Record envelope, standing records and threshold days for Blackwater Dam (USC00270741), New Hampshire, United States, with 44 years of record.
Key Facts for Blackwater Dam
Blackwater Dam (USC00270741) is a weather station in New Hampshire, United States at 43.32 latitude and -71.72 longitude, 183 m (600 ft) above sea level.
The station reports from 1948 to 1991, 44 years of record.
1,464 records set at Blackwater Dam still stand.
Records are tracked for tmax, tmin, prcp, snow, snwd: an element needs 30 years of data to be eligible.
Blackwater Dam set a daily record high maximum temperature of 34.4 C (93.9 F) on 29 June 1991.
About the Station
Location: New Hampshire, United States, 43.32 latitude, -71.72 longitude.
Elevation: 183 m (600 ft).
Period of record: 1948 to 1991, 44 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 Blackwater Dam. 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 Blackwater Dam, 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)
-35.6 C (-32.1 F)
n/a
n/a
Feb
18.9 C (66.0 F)
-33.3 C (-27.9 F)
n/a
n/a
Mar
27.2 C (81.0 F)
-27.2 C (-17.0 F)
n/a
n/a
Apr
33.3 C (91.9 F)
-15.0 C (5.0 F)
n/a
n/a
May
35.0 C (95.0 F)
-5.6 C (21.9 F)
n/a
n/a
Jun
35.6 C (96.1 F)
-1.1 C (30.0 F)
n/a
n/a
Jul
37.2 C (99.0 F)
2.8 C (37.0 F)
n/a
n/a
Aug
36.1 C (97.0 F)
-1.1 C (30.0 F)
n/a
n/a
Sep
34.4 C (93.9 F)
-4.4 C (24.1 F)
n/a
n/a
Oct
31.1 C (88.0 F)
-10.0 C (14.0 F)
n/a
n/a
Nov
26.7 C (80.1 F)
-17.8 C (0.0 F)
n/a
n/a
Dec
18.9 C (66.0 F)
-28.9 C (-20.0 F)
n/a
n/a
Which Years Hold Standing Records
1,464 standing records
Year with most
1,464 records at Blackwater Dam still stand. 1949 holds the most, with 61.
Standing records at Blackwater Dam by the year they were set
Year set
Standing records
1948
21
1949
61
1950
36
1951
42
1952
24
1953
56
1954
37
1955
35
1956
46
1957
42
1958
33
1959
41
1960
21
1961
36
1962
34
1963
40
1964
43
1965
36
1966
32
1967
49
1968
38
1969
24
1970
28
1971
29
1972
27
1973
21
1974
33
1975
25
1976
52
1977
30
1978
23
1979
49
1980
19
1981
32
1982
40
1983
29
1984
27
1985
16
1986
23
1987
23
1988
39
1989
36
1990
24
1991
12
All-Time Record Progression
1 new records
1 all-time records were set at Blackwater Dam between 26 December 1980 and 26 December 1980. Each dot is a new record.
When Blackwater Dam set new all-time records
Date
Kind
Detail
1980-12-26
Record low maximum temperature
Record low maximum temperature -23.9 C (-11.0 F)
Wettest Day of Each Month
Aug: 113.0 mm (4.4 in)
The wettest day on record for each calendar month at Blackwater Dam. The most was 113.0 mm (4.4 in) on 31 August 1954.
Record daily precipitation for each month at Blackwater Dam
Month
Record daily precipitation (mm)
Date
Jan
63.2 mm (2.5 in)
30 January 1990
Feb
67.3 mm (2.6 in)
26 February 1981
Mar
54.1 mm (2.1 in)
14 March 1977
Apr
75.4 mm (3.0 in)
29 April 1988
May
83.6 mm (3.3 in)
30 May 1984
Jun
95.0 mm (3.7 in)
23 June 1987
Jul
96.5 mm (3.8 in)
20 July 1972
Aug
113.0 mm (4.4 in)
31 August 1954
Sep
109.2 mm (4.3 in)
13 September 1960
Oct
101.6 mm (4.0 in)
7 October 1962
Nov
79.2 mm (3.1 in)
2 November 1988
Dec
91.4 mm (3.6 in)
27 December 1969
Period of Record Coverage
1948 to 1991
Complete yearUnder 90 percent of days
44 years of record at Blackwater Dam, 1948 to 1991. 4 years have data for under 90 percent of days and are left out of rankings: 1948, 1952, 1954, 1991.
Cooler than the station meanWarmer than the station mean
One stripe for each of 34 complete years at Blackwater Dam, 1949 to 1989. Blue stripes are years cooler than the station's own mean of 6.8 C (44.2 F); red stripes are warmer. The coolest year was 1978, at 5.9 C (42.6 F), and the warmest was 1949, at 9.1 C (48.4 F). The strongest colour marks a difference of 2.3 C (4.1 F).
Annual mean temperature at Blackwater Dam as warming stripes, 1949 to 1989
Year
Annual mean temperature
Difference from the station mean
1949
9.1 C
+2.30 C
1957
7.9 C
+1.10 C
1958
6.4 C
-0.38 C
1959
7.1 C
+0.31 C
1960
6.9 C
+0.06 C
1961
7.1 C
+0.33 C
1962
6.2 C
-0.56 C
1963
6.6 C
-0.16 C
1964
6.5 C
-0.29 C
1965
6.4 C
-0.42 C
1966
6.7 C
-0.12 C
1967
6.0 C
-0.80 C
1968
6.1 C
-0.66 C
1969
6.9 C
+0.10 C
1970
6.8 C
-0.04 C
1971
6.6 C
-0.17 C
1972
6.0 C
-0.85 C
1973
7.8 C
+0.97 C
1974
6.5 C
-0.26 C
1975
7.0 C
+0.21 C
1976
6.2 C
-0.59 C
1977
6.8 C
+0.03 C
1978
5.9 C
-0.89 C
1979
7.0 C
+0.17 C
1980
6.4 C
-0.39 C
1981
7.3 C
+0.48 C
1982
6.5 C
-0.31 C
1983
7.7 C
+0.85 C
1984
7.5 C
+0.70 C
1985
6.9 C
+0.07 C
1986
6.6 C
-0.17 C
1987
6.9 C
+0.06 C
1988
6.6 C
-0.19 C
1989
6.5 C
-0.35 C
The fitted trend in annual mean temperature here over 1949 to 1989 is -0.1 C (-0.4 to 0.1) per decade. The interval includes zero, so the trend is not clearly different from zero. In Fahrenheit: -0.3 F (-0.6 to 0.1) per decade. The slope is a straight line fitted to 34 complete years; the brackets give its 95 percent interval.
Fitted temperature trends per decade at Blackwater Dam
Measure
Per decade (C)
Per decade (F)
Period
Complete years
Reading
Annual mean temperature
-0.1 C (-0.4 to 0.1) per decade
-0.3 F (-0.6 to 0.1) per decade
1949 to 1989
34
Not clearly different from zero
Mean daily maximum
-0.3 C (-0.5 to -0.1) per decade
-0.5 F (-0.9 to -0.1) per decade
1949 to 1989
34
Fall
Mean daily minimum
0.00 C (-0.24 to 0.23) per decade
-0.01 F (-0.43 to 0.42) per decade
1949 to 1989
34
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
1948 to 1991
Yearly extremes at Blackwater Dam: the record and the median year
Measure
Record
Year of the record
Median year
Years with a value
Hottest day (TXx)
37.2 C (99.0 F)
1955
33.9 C (93.0 F)
44
Coldest night (TNn)
-35.6 C (-32.1 F)
1957
-26.7 C (-16.1 F)
44
Wettest day (Rx1day)
113.0 mm (4.4 in)
1954
61.8 mm (2.4 in)
44
Wettest five days (Rx5day)
186.9 mm (7.4 in)
1990
89.3 mm (3.5 in)
44
Longest dry spell (CDD)
24 days
1950
15 days
44
Hottest day (TXx)
The hottest day of the year at Blackwater Dam, 1948 to 1991. The record is 37.2 C (99.0 F) in 1955, marked on the chart; the median year is 33.9 C (93.0 F).
Hottest day (TXx) at Blackwater Dam by year
Year
Hottest day (TXx)
1948
36.1 C (97.0 F)
1949
35.6 C (96.1 F)
1950
32.2 C (90.0 F)
1951
31.1 C (88.0 F)
1952
35.0 C (95.0 F)
1953
35.0 C (95.0 F)
1954
34.4 C (93.9 F)
1955
37.2 C (99.0 F)
1956
35.6 C (96.1 F)
1957
35.6 C (96.1 F)
1958
33.3 C (91.9 F)
1959
35.6 C (96.1 F)
1960
32.8 C (91.0 F)
1961
33.9 C (93.0 F)
1962
35.0 C (95.0 F)
1963
36.7 C (98.1 F)
1964
34.4 C (93.9 F)
1965
36.1 C (97.0 F)
1966
35.6 C (96.1 F)
1967
32.8 C (91.0 F)
1968
33.9 C (93.0 F)
1969
33.9 C (93.0 F)
1970
35.0 C (95.0 F)
1971
34.4 C (93.9 F)
1972
32.2 C (90.0 F)
1973
33.9 C (93.0 F)
1974
32.8 C (91.0 F)
1975
36.1 C (97.0 F)
1976
33.3 C (91.9 F)
1977
35.6 C (96.1 F)
1978
33.9 C (93.0 F)
1979
32.8 C (91.0 F)
1980
32.8 C (91.0 F)
1981
33.3 C (91.9 F)
1982
33.3 C (91.9 F)
1983
35.0 C (95.0 F)
1984
33.9 C (93.0 F)
1985
32.8 C (91.0 F)
1986
33.3 C (91.9 F)
1987
33.9 C (93.0 F)
1988
36.1 C (97.0 F)
1989
33.3 C (91.9 F)
1990
33.3 C (91.9 F)
1991
34.4 C (93.9 F)
Coldest night (TNn)
The coldest night of the year at Blackwater Dam, 1948 to 1991. The record is -35.6 C (-32.1 F) in 1957, marked on the chart; the median year is -26.7 C (-16.1 F).
Coldest night (TNn) at Blackwater Dam by year
Year
Coldest night (TNn)
1948
-19.4 C (-2.9 F)
1949
-24.4 C (-11.9 F)
1950
-28.9 C (-20.0 F)
1951
-28.9 C (-20.0 F)
1952
-25.0 C (-13.0 F)
1953
-19.4 C (-2.9 F)
1954
-27.2 C (-17.0 F)
1955
-25.0 C (-13.0 F)
1956
-25.6 C (-14.1 F)
1957
-35.6 C (-32.1 F)
1958
-27.2 C (-17.0 F)
1959
-23.9 C (-11.0 F)
1960
-26.1 C (-15.0 F)
1961
-32.8 C (-27.0 F)
1962
-27.8 C (-18.0 F)
1963
-28.3 C (-18.9 F)
1964
-27.8 C (-18.0 F)
1965
-26.7 C (-16.1 F)
1966
-25.0 C (-13.0 F)
1967
-26.7 C (-16.1 F)
1968
-26.7 C (-16.1 F)
1969
-26.1 C (-15.0 F)
1970
-27.2 C (-17.0 F)
1971
-33.3 C (-27.9 F)
1972
-27.2 C (-17.0 F)
1973
-26.1 C (-15.0 F)
1974
-29.4 C (-20.9 F)
1975
-29.4 C (-20.9 F)
1976
-31.7 C (-25.1 F)
1977
-26.7 C (-16.1 F)
1978
-25.6 C (-14.1 F)
1979
-25.6 C (-14.1 F)
1980
-28.9 C (-20.0 F)
1981
-27.8 C (-18.0 F)
1982
-28.3 C (-18.9 F)
1983
-22.8 C (-9.0 F)
1984
-32.8 C (-27.0 F)
1985
-24.4 C (-11.9 F)
1986
-23.3 C (-9.9 F)
1987
-25.6 C (-14.1 F)
1988
-28.3 C (-18.9 F)
1989
-26.1 C (-15.0 F)
1990
-24.4 C (-11.9 F)
1991
-23.9 C (-11.0 F)
Wettest day (Rx1day)
The wettest day of the year at Blackwater Dam, 1948 to 1991. The record is 113.0 mm (4.4 in) in 1954, marked on the chart; the median year is 61.8 mm (2.4 in).
Wettest day (Rx1day) at Blackwater Dam by year
Year
Wettest day (Rx1day)
1948
51.6 mm (2.0 in)
1949
43.9 mm (1.7 in)
1950
66.0 mm (2.6 in)
1951
62.7 mm (2.5 in)
1952
58.7 mm (2.3 in)
1953
51.6 mm (2.0 in)
1954
113.0 mm (4.4 in)
1955
44.5 mm (1.8 in)
1956
52.8 mm (2.1 in)
1957
62.2 mm (2.4 in)
1958
43.9 mm (1.7 in)
1959
55.9 mm (2.2 in)
1960
109.2 mm (4.3 in)
1961
31.2 mm (1.2 in)
1962
101.6 mm (4.0 in)
1963
66.0 mm (2.6 in)
1964
41.9 mm (1.6 in)
1965
32.3 mm (1.3 in)
1966
60.2 mm (2.4 in)
1967
34.3 mm (1.4 in)
1968
45.5 mm (1.8 in)
1969
91.4 mm (3.6 in)
1970
62.0 mm (2.4 in)
1971
48.3 mm (1.9 in)
1972
96.5 mm (3.8 in)
1973
75.7 mm (3.0 in)
1974
58.7 mm (2.3 in)
1975
62.7 mm (2.5 in)
1976
58.9 mm (2.3 in)
1977
75.4 mm (3.0 in)
1978
59.7 mm (2.4 in)
1979
62.0 mm (2.4 in)
1980
50.3 mm (2.0 in)
1981
67.3 mm (2.6 in)
1982
43.9 mm (1.7 in)
1983
66.5 mm (2.6 in)
1984
83.6 mm (3.3 in)
1985
75.4 mm (3.0 in)
1986
62.2 mm (2.4 in)
1987
95.0 mm (3.7 in)
1988
79.2 mm (3.1 in)
1989
61.5 mm (2.4 in)
1990
107.4 mm (4.2 in)
1991
38.9 mm (1.5 in)
Wettest five days (Rx5day)
The wettest five days of the year at Blackwater Dam, 1948 to 1991. The record is 186.9 mm (7.4 in) in 1990, marked on the chart; the median year is 89.3 mm (3.5 in).
Wettest five days (Rx5day) at Blackwater Dam by year
Year
Wettest five days (Rx5day)
1948
70.1 mm (2.8 in)
1949
55.4 mm (2.2 in)
1950
90.9 mm (3.6 in)
1951
89.7 mm (3.5 in)
1952
86.4 mm (3.4 in)
1953
88.9 mm (3.5 in)
1954
116.8 mm (4.6 in)
1955
72.4 mm (2.9 in)
1956
80.0 mm (3.1 in)
1957
74.9 mm (2.9 in)
1958
66.3 mm (2.6 in)
1959
86.4 mm (3.4 in)
1960
153.7 mm (6.1 in)
1961
56.8 mm (2.2 in)
1962
174.7 mm (6.9 in)
1963
122.4 mm (4.8 in)
1964
63.7 mm (2.5 in)
1965
43.5 mm (1.7 in)
1966
99.3 mm (3.9 in)
1967
61.9 mm (2.4 in)
1968
71.8 mm (2.8 in)
1969
118.8 mm (4.7 in)
1970
64.3 mm (2.5 in)
1971
58.5 mm (2.3 in)
1972
121.9 mm (4.8 in)
1973
153.6 mm (6.0 in)
1974
85.1 mm (3.4 in)
1975
103.2 mm (4.1 in)
1976
71.1 mm (2.8 in)
1977
91.4 mm (3.6 in)
1978
93.3 mm (3.7 in)
1979
110.7 mm (4.4 in)
1980
67.9 mm (2.7 in)
1981
123.7 mm (4.9 in)
1982
78.8 mm (3.1 in)
1983
92.9 mm (3.7 in)
1984
180.7 mm (7.1 in)
1985
84.3 mm (3.3 in)
1986
104.1 mm (4.1 in)
1987
112.0 mm (4.4 in)
1988
118.8 mm (4.7 in)
1989
108.0 mm (4.3 in)
1990
186.9 mm (7.4 in)
1991
54.7 mm (2.2 in)
Longest dry spell (CDD)
The longest dry spell of the year at Blackwater Dam, 1948 to 1991. The record is 24 days in 1950, marked on the chart; the median year is 15 days.
Longest dry spell (CDD) at Blackwater Dam by year
Year
Longest dry spell (CDD)
1948
13 days
1949
21 days
1950
24 days
1951
14 days
1952
11 days
1953
15 days
1954
13 days
1955
15 days
1956
15 days
1957
20 days
1958
14 days
1959
15 days
1960
15 days
1961
17 days
1962
15 days
1963
23 days
1964
18 days
1965
19 days
1966
13 days
1967
12 days
1968
14 days
1969
17 days
1970
17 days
1971
15 days
1972
10 days
1973
15 days
1974
13 days
1975
15 days
1976
20 days
1977
18 days
1978
17 days
1979
18 days
1980
23 days
1981
14 days
1982
17 days
1983
17 days
1984
18 days
1985
14 days
1986
12 days
1987
19 days
1988
17 days
1989
12 days
1990
11 days
1991
13 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
34 years with a frost
Across 34 years with a frost, the median last spring frost at Blackwater Dam falls on 15 May and the median first autumn frost on 21 September, which leaves a median of 129 days between them.
Fitted over all years, the growing season changes by +7.0 days per decade at this station.
Frost dates and growing season at Blackwater Dam
Measure
Median, all years
Earliest period
Recent period (1960 to 1989)
Recent against earliest
Fitted trend
Last spring frost
15 May
n/a
14 May
n/a
-5.4 days per decade
First autumn frost
21 September
n/a
21 September
n/a
+1.6 days per decade
Growing days
129 days
n/a
131 days
n/a
+7.0 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, 1949 to 1990
A day with at least 61.4 mm (2.4 in) of rain is expected about once in 2 years. A day with at least 130.7 mm (5.1 in) of rain is expected about once in 100 years.
Rainfall return levels at Blackwater Dam: the daily rain expected about once in a given number of years
Expected about once in
A day with at least
Note
2 years
61.4 mm (2.4 in)
5 years
80.4 mm (3.2 in)
10 years
92.8 mm (3.7 in)
25 years
108.3 mm (4.3 in)
50 years
119.6 mm (4.7 in)
Longer than the 42 years of record
100 years
130.7 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 1949 to 1990.
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: 113.0 mm (4.4 in) in 1954; 109.2 mm (4.3 in) in 1960; 107.4 mm (4.2 in) in 1990.
Download the Data
Data for Blackwater Dam standing records by year: CSV or JSON. Field meanings are on the data page.
Data for Blackwater Dam 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 2026-10-15 (15 October 2026). Records are computed by this site and are not official.