Record highRecord low2026 daily maximum2026 daily minimum
The band shows the record high and record low for each calendar day at Sion. 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 Sion, with 2026 drawn through them
Month
Highest record high
Lowest record low
2026 highest maximum
2026 lowest minimum
Jan
13.3 C (55.9 F)
-51.7 C (-61.1 F)
n/a
n/a
Feb
17.8 C (64.0 F)
-52.8 C (-63.0 F)
n/a
n/a
Mar
21.1 C (70.0 F)
-40.0 C (-40.0 F)
n/a
n/a
Apr
28.9 C (84.0 F)
-34.4 C (-29.9 F)
n/a
n/a
May
35.0 C (95.0 F)
-12.2 C (10.0 F)
n/a
n/a
Jun
36.7 C (98.1 F)
-8.9 C (16.0 F)
n/a
n/a
Jul
38.9 C (102.0 F)
-4.4 C (24.1 F)
n/a
n/a
Aug
33.9 C (93.0 F)
-4.4 C (24.1 F)
n/a
n/a
Sep
34.0 C (93.2 F)
-13.9 C (7.0 F)
n/a
n/a
Oct
30.0 C (86.0 F)
-26.1 C (-15.0 F)
n/a
n/a
Nov
23.0 C (73.4 F)
-36.1 C (-33.0 F)
n/a
n/a
Dec
18.3 C (64.9 F)
-50.0 C (-58.0 F)
n/a
n/a
Which Years Hold Standing Records
1,464 standing records
Year with most
1,464 records at Sion still stand. 1936 holds the most, with 64.
Standing records at Sion by the year they were set
Year set
Standing records
1908
5
1911
24
1912
34
1913
22
1914
13
1915
21
1916
31
1917
31
1918
23
1919
50
1920
9
1921
23
1922
11
1923
21
1924
42
1925
29
1926
18
1927
18
1928
19
1929
10
1930
5
1931
4
1932
14
1933
20
1934
28
1935
34
1936
64
1937
13
1938
19
1939
33
1940
26
1941
22
1942
39
1943
39
1944
26
1945
23
1946
13
1947
4
1948
14
1949
18
1950
18
1951
23
1952
15
1953
11
1954
54
1955
15
1956
32
1957
21
1958
11
1959
17
1960
5
1961
24
1962
13
1963
17
1964
13
1965
14
1966
18
1967
17
1968
19
1969
10
1970
29
1971
9
1972
8
1973
6
1974
6
1975
4
1976
16
1977
3
1978
8
1979
12
1980
24
1981
25
1982
16
1983
19
All-Time Record Progression
3 new records
3 all-time records were set at Sion between 31 July 1953 and 11 August 1983. Each dot is a new record.
When Sion set new all-time records
Date
Kind
Detail
1953-07-31
Record daily precipitation
Record daily precipitation 95.3 mm (3.8 in)
1955-07-18
Record high minimum temperature
Record high minimum temperature 19.4 C (66.9 F)
1983-08-11
Record high minimum temperature
Record high minimum temperature 20.5 C (68.9 F)
Wettest Day of Each Month
Jul: 95.3 mm (3.8 in)
The wettest day on record for each calendar month at Sion. The most was 95.3 mm (3.8 in) on 31 July 1953.
Record daily precipitation for each month at Sion
Month
Record daily precipitation (mm)
Date
Jan
27.9 mm (1.1 in)
1 January 1935
Feb
24.1 mm (0.9 in)
21 February 1956
Mar
50.8 mm (2.0 in)
9 March 1923
Apr
30.5 mm (1.2 in)
22 April 1924
May
47.2 mm (1.9 in)
8 May 1953
Jun
85.6 mm (3.4 in)
4 June 1914
Jul
95.3 mm (3.8 in)
31 July 1953
Aug
54.6 mm (2.1 in)
5 August 1969
Sep
63.5 mm (2.5 in)
4 September 1969
Oct
71.1 mm (2.8 in)
30 October 1924
Nov
30.5 mm (1.2 in)
16 November 1942
Dec
45.7 mm (1.8 in)
17 December 1916
Period of Record Coverage
1908 to 1983
Complete yearUnder 90 percent of days
74 years of record at Sion, 1908 to 1983. 17 years have data for under 90 percent of days and are left out of rankings: 1908, 1919, 1920, 1921, 1922, 1927, 1930, 1931 and others.
Cooler than the station meanWarmer than the station mean
One stripe for each of 49 complete years at Sion, 1911 to 1983. Blue stripes are years cooler than the station's own mean of 2.1 C (35.7 F); red stripes are warmer. The coolest year was 1924, at -0.4 C (31.3 F), and the warmest was 1981, at 5.0 C (41.0 F). The strongest colour marks a difference of 3.0 C (5.4 F).
Annual mean temperature at Sion as warming stripes, 1911 to 1983
Year
Annual mean temperature
Difference from the station mean
1911
2.2 C
+0.16 C
1912
2.8 C
+0.70 C
1914
1.6 C
-0.47 C
1915
2.8 C
+0.71 C
1916
-0.1 C
-2.17 C
1918
1.4 C
-0.72 C
1923
2.1 C
+0.00 C
1924
-0.4 C
-2.45 C
1925
0.4 C
-1.64 C
1926
2.4 C
+0.33 C
1928
2.9 C
+0.78 C
1929
1.6 C
-0.44 C
1932
1.0 C
-1.13 C
1933
-0.2 C
-2.30 C
1934
2.6 C
+0.47 C
1935
0.2 C
-1.85 C
1936
-0.1 C
-2.14 C
1937
1.3 C
-0.77 C
1938
3.5 C
+1.42 C
1939
3.9 C
+1.84 C
1940
3.0 C
+0.94 C
1941
2.7 C
+0.58 C
1942
4.0 C
+1.92 C
1943
4.3 C
+2.24 C
1944
3.6 C
+1.53 C
1946
1.6 C
-0.47 C
1954
2.5 C
+0.40 C
1955
1.1 C
-1.00 C
1956
2.5 C
+0.43 C
1957
2.8 C
+0.71 C
1958
3.4 C
+1.28 C
1959
2.1 C
+0.05 C
1960
2.5 C
+0.37 C
1961
2.2 C
+0.16 C
1963
3.0 C
+0.94 C
1966
1.1 C
-1.01 C
1967
2.2 C
+0.07 C
1968
1.6 C
-0.51 C
1969
1.0 C
-1.07 C
1970
1.0 C
-1.13 C
1971
1.1 C
-0.95 C
1973
1.6 C
-0.51 C
1975
1.5 C
-0.58 C
1976
3.8 C
+1.72 C
1979
2.2 C
+0.07 C
1980
3.0 C
+0.89 C
1981
5.0 C
+2.94 C
1982
1.0 C
-1.05 C
1983
2.8 C
+0.67 C
The fitted trend in annual mean temperature here over 1911 to 1983 is 0.1 C (-0.1 to 0.3) per decade. The interval includes zero, so the trend is not clearly different from zero. In Fahrenheit: 0.2 F (-0.1 to 0.5) per decade. The slope is a straight line fitted to 49 complete years; the brackets give its 95 percent interval.
Fitted temperature trends per decade at Sion
Measure
Per decade (C)
Per decade (F)
Period
Complete years
Reading
Annual mean temperature
0.1 C (-0.1 to 0.3) per decade
0.2 F (-0.1 to 0.5) per decade
1911 to 1983
49
Not clearly different from zero
Mean daily maximum
-0.20 C (-0.42 to 0.01) per decade
-0.36 F (-0.75 to 0.03) per decade
1911 to 1983
49
Not clearly different from zero
Mean daily minimum
0.4 C (0.3 to 0.6) per decade
0.8 F (0.5 to 1.1) per decade
1911 to 1983
49
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
1906 to 1983
Yearly extremes at Sion: the record and the median year
Measure
Record
Year of the record
Median year
Years with a value
Hottest day (TXx)
38.9 C (102.0 F)
1924
31.1 C (88.0 F)
74
Coldest night (TNn)
-52.8 C (-63.0 F)
1936
-38.3 C (-36.9 F)
74
Wettest day (Rx1day)
95.3 mm (3.8 in)
1953
34.6 mm (1.4 in)
78
Wettest five days (Rx5day)
179.4 mm (7.1 in)
1914
59.4 mm (2.3 in)
78
Longest dry spell (CDD)
69 days
1942
29 days
78
Hottest day (TXx)
The hottest day of the year at Sion, 1906 to 1983. The record is 38.9 C (102.0 F) in 1924, marked on the chart; the median year is 31.1 C (88.0 F).
Hottest day (TXx) at Sion by year
Year
Hottest day (TXx)
1906
n/a
1907
n/a
1908
13.3 C (55.9 F)
1909
n/a
1910
n/a
1911
32.2 C (90.0 F)
1912
34.4 C (93.9 F)
1913
30.0 C (86.0 F)
1914
31.7 C (89.1 F)
1915
30.6 C (87.1 F)
1916
27.8 C (82.0 F)
1917
32.2 C (90.0 F)
1918
32.2 C (90.0 F)
1919
31.1 C (88.0 F)
1920
33.9 C (93.0 F)
1921
27.8 C (82.0 F)
1922
31.1 C (88.0 F)
1923
28.3 C (82.9 F)
1924
38.9 C (102.0 F)
1925
31.1 C (88.0 F)
1926
32.2 C (90.0 F)
1927
26.7 C (80.1 F)
1928
33.3 C (91.9 F)
1929
29.4 C (84.9 F)
1930
17.8 C (64.0 F)
1931
23.3 C (73.9 F)
1932
31.1 C (88.0 F)
1933
32.2 C (90.0 F)
1934
29.4 C (84.9 F)
1935
31.7 C (89.1 F)
1936
34.4 C (93.9 F)
1937
36.7 C (98.1 F)
1938
32.2 C (90.0 F)
1939
36.1 C (97.0 F)
1940
35.0 C (95.0 F)
1941
35.0 C (95.0 F)
1942
33.9 C (93.0 F)
1943
30.6 C (87.1 F)
1944
30.0 C (86.0 F)
1945
36.7 C (98.1 F)
1946
31.7 C (89.1 F)
1947
29.4 C (84.9 F)
1948
32.2 C (90.0 F)
1949
33.3 C (91.9 F)
1950
34.4 C (93.9 F)
1951
32.2 C (90.0 F)
1952
30.0 C (86.0 F)
1953
28.9 C (84.0 F)
1954
30.6 C (87.1 F)
1955
32.2 C (90.0 F)
1956
31.7 C (89.1 F)
1957
29.4 C (84.9 F)
1958
31.1 C (88.0 F)
1959
32.2 C (90.0 F)
1960
32.2 C (90.0 F)
1961
33.9 C (93.0 F)
1962
28.9 C (84.0 F)
1963
32.2 C (90.0 F)
1964
31.7 C (89.1 F)
1965
31.1 C (88.0 F)
1966
29.4 C (84.9 F)
1967
33.3 C (91.9 F)
1968
31.1 C (88.0 F)
1969
31.1 C (88.0 F)
1970
33.9 C (93.0 F)
1971
30.6 C (87.1 F)
1972
31.1 C (88.0 F)
1973
31.1 C (88.0 F)
1974
28.9 C (84.0 F)
1975
30.0 C (86.0 F)
1976
28.9 C (84.0 F)
1977
21.7 C (71.1 F)
1978
23.0 C (73.4 F)
1979
30.0 C (86.0 F)
1980
29.0 C (84.2 F)
1981
34.0 C (93.2 F)
1982
31.0 C (87.8 F)
1983
31.5 C (88.7 F)
Coldest night (TNn)
The coldest night of the year at Sion, 1906 to 1983. The record is -52.8 C (-63.0 F) in 1936, marked on the chart; the median year is -38.3 C (-36.9 F).
Coldest night (TNn) at Sion by year
Year
Coldest night (TNn)
1906
n/a
1907
n/a
1908
-31.7 C (-25.1 F)
1909
n/a
1910
n/a
1911
-45.6 C (-50.1 F)
1912
-42.8 C (-45.0 F)
1913
-42.2 C (-44.0 F)
1914
-38.3 C (-36.9 F)
1915
-30.6 C (-23.1 F)
1916
-47.8 C (-54.0 F)
1917
-47.2 C (-53.0 F)
1918
-44.4 C (-47.9 F)
1919
-43.9 C (-47.0 F)
1920
-49.4 C (-56.9 F)
1921
-44.4 C (-47.9 F)
1922
-37.8 C (-36.0 F)
1923
-40.6 C (-41.1 F)
1924
-50.0 C (-58.0 F)
1925
-36.7 C (-34.1 F)
1926
-32.2 C (-26.0 F)
1927
-43.3 C (-45.9 F)
1928
-37.8 C (-36.0 F)
1929
-46.7 C (-52.1 F)
1930
-41.1 C (-42.0 F)
1931
-30.0 C (-22.0 F)
1932
-43.3 C (-45.9 F)
1933
-46.7 C (-52.1 F)
1934
-45.6 C (-50.1 F)
1935
-51.7 C (-61.1 F)
1936
-52.8 C (-63.0 F)
1937
-45.0 C (-49.0 F)
1938
-46.7 C (-52.1 F)
1939
-43.3 C (-45.9 F)
1940
-34.4 C (-29.9 F)
1941
-37.2 C (-35.0 F)
1942
-33.3 C (-27.9 F)
1943
-45.6 C (-50.1 F)
1944
-33.3 C (-27.9 F)
1945
-33.9 C (-29.0 F)
1946
-35.0 C (-31.0 F)
1947
-43.3 C (-45.9 F)
1948
-33.9 C (-29.0 F)
1949
-37.8 C (-36.0 F)
1950
-41.1 C (-42.0 F)
1951
-36.7 C (-34.1 F)
1952
-37.8 C (-36.0 F)
1953
-38.3 C (-36.9 F)
1954
-40.0 C (-40.0 F)
1955
-35.0 C (-31.0 F)
1956
-37.8 C (-36.0 F)
1957
-33.3 C (-27.9 F)
1958
-31.7 C (-25.1 F)
1959
-36.1 C (-33.0 F)
1960
-31.7 C (-25.1 F)
1961
-38.3 C (-36.9 F)
1962
-42.8 C (-45.0 F)
1963
-36.1 C (-33.0 F)
1964
-32.2 C (-26.0 F)
1965
-35.6 C (-32.1 F)
1966
-40.6 C (-41.1 F)
1967
-35.0 C (-31.0 F)
1968
-40.0 C (-40.0 F)
1969
-44.4 C (-47.9 F)
1970
-43.9 C (-47.0 F)
1971
-43.9 C (-47.0 F)
1972
-46.1 C (-51.0 F)
1973
-35.6 C (-32.1 F)
1974
-42.2 C (-44.0 F)
1975
-36.7 C (-34.1 F)
1976
-44.4 C (-47.9 F)
1977
-31.7 C (-25.1 F)
1978
-35.5 C (-31.9 F)
1979
-36.0 C (-32.8 F)
1980
-36.5 C (-33.7 F)
1981
-33.5 C (-28.3 F)
1982
-39.5 C (-39.1 F)
1983
-36.0 C (-32.8 F)
Wettest day (Rx1day)
The wettest day of the year at Sion, 1906 to 1983. The record is 95.3 mm (3.8 in) in 1953, marked on the chart; the median year is 34.6 mm (1.4 in).
Wettest day (Rx1day) at Sion by year
Year
Wettest day (Rx1day)
1906
50.8 mm (2.0 in)
1907
30.0 mm (1.2 in)
1908
65.0 mm (2.6 in)
1909
45.7 mm (1.8 in)
1910
28.4 mm (1.1 in)
1911
31.8 mm (1.3 in)
1912
47.8 mm (1.9 in)
1913
35.3 mm (1.4 in)
1914
85.6 mm (3.4 in)
1915
43.7 mm (1.7 in)
1916
45.7 mm (1.8 in)
1917
33.0 mm (1.3 in)
1918
35.6 mm (1.4 in)
1919
30.5 mm (1.2 in)
1920
22.9 mm (0.9 in)
1921
30.5 mm (1.2 in)
1922
15.2 mm (0.6 in)
1923
50.8 mm (2.0 in)
1924
71.1 mm (2.8 in)
1925
38.1 mm (1.5 in)
1926
43.2 mm (1.7 in)
1927
45.7 mm (1.8 in)
1928
40.6 mm (1.6 in)
1929
37.1 mm (1.5 in)
1930
3.3 mm (0.13 in)
1931
22.9 mm (0.9 in)
1932
23.1 mm (0.9 in)
1933
52.3 mm (2.1 in)
1934
41.1 mm (1.6 in)
1935
27.9 mm (1.1 in)
1936
28.2 mm (1.1 in)
1937
50.5 mm (2.0 in)
1938
32.5 mm (1.3 in)
1939
25.4 mm (1.0 in)
1940
19.1 mm (0.8 in)
1941
31.8 mm (1.3 in)
1942
38.1 mm (1.5 in)
1943
25.4 mm (1.0 in)
1944
45.7 mm (1.8 in)
1945
30.5 mm (1.2 in)
1946
27.4 mm (1.1 in)
1947
25.4 mm (1.0 in)
1948
27.9 mm (1.1 in)
1949
21.1 mm (0.8 in)
1950
19.1 mm (0.8 in)
1951
49.8 mm (2.0 in)
1952
63.5 mm (2.5 in)
1953
95.3 mm (3.8 in)
1954
26.7 mm (1.1 in)
1955
31.5 mm (1.2 in)
1956
46.2 mm (1.8 in)
1957
39.9 mm (1.6 in)
1958
49.3 mm (1.9 in)
1959
20.3 mm (0.8 in)
1960
33.5 mm (1.3 in)
1961
35.3 mm (1.4 in)
1962
21.8 mm (0.9 in)
1963
23.9 mm (0.9 in)
1964
22.6 mm (0.9 in)
1965
48.5 mm (1.9 in)
1966
47.5 mm (1.9 in)
1967
14.2 mm (0.6 in)
1968
24.6 mm (1.0 in)
1969
63.5 mm (2.5 in)
1970
33.8 mm (1.3 in)
1971
36.6 mm (1.4 in)
1972
28.7 mm (1.1 in)
1973
36.8 mm (1.4 in)
1974
93.7 mm (3.7 in)
1975
33.0 mm (1.3 in)
1976
46.0 mm (1.8 in)
1977
25.7 mm (1.0 in)
1978
10.8 mm (0.4 in)
1979
37.6 mm (1.5 in)
1980
40.6 mm (1.6 in)
1981
27.8 mm (1.1 in)
1982
41.4 mm (1.6 in)
1983
46.0 mm (1.8 in)
Wettest five days (Rx5day)
The wettest five days of the year at Sion, 1906 to 1983. The record is 179.4 mm (7.1 in) in 1914, marked on the chart; the median year is 59.4 mm (2.3 in).
Wettest five days (Rx5day) at Sion by year
Year
Wettest five days (Rx5day)
1906
104.4 mm (4.1 in)
1907
36.3 mm (1.4 in)
1908
88.6 mm (3.5 in)
1909
57.1 mm (2.2 in)
1910
42.4 mm (1.7 in)
1911
98.5 mm (3.9 in)
1912
55.4 mm (2.2 in)
1913
82.8 mm (3.3 in)
1914
179.4 mm (7.1 in)
1915
71.1 mm (2.8 in)
1916
56.6 mm (2.2 in)
1917
58.4 mm (2.3 in)
1918
42.4 mm (1.7 in)
1919
47.0 mm (1.9 in)
1920
56.0 mm (2.2 in)
1921
43.2 mm (1.7 in)
1922
22.8 mm (0.9 in)
1923
64.8 mm (2.6 in)
1924
88.4 mm (3.5 in)
1925
91.5 mm (3.6 in)
1926
63.5 mm (2.5 in)
1927
63.5 mm (2.5 in)
1928
81.2 mm (3.2 in)
1929
70.1 mm (2.8 in)
1930
3.3 mm (0.13 in)
1931
30.5 mm (1.2 in)
1932
31.3 mm (1.2 in)
1933
74.4 mm (2.9 in)
1934
43.6 mm (1.7 in)
1935
40.9 mm (1.6 in)
1936
75.4 mm (3.0 in)
1937
104.3 mm (4.1 in)
1938
48.5 mm (1.9 in)
1939
54.9 mm (2.2 in)
1940
33.8 mm (1.3 in)
1941
57.2 mm (2.3 in)
1942
114.4 mm (4.5 in)
1943
64.9 mm (2.6 in)
1944
97.9 mm (3.9 in)
1945
45.8 mm (1.8 in)
1946
53.3 mm (2.1 in)
1947
72.4 mm (2.9 in)
1948
49.0 mm (1.9 in)
1949
46.3 mm (1.8 in)
1950
50.1 mm (2.0 in)
1951
87.9 mm (3.5 in)
1952
126.8 mm (5.0 in)
1953
172.0 mm (6.8 in)
1954
59.2 mm (2.3 in)
1955
64.0 mm (2.5 in)
1956
65.5 mm (2.6 in)
1957
68.3 mm (2.7 in)
1958
84.6 mm (3.3 in)
1959
42.1 mm (1.7 in)
1960
54.9 mm (2.2 in)
1961
70.7 mm (2.8 in)
1962
38.8 mm (1.5 in)
1963
35.4 mm (1.4 in)
1964
58.1 mm (2.3 in)
1965
91.3 mm (3.6 in)
1966
66.4 mm (2.6 in)
1967
23.3 mm (0.9 in)
1968
43.8 mm (1.7 in)
1969
110.8 mm (4.4 in)
1970
59.5 mm (2.3 in)
1971
80.6 mm (3.2 in)
1972
41.1 mm (1.6 in)
1973
66.6 mm (2.6 in)
1974
118.8 mm (4.7 in)
1975
51.2 mm (2.0 in)
1976
84.6 mm (3.3 in)
1977
27.2 mm (1.1 in)
1978
18.3 mm (0.7 in)
1979
61.8 mm (2.4 in)
1980
58.4 mm (2.3 in)
1981
51.2 mm (2.0 in)
1982
89.0 mm (3.5 in)
1983
64.2 mm (2.5 in)
Longest dry spell (CDD)
The longest dry spell of the year at Sion, 1906 to 1983. The record is 69 days in 1942, marked on the chart; the median year is 29 days.
Longest dry spell (CDD) at Sion by year
Year
Longest dry spell (CDD)
1906
18 days
1907
41 days
1908
15 days
1909
30 days
1910
26 days
1911
28 days
1912
29 days
1913
33 days
1914
29 days
1915
26 days
1916
19 days
1917
28 days
1918
43 days
1919
52 days
1920
35 days
1921
31 days
1922
31 days
1923
34 days
1924
44 days
1925
29 days
1926
52 days
1927
26 days
1928
44 days
1929
26 days
1930
16 days
1931
27 days
1932
26 days
1933
21 days
1934
27 days
1935
25 days
1936
38 days
1937
45 days
1938
58 days
1939
41 days
1940
67 days
1941
49 days
1942
69 days
1943
65 days
1944
26 days
1945
45 days
1946
33 days
1947
28 days
1948
22 days
1949
41 days
1950
30 days
1951
28 days
1952
34 days
1953
39 days
1954
25 days
1955
23 days
1956
25 days
1957
21 days
1958
27 days
1959
29 days
1960
16 days
1961
28 days
1962
23 days
1963
20 days
1964
21 days
1965
38 days
1966
35 days
1967
29 days
1968
27 days
1969
24 days
1970
25 days
1971
32 days
1972
23 days
1973
39 days
1974
35 days
1975
25 days
1976
36 days
1977
35 days
1978
13 days
1979
30 days
1980
41 days
1981
60 days
1982
28 days
1983
16 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
49 years with a frost
Across 49 years with a frost, the median last spring frost at Sion falls on 6 June and the median first autumn frost on 2 September, which leaves a median of 89 days between them.
Fitted over all years, the growing season changes by +9.8 days per decade at this station.
Frost dates and growing season at Sion
Measure
Median, all years
Earliest period
Recent period (1939 to 1983)
Recent against earliest
Fitted trend
Last spring frost
6 June
n/a
30 May
n/a
-3.0 days per decade
First autumn frost
2 September
n/a
13 September
n/a
+6.8 days per decade
Growing days
89 days
n/a
105 days
n/a
+9.8 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
62 years, 1907 to 1983
A day with at least 35.8 mm (1.4 in) of rain is expected about once in 2 years. A day with at least 100.3 mm (3.9 in) of rain is expected about once in 100 years.
Rainfall return levels at Sion: the daily rain expected about once in a given number of years
Expected about once in
A day with at least
Note
2 years
35.8 mm (1.4 in)
5 years
50.2 mm (2.0 in)
10 years
60.8 mm (2.4 in)
25 years
75.5 mm (3.0 in)
50 years
87.5 mm (3.4 in)
100 years
100.3 mm (3.9 in)
Longer than the 62 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, 62 years of values from 1907 to 1983.
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: 95.3 mm (3.8 in) in 1953; 93.7 mm (3.7 in) in 1974; 85.6 mm (3.4 in) in 1914.
Station Changes
1 suspected
One change was suspected in the annual mean temperature of Sion, at 1937. Each is measured against neighbouring stations.
Relative to 5 neighbouring stations, the station's annual mean temperature from 1937 ran 0.9 C (1.7 F) higher than in the years before (likely change).
Suspected changes in the annual mean temperature at Sion, against neighbouring stations
Year
Shift (C)
Shift (F)
Strength
Neighbours
1937
+0.9
+1.7
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 Sion standing records by year: CSV or JSON. Field meanings are on the data page.
Data for Sion 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 2026-10-14 (14 October 2026). Records are computed by this site and are not official.