Record envelope, standing records and threshold days for Unionville (USC00189030), Maryland, United States, with 57 years of record.
Key Facts for Unionville
Unionville (USC00189030) is a weather station in Maryland, United States at 39.45 latitude and -77.18 longitude, 131 m (430 ft) above sea level.
The station reports from 1940 to 1996, 57 years of record.
1,464 records set at Unionville still stand.
Records are tracked for tmax, tmin, prcp, snow, snwd: an element needs 30 years of data to be eligible.
Unionville set a daily record low maximum temperature of 0.0 C (32.0 F) on 28 November 1996.
About the Station
Location: Maryland, United States, 39.45 latitude, -77.18 longitude.
Elevation: 131 m (430 ft).
Period of record: 1940 to 1996, 57 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 Unionville. 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 Unionville, with 2026 drawn through them
Month
Highest record high
Lowest record low
2026 highest maximum
2026 lowest minimum
Jan
25.0 C (77.0 F)
-30.0 C (-22.0 F)
n/a
n/a
Feb
26.1 C (79.0 F)
-28.9 C (-20.0 F)
n/a
n/a
Mar
30.0 C (86.0 F)
-22.8 C (-9.0 F)
n/a
n/a
Apr
33.9 C (93.0 F)
-9.4 C (15.1 F)
n/a
n/a
May
35.6 C (96.1 F)
-6.1 C (21.0 F)
n/a
n/a
Jun
37.8 C (100.0 F)
0.6 C (33.1 F)
n/a
n/a
Jul
39.4 C (102.9 F)
3.9 C (39.0 F)
n/a
n/a
Aug
39.4 C (102.9 F)
1.7 C (35.1 F)
n/a
n/a
Sep
39.4 C (102.9 F)
-3.3 C (26.1 F)
n/a
n/a
Oct
37.2 C (99.0 F)
-10.0 C (14.0 F)
n/a
n/a
Nov
28.3 C (82.9 F)
-15.0 C (5.0 F)
n/a
n/a
Dec
25.6 C (78.1 F)
-28.3 C (-18.9 F)
n/a
n/a
Which Years Hold Standing Records
1,464 standing records
Year with most
1,464 records at Unionville still stand. 1979 holds the most, with 43.
Standing records at Unionville by the year they were set
Year set
Standing records
1940
20
1941
32
1942
25
1943
38
1944
13
1945
35
1946
29
1947
33
1948
28
1949
35
1950
31
1951
27
1952
20
1953
38
1954
32
1955
23
1956
25
1957
30
1958
20
1959
33
1960
32
1961
28
1962
17
1963
34
1964
26
1965
27
1966
26
1967
28
1968
26
1969
19
1970
19
1971
22
1972
26
1973
15
1974
22
1975
21
1976
30
1977
31
1978
16
1979
43
1980
18
1981
15
1982
23
1983
23
1984
30
1985
13
1986
29
1987
11
1988
35
1989
41
1990
34
1991
37
1992
19
1993
21
1994
16
1995
11
1996
13
All-Time Record Progression
7 new records
7 all-time records were set at Unionville between 9 January 1970 and 21 January 1994. Each dot is a new record.
When Unionville set new all-time records
Date
Kind
Detail
1970-01-09
Record low maximum temperature
Record low maximum temperature -12.8 C (9.0 F)
1972-06-22
Record daily precipitation
Record daily precipitation 217.9 mm (8.6 in)
1979-02-13
Record low minimum temperature
Record low minimum temperature -28.9 C (-20.0 F)
1979-02-18
Record low maximum temperature
Record low maximum temperature -13.3 C (8.1 F)
1983-02-12
Record snow depth
Record snow depth 68.6 cm (27.0 in)
1994-01-19
Record low maximum temperature
Record low maximum temperature -17.8 C (0.0 F)
1994-01-21
Record low minimum temperature
Record low minimum temperature -30.0 C (-22.0 F)
Wettest Day of Each Month
Jun: 217.9 mm (8.6 in)
The wettest day on record for each calendar month at Unionville. The most was 217.9 mm (8.6 in) on 22 June 1972.
Record daily precipitation for each month at Unionville
Month
Record daily precipitation (mm)
Date
Jan
84.8 mm (3.3 in)
4 January 1944
Feb
45.7 mm (1.8 in)
3 February 1982
Mar
63.5 mm (2.5 in)
29 March 1942
Apr
69.6 mm (2.7 in)
27 April 1952
May
121.9 mm (4.8 in)
22 May 1942
Jun
217.9 mm (8.6 in)
22 June 1972
Jul
100.6 mm (4.0 in)
4 July 1956
Aug
121.9 mm (4.8 in)
13 August 1955
Sep
181.6 mm (7.1 in)
14 September 1966
Oct
103.1 mm (4.1 in)
1 October 1979
Nov
153.9 mm (6.1 in)
28 November 1993
Dec
68.6 mm (2.7 in)
5 December 1993
Period of Record Coverage
1940 to 1996
Complete yearUnder 90 percent of days
57 years of record at Unionville, 1940 to 1996. 2 years have data for under 90 percent of days and are left out of rankings: 1940, 1996.
Cooler than the station meanWarmer than the station mean
One stripe for each of 51 complete years at Unionville, 1941 to 1995. Blue stripes are years cooler than the station's own mean of 11.3 C (52.4 F); red stripes are warmer. The coolest year was 1958, at 10.5 C (50.8 F), and the warmest was 1990, at 12.8 C (55.1 F). The strongest colour marks a difference of 1.5 C (2.7 F).
Annual mean temperature at Unionville as warming stripes, 1941 to 1995
Year
Annual mean temperature
Difference from the station mean
1941
11.7 C
+0.36 C
1942
11.7 C
+0.38 C
1943
11.5 C
+0.19 C
1944
11.6 C
+0.21 C
1945
11.5 C
+0.15 C
1946
11.9 C
+0.54 C
1948
10.6 C
-0.70 C
1949
12.2 C
+0.83 C
1950
11.4 C
+0.09 C
1951
11.6 C
+0.26 C
1952
11.7 C
+0.37 C
1953
12.6 C
+1.29 C
1954
11.9 C
+0.53 C
1955
11.6 C
+0.30 C
1956
11.4 C
+0.04 C
1957
11.9 C
+0.54 C
1958
10.5 C
-0.88 C
1959
12.3 C
+0.95 C
1960
10.7 C
-0.64 C
1961
10.9 C
-0.41 C
1962
10.5 C
-0.88 C
1964
11.0 C
-0.36 C
1965
11.0 C
-0.33 C
1966
10.8 C
-0.58 C
1967
10.5 C
-0.88 C
1968
10.9 C
-0.45 C
1969
10.7 C
-0.65 C
1970
11.1 C
-0.20 C
1971
11.2 C
-0.15 C
1972
11.0 C
-0.38 C
1973
12.1 C
+0.72 C
1974
11.4 C
+0.09 C
1975
11.6 C
+0.24 C
1976
10.7 C
-0.60 C
1978
10.5 C
-0.85 C
1979
11.0 C
-0.37 C
1980
11.0 C
-0.38 C
1981
11.1 C
-0.27 C
1982
11.4 C
+0.08 C
1983
11.3 C
-0.06 C
1984
11.4 C
+0.04 C
1985
11.5 C
+0.18 C
1986
11.1 C
-0.25 C
1987
11.1 C
-0.25 C
1988
11.1 C
-0.29 C
1989
11.1 C
-0.21 C
1990
12.8 C
+1.47 C
1991
12.7 C
+1.38 C
1992
11.2 C
-0.19 C
1994
11.2 C
-0.18 C
1995
11.6 C
+0.30 C
The fitted trend in annual mean temperature here over 1941 to 1995 is -0.04 C (-0.14 to 0.06) per decade. The interval includes zero, so the trend is not clearly different from zero. In Fahrenheit: -0.1 F (-0.3 to 0.1) per decade. The slope is a straight line fitted to 51 complete years; the brackets give its 95 percent interval.
Fitted temperature trends per decade at Unionville
Measure
Per decade (C)
Per decade (F)
Period
Complete years
Reading
Annual mean temperature
-0.04 C (-0.14 to 0.06) per decade
-0.1 F (-0.3 to 0.1) per decade
1941 to 1995
51
Not clearly different from zero
Mean daily maximum
0.03 C (-0.12 to 0.17) per decade
0.05 F (-0.21 to 0.31) per decade
1941 to 1995
51
Not clearly different from zero
Mean daily minimum
-0.11 C (-0.23 to 0.01) per decade
-0.20 F (-0.41 to 0.02) per decade
1941 to 1995
51
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
1940 to 1996
Yearly extremes at Unionville: the record and the median year
Measure
Record
Year of the record
Median year
Years with a value
Hottest day (TXx)
39.4 C (102.9 F)
1953
35.6 C (96.1 F)
57
Coldest night (TNn)
-30.0 C (-22.0 F)
1994
-20.6 C (-5.1 F)
57
Wettest day (Rx1day)
217.9 mm (8.6 in)
1972
61.0 mm (2.4 in)
57
Wettest five days (Rx5day)
305.3 mm (12.0 in)
1972
96.7 mm (3.8 in)
57
Longest dry spell (CDD)
41 days
1995
19 days
57
Hottest day (TXx)
The hottest day of the year at Unionville, 1940 to 1996. The record is 39.4 C (102.9 F) in 1953, marked on the chart; the median year is 35.6 C (96.1 F).
Hottest day (TXx) at Unionville by year
Year
Hottest day (TXx)
1940
36.1 C (97.0 F)
1941
37.8 C (100.0 F)
1942
35.0 C (95.0 F)
1943
37.8 C (100.0 F)
1944
36.1 C (97.0 F)
1945
36.1 C (97.0 F)
1946
36.1 C (97.0 F)
1947
35.0 C (95.0 F)
1948
36.7 C (98.1 F)
1949
36.1 C (97.0 F)
1950
33.3 C (91.9 F)
1951
35.0 C (95.0 F)
1952
36.1 C (97.0 F)
1953
39.4 C (102.9 F)
1954
38.3 C (100.9 F)
1955
37.2 C (99.0 F)
1956
35.6 C (96.1 F)
1957
38.3 C (100.9 F)
1958
33.9 C (93.0 F)
1959
37.2 C (99.0 F)
1960
33.9 C (93.0 F)
1961
34.4 C (93.9 F)
1962
35.6 C (96.1 F)
1963
35.0 C (95.0 F)
1964
36.1 C (97.0 F)
1965
33.9 C (93.0 F)
1966
37.2 C (99.0 F)
1967
33.9 C (93.0 F)
1968
33.9 C (93.0 F)
1969
35.6 C (96.1 F)
1970
33.3 C (91.9 F)
1971
33.9 C (93.0 F)
1972
33.9 C (93.0 F)
1973
34.4 C (93.9 F)
1974
33.3 C (91.9 F)
1975
33.9 C (93.0 F)
1976
33.9 C (93.0 F)
1977
35.6 C (96.1 F)
1978
33.9 C (93.0 F)
1979
33.3 C (91.9 F)
1980
37.2 C (99.0 F)
1981
33.9 C (93.0 F)
1982
35.6 C (96.1 F)
1983
38.3 C (100.9 F)
1984
35.6 C (96.1 F)
1985
35.6 C (96.1 F)
1986
36.7 C (98.1 F)
1987
35.6 C (96.1 F)
1988
39.4 C (102.9 F)
1989
35.0 C (95.0 F)
1990
35.0 C (95.0 F)
1991
38.3 C (100.9 F)
1992
35.0 C (95.0 F)
1993
36.7 C (98.1 F)
1994
37.2 C (99.0 F)
1995
37.2 C (99.0 F)
1996
35.6 C (96.1 F)
Coldest night (TNn)
The coldest night of the year at Unionville, 1940 to 1996. The record is -30.0 C (-22.0 F) in 1994, marked on the chart; the median year is -20.6 C (-5.1 F).
Coldest night (TNn) at Unionville by year
Year
Coldest night (TNn)
1940
-12.8 C (9.0 F)
1941
-14.4 C (6.1 F)
1942
-28.3 C (-18.9 F)
1943
-17.8 C (0.0 F)
1944
-15.6 C (3.9 F)
1945
-20.0 C (-4.0 F)
1946
-16.1 C (3.0 F)
1947
-15.6 C (3.9 F)
1948
-22.8 C (-9.0 F)
1949
-16.7 C (1.9 F)
1950
-15.6 C (3.9 F)
1951
-21.7 C (-7.1 F)
1952
-13.3 C (8.1 F)
1953
-12.2 C (10.0 F)
1954
-18.3 C (-0.9 F)
1955
-19.4 C (-2.9 F)
1956
-18.9 C (-2.0 F)
1957
-26.7 C (-16.1 F)
1958
-17.2 C (1.0 F)
1959
-22.2 C (-8.0 F)
1960
-24.4 C (-11.9 F)
1961
-28.3 C (-18.9 F)
1962
-22.2 C (-8.0 F)
1963
-27.2 C (-17.0 F)
1964
-22.2 C (-8.0 F)
1965
-23.3 C (-9.9 F)
1966
-22.2 C (-8.0 F)
1967
-25.6 C (-14.1 F)
1968
-27.2 C (-17.0 F)
1969
-17.2 C (1.0 F)
1970
-20.6 C (-5.1 F)
1971
-17.2 C (1.0 F)
1972
-17.8 C (0.0 F)
1973
-15.6 C (3.9 F)
1974
-12.2 C (10.0 F)
1975
-18.9 C (-2.0 F)
1976
-18.3 C (-0.9 F)
1977
-17.8 C (0.0 F)
1978
-22.2 C (-8.0 F)
1979
-28.9 C (-20.0 F)
1980
-22.2 C (-8.0 F)
1981
-20.6 C (-5.1 F)
1982
-25.6 C (-14.1 F)
1983
-26.7 C (-16.1 F)
1984
-28.9 C (-20.0 F)
1985
-23.3 C (-9.9 F)
1986
-16.7 C (1.9 F)
1987
-28.3 C (-18.9 F)
1988
-23.3 C (-9.9 F)
1989
-21.1 C (-6.0 F)
1990
-13.3 C (8.1 F)
1991
-16.1 C (3.0 F)
1992
-15.0 C (5.0 F)
1993
-21.7 C (-7.1 F)
1994
-30.0 C (-22.0 F)
1995
-17.2 C (1.0 F)
1996
-28.9 C (-20.0 F)
Wettest day (Rx1day)
The wettest day of the year at Unionville, 1940 to 1996. The record is 217.9 mm (8.6 in) in 1972, marked on the chart; the median year is 61.0 mm (2.4 in).
Wettest day (Rx1day) at Unionville by year
Year
Wettest day (Rx1day)
1940
106.7 mm (4.2 in)
1941
70.6 mm (2.8 in)
1942
121.9 mm (4.8 in)
1943
63.0 mm (2.5 in)
1944
84.8 mm (3.3 in)
1945
59.7 mm (2.4 in)
1946
98.3 mm (3.9 in)
1947
42.9 mm (1.7 in)
1948
61.7 mm (2.4 in)
1949
64.8 mm (2.6 in)
1950
76.2 mm (3.0 in)
1951
66.5 mm (2.6 in)
1952
70.6 mm (2.8 in)
1953
39.1 mm (1.5 in)
1954
52.6 mm (2.1 in)
1955
121.9 mm (4.8 in)
1956
100.6 mm (4.0 in)
1957
54.6 mm (2.1 in)
1958
36.6 mm (1.4 in)
1959
50.3 mm (2.0 in)
1960
39.6 mm (1.6 in)
1961
31.8 mm (1.3 in)
1962
39.4 mm (1.6 in)
1963
55.9 mm (2.2 in)
1964
53.1 mm (2.1 in)
1965
65.0 mm (2.6 in)
1966
181.6 mm (7.1 in)
1967
36.3 mm (1.4 in)
1968
61.0 mm (2.4 in)
1969
50.8 mm (2.0 in)
1970
52.6 mm (2.1 in)
1971
69.3 mm (2.7 in)
1972
217.9 mm (8.6 in)
1973
57.9 mm (2.3 in)
1974
53.1 mm (2.1 in)
1975
90.4 mm (3.6 in)
1976
43.4 mm (1.7 in)
1977
53.3 mm (2.1 in)
1978
50.3 mm (2.0 in)
1979
103.1 mm (4.1 in)
1980
55.6 mm (2.2 in)
1981
49.5 mm (1.9 in)
1982
63.5 mm (2.5 in)
1983
56.9 mm (2.2 in)
1984
84.3 mm (3.3 in)
1985
71.1 mm (2.8 in)
1986
40.4 mm (1.6 in)
1987
45.7 mm (1.8 in)
1988
52.3 mm (2.1 in)
1989
65.8 mm (2.6 in)
1990
63.2 mm (2.5 in)
1991
86.4 mm (3.4 in)
1992
72.6 mm (2.9 in)
1993
153.9 mm (6.1 in)
1994
39.1 mm (1.5 in)
1995
51.8 mm (2.0 in)
1996
66.0 mm (2.6 in)
Wettest five days (Rx5day)
The wettest five days of the year at Unionville, 1940 to 1996. The record is 305.3 mm (12.0 in) in 1972, marked on the chart; the median year is 96.7 mm (3.8 in).
Wettest five days (Rx5day) at Unionville by year
Year
Wettest five days (Rx5day)
1940
107.7 mm (4.2 in)
1941
109.7 mm (4.3 in)
1942
166.0 mm (6.5 in)
1943
95.2 mm (3.7 in)
1944
124.9 mm (4.9 in)
1945
123.5 mm (4.9 in)
1946
150.9 mm (5.9 in)
1947
95.5 mm (3.8 in)
1948
74.1 mm (2.9 in)
1949
116.3 mm (4.6 in)
1950
79.0 mm (3.1 in)
1951
113.8 mm (4.5 in)
1952
169.2 mm (6.7 in)
1953
71.8 mm (2.8 in)
1954
66.5 mm (2.6 in)
1955
196.3 mm (7.7 in)
1956
147.9 mm (5.8 in)
1957
103.1 mm (4.1 in)
1958
57.4 mm (2.3 in)
1959
56.1 mm (2.2 in)
1960
80.0 mm (3.1 in)
1961
68.4 mm (2.7 in)
1962
58.3 mm (2.3 in)
1963
68.6 mm (2.7 in)
1964
65.1 mm (2.6 in)
1965
67.8 mm (2.7 in)
1966
202.4 mm (8.0 in)
1967
102.1 mm (4.0 in)
1968
113.2 mm (4.5 in)
1969
78.2 mm (3.1 in)
1970
60.9 mm (2.4 in)
1971
136.9 mm (5.4 in)
1972
305.3 mm (12.0 in)
1973
78.2 mm (3.1 in)
1974
82.5 mm (3.2 in)
1975
226.5 mm (8.9 in)
1976
97.8 mm (3.9 in)
1977
84.0 mm (3.3 in)
1978
91.5 mm (3.6 in)
1979
134.1 mm (5.3 in)
1980
69.4 mm (2.7 in)
1981
67.8 mm (2.7 in)
1982
85.4 mm (3.4 in)
1983
133.2 mm (5.2 in)
1984
96.7 mm (3.8 in)
1985
71.1 mm (2.8 in)
1986
60.9 mm (2.4 in)
1987
102.9 mm (4.1 in)
1988
106.8 mm (4.2 in)
1989
107.2 mm (4.2 in)
1990
77.2 mm (3.0 in)
1991
142.3 mm (5.6 in)
1992
124.9 mm (4.9 in)
1993
188.2 mm (7.4 in)
1994
74.9 mm (2.9 in)
1995
82.4 mm (3.2 in)
1996
133.3 mm (5.2 in)
Longest dry spell (CDD)
The longest dry spell of the year at Unionville, 1940 to 1996. The record is 41 days in 1995, marked on the chart; the median year is 19 days.
Longest dry spell (CDD) at Unionville by year
Year
Longest dry spell (CDD)
1940
14 days
1941
28 days
1942
18 days
1943
18 days
1944
19 days
1945
15 days
1946
16 days
1947
32 days
1948
13 days
1949
19 days
1950
16 days
1951
22 days
1952
29 days
1953
18 days
1954
21 days
1955
22 days
1956
15 days
1957
15 days
1958
24 days
1959
17 days
1960
20 days
1961
24 days
1962
21 days
1963
28 days
1964
27 days
1965
16 days
1966
27 days
1967
19 days
1968
26 days
1969
17 days
1970
15 days
1971
14 days
1972
27 days
1973
26 days
1974
19 days
1975
14 days
1976
25 days
1977
25 days
1978
16 days
1979
16 days
1980
12 days
1981
18 days
1982
16 days
1983
16 days
1984
23 days
1985
26 days
1986
21 days
1987
23 days
1988
22 days
1989
16 days
1990
20 days
1991
23 days
1992
12 days
1993
14 days
1994
10 days
1995
41 days
1996
18 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
51 years with a frost
Across 51 years with a frost, the median last spring frost at Unionville falls on 7 May and the median first autumn frost on 6 October, which leaves a median of 152 days between them.
Fitted over all years, the growing season changes by -1.1 days per decade at this station.
Frost dates and growing season at Unionville
Measure
Median, all years
Earliest period
Recent period (1964 to 1995)
Recent against earliest
Fitted trend
Last spring frost
7 May
n/a
8 May
n/a
+0.5 days per decade
First autumn frost
6 October
n/a
6 October
n/a
-0.6 days per decade
Growing days
152 days
n/a
151 days
n/a
-1.1 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
55 years, 1941 to 1996
A day with at least 59.1 mm (2.3 in) of rain is expected about once in 2 years. A day with at least 218.5 mm (8.6 in) of rain is expected about once in 100 years.
Rainfall return levels at Unionville: the daily rain expected about once in a given number of years
Expected about once in
A day with at least
Note
2 years
59.1 mm (2.3 in)
5 years
83.6 mm (3.3 in)
10 years
105.4 mm (4.1 in)
25 years
141.3 mm (5.6 in)
50 years
175.8 mm (6.9 in)
100 years
218.5 mm (8.6 in)
Longer than the 55 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, 55 years of values from 1941 to 1996.
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: 217.9 mm (8.6 in) in 1972; 181.6 mm (7.1 in) in 1966; 153.9 mm (6.1 in) in 1993.
Station Changes
No change in the annual mean temperature of this station was found against its neighbours.
Download the Data
Data for Unionville standing records by year: CSV or JSON. Field meanings are on the data page.
Data for Unionville 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.