Heavy Rain and Flash Flooding Threat in Montana; Severe Thunderstorms in the Middle Missouri Valley

A low pressure system will bring heavy to excessive rainfall and high winds across Montana this afternoon. Heavy rainfall totals may lead to scattered flash flooding concerns. A line of showers and strong to severe thunderstorms will move into the mid Missouri Valley region this afternoon producing severe winds and isolated large hail with stronger storms. Read More >

Riverton Climate Summary Banner

...Highlights of 2018...

Annual: Near normal average temperature and precipitation, and above average snowfall for 2108.
- Average annual temperature 43.9 degrees was the 43rd warmest year on 96 years of record (1918-2018).
- 2018 precipitation total was 8.94 inches which was the 47th wettest year on 101 years of record (1918-2018).
- 2018 snowfall total was 47.6 inches which was the 18th snowiest year on 93 years of record .
Seasonal: 10th wettest first three months of the year (January, February, March) with 1.93 inches of precipitation, and 7th snowiest first three months of the year with 26.1 inches of snowfall.
Monthly Temperatures: No months ranked in the top 10 warmest or coldest during 2018.
Monthly Precipitation: 10th wettest February and 8th driest September on record.
Monthly Snowfall: No cold season months (October through April) ranked in the top 10 snowiest or least snowiest months.

Temperature

Precipitation

Snowfall

Temperature Banner

Element	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Average High	31.6	24.9	47.6	56.1	71.3	80.5	89.2	90.6	75.3	59.6	49.1	33.8	59.1
Mean High (1981-2010 Normals)	31.0	37.4	49.6	60.3	69.2	79.4	88.2	86.7	74.9	60.0	43.1	29.5	59.1
Average Low	6.6	1.2	21.9	27.4	41.1	50.1	53.7	53.0	41.5	27.5	16.9	7.8	29.1
Mean Low (1981-2010 Normals)	6.2	11.0	22.5	30.6	40.1	48.1	54.0	51.4	41.4	30.0	17.6	5.4	29.9
Average Temperature	19.1	13.0	34.8	41.8	56.2	65.3	71.5	71.8	58.4	43.1	33.0	22.2	44.2
Mean Average Temperature (1981-2010 Normals)	18.6	24.2	36.1	45.4	54.6	63.8	71.1	69.0	58.2	45.0	30.3	17.4	44.5
Departure from Normal	0.5	-11.2	-1.3	-3.6	1.6	1.5	0.4	2.8	0.2	-1.9	2.7	4.8	-0.3
Rank: Coldest to Warmest 103 years of record (P.O.R 12/1918-2020)	66	13	57	23	78	73	68	97	62	26	78	78	66
Highest Daily Maximum	44	50	59	77	90	95	97	96	97	84	72	53	97
Date of Occurrence	8	2	31	30	31	6	13	7,18	6	7	6	23	7/13, 9/6
Lowest Daily Minimum	-5	-16	-2	2	28	39	44	38	26	-12	1	-6	-16
Date of Occurrence	16	20,21	2	3	5	8	1	31	9	26	30	13	2/20, 2/21
Number of Days with:
Maximum >= 90°	0	0	0	0	1	6	16	23	1	0	0	0	47
Maximum <= 32°	19	4	1	2	0	0	0	0	0	3	0	13	42
Minimum <= 32°	31	29	30	21	5	0	0	0	5	18	27	31	197
Minimum <= 0°	5	12	1	0	0	0	0	0	0	1	0	4	23
Record Highs Set or Tied	0	0	0	0	0	1	0	1	1	0	1	0	7
Record Lows Set or Tied	0	0	0	0	0	0	0	0	0	1	0	0	1
* Multiple day occurrence

Temperature Ranks and Records:

Daily Records:

Max:

June: ^{78 on the 13th.}

August: ^{96 on the 18th (tie).}

September: ^{97 on the 6th.}

November: ^{64 on the 19th.}

Min:

October: -12th the 26th.

Top Ten Warmest August's on Record
Rank	Year	Average Temperature °F
1	2003	73.8
2	2013	73.0
2	2000	73.0
4	2001	72.9
5	2012	71.9
6	2020	71.8
6	2011	71.8
8	2007	71.6
9	1922	71.3
10	1999	71.0

Warmest Years on Record (101 Years)
Rank	Year	Average Temperature °F
1	2012	48.5
2	2006, 1999	47.0
4	1934	46.9
5	2007	46.5
6	2005, 1981	46.3
8	1954	46.2
9	2015	45.9
10	1953	45.8
33	2020	44.2

Top Ten Coldest Years on Record
Rank	Year	Average Temperature °F
1	1993	38.8
2	1924	39.5
3	1984, 1944	39.7
5	1978	40.1
6	1985	40.3
7	1968, 1929	40.5
9	1975	40.8
10	1986, 1932	41.0
66	2020	44.2


Average Annual Temperature for Period of Record - Click on Graph to Enlarge

Learn more about the National Weather Service's efforts to build a Weather-Ready Nation!

Precipitation Banner

Element	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Total (inches)	0.29	0.98	0.24	1.84	0.34	0.41	0.25	0.001	0.7	0.18	0.03	0.36	5.62
Mean Precipitation (1981-2010 Normals)	0.28	0.34	0.56	0.98	1.45	1.21	0.78	0.50	0.83	0.85	0.41	0.24	8.42
Departure from Normal	0.01	0.64	-0.32	0.86	-1.11	-0.8	-0.53	-0.50	-0.13	-0.67	-0.38	0.12	-2.8
Percent of Normal	104	288	43	188	23	34	32	0	84	21	7	150	67
Rank - Driest to Wettest 103 years (P.O.R. 1918-2020)	72	98	34	82	8 Tie	24	29	6	60	16	8 Tie	78	7

Greatest 24-HR Total	0.2	0.42	0.12	0.64	0.26	0.19	0.13	T	0.63	0.1	0.03	0.12	0.64
Dates of Occurrence	28	3	2	12	31	7	1	8,19,20,26	8	25	8	15	4/12
Number of Days with:
Precipitation >= 0.01	3	7	4	8	4	6	3	0	3	3	1	7	49
Precipitation >= 0.10	1	3	1	4	1	1	1	0	1	1	0	1	15
Precipitation >= 1.00	0	0	0	0	0	0	0	0	0	0	0	0	0
Daily Precipitation Records Set or Tied	0	0	0	1	0	0	0	0	0	0	0	0	1

Precipitation Ranks and Records:

One Day Precipitation Records:

April: 0.64" on the 12th.

Top Ten Wettest February's on Record
Rank	Year	Precipitation (inches)
1	2004	1.33
2	2015	1.28
3	2003	1.15
4	2020	0.98
5	1986	0.97
6	2017	0.96
7	1955	0.90
8	1935	0.86
9	1920	0.80
10	2011	0.75

Top Ten Driest May's on Record
Rank	Year	Precipitation (inches)
1	1936	0.08
2	1963	0.11
3	1994	0.17
4	1984	0.18
5	1974	0.20
6	2006	0.26
7	2001	0.31
8	1969	0.34
8	2020	0.34
10	1948	0.35

Top Ten Driest August's on Record
Rank	Year	Precipitation (inches)
1	1929	0
1	1944	0
1	1949	0
1	1969	0
1	1985	0
6	2020	0.001
7	1937	0.01
7	1967	0.01
9	1924	0.02
10	1956	0.02

Top Ten Driest November's on Record
Rank	Year	Precipitation (inches)
1	1939	0
1	1949	0
1	1976	0
1	1989	0
5	1981	0.01
5	1982	0.01
5	2009	0.01
8	1954	0.03
8	2020	0.03
10	1988	0.04

Top Ten Driest Years on Record
Rank	Year	Precipitation (inches)
1	1988	3.75
2	2012	3.98
3	1974	4.12
4	1954	4.85
5	2001, 2006	5.07
7	2020	5.62
8	1966	5.66
9	1990	5.71
10	1922	5.91

Top Ten Wettest Years on Record
Rank	Year	Precipitation (inches)
1	1923	18.43
2	2017	15.86
3	2016	15.24
4	1941	14.74
5	1912	14.73
6	1993	13.49
7	1998, 1995	13.41
9	1971	13.11
10	1947	12.45
97	2020	5.62


Annual Precipitation for Period of Record - Click on Graph to Enlarge

Click on Graph to Enlarge

Learn more about the National Weather Service's efforts to build a Weather-Ready Nation!

Snow Banner

Element	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Total (inches)	4	19.5	4.4	20.3	0.01	0	0	0	3.3	3.8	0.001	6.4	61.7
Mean Snowfall (1981-2010 Normals)	4.8	6.0	5.9	6.1	1.2	0.0	0.0	0.0	0.3	3.7	4.3	4.8	37.1
Departure from Normal	-0.8	13.5	-1.5	14.2	-1.19	0.0	0.0	0.0	3	0.1	-4.3	1.6	24.6
Percent of Normal	83	325	75	333	1	0	0	0	1100	103	0	133	166
Rank - Least to Most 103 years (P.O.R 1918-2020)	57	97	82	94	70	NA	NA	NA	95	66	15	71	100

Greatest 24-HR Total	2.5	9	2	8	T	0	0	0	2.9	2.5	T	2.3	2.9
Dates of Occurrence	28	3	2	12	31	NA	NA	NA	8	25	9,10	15	9/8
Number of Days with:
Snowfall >= 1.0 inch	1	5	3	4	0	0	0	0	1	2	0	3	19
Daily Snowfall Records Set or Tied	0	0	0	1	0	0	0	0	2	0	0	0	3
* 69 months of May on record a trace or 0.0" of snowfall. * 83 months of September on record with no snowfall.

Snowfall Ranks and Records:

One Day Snowfall Records (inches):

April: 8.0" on the 12th.
September: 2.9" on the 8th, and 0.4" on the 9th.

Top Ten Snowiest February's on Record
Rank	Year	Snowfall (inches)
1	1986	22.5
2	2020	19.5
3	2014	17.8
4	2003	16.9
5	1958	16.0
6	2002	15.3
7	2016	15.1
8	1964	13.5
9	1934,1919	13.0

Top Ten Snowiest April's on Record
Rank	Year	Snowfall (inches)
1	1998	31.7
2	1919	29.0
3	2012	24.7
4	1944	22.1
5	1921	21.0
6	2016	20.9
7	2020	20.3
8	1926	18.0
9	1978, 1933	17.0

Top Ten Snowiest September's on Record
Rank	Year	Snowfall (inches)
1	1982	13.0
2	2013	5.7
2	2000	5.7
4	1965	5.0
5	1946	4.0
5	1944	4.0
7	2020	3.3
8	1929	3.0
9	1999	2.8
10	1945	2.0

Top Ten Snowiest Years on Record
Rank	Year	Snowfall (inches)
1	1920	77.0
2	2017	71.1
3	2013	70.6
4	2009	62.5
5	2020	61.7
5	2016	61.7
7	2010	60.1
8	1919	58.0
9	1923	56.2
10	1944	55.4