing records
1905
17
1906
22
1907
29
1908
26
1909
44
1910
38
1911
38
1912
35
1913
50
1914
32
1915
31
1916
27
1917
43
1918
30
1919
24
1920
24
1921
31
1922
18
1923
32
1924
41
1925
39
1926
25
1927
27
1928
34
1929
20
1930
38
1931
52
1932
25
1933
33
1934
57
1935
26
1936
63
1937
33
1938
27
1939
33
1940
21
1941
29
1942
28
1943
16
1944
22
1945
16
1946
30
1947
31
1948
16
1949
20
1950
17
1951
21
1952
23
1953
10
All-Time Record Progression
7 new records
7 all-time records were set at Alton between 4 July 1936 and 3 March 1977. Each dot is a new record.
When Alton set new all-time records
Date
Kind
Detail
1936-07-04
Record high maximum temperature
Record high maximum temperature 43.3 C (109.9 F)
1936-08-18
Record high minimum temperature
Record high minimum temperature 26.7 C (80.1 F)
1937-08-16
Record high minimum temperature
Record high minimum temperature 27.2 C (81.0 F)
1940-11-11
Record daily snowfall
Record daily snowfall 25.4 cm (10.0 in)
1951-03-18
Record daily snowfall
Record daily snowfall 27.9 cm (11.0 in)
1970-09-03
Record daily precipitation
Record daily precipitation 145.5 mm (5.7 in)
1977-03-03
Record daily snowfall
Record daily snowfall 35.6 cm (14.0 in)
Wettest Day of Each Month
Sep: 145.5 mm (5.7 in)
The wettest day on record for each calendar month at Alton. The most was 145.5 mm (5.7 in) on 3 September 1970.
Record daily precipitation for each month at Alton
Month
Record daily precipitation (mm)
Date
Jan
34.5 mm (1.4 in)
23 January 1982
Feb
41.1 mm (1.6 in)
19 February 1971
Mar
65.5 mm (2.6 in)
23 March 1987
Apr
49.8 mm (2.0 in)
16 April 1938
May
90.9 mm (3.6 in)
25 May 1937
Jun
84.3 mm (3.3 in)
25 June 1935
Jul
88.1 mm (3.5 in)
21 July 1928
Aug
137.7 mm (5.4 in)
22 August 1988
Sep
145.5 mm (5.7 in)
3 September 1970
Oct
81.0 mm (3.2 in)
31 October 1979
Nov
51.8 mm (2.0 in)
20 November 1930
Dec
36.6 mm (1.4 in)
28 December 1982
Period of Record Coverage
1905 to 1953
Complete yearUnder 90 percent of days
49 years of record at Alton, 1905 to 1953. 3 years have data for under 90 percent of days and are left out of rankings: 1905, 1911, 1953.
Cooler than the station meanWarmer than the station mean
One stripe for each of 44 complete years at Alton, 1906 to 1952. Blue stripes are years cooler than the station's own mean of 8.5 C (47.3 F); red stripes are warmer. The coolest year was 1917, at 5.9 C (42.7 F), and the warmest was 1931, at 11.4 C (52.5 F). The strongest colour marks a difference of 2.9 C (5.2 F).
Annual mean temperature at Alton as warming stripes, 1906 to 1952
Year
Annual mean temperature
Difference from the station mean
1906
8.1 C
-0.45 C
1907
7.6 C
-0.91 C
1908
8.9 C
+0.37 C
1909
7.5 C
-1.03 C
1910
8.4 C
-0.15 C
1912
7.0 C
-1.55 C
1913
8.4 C
-0.11 C
1914
8.4 C
-0.17 C
1915
7.7 C
-0.81 C
1916
7.1 C
-1.44 C
1917
5.9 C
-2.61 C
1918
8.4 C
-0.11 C
1919
8.0 C
-0.49 C
1920
8.1 C
-0.48 C
1921
10.2 C
+1.62 C
1922
9.0 C
+0.44 C
1923
8.4 C
-0.14 C
1924
6.8 C
-1.74 C
1925
8.3 C
-0.25 C
1926
8.3 C
-0.26 C
1927
7.8 C
-0.76 C
1928
8.5 C
-0.07 C
1929
7.0 C
-1.54 C
1930
9.2 C
+0.65 C
1931
11.4 C
+2.84 C
1932
8.1 C
-0.39 C
1933
9.7 C
+1.12 C
1934
10.1 C
+1.60 C
1935
8.8 C
+0.28 C
1936
8.2 C
-0.30 C
1937
8.0 C
-0.52 C
1938
9.8 C
+1.23 C
1939
9.8 C
+1.30 C
1940
8.2 C
-0.36 C
1941
9.9 C
+1.32 C
1942
8.9 C
+0.35 C
1943
8.4 C
-0.14 C
1945
8.5 C
-0.05 C
1946
10.0 C
+1.44 C
1947
9.1 C
+0.58 C
1948
9.2 C
+0.65 C
1949
9.4 C
+0.87 C
1950
7.7 C
-0.86 C
1952
9.5 C
+0.92 C
The annual mean temperature here has risen by 0.3 C (0.1 to 0.6) per decade over 1906 to 1952. In Fahrenheit: 0.6 F (0.2 to 1.0) per decade. The slope is a straight line fitted to 44 complete years; the brackets give its 95 percent interval.
Fitted temperature trends per decade at Alton
Measure
Per decade (C)
Per decade (F)
Period
Complete years
Reading
Annual mean temperature
0.3 C (0.1 to 0.6) per decade
0.6 F (0.2 to 1.0) per decade
1906 to 1952
44
Rise
Mean daily maximum
0.5 C (0.2 to 0.7) per decade
0.8 F (0.4 to 1.3) per decade
1906 to 1952
44
Rise
Mean daily minimum
0.23 C (0.02 to 0.45) per decade
0.42 F (0.03 to 0.81) per decade
1906 to 1952
44
Rise
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
1905 to 2009
Yearly extremes at Alton: the record and the median year
Measure
Record
Year of the record
Median year
Years with a value
Hottest day (TXx)
43.3 C (109.9 F)
1936
37.8 C (100.0 F)
49
Coldest night (TNn)
-41.1 C (-42.0 F)
1912
-28.9 C (-20.0 F)
49
Wettest day (Rx1day)
145.5 mm (5.7 in)
1970
56.1 mm (2.2 in)
105
Wettest five days (Rx5day)
212.4 mm (8.4 in)
2004
84.3 mm (3.3 in)
105
Longest dry spell (CDD)
62 days
1952
29 days
105
Hottest day (TXx)
The hottest day of the year at Alton, 1905 to 2009. The record is 43.3 C (109.9 F) in 1936, marked on the chart; the median year is 37.8 C (100.0 F).
Hottest day (TXx) at Alton by year
Year
Hottest day (TXx)
1905
35.0 C (95.0 F)
1906
34.4 C (93.9 F)
1907
36.1 C (97.0 F)
1908
36.7 C (98.1 F)
1909
36.7 C (98.1 F)
1910
36.7 C (98.1 F)
1911
39.4 C (102.9 F)
1912
37.8 C (100.0 F)
1913
37.8 C (100.0 F)
1914
37.8 C (100.0 F)
1915
33.3 C (91.9 F)
1916
36.7 C (98.1 F)
1917
41.7 C (107.1 F)
1918
35.6 C (96.1 F)
1919
37.2 C (99.0 F)
1920
36.7 C (98.1 F)
1921
37.8 C (100.0 F)
1922
37.8 C (100.0 F)
1923
35.6 C (96.1 F)
1924
34.4 C (93.9 F)
1925
38.3 C (100.9 F)
1926
40.6 C (105.1 F)
1927
36.7 C (98.1 F)
1928
35.0 C (95.0 F)
1929
36.1 C (97.0 F)
1930
41.7 C (107.1 F)
1931
38.9 C (102.0 F)
1932
39.4 C (102.9 F)
1933
40.0 C (104.0 F)
1934
41.1 C (106.0 F)
1935
38.3 C (100.9 F)
1936
43.3 C (109.9 F)
1937
39.4 C (102.9 F)
1938
37.8 C (100.0 F)
1939
37.8 C (100.0 F)
1940
40.6 C (105.1 F)
1941
37.8 C (100.0 F)
1942
37.8 C (100.0 F)
1943
35.6 C (96.1 F)
1944
33.9 C (93.0 F)
1945
34.4 C (93.9 F)
1946
36.7 C (98.1 F)
1947
40.6 C (105.1 F)
1948
36.7 C (98.1 F)
1949
35.0 C (95.0 F)
1950
33.9 C (93.0 F)
1951
35.6 C (96.1 F)
1952
38.3 C (100.9 F)
1953
38.3 C (100.9 F)
1954
n/a
1955
n/a
1956
n/a
1957
n/a
1958
n/a
1959
n/a
1960
n/a
1961
n/a
1962
n/a
1963
n/a
1964
n/a
1965
n/a
1966
n/a
1967
n/a
1968
n/a
1969
n/a
1970
n/a
1971
n/a
1972
n/a
1973
n/a
1974
n/a
1975
n/a
1976
n/a
1977
n/a
1978
n/a
1979
n/a
1980
n/a
1981
n/a
1982
n/a
1983
n/a
1984
n/a
1985
n/a
1986
n/a
1987
n/a
1988
n/a
1989
n/a
1990
n/a
1991
n/a
1992
n/a
1993
n/a
1994
n/a
1995
n/a
1996
n/a
1997
n/a
1998
n/a
1999
n/a
2000
n/a
2001
n/a
2002
n/a
2003
n/a
2004
n/a
2005
n/a
2006
n/a
2007
n/a
2008
n/a
2009
n/a
Coldest night (TNn)
The coldest night of the year at Alton, 1905 to 2009. The record is -41.1 C (-42.0 F) in 1912, marked on the chart; the median year is -28.9 C (-20.0 F).
Coldest night (TNn) at Alton by year
Year
Coldest night (TNn)
1905
-21.1 C (-6.0 F)
1906
-27.2 C (-17.0 F)
1907
-30.0 C (-22.0 F)
1908
-27.2 C (-17.0 F)
1909
-28.9 C (-20.0 F)
1910
-33.9 C (-29.0 F)
1911
-36.1 C (-33.0 F)
1912
-41.1 C (-42.0 F)
1913
-28.9 C (-20.0 F)
1914
-33.3 C (-27.9 F)
1915
-28.9 C (-20.0 F)
1916
-34.4 C (-29.9 F)
1917
-36.7 C (-34.1 F)
1918
-36.7 C (-34.1 F)
1919
-32.2 C (-26.0 F)
1920
-30.0 C (-22.0 F)
1921
-26.7 C (-16.1 F)
1922
-28.9 C (-20.0 F)
1923
-27.8 C (-18.0 F)
1924
-34.4 C (-29.9 F)
1925
-27.2 C (-17.0 F)
1926
-26.7 C (-16.1 F)
1927
-27.8 C (-18.0 F)
1928
-25.0 C (-13.0 F)
1929
-31.1 C (-24.0 F)
1930
-32.8 C (-27.0 F)
1931
-22.2 C (-8.0 F)
1932
-30.6 C (-23.1 F)
1933
-31.7 C (-25.1 F)
1934
-25.0 C (-13.0 F)
1935
-29.4 C (-20.9 F)
1936
-35.0 C (-31.0 F)
1937
-30.0 C (-22.0 F)
1938
-26.7 C (-16.1 F)
1939
-26.7 C (-16.1 F)
1940
-30.6 C (-23.1 F)
1941
-23.3 C (-9.9 F)
1942
-32.2 C (-26.0 F)
1943
-31.7 C (-25.1 F)
1944
-31.7 C (-25.1 F)
1945
-25.6 C (-14.1 F)
1946
-28.9 C (-20.0 F)
1947
-26.1 C (-15.0 F)
1948
-30.0 C (-22.0 F)
1949
-28.9 C (-20.0 F)
1950
-29.4 C (-20.9 F)
1951
-27.8 C (-18.0 F)
1952
-28.3 C (-18.9 F)
1953
-28.9 C (-20.0 F)
1954
n/a
1955
n/a
1956
n/a
1957
n/a
1958
n/a
1959
n/a
1960
n/a
1961
n/a
1962
n/a
1963
n/a
1964
n/a
1965
n/a
1966
n/a
1967
n/a
1968
n/a
1969
n/a
1970
n/a
1971
n/a
1972
n/a
1973
n/a
1974
n/a
1975
n/a
1976
n/a
1977
n/a
1978
n/a
1979
n/a
1980
n/a
1981
n/a
1982
n/a
1983
n/a
1984
n/a
1985
n/a
1986
n/a
1987
n/a
1988
n/a
1989
n/a
1990
n/a
1991
n/a
1992
n/a
1993
n/a
1994
n/a
1995
n/a
1996
n/a
1997
n/a
1998
n/a
1999
n/a
2000
n/a
2001
n/a
2002
n/a
2003
n/a
2004
n/a
2005
n/a
2006
n/a
2007
n/a
2008
n/a
2009
n/a
Wettest day (Rx1day)
The wettest day of the year at Alton, 1905 to 2009. The record is 145.5 mm (5.7 in) in 1970, marked on the chart; the median year is 56.1 mm (2.2 in).
Wettest day (Rx1day) at Alton by year
Year
Wettest day (Rx1day)
1905
59.4 mm (2.3 in)
1906
87.9 mm (3.5 in)
1907
74.9 mm (2.9 in)
1908
39.6 mm (1.6 in)
1909
68.6 mm (2.7 in)
1910
32.5 mm (1.3 in)
1911
38.6 mm (1.5 in)
1912
47.2 mm (1.9 in)
1913
69.3 mm (2.7 in)
1914
43.7 mm (1.7 in)
1915
37.8 mm (1.5 in)
1916
50.3 mm (2.0 in)
1917
37.1 mm (1.5 in)
1918
42.2 mm (1.7 in)
1919
35.1 mm (1.4 in)
1920
60.5 mm (2.4 in)
1921
62.5 mm (2.5 in)
1922
58.4 mm (2.3 in)
1923
70.1 mm (2.8 in)
1924
64.3 mm (2.5 in)
1925
21.8 mm (0.9 in)
1926
81.8 mm (3.2 in)
1927
29.0 mm (1.1 in)
1928
88.1 mm (3.5 in)
1929
40.9 mm (1.6 in)
1930
51.8 mm (2.0 in)
1931
79.2 mm (3.1 in)
1932
61.5 mm (2.4 in)
1933
54.6 mm (2.1 in)
1934
75.2 mm (3.0 in)
1935
84.3 mm (3.3 in)
1936
62.7 mm (2.5 in)
1937
90.9 mm (3.6 in)
1938
56.1 mm (2.2 in)
1939
44.7 mm (1.8 in)
1940
48.5 mm (1.9 in)
1941
61.0 mm (2.4 in)
1942
62.0 mm (2.4 in)
1943
35.8 mm (1.4 in)
1944
48.8 mm (1.9 in)
1945
42.9 mm (1.7 in)
1946
38.6 mm (1.5 in)
1947
64.5 mm (2.5 in)
1948
58.4 mm (2.3 in)
1949
87.9 mm (3.5 in)
1950
41.4 mm (1.6 in)
1951
74.4 mm (2.9 in)
1952
49.5 mm (1.9 in)
1953
35.6 mm (1.4 in)
1954
72.6 mm (2.9 in)
1955
62.5 mm (2.5 in)
1956
40.6 mm (1.6 in)
1957
32.0 mm (1.3 in)
1958
27.9 mm (1.1 in)
1959
68.6 mm (2.7 in)
1960
40.6 mm (1.6 in)
1961
70.6 mm (2.8 in)
1962
76.2 mm (3.0 in)
1963
50.8 mm (2.0 in)
1964
79.2 mm (3.1 in)
1965
63.0 mm (2.5 in)
1966
62.5 mm (2.5 in)
1967
39.1 mm (1.5 in)
1968
57.2 mm (2.3 in)
1969
43.2 mm (1.7 in)
1970
145.5 mm (5.7 in)
1971
42.7 mm (1.7 in)
1972
46.0 mm (1.8 in)
1973
52.6 mm (2.1 in)
1974
47.0 mm (1.9 in)
1975
38.4 mm (1.5 in)
1976
33.8 mm (1.3 in)
1977
45.7 mm (1.8 in)
1978
78.5 mm (3.1 in)
1979
84.1 mm (3.3 in)
1980
45.7 mm (1.8 in)
1981
72.6 mm (2.9 in)
1982
84.3 mm (3.3 in)
1983
63.5 mm (2.5 in)
1984
47.2 mm (1.9 in)
1985
58.2 mm (2.3 in)
1986
50.3 mm (2.0 in)
1987
71.9 mm (2.8 in)
1988
137.7 mm (5.4 in)
1989
44.5 mm (1.8 in)
1990
64.8 mm (2.6 in)
1991
42.7 mm (1.7 in)
1992
61.5 mm (2.4 in)
1993
41.4 mm (1.6 in)
1994
73.9 mm (2.9 in)
1995
115.1 mm (4.5 in)
1996
56.4 mm (2.2 in)
1997
40.6 mm (1.6 in)
1998
48.8 mm (1.9 in)
1999
53.3 mm (2.1 in)
2000
53.6 mm (2.1 in)
2001
49.5 mm (1.9 in)
2002
59.2 mm (2.3 in)
2003
72.6 mm (2.9 in)
2004
79.8 mm (3.1 in)
2005
49.8 mm (2.0 in)
2006
58.2 mm (2.3 in)
2007
44.2 mm (1.7 in)
2008
69.9 mm (2.8 in)
2009
36.8 mm (1.4 in)
Wettest five days (Rx5day)
The wettest five days of the year at Alton, 1905 to 2009. The record is 212.4 mm (8.4 in) in 2004, marked on the chart; the median year is 84.3 mm (3.3 in).
Wettest five days (Rx5day) at Alton by year
Year
Wettest five days (Rx5day)
1905
122.7 mm (4.8 in)
1906
121.2 mm (4.8 in)
1907
135.1 mm (5.3 in)
1908
18.0 mm (0.7 in)
1909
95.8 mm (3.8 in)
1910
76.2 mm (3.0 in)
1911
61.0 mm (2.4 in)
1912
51.3 mm (2.0 in)
1913
78.2 mm (3.1 in)
1914
80.7 mm (3.2 in)
1915
63.8 mm (2.5 in)
1916
68.9 mm (2.7 in)
1917
69.1 mm (2.7 in)
1918
87.1 mm (3.4 in)
1919
71.1 mm (2.8 in)
1920
92.3 mm (3.6 in)
1921
109.9 mm (4.3 in)
1922
83.8 mm (3.3 in)
1923
107.4 mm (4.2 in)
1924
84.1 mm (3.3 in)
1925
32.5 mm (1.3 in)
1926
84.3 mm (3.3 in)
1927
53.1 mm (2.1 in)
1928
88.4 mm (3.5 in)
1929
65.9 mm (2.6 in)
1930
101.3 mm (4.0 in)
1931
85.0 mm (3.3 in)
1932
105.0 mm (4.1 in)
1933
77.0 mm (3.0 in)
1934
145.2 mm (5.7 in)
1935
88.1 mm (3.5 in)
1936
62.7 mm (2.5 in)
1937
93.9 mm (3.7 in)
1938
96.6 mm (3.8 in)
1939
48.2 mm (1.9 in)
1940
100.1 mm (3.9 in)
1941
87.2 mm (3.4 in)
1942
84.9 mm (3.3 in)
1943
78.8 mm (3.1 in)
1944
130.7 mm (5.1 in)
1945
56.1 mm (2.2 in)
1946
110.4 mm (4.3 in)
1947
65.5 mm (2.6 in)
1948
71.4 mm (2.8 in)
1949
109.5 mm (4.3 in)
1950
62.2 mm (2.4 in)
1951
104.2 mm (4.1 in)
1952
64.3 mm (2.5 in)
1953
53.4 mm (2.1 in)
1954
94.2 mm (3.7 in)
1955
65.1 mm (2.6 in)
1956
61.5 mm (2.4 in)
1957
55.6 mm (2.2 in)
1958
38.9 mm (1.5 in)
1959
117.9 mm (4.6 in)
1960
99.5 mm (3.9 in)
1961
102.9 mm (4.1 in)
1962
110.8 mm (4.4 in)
1963
63.8 mm (2.5 in)
1964
95.7 mm (3.8 in)
1965
92.9 mm (3.7 in)
1966
62.5 mm (2.5 in)
1967
89.6 mm (3.5 in)
1968
115.9 mm (4.6 in)
1969
62.0 mm (2.4 in)
1970
145.8 mm (5.7 in)
1971
92.5 mm (3.6 in)
1972
85.6 mm (3.4 in)
1973
64.0 mm (2.5 in)
1974
78.7 mm (3.1 in)
1975
53.4 mm (2.1 in)
1976
60.2 mm (2.4 in)
1977
67.0 mm (2.6 in)
1978
117.6 mm (4.6 in)
1979
103.6 mm (4.1 in)
1980
69.1 mm (2.7 in)
1981
110.4 mm (4.3 in)
1982
100.0 mm (3.9 in)
1983
115.8 mm (4.6 in)
1984
83.3 mm (3.3 in)
1985
129.7 mm (5.1 in)
1986
78.0 mm (3.1 in)
1987
93.4 mm (3.7 in)
1988
154.7 mm (6.1 in)
1989
61.3 mm (2.4 in)
1990
96.0 mm (3.8 in)
1991
64.2 mm (2.5 in)
1992
110.5 mm (4.4 in)
1993
79.8 mm (3.1 in)
1994
94.0 mm (3.7 in)
1995
115.1 mm (4.5 in)
1996
128.2 mm (5.0 in)
1997
63.5 mm (2.5 in)
1998
60.2 mm (2.4 in)
1999
99.0 mm (3.9 in)
2000
80.2 mm (3.2 in)
2001
94.2 mm (3.7 in)
2002
78.5 mm (3.1 in)
2003
128.4 mm (5.1 in)
2004
212.4 mm (8.4 in)
2005
65.5 mm (2.6 in)
2006
68.4 mm (2.7 in)
2007
78.0 mm (3.1 in)
2008
83.9 mm (3.3 in)
2009
57.6 mm (2.3 in)
Longest dry spell (CDD)
The longest dry spell of the year at Alton, 1905 to 2009. The record is 62 days in 1952, marked on the chart; the median year is 29 days.
Longest dry spell (CDD) at Alton by year
Year
Longest dry spell (CDD)
1905
31 days
1906
11 days
1907
24 days
1908
14 days
1909
16 days
1910
50 days
1911
46 days
1912
31 days
1913
29 days
1914
53 days
1915
23 days
1916
32 days
1917
27 days
1918
19 days
1919
27 days
1920
20 days
1921
35 days
1922
23 days
1923
44 days
1924
28 days
1925
24 days
1926
34 days
1927
18 days
1928
29 days
1929
17 days
1930
31 days
1931
41 days
1932
28 days
1933
26 days
1934
28 days
1935
23 days
1936
35 days
1937
25 days
1938
28 days
1939
41 days
1940
26 days
1941
21 days
1942
38 days
1943
19 days
1944
33 days
1945
37 days
1946
27 days
1947
24 days
1948
31 days
1949
48 days
1950
29 days
1951
32 days
1952
62 days
1953
24 days
1954
26 days
1955
35 days
1956
60 days
1957
42 days
1958
54 days
1959
19 days
1960
48 days
1961
30 days
1962
37 days
1963
31 days
1964
34 days
1965
21 days
1966
25 days
1967
26 days
1968
55 days
1969
17 days
1970
57 days
1971
31 days
1972
22 days
1973
19 days
1974
46 days
1975
31 days
1976
42 days
1977
24 days
1978
29 days
1979
31 days
1980
35 days
1981
31 days
1982
20 days
1983
17 days
1984
29 days
1985
32 days
1986
48 days
1987
28 days
1988
24 days
1989
54 days
1990
20 days
1991
23 days
1992
22 days
1993
19 days
1994
38 days
1995
30 days
1996
21 days
1997
23 days
1998
45 days
1999
46 days
2000
15 days
2001
41 days
2002
29 days
2003
19 days
2004
25 days
2005
37 days
2006
24 days
2007
42 days
2008
16 days
2009
24 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
44 years with a frost
Across 44 years with a frost, the median last spring frost at Alton falls on 10 May and the median first autumn frost on 29 September, which leaves a median of 147 days between them.
Fitted over all years, the growing season changes by +3.4 days per decade at this station.
Frost dates and growing season at Alton
Measure
Median, all years
Earliest period
Recent period (1921 to 1952)
Recent against earliest
Fitted trend
Last spring frost
10 May
n/a
4 May
n/a
-3.5 days per decade
First autumn frost
29 September
n/a
29 September
n/a
-0.1 days per decade
Growing days
147 days
n/a
149 days
n/a
+3.4 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
94 years, 1910 to 2009
A day with at least 53.2 mm (2.1 in) of rain is expected about once in 2 years. A day with at least 127.5 mm (5.0 in) of rain is expected about once in 100 years.
Rainfall return levels at Alton: the daily rain expected about once in a given number of years
Expected about once in
A day with at least
Note
2 years
53.2 mm (2.1 in)
5 years
71.0 mm (2.8 in)
10 years
83.6 mm (3.3 in)
25 years
100.4 mm (4.0 in)
50 years
113.7 mm (4.5 in)
100 years
127.5 mm (5.0 in)
Longer than the 94 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, 94 years of values from 1910 to 2009.
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: 145.5 mm (5.7 in) in 1970; 137.7 mm (5.4 in) in 1988; 115.1 mm (4.5 in) in 1995.
Station Changes
3 suspected
3 changes were suspected in the annual mean temperature of Alton, at 1913, 1931 and 1947. Each is measured against neighbouring stations.
Relative to 5 neighbouring stations, the station's annual mean temperature from 1913 ran 0.3 C (0.6 F) lower than in the years before (possible change).
Relative to 5 neighbouring stations, the station's annual mean temperature from 1931 ran 0.2 C (0.4 F) higher than in the years before (likely change).
Relative to 5 neighbouring stations, the station's annual mean temperature from 1947 ran 0.3 C (0.5 F) higher than in the years before (likely change).
Suspected changes in the annual mean temperature at Alton, against neighbouring stations
Year
Shift (C)
Shift (F)
Strength
Neighbours
1913
-0.3
-0.6
possible
5
1931
+0.2
+0.4
likely
5
1947
+0.3
+0.5
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
Data for Alton standing records by year: CSV or JSON. Field meanings are on the data page.
Data for Alton 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 2026-10-16 (16 October 2026). Records are computed by this site and are not official.