Record highRecord low2026 daily maximum2026 daily minimum
The band shows the record high and record low for each calendar day at Thunder Bay A. 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 Thunder Bay A, with 2026 drawn through them
Month
Highest record high
Lowest record low
2026 highest maximum
2026 lowest minimum
Jan
8.3 C (46.9 F)
-41.1 C (-42.0 F)
n/a
n/a
Feb
12.2 C (54.0 F)
-40.0 C (-40.0 F)
n/a
n/a
Mar
22.8 C (73.0 F)
-36.7 C (-34.1 F)
n/a
n/a
Apr
28.3 C (82.9 F)
-22.2 C (-8.0 F)
n/a
n/a
May
34.8 C (94.6 F)
-8.9 C (16.0 F)
n/a
n/a
Jun
35.6 C (96.1 F)
-2.8 C (27.0 F)
n/a
n/a
Jul
37.2 C (99.0 F)
0.0 C (32.0 F)
n/a
n/a
Aug
40.3 C (104.5 F)
-1.1 C (30.0 F)
n/a
n/a
Sep
31.7 C (89.1 F)
-8.3 C (17.1 F)
n/a
n/a
Oct
28.3 C (82.9 F)
-13.3 C (8.1 F)
n/a
n/a
Nov
21.7 C (71.1 F)
-30.6 C (-23.1 F)
n/a
n/a
Dec
12.2 C (54.0 F)
-37.8 C (-36.0 F)
n/a
n/a
Which Years Hold Standing Records
1,464 standing records
Year with most
1,464 records at Thunder Bay A still stand. 1951 holds the most, with 50.
Standing records at Thunder Bay A by the year they were set
Year set
Standing records
1941
12
1942
41
1943
44
1944
41
1945
46
1946
44
1947
41
1948
32
1949
31
1950
48
1951
50
1952
35
1953
37
1954
36
1955
47
1956
48
1957
26
1958
45
1959
31
1960
12
1961
17
1962
36
1963
39
1964
45
1965
37
1966
30
1967
35
1968
34
1969
22
1970
16
1971
25
1972
30
1973
24
1974
25
1975
27
1976
38
1977
37
1978
22
1979
31
1980
33
1981
36
1982
28
1983
50
All-Time Record Progression
4 new records
4 all-time records were set at Thunder Bay A between 30 July 1975 and 7 August 1983. Each dot is a new record.
When Thunder Bay A set new all-time records
Date
Kind
Detail
1975-07-30
Record high maximum temperature
Record high maximum temperature 37.2 C (99.0 F)
1977-09-08
Record daily precipitation
Record daily precipitation 131.2 mm (5.2 in)
1982-01-09
Record low maximum temperature
Record low maximum temperature -29.5 C (-21.1 F)
1983-08-07
Record high maximum temperature
Record high maximum temperature 40.3 C (104.5 F)
Wettest Day of Each Month
Sep: 131.2 mm (5.2 in)
The wettest day on record for each calendar month at Thunder Bay A. The most was 131.2 mm (5.2 in) on 8 September 1977.
Record daily precipitation for each month at Thunder Bay A
Month
Record daily precipitation (mm)
Date
Jan
51.6 mm (2.0 in)
20 January 1956
Feb
33.5 mm (1.3 in)
26 February 1951
Mar
41.9 mm (1.6 in)
14 March 1957
Apr
69.3 mm (2.7 in)
30 April 1954
May
76.2 mm (3.0 in)
24 May 1971
Jun
49.3 mm (1.9 in)
4 June 1947
Jul
53.8 mm (2.1 in)
27 July 1973
Aug
87.1 mm (3.4 in)
19 August 1973
Sep
131.2 mm (5.2 in)
8 September 1977
Oct
47.8 mm (1.9 in)
9 October 1968
Nov
63.0 mm (2.5 in)
21 November 1973
Dec
42.7 mm (1.7 in)
5 December 1948
Period of Record Coverage
1941 to 1983
Complete yearUnder 90 percent of days
43 years of record at Thunder Bay A, 1941 to 1983. 1 years have data for under 90 percent of days and are left out of rankings: 1941.
Cooler than the station meanWarmer than the station mean
One stripe for each of 42 complete years at Thunder Bay A, 1942 to 1983. Blue stripes are years cooler than the station's own mean of 2.3 C (36.2 F); red stripes are warmer. The coolest year was 1950, at 0.4 C (32.8 F), and the warmest was 1981, at 3.5 C (38.3 F). The strongest colour marks a difference of 2.0 C (3.6 F).
Annual mean temperature at Thunder Bay A as warming stripes, 1942 to 1983
Year
Annual mean temperature
Difference from the station mean
1942
2.9 C
+0.57 C
1943
1.6 C
-0.75 C
1944
3.5 C
+1.13 C
1945
2.0 C
-0.39 C
1946
2.5 C
+0.18 C
1947
2.5 C
+0.13 C
1948
2.6 C
+0.24 C
1949
2.8 C
+0.49 C
1950
0.4 C
-1.91 C
1951
1.5 C
-0.87 C
1952
3.3 C
+0.95 C
1953
3.5 C
+1.16 C
1954
2.5 C
+0.17 C
1955
2.9 C
+0.53 C
1956
2.3 C
-0.06 C
1957
2.2 C
-0.18 C
1958
2.9 C
+0.51 C
1959
2.3 C
-0.09 C
1960
2.8 C
+0.44 C
1961
3.2 C
+0.85 C
1962
2.0 C
-0.36 C
1963
2.1 C
-0.25 C
1964
2.2 C
-0.11 C
1965
1.4 C
-0.96 C
1966
2.0 C
-0.32 C
1967
1.5 C
-0.89 C
1968
2.6 C
+0.25 C
1969
2.4 C
+0.07 C
1970
2.2 C
-0.17 C
1971
2.4 C
+0.08 C
1972
0.8 C
-1.60 C
1973
3.5 C
+1.15 C
1974
1.9 C
-0.46 C
1975
2.9 C
+0.58 C
1976
1.8 C
-0.52 C
1977
3.0 C
+0.65 C
1978
1.6 C
-0.74 C
1979
1.4 C
-0.99 C
1980
2.3 C
-0.01 C
1981
3.5 C
+1.17 C
1982
1.6 C
-0.73 C
1983
3.3 C
+0.94 C
The fitted trend in annual mean temperature here over 1942 to 1983 is -0.05 C (-0.24 to 0.15) per decade. The interval includes zero, so the trend is not clearly different from zero. In Fahrenheit: -0.1 F (-0.4 to 0.3) per decade. The slope is a straight line fitted to 42 complete years; the brackets give its 95 percent interval.
Fitted temperature trends per decade at Thunder Bay A
Measure
Per decade (C)
Per decade (F)
Period
Complete years
Reading
Annual mean temperature
-0.05 C (-0.24 to 0.15) per decade
-0.1 F (-0.4 to 0.3) per decade
1942 to 1983
42
Not clearly different from zero
Mean daily maximum
-0.02 C (-0.20 to 0.15) per decade
-0.04 F (-0.36 to 0.27) per decade
1942 to 1983
42
Not clearly different from zero
Mean daily minimum
-0.1 C (-0.3 to 0.2) per decade
-0.1 F (-0.5 to 0.3) per decade
1942 to 1983
42
Not clearly different from zero
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
1941 to 1983
Yearly extremes at Thunder Bay A: the record and the median year
Measure
Record
Year of the record
Median year
Years with a value
Hottest day (TXx)
40.3 C (104.5 F)
1983
32.8 C (91.0 F)
43
Coldest night (TNn)
-41.1 C (-42.0 F)
1951
-35.0 C (-31.0 F)
43
Wettest day (Rx1day)
131.2 mm (5.2 in)
1977
44.2 mm (1.7 in)
43
Wettest five days (Rx5day)
156.8 mm (6.2 in)
1977
75.3 mm (3.0 in)
43
Longest dry spell (CDD)
36 days
1978
20 days
43
Hottest day (TXx)
The hottest day of the year at Thunder Bay A, 1941 to 1983. The record is 40.3 C (104.5 F) in 1983, marked on the chart; the median year is 32.8 C (91.0 F).
Hottest day (TXx) at Thunder Bay A by year
Year
Hottest day (TXx)
1941
29.4 C (84.9 F)
1942
33.3 C (91.9 F)
1943
31.1 C (88.0 F)
1944
31.7 C (89.1 F)
1945
32.8 C (91.0 F)
1946
30.6 C (87.1 F)
1947
35.0 C (95.0 F)
1948
31.7 C (89.1 F)
1949
35.6 C (96.1 F)
1950
30.6 C (87.1 F)
1951
32.2 C (90.0 F)
1952
30.6 C (87.1 F)
1953
32.8 C (91.0 F)
1954
32.2 C (90.0 F)
1955
35.0 C (95.0 F)
1956
35.6 C (96.1 F)
1957
33.3 C (91.9 F)
1958
33.9 C (93.0 F)
1959
31.1 C (88.0 F)
1960
31.1 C (88.0 F)
1961
30.6 C (87.1 F)
1962
30.0 C (86.0 F)
1963
32.2 C (90.0 F)
1964
33.3 C (91.9 F)
1965
32.2 C (90.0 F)
1966
34.4 C (93.9 F)
1967
29.4 C (84.9 F)
1968
31.7 C (89.1 F)
1969
33.9 C (93.0 F)
1970
34.4 C (93.9 F)
1971
32.8 C (91.0 F)
1972
32.8 C (91.0 F)
1973
31.7 C (89.1 F)
1974
35.0 C (95.0 F)
1975
37.2 C (99.0 F)
1976
33.3 C (91.9 F)
1977
33.6 C (92.5 F)
1978
31.6 C (88.9 F)
1979
33.8 C (92.8 F)
1980
34.8 C (94.6 F)
1981
32.8 C (91.0 F)
1982
30.0 C (86.0 F)
1983
40.3 C (104.5 F)
Coldest night (TNn)
The coldest night of the year at Thunder Bay A, 1941 to 1983. The record is -41.1 C (-42.0 F) in 1951, marked on the chart; the median year is -35.0 C (-31.0 F).
Coldest night (TNn) at Thunder Bay A by year
Year
Coldest night (TNn)
1941
-22.8 C (-9.0 F)
1942
-33.9 C (-29.0 F)
1943
-36.7 C (-34.1 F)
1944
-33.3 C (-27.9 F)
1945
-33.9 C (-29.0 F)
1946
-34.4 C (-29.9 F)
1947
-32.8 C (-27.0 F)
1948
-38.3 C (-36.9 F)
1949
-34.4 C (-29.9 F)
1950
-40.6 C (-41.1 F)
1951
-41.1 C (-42.0 F)
1952
-32.2 C (-26.0 F)
1953
-35.0 C (-31.0 F)
1954
-35.0 C (-31.0 F)
1955
-36.7 C (-34.1 F)
1956
-33.3 C (-27.9 F)
1957
-38.3 C (-36.9 F)
1958
-32.8 C (-27.0 F)
1959
-34.4 C (-29.9 F)
1960
-32.2 C (-26.0 F)
1961
-33.3 C (-27.9 F)
1962
-36.7 C (-34.1 F)
1963
-38.3 C (-36.9 F)
1964
-32.8 C (-27.0 F)
1965
-37.8 C (-36.0 F)
1966
-35.0 C (-31.0 F)
1967
-39.4 C (-38.9 F)
1968
-38.3 C (-36.9 F)
1969
-28.9 C (-20.0 F)
1970
-40.0 C (-40.0 F)
1971
-34.4 C (-29.9 F)
1972
-37.2 C (-35.0 F)
1973
-34.4 C (-29.9 F)
1974
-36.7 C (-34.1 F)
1975
-35.0 C (-31.0 F)
1976
-37.8 C (-36.0 F)
1977
-37.9 C (-36.2 F)
1978
-34.0 C (-29.2 F)
1979
-39.0 C (-38.2 F)
1980
-31.6 C (-24.9 F)
1981
-36.9 C (-34.4 F)
1982
-40.4 C (-40.7 F)
1983
-33.3 C (-27.9 F)
Wettest day (Rx1day)
The wettest day of the year at Thunder Bay A, 1941 to 1983. The record is 131.2 mm (5.2 in) in 1977, marked on the chart; the median year is 44.2 mm (1.7 in).
Wettest day (Rx1day) at Thunder Bay A by year
Year
Wettest day (Rx1day)
1941
54.1 mm (2.1 in)
1942
35.6 mm (1.4 in)
1943
32.3 mm (1.3 in)
1944
48.8 mm (1.9 in)
1945
61.0 mm (2.4 in)
1946
40.1 mm (1.6 in)
1947
49.3 mm (1.9 in)
1948
52.6 mm (2.1 in)
1949
43.7 mm (1.7 in)
1950
46.7 mm (1.8 in)
1951
51.6 mm (2.0 in)
1952
37.3 mm (1.5 in)
1953
54.1 mm (2.1 in)
1954
69.3 mm (2.7 in)
1955
49.3 mm (1.9 in)
1956
51.6 mm (2.0 in)
1957
41.9 mm (1.6 in)
1958
69.9 mm (2.8 in)
1959
54.9 mm (2.2 in)
1960
33.3 mm (1.3 in)
1961
98.0 mm (3.9 in)
1962
44.2 mm (1.7 in)
1963
33.5 mm (1.3 in)
1964
43.4 mm (1.7 in)
1965
38.9 mm (1.5 in)
1966
29.5 mm (1.2 in)
1967
30.0 mm (1.2 in)
1968
47.8 mm (1.9 in)
1969
24.1 mm (0.9 in)
1970
35.1 mm (1.4 in)
1971
76.2 mm (3.0 in)
1972
38.1 mm (1.5 in)
1973
87.1 mm (3.4 in)
1974
37.6 mm (1.5 in)
1975
29.5 mm (1.2 in)
1976
25.7 mm (1.0 in)
1977
131.2 mm (5.2 in)
1978
23.4 mm (0.9 in)
1979
34.4 mm (1.4 in)
1980
44.7 mm (1.8 in)
1981
57.9 mm (2.3 in)
1982
52.4 mm (2.1 in)
1983
38.9 mm (1.5 in)
Wettest five days (Rx5day)
The wettest five days of the year at Thunder Bay A, 1941 to 1983. The record is 156.8 mm (6.2 in) in 1977, marked on the chart; the median year is 75.3 mm (3.0 in).
Wettest five days (Rx5day) at Thunder Bay A by year
Year
Wettest five days (Rx5day)
1941
98.6 mm (3.9 in)
1942
61.2 mm (2.4 in)
1943
43.5 mm (1.7 in)
1944
66.3 mm (2.6 in)
1945
83.1 mm (3.3 in)
1946
88.9 mm (3.5 in)
1947
81.2 mm (3.2 in)
1948
59.2 mm (2.3 in)
1949
100.3 mm (3.9 in)
1950
75.3 mm (3.0 in)
1951
68.6 mm (2.7 in)
1952
42.6 mm (1.7 in)
1953
78.2 mm (3.1 in)
1954
98.6 mm (3.9 in)
1955
84.7 mm (3.3 in)
1956
107.7 mm (4.2 in)
1957
55.9 mm (2.2 in)
1958
92.5 mm (3.6 in)
1959
80.5 mm (3.2 in)
1960
54.9 mm (2.2 in)
1961
116.1 mm (4.6 in)
1962
71.4 mm (2.8 in)
1963
59.8 mm (2.4 in)
1964
76.2 mm (3.0 in)
1965
64.5 mm (2.5 in)
1966
50.7 mm (2.0 in)
1967
49.9 mm (2.0 in)
1968
99.9 mm (3.9 in)
1969
38.9 mm (1.5 in)
1970
77.5 mm (3.1 in)
1971
123.7 mm (4.9 in)
1972
58.0 mm (2.3 in)
1973
92.0 mm (3.6 in)
1974
51.4 mm (2.0 in)
1975
57.5 mm (2.3 in)
1976
69.4 mm (2.7 in)
1977
156.8 mm (6.2 in)
1978
56.1 mm (2.2 in)
1979
76.8 mm (3.0 in)
1980
74.5 mm (2.9 in)
1981
72.7 mm (2.9 in)
1982
125.1 mm (4.9 in)
1983
88.9 mm (3.5 in)
Longest dry spell (CDD)
The longest dry spell of the year at Thunder Bay A, 1941 to 1983. The record is 36 days in 1978, marked on the chart; the median year is 20 days.
Longest dry spell (CDD) at Thunder Bay A by year
Year
Longest dry spell (CDD)
1941
14 days
1942
27 days
1943
19 days
1944
25 days
1945
14 days
1946
15 days
1947
25 days
1948
18 days
1949
21 days
1950
14 days
1951
13 days
1952
25 days
1953
21 days
1954
14 days
1955
14 days
1956
21 days
1957
19 days
1958
33 days
1959
21 days
1960
34 days
1961
35 days
1962
28 days
1963
22 days
1964
15 days
1965
12 days
1966
21 days
1967
15 days
1968
31 days
1969
24 days
1970
20 days
1971
17 days
1972
17 days
1973
21 days
1974
13 days
1975
19 days
1976
24 days
1977
19 days
1978
36 days
1979
16 days
1980
15 days
1981
25 days
1982
17 days
1983
21 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
42 years with a frost
Across 42 years with a frost, the median last spring frost at Thunder Bay A falls on 31 May and the median first autumn frost on 12 September, which leaves a median of 106 days between them.
Fitted over all years, the growing season changes by +2.6 days per decade at this station.
Frost dates and growing season at Thunder Bay A
Measure
Median, all years
Earliest period
Recent period (1954 to 1983)
Recent against earliest
Fitted trend
Last spring frost
31 May
n/a
29 May
n/a
-0.5 days per decade
First autumn frost
12 September
n/a
15 September
n/a
+2.1 days per decade
Growing days
106 days
n/a
107 days
n/a
+2.6 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
42 years, 1942 to 1983
A day with at least 42.9 mm (1.7 in) of rain is expected about once in 2 years. A day with at least 129.2 mm (5.1 in) of rain is expected about once in 100 years.
Rainfall return levels at Thunder Bay A: the daily rain expected about once in a given number of years
Expected about once in
A day with at least
Note
2 years
42.9 mm (1.7 in)
5 years
59.2 mm (2.3 in)
10 years
72.3 mm (2.8 in)
25 years
92.0 mm (3.6 in)
50 years
109.3 mm (4.3 in)
Longer than the 42 years of record
100 years
129.2 mm (5.1 in)
Longer than the 42 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, 42 years of values from 1942 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: 131.2 mm (5.2 in) in 1977; 98.0 mm (3.9 in) in 1961; 87.1 mm (3.4 in) in 1973.
Station Changes
No change in the annual mean temperature of this station was found against its neighbours.
Download the Data
Data for Thunder Bay A standing records by year: CSV or JSON. Field meanings are on the data page.
Data for Thunder Bay A 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.