Record envelope, standing records and threshold days for Blackwater Refuge (USC00180915), Maryland, United States, with 36 years of record.
Key Facts for Blackwater Refuge
Blackwater Refuge (USC00180915) is a weather station in Maryland, United States at 38.43 latitude and -76.13 longitude, 3 m (10 ft) above sea level.
The station reports from 1941 to 1976, 36 years of record.
1,464 records set at Blackwater Refuge still stand.
Records are tracked for tmax, tmin, prcp, snow: an element needs 30 years of data to be eligible.
Blackwater Refuge set a daily record low minimum temperature of -7.8 C (18.0 F) on 30 November 1976.
About the Station
Location: Maryland, United States, 38.43 latitude, -76.13 longitude.
Elevation: 3 m (10 ft).
Period of record: 1941 to 1976, 36 years.
Eligible elements: tmax, tmin, prcp, snow.
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 Refuge. 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 Refuge, with 2026 drawn through them
Month
Highest record high
Lowest record low
2026 highest maximum
2026 lowest minimum
Jan
23.9 C (75.0 F)
-25.6 C (-14.1 F)
n/a
n/a
Feb
25.6 C (78.1 F)
-20.0 C (-4.0 F)
n/a
n/a
Mar
29.4 C (84.9 F)
-11.1 C (12.0 F)
n/a
n/a
Apr
33.9 C (93.0 F)
-6.1 C (21.0 F)
n/a
n/a
May
36.1 C (97.0 F)
-3.3 C (26.1 F)
n/a
n/a
Jun
38.9 C (102.0 F)
4.4 C (39.9 F)
n/a
n/a
Jul
37.8 C (100.0 F)
8.9 C (48.0 F)
n/a
n/a
Aug
37.8 C (100.0 F)
6.7 C (44.1 F)
n/a
n/a
Sep
37.8 C (100.0 F)
1.1 C (34.0 F)
n/a
n/a
Oct
37.2 C (99.0 F)
-6.1 C (21.0 F)
n/a
n/a
Nov
27.8 C (82.0 F)
-8.9 C (16.0 F)
n/a
n/a
Dec
24.4 C (75.9 F)
-16.7 C (1.9 F)
n/a
n/a
Which Years Hold Standing Records
1,464 standing records
Year with most
1,464 records at Blackwater Refuge still stand. 1943 holds the most, with 70.
Standing records at Blackwater Refuge by the year they were set
Year set
Standing records
1941
28
1942
53
1943
70
1944
49
1945
56
1946
59
1947
59
1948
48
1949
37
1950
60
1951
36
1952
40
1953
25
1954
37
1955
44
1956
39
1957
36
1958
35
1959
41
1960
44
1961
48
1962
33
1963
53
1964
43
1965
45
1966
37
1967
48
1968
26
1969
20
1970
32
1971
34
1972
21
1973
34
1974
35
1975
22
1976
37
Wettest Day of Each Month
Aug: 218.4 mm (8.6 in)
The wettest day on record for each calendar month at Blackwater Refuge. The most was 218.4 mm (8.6 in) on 13 August 1955.
Record daily precipitation for each month at Blackwater Refuge
Month
Record daily precipitation (mm)
Date
Jan
72.4 mm (2.9 in)
13 January 1948
Feb
50.3 mm (2.0 in)
2 February 1973
Mar
54.6 mm (2.1 in)
30 March 1974
Apr
45.2 mm (1.8 in)
28 April 1954
May
72.6 mm (2.9 in)
26 May 1948
Jun
99.1 mm (3.9 in)
19 June 1967
Jul
104.4 mm (4.1 in)
18 July 1945
Aug
218.4 mm (8.6 in)
13 August 1955
Sep
182.1 mm (7.2 in)
12 September 1960
Oct
88.4 mm (3.5 in)
31 October 1949
Nov
86.4 mm (3.4 in)
7 November 1963
Dec
48.3 mm (1.9 in)
26 December 1969
Period of Record Coverage
1941 to 1976
Complete yearUnder 90 percent of days
36 years of record at Blackwater Refuge, 1941 to 1976. 4 years have data for under 90 percent of days and are left out of rankings: 1941, 1953, 1972, 1974.
Cooler than the station meanWarmer than the station mean
One stripe for each of 29 complete years at Blackwater Refuge, 1942 to 1971. Blue stripes are years cooler than the station's own mean of 13.6 C (56.5 F); red stripes are warmer. The coolest year was 1945, at 12.5 C (54.5 F), and the warmest was 1959, at 14.9 C (58.7 F). The strongest colour marks a difference of 1.3 C (2.3 F).
Annual mean temperature at Blackwater Refuge as warming stripes, 1942 to 1971
Year
Annual mean temperature
Difference from the station mean
1942
13.3 C
-0.32 C
1943
12.6 C
-1.03 C
1944
12.9 C
-0.69 C
1945
12.5 C
-1.12 C
1946
13.2 C
-0.40 C
1947
13.7 C
+0.14 C
1948
14.3 C
+0.65 C
1949
14.7 C
+1.07 C
1950
13.2 C
-0.43 C
1951
13.3 C
-0.34 C
1952
13.8 C
+0.20 C
1954
14.2 C
+0.57 C
1955
14.0 C
+0.41 C
1956
13.5 C
-0.10 C
1957
14.0 C
+0.43 C
1958
12.6 C
-0.96 C
1959
14.9 C
+1.26 C
1960
13.7 C
+0.13 C
1961
14.6 C
+1.01 C
1962
13.3 C
-0.28 C
1963
13.4 C
-0.21 C
1964
14.4 C
+0.76 C
1965
13.5 C
-0.09 C
1966
13.3 C
-0.29 C
1967
13.1 C
-0.54 C
1968
13.0 C
-0.57 C
1969
13.6 C
0.00 C
1970
14.0 C
+0.38 C
1971
14.1 C
+0.46 C
This station does not have enough complete years (30 are needed) to fit a temperature trend.
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 1976
Yearly extremes at Blackwater Refuge: 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)
1959
35.3 C (95.5 F)
36
Coldest night (TNn)
-25.6 C (-14.1 F)
1942
-12.8 C (9.0 F)
36
Wettest day (Rx1day)
218.4 mm (8.6 in)
1955
70.0 mm (2.8 in)
36
Wettest five days (Rx5day)
284.1 mm (11.2 in)
1955
101.4 mm (4.0 in)
36
Longest dry spell (CDD)
30 days
1965
19 days
36
Hottest day (TXx)
The hottest day of the year at Blackwater Refuge, 1941 to 1976. The record is 38.9 C (102.0 F) in 1959, marked on the chart; the median year is 35.3 C (95.5 F).
Hottest day (TXx) at Blackwater Refuge by year
Year
Hottest day (TXx)
1941
37.2 C (99.0 F)
1942
36.7 C (98.1 F)
1943
35.0 C (95.0 F)
1944
35.0 C (95.0 F)
1945
33.9 C (93.0 F)
1946
32.2 C (90.0 F)
1947
34.4 C (93.9 F)
1948
36.7 C (98.1 F)
1949
35.6 C (96.1 F)
1950
33.3 C (91.9 F)
1951
34.4 C (93.9 F)
1952
37.2 C (99.0 F)
1953
37.8 C (100.0 F)
1954
35.0 C (95.0 F)
1955
36.7 C (98.1 F)
1956
35.0 C (95.0 F)
1957
36.7 C (98.1 F)
1958
33.3 C (91.9 F)
1959
38.9 C (102.0 F)
1960
33.9 C (93.0 F)
1961
35.6 C (96.1 F)
1962
37.2 C (99.0 F)
1963
37.8 C (100.0 F)
1964
36.1 C (97.0 F)
1965
35.0 C (95.0 F)
1966
35.6 C (96.1 F)
1967
32.2 C (90.0 F)
1968
36.7 C (98.1 F)
1969
36.1 C (97.0 F)
1970
33.9 C (93.0 F)
1971
33.9 C (93.0 F)
1972
28.3 C (82.9 F)
1973
35.6 C (96.1 F)
1974
32.2 C (90.0 F)
1975
35.6 C (96.1 F)
1976
34.4 C (93.9 F)
Coldest night (TNn)
The coldest night of the year at Blackwater Refuge, 1941 to 1976. The record is -25.6 C (-14.1 F) in 1942, marked on the chart; the median year is -12.8 C (9.0 F).
Coldest night (TNn) at Blackwater Refuge by year
Year
Coldest night (TNn)
1941
-7.2 C (19.0 F)
1942
-25.6 C (-14.1 F)
1943
-13.9 C (7.0 F)
1944
-9.4 C (15.1 F)
1945
-12.2 C (10.0 F)
1946
-12.2 C (10.0 F)
1947
-15.0 C (5.0 F)
1948
-18.3 C (-0.9 F)
1949
-8.9 C (16.0 F)
1950
-12.2 C (10.0 F)
1951
-12.2 C (10.0 F)
1952
-10.0 C (14.0 F)
1953
-7.8 C (18.0 F)
1954
-11.7 C (10.9 F)
1955
-12.2 C (10.0 F)
1956
-9.4 C (15.1 F)
1957
-17.8 C (0.0 F)
1958
-16.7 C (1.9 F)
1959
-10.6 C (12.9 F)
1960
-12.8 C (9.0 F)
1961
-21.1 C (-6.0 F)
1962
-15.6 C (3.9 F)
1963
-18.9 C (-2.0 F)
1964
-13.9 C (7.0 F)
1965
-21.7 C (-7.1 F)
1966
-16.1 C (3.0 F)
1967
-15.0 C (5.0 F)
1968
-14.4 C (6.1 F)
1969
-11.1 C (12.0 F)
1970
-14.4 C (6.1 F)
1971
-15.6 C (3.9 F)
1972
-15.0 C (5.0 F)
1973
-11.7 C (10.9 F)
1974
-11.1 C (12.0 F)
1975
-8.9 C (16.0 F)
1976
-12.8 C (9.0 F)
Wettest day (Rx1day)
The wettest day of the year at Blackwater Refuge, 1941 to 1976. The record is 218.4 mm (8.6 in) in 1955, marked on the chart; the median year is 70.0 mm (2.8 in).
Wettest day (Rx1day) at Blackwater Refuge by year
Year
Wettest day (Rx1day)
1941
40.6 mm (1.6 in)
1942
57.2 mm (2.3 in)
1943
45.7 mm (1.8 in)
1944
43.2 mm (1.7 in)
1945
104.4 mm (4.1 in)
1946
47.8 mm (1.9 in)
1947
82.8 mm (3.3 in)
1948
86.9 mm (3.4 in)
1949
88.4 mm (3.5 in)
1950
48.3 mm (1.9 in)
1951
67.3 mm (2.6 in)
1952
58.9 mm (2.3 in)
1953
83.1 mm (3.3 in)
1954
45.7 mm (1.8 in)
1955
218.4 mm (8.6 in)
1956
73.7 mm (2.9 in)
1957
117.3 mm (4.6 in)
1958
79.8 mm (3.1 in)
1959
198.6 mm (7.8 in)
1960
182.1 mm (7.2 in)
1961
56.9 mm (2.2 in)
1962
57.2 mm (2.3 in)
1963
86.4 mm (3.4 in)
1964
102.1 mm (4.0 in)
1965
55.1 mm (2.2 in)
1966
85.6 mm (3.4 in)
1967
115.1 mm (4.5 in)
1968
70.9 mm (2.8 in)
1969
90.2 mm (3.6 in)
1970
45.7 mm (1.8 in)
1971
121.9 mm (4.8 in)
1972
38.1 mm (1.5 in)
1973
50.3 mm (2.0 in)
1974
54.6 mm (2.1 in)
1975
69.1 mm (2.7 in)
1976
53.3 mm (2.1 in)
Wettest five days (Rx5day)
The wettest five days of the year at Blackwater Refuge, 1941 to 1976. The record is 284.1 mm (11.2 in) in 1955, marked on the chart; the median year is 101.4 mm (4.0 in).
Wettest five days (Rx5day) at Blackwater Refuge by year
Year
Wettest five days (Rx5day)
1941
71.2 mm (2.8 in)
1942
91.4 mm (3.6 in)
1943
82.2 mm (3.2 in)
1944
84.0 mm (3.3 in)
1945
231.0 mm (9.1 in)
1946
87.6 mm (3.4 in)
1947
88.9 mm (3.5 in)
1948
179.9 mm (7.1 in)
1949
109.2 mm (4.3 in)
1950
98.0 mm (3.9 in)
1951
68.6 mm (2.7 in)
1952
137.1 mm (5.4 in)
1953
100.6 mm (4.0 in)
1954
61.4 mm (2.4 in)
1955
284.1 mm (11.2 in)
1956
119.9 mm (4.7 in)
1957
139.2 mm (5.5 in)
1958
144.9 mm (5.7 in)
1959
255.2 mm (10.0 in)
1960
213.9 mm (8.4 in)
1961
110.0 mm (4.3 in)
1962
72.1 mm (2.8 in)
1963
127.0 mm (5.0 in)
1964
120.4 mm (4.7 in)
1965
92.2 mm (3.6 in)
1966
102.1 mm (4.0 in)
1967
188.7 mm (7.4 in)
1968
83.1 mm (3.3 in)
1969
92.7 mm (3.6 in)
1970
56.9 mm (2.2 in)
1971
169.7 mm (6.7 in)
1972
60.0 mm (2.4 in)
1973
85.9 mm (3.4 in)
1974
67.3 mm (2.6 in)
1975
162.4 mm (6.4 in)
1976
110.0 mm (4.3 in)
Longest dry spell (CDD)
The longest dry spell of the year at Blackwater Refuge, 1941 to 1976. The record is 30 days in 1965, marked on the chart; the median year is 19 days.
Longest dry spell (CDD) at Blackwater Refuge by year
Year
Longest dry spell (CDD)
1941
27 days
1942
23 days
1943
19 days
1944
19 days
1945
20 days
1946
18 days
1947
22 days
1948
19 days
1949
29 days
1950
16 days
1951
13 days
1952
23 days
1953
19 days
1954
24 days
1955
13 days
1956
16 days
1957
20 days
1958
18 days
1959
22 days
1960
16 days
1961
18 days
1962
17 days
1963
29 days
1964
29 days
1965
30 days
1966
23 days
1967
19 days
1968
27 days
1969
17 days
1970
20 days
1971
16 days
1972
7 days
1973
25 days
1974
14 days
1975
18 days
1976
20 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
29 years with a frost
Across 29 years with a frost, the median last spring frost at Blackwater Refuge falls on 11 April and the median first autumn frost on 31 October, which leaves a median of 200 days between them.
Fitted over all years, the growing season changes by +4.8 days per decade at this station.
Frost dates and growing season at Blackwater Refuge
Measure
Median, all years
Earliest period
Recent period (1942 to 1971)
Recent against earliest
Fitted trend
Last spring frost
11 April
n/a
11 April
n/a
-3.1 days per decade
First autumn frost
31 October
n/a
31 October
n/a
+1.7 days per decade
Growing days
200 days
n/a
200 days
n/a
+4.8 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
33 years, 1942 to 1976
A day with at least 71.7 mm (2.8 in) of rain is expected about once in 2 years. A day with at least 274.5 mm (10.8 in) of rain is expected about once in 100 years.
Rainfall return levels at Blackwater Refuge: the daily rain expected about once in a given number of years
Expected about once in
A day with at least
Note
2 years
71.7 mm (2.8 in)
5 years
105.1 mm (4.1 in)
10 years
133.8 mm (5.3 in)
25 years
179.8 mm (7.1 in)
50 years
222.7 mm (8.8 in)
Longer than the 33 years of record
100 years
274.5 mm (10.8 in)
Longer than the 33 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, 33 years of values from 1942 to 1976.
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: 218.4 mm (8.6 in) in 1955; 198.6 mm (7.8 in) in 1959; 182.1 mm (7.2 in) in 1960.
Download the Data
Data for Blackwater Refuge standing records by year: CSV or JSON. Field meanings are on the data page.
Data for Blackwater Refuge 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.