Merwin Dam Weather Records (USC00455305)

Record envelope, standing records and threshold days for Merwin Dam (USC00455305), Washington, United States, with 56 years of record.

Key Facts for Merwin Dam

Merwin Dam (USC00455305) is a weather station in Washington, United States at 45.95 latitude and -122.56 longitude, 68 m (224 ft) above sea level.
The station reports from 1971 to 2026, 56 years of record.
1,328 records set at Merwin Dam still stand.
Records are tracked for prcp, snow, snwd: an element needs 30 years of data to be eligible.
Merwin Dam set a daily record precipitation of 22.1 mm (0.9 in) on 13 September 2026 (provisional).

Provisional Records

Records set in the last 60 days are provisional until they clear the revision window.

About the Station

Location: Washington, United States, 45.95 latitude, -122.56 longitude.
Elevation: 68 m (224 ft).
Period of record: 1971 to 2026, 56 years.
Eligible elements: prcp, snow, snwd.

Daily Record Envelope and 2026

0 days at or beyond a record

The band shows the record high and record low for each calendar day at Merwin 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 Merwin Dam, with 2026 drawn through them
Month	Highest record high	Lowest record low	2026 highest maximum	2026 lowest minimum
Jan	13.9 C (57.0 F)	-6.7 C (19.9 F)	n/a	n/a
Feb	21.1 C (70.0 F)	-15.6 C (3.9 F)	n/a	n/a
Mar	19.4 C (66.9 F)	-2.8 C (27.0 F)	n/a	n/a
Apr	26.7 C (80.1 F)	0.0 C (32.0 F)	n/a	n/a
May	28.9 C (84.0 F)	4.4 C (39.9 F)	n/a	n/a
Jun	n/a	n/a	n/a	n/a
Jul	35.0 C (95.0 F)	8.3 C (46.9 F)	n/a	n/a
Aug	38.9 C (102.0 F)	10.0 C (50.0 F)	n/a	n/a
Sep	33.3 C (91.9 F)	3.3 C (37.9 F)	n/a	n/a
Oct	27.8 C (82.0 F)	4.4 C (39.9 F)	n/a	n/a
Nov	20.6 C (69.1 F)	-3.3 C (26.1 F)	n/a	n/a
Dec	11.7 C (53.1 F)	0.6 C (33.1 F)	n/a	n/a

Which Years Hold Standing Records

1,328 standing records

1,328 records at Merwin Dam still stand. 1977 holds the most, with 615.

All-Time Record Progression

1 new records

1 all-time records were set at Merwin Dam between 5 November 2022 and 5 November 2022. Each dot is a new record.

Wettest Day of Each Month

Nov: 127.0 mm (5.0 in)

The wettest day on record for each calendar month at Merwin Dam. The most was 127.0 mm (5.0 in) on 5 November 2022.

Record daily precipitation for each month at Merwin Dam
Month	Record daily precipitation (mm)	Date
Jan	124.5 mm (4.9 in)	11 January 1972
Feb	79.2 mm (3.1 in)	10 February 1990
Mar	70.6 mm (2.8 in)	30 March 2012
Apr	75.4 mm (3.0 in)	5 April 1991
May	64.0 mm (2.5 in)	23 May 2013
Jun	63.5 mm (2.5 in)	7 June 1985
Jul	38.1 mm (1.5 in)	9 July 1974
Aug	51.8 mm (2.0 in)	24 August 1977
Sep	65.8 mm (2.6 in)	3 September 1979
Oct	80.0 mm (3.1 in)	22 October 2017
Nov	127.0 mm (5.0 in)	5 November 2022
Dec	126.5 mm (5.0 in)	2 December 1977

Period of Record Coverage

1971 to 1980

6 years of record at Merwin Dam, 1971 to 1980. 6 years have data for under 90 percent of days and are left out of rankings: 1971, 1972, 1976, 1977, 1978, 1980.

Latest Records

Latest records at Merwin Dam
Date	Station	Record	Value	Beat old record by	Old record stood	Significance
13 September 2026	Merwin Dam, US	daily rain (Provisional)	22.1 mm (0.9 in)	9.4 mm (0.37 in)	40 years	20 of 100 (Routine)
26 May 2026	Merwin Dam, US	daily rain	15.2 mm (0.6 in)	0.5 mm (0.02 in)	41 years	17 of 100 (Routine)
14 March 2026	Merwin Dam, US	daily rain	46.2 mm (1.8 in)	5.1 mm (0.20 in)	8 years	12 of 100 (Routine)
12 March 2026	Merwin Dam, US	daily rain	50.8 mm (2.0 in)	16.5 mm (0.6 in)	16 years	27 of 100 (Routine)
19 December 2025	Merwin Dam, US	daily rain	45.7 mm (1.8 in)	15.7 mm (0.6 in)	4 years	17 of 100 (Routine)
9 December 2025	Merwin Dam, US	daily rain	108.0 mm (4.3 in)	52.1 mm (2.1 in)	10 years	45 of 100 (Notable)
26 October 2025	Merwin Dam, US	daily rain	36.1 mm (1.4 in)	12.5 mm (0.5 in)	15 years	20 of 100 (Routine)
1 October 2025	Merwin Dam, US	daily rain	40.6 mm (1.6 in)	11.9 mm (0.5 in)	24 years	23 of 100 (Routine)
22 June 2025	Merwin Dam, US	daily rain	33.0 mm (1.3 in)	13.9 mm (0.5 in)	28 years	30 of 100 (Routine)
21 March 2025	Merwin Dam, US	daily rain	30.5 mm (1.2 in)	0.8 mm (0.03 in)	22 years	11 of 100 (Routine)
17 February 2025	Merwin Dam, US	daily rain	51.3 mm (2.0 in)	11.7 mm (0.5 in)	36 years	25 of 100 (Routine)
18 December 2024	Merwin Dam, US	daily rain	51.6 mm (2.0 in)	12.2 mm (0.5 in)	9 years	15 of 100 (Routine)
30 July 2024	Merwin Dam, US	daily rain	18.0 mm (0.7 in)	7.3 mm (0.29 in)	23 years	20 of 100 (Routine)
3 June 2024	Merwin Dam, US	daily rain	44.5 mm (1.8 in)	19.1 mm (0.8 in)	16 years	34 of 100 (Routine)
22 May 2024	Merwin Dam, US	daily rain	27.4 mm (1.1 in)	11.9 mm (0.5 in)	12 years	23 of 100 (Routine)
6 May 2024	Merwin Dam, US	daily rain	22.9 mm (0.9 in)	5.1 mm (0.20 in)	2 years	11 of 100 (Routine)
5 May 2024	Merwin Dam, US	daily rain	32.3 mm (1.3 in)	7.4 mm (0.29 in)	45 years	27 of 100 (Routine)
4 May 2024	Merwin Dam, US	daily rain	28.2 mm (1.1 in)	10.4 mm (0.4 in)	21 years	24 of 100 (Routine)
4 March 2024	Merwin Dam, US	daily snowfall	1.3 cm (0.5 in)	1.3 cm (0.5 in)	51 years	20 of 100 (Routine)
26 February 2024	Merwin Dam, US	daily rain	26.7 mm (1.1 in)	1.0 mm (0.04 in)	45 years	18 of 100 (Routine)

Extremes by Year

1971 to 2026

Yearly extremes at Merwin Dam: 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)	1977	32.0 C (89.5 F)	6
Coldest night (TNn)	-15.6 C (3.9 F)	1972	-1.6 C (29.0 F)	6
Wettest day (Rx1day)	127.0 mm (5.0 in)	2022	66.6 mm (2.6 in)	56
Wettest five days (Rx5day)	229.5 mm (9.0 in)	2006	143.6 mm (5.7 in)	56
Longest dry spell (CDD)	66 days	2022	30 days	56

Hottest day (TXx)

The hottest day of the year at Merwin Dam, 1971 to 2026. The record is 38.9 C (102.0 F) in 1977, marked on the chart; the median year is 32.0 C (89.5 F).

Hottest day (TXx) at Merwin Dam by year
Year	Hottest day (TXx)
1971	15.0 C (59.0 F)
1972	35.0 C (95.0 F)
1973	n/a
1974	n/a
1975	n/a
1976	28.9 C (84.0 F)
1977	38.9 C (102.0 F)
1978	37.2 C (99.0 F)
1979	n/a
1980	27.2 C (81.0 F)
1981	n/a
1982	n/a
1983	n/a
1984	n/a
1985	n/a
1986	n/a
1987	n/a
1988	n/a
1989	n/a
1990	n/a
1991	n/a
1992	n/a
1993	n/a
1994	n/a
1995	n/a
1996	n/a
1997	n/a
1998	n/a
1999	n/a
2000	n/a
2001	n/a
2002	n/a
2003	n/a
2004	n/a
2005	n/a
2006	n/a
2007	n/a
2008	n/a
2009	n/a
2010	n/a
2011	n/a
2012	n/a
2013	n/a
2014	n/a
2015	n/a
2016	n/a
2017	n/a
2018	n/a
2019	n/a
2020	n/a
2021	n/a
2022	n/a
2023	n/a
2024	n/a
2025	n/a
2026	n/a

Coldest night (TNn)

The coldest night of the year at Merwin Dam, 1971 to 2026. The record is -15.6 C (3.9 F) in 1972, marked on the chart; the median year is -1.6 C (29.0 F).

Coldest night (TNn) at Merwin Dam by year
Year	Coldest night (TNn)
1971	0.0 C (32.0 F)
1972	-15.6 C (3.9 F)
1973	n/a
1974	n/a
1975	n/a
1976	-3.3 C (26.1 F)
1977	-6.7 C (19.9 F)
1978	8.3 C (46.9 F)
1979	n/a
1980	5.6 C (42.1 F)
1981	n/a
1982	n/a
1983	n/a
1984	n/a
1985	n/a
1986	n/a
1987	n/a
1988	n/a
1989	n/a
1990	n/a
1991	n/a
1992	n/a
1993	n/a
1994	n/a
1995	n/a
1996	n/a
1997	n/a
1998	n/a
1999	n/a
2000	n/a
2001	n/a
2002	n/a
2003	n/a
2004	n/a
2005	n/a
2006	n/a
2007	n/a
2008	n/a
2009	n/a
2010	n/a
2011	n/a
2012	n/a
2013	n/a
2014	n/a
2015	n/a
2016	n/a
2017	n/a
2018	n/a
2019	n/a
2020	n/a
2021	n/a
2022	n/a
2023	n/a
2024	n/a
2025	n/a
2026	n/a

Wettest day (Rx1day)

The wettest day of the year at Merwin Dam, 1971 to 2026. The record is 127.0 mm (5.0 in) in 2022, marked on the chart; the median year is 66.6 mm (2.6 in).

Wettest day (Rx1day) at Merwin Dam by year
Year	Wettest day (Rx1day)
1971	88.4 mm (3.5 in)
1972	124.5 mm (4.9 in)
1973	67.3 mm (2.6 in)
1974	72.6 mm (2.9 in)
1975	66.3 mm (2.6 in)
1976	43.9 mm (1.7 in)
1977	126.5 mm (5.0 in)
1978	36.3 mm (1.4 in)
1979	65.8 mm (2.6 in)
1980	59.9 mm (2.4 in)
1981	50.3 mm (2.0 in)
1982	121.4 mm (4.8 in)
1983	51.3 mm (2.0 in)
1984	73.2 mm (2.9 in)
1985	63.5 mm (2.5 in)
1986	57.9 mm (2.3 in)
1987	70.1 mm (2.8 in)
1988	54.6 mm (2.1 in)
1989	43.9 mm (1.7 in)
1990	79.2 mm (3.1 in)
1991	88.9 mm (3.5 in)
1992	60.5 mm (2.4 in)
1993	52.1 mm (2.1 in)
1994	85.1 mm (3.4 in)
1995	113.0 mm (4.4 in)
1996	68.6 mm (2.7 in)
1997	62.5 mm (2.5 in)
1998	66.8 mm (2.6 in)
1999	111.3 mm (4.4 in)
2000	29.0 mm (1.1 in)
2001	52.8 mm (2.1 in)
2002	50.5 mm (2.0 in)
2003	45.7 mm (1.8 in)
2004	70.1 mm (2.8 in)
2005	53.8 mm (2.1 in)
2006	81.0 mm (3.2 in)
2007	80.0 mm (3.1 in)
2008	50.8 mm (2.0 in)
2009	61.0 mm (2.4 in)
2010	41.4 mm (1.6 in)
2011	69.6 mm (2.7 in)
2012	70.6 mm (2.8 in)
2013	71.6 mm (2.8 in)
2014	61.0 mm (2.4 in)
2015	94.5 mm (3.7 in)
2016	67.3 mm (2.6 in)
2017	80.0 mm (3.1 in)
2018	45.7 mm (1.8 in)
2019	57.2 mm (2.3 in)
2020	53.3 mm (2.1 in)
2021	77.7 mm (3.1 in)
2022	127.0 mm (5.0 in)
2023	89.2 mm (3.5 in)
2024	52.1 mm (2.1 in)
2025	108.0 mm (4.3 in)
2026	50.8 mm (2.0 in)

Wettest five days (Rx5day)

The wettest five days of the year at Merwin Dam, 1971 to 2026. The record is 229.5 mm (9.0 in) in 2006, marked on the chart; the median year is 143.6 mm (5.7 in).

Wettest five days (Rx5day) at Merwin Dam by year
Year	Wettest five days (Rx5day)
1971	170.2 mm (6.7 in)
1972	218.2 mm (8.6 in)
1973	157.5 mm (6.2 in)
1974	168.3 mm (6.6 in)
1975	184.4 mm (7.3 in)
1976	141.4 mm (5.6 in)
1977	212.4 mm (8.4 in)
1978	98.3 mm (3.9 in)
1979	149.4 mm (5.9 in)
1980	149.4 mm (5.9 in)
1981	130.4 mm (5.1 in)
1982	174.0 mm (6.9 in)
1983	175.5 mm (6.9 in)
1984	128.8 mm (5.1 in)
1985	121.2 mm (4.8 in)
1986	147.7 mm (5.8 in)
1987	136.0 mm (5.4 in)
1988	127.5 mm (5.0 in)
1989	103.4 mm (4.1 in)
1990	196.2 mm (7.7 in)
1991	171.4 mm (6.7 in)
1992	131.7 mm (5.2 in)
1993	112.3 mm (4.4 in)
1994	189.5 mm (7.5 in)
1995	200.6 mm (7.9 in)
1996	211.6 mm (8.3 in)
1997	166.4 mm (6.6 in)
1998	158.5 mm (6.2 in)
1999	166.0 mm (6.5 in)
2000	92.9 mm (3.7 in)
2001	122.8 mm (4.8 in)
2002	135.3 mm (5.3 in)
2003	117.2 mm (4.6 in)
2004	129.7 mm (5.1 in)
2005	133.0 mm (5.2 in)
2006	229.5 mm (9.0 in)
2007	154.7 mm (6.1 in)
2008	156.7 mm (6.2 in)
2009	133.4 mm (5.3 in)
2010	95.0 mm (3.7 in)
2011	135.2 mm (5.3 in)
2012	129.8 mm (5.1 in)
2013	113.0 mm (4.4 in)
2014	143.0 mm (5.6 in)
2015	170.2 mm (6.7 in)
2016	125.1 mm (4.9 in)
2017	125.1 mm (4.9 in)
2018	110.2 mm (4.3 in)
2019	114.5 mm (4.5 in)
2020	120.4 mm (4.7 in)
2021	144.1 mm (5.7 in)
2022	215.5 mm (8.5 in)
2023	203.5 mm (8.0 in)
2024	129.1 mm (5.1 in)
2025	214.7 mm (8.5 in)
2026	156.9 mm (6.2 in)

Longest dry spell (CDD)

The longest dry spell of the year at Merwin Dam, 1971 to 2026. The record is 66 days in 2022, marked on the chart; the median year is 30 days.

Longest dry spell (CDD) at Merwin Dam by year
Year	Longest dry spell (CDD)
1971	2 days
1972	32 days
1973	23 days
1974	26 days
1975	26 days
1976	25 days
1977	25 days
1978	25 days
1979	33 days
1980	33 days
1981	30 days
1982	15 days
1983	15 days
1984	44 days
1985	51 days
1986	42 days
1987	34 days
1988	33 days
1989	24 days
1990	41 days
1991	32 days
1992	33 days
1993	22 days
1994	33 days
1995	17 days
1996	19 days
1997	40 days
1998	47 days
1999	24 days
2000	44 days
2001	25 days
2002	42 days
2003	31 days
2004	28 days
2005	25 days
2006	29 days
2007	28 days
2008	24 days
2009	29 days
2010	59 days
2011	31 days
2012	25 days
2013	41 days
2014	22 days
2015	51 days
2016	22 days
2017	55 days
2018	57 days
2019	20 days
2020	27 days
2021	50 days
2022	66 days
2023	34 days
2024	29 days
2025	39 days
2026	8 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.

Rainfall Return Levels

50 years, 1972 to 2023

A day with at least 64.6 mm (2.5 in) of rain is expected about once in 2 years. A day with at least 152.5 mm (6.0 in) of rain is expected about once in 100 years.

Rainfall return levels at Merwin 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	64.6 mm (2.5 in)
5 years	85.6 mm (3.4 in)
10 years	100.5 mm (4.0 in)
25 years	120.5 mm (4.7 in)
50 years	136.1 mm (5.4 in)
100 years	152.5 mm (6.0 in)	Longer than the 50 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, 50 years of values from 1972 to 2023.

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: 127.0 mm (5.0 in) in 2022; 126.5 mm (5.0 in) in 1977; 124.5 mm (4.9 in) in 1972.

Download the Data

Data for Merwin Dam standing records by year: CSV or JSON. Field meanings are on the data page.
Data for Merwin 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 2026-10-14 (14 October 2026). Records are computed by this site and are not official.

Data as of 2026-10-14. Last revised 14 October 2026 (2026-10-14).

Days with data per year at Merwin Dam
Year	Days with data	Share of year	Complete
1971	27	7%	No
1972	146	40%	No
1976	153	42%	No
1977	302	83%	No
1978	92	25%	No
1980	31	8%	No