Tri-Cities weather in September

In September, Tri-Cities sees average daytime highs of 81°F and overnight lows near 54°F, with 0.3 in of rain across 1.8 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 10th-wettest month of the year here.

Highs ease over the month, from about 86°F in the first days to 76°F by the end. The sky is clear or mostly clear about 60% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 h 12 min at the start of September to 11 h 30 min by month's end. Set against the rest of the year, September is Tri-Cities's 3rd-clearest and 10th-windiest month. For the whole year in context, see Tri-Cities's year-round climate.

Daytime high: 81°; 4th warmest
Overnight low: 54°; 9th coldest
Rainfall: 0.3 in; 1.8 wet days
Daylight: 12 h 18 min; 5:41 AM – 6:01 PM
Cloud cover: 33%; 3rd clearest
Wind: 5 mph; 10th windiest
Solar energy: 5.04 kWh/m²
Travel score: 7.7; out of 10

← August Tri-Cities year-round climate October →Best places to visit in September

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 86°F in the first days to 76°F by the end.

A typical September day in Tri-Cities reaches about 81°F in the afternoon and slips back to 54°F overnight — a 27°F spread between the day's warmth and the night's chill. On most days the high lands between 71°F and 92°F. Set against its neighbours, September runs about 10°F cooler than August and about 15°F warmer than October.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Avg high (°F)	87	86	86	86	85	85	85	84	84	83	83	83	82	82	81	81	81	80	80	79	79	79	78	78	77	77	76	76	75	75
Avg low (°F)	58	58	58	57	57	57	56	56	56	56	55	55	55	55	54	54	54	53	53	53	52	52	52	51	51	51	50	50	50	49

	Avg high (°F)	Avg low (°F)
1	87	58
2	86	58
3	86	58
4	86	57
5	85	57
6	85	57
7	85	56
8	84	56
9	84	56
10	83	56
11	83	55
12	83	55
13	82	55
14	82	55
15	81	54
16	81	54
17	81	54
18	80	53
19	80	53
20	79	53
21	79	52
22	79	52
23	78	52
24	78	51
25	77	51
26	77	51
27	76	50
28	76	50
29	75	50
30	75	49

How September really feels in Tri-Cities

Once humidity and wind are folded in, September averages 0 days that feel above 90°F and 0 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F

heat index over the day's high

Days feeling ≤ 32°F

wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Tri-Cities weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 10th-wettest month here — the current month is highlighted below.

Month	High / Low (°F)	Rainfall (inches)	Wet days	Snow days	Daylight (hours)	Travel score
Jan	41° / 29°	1.3	8.1	2.3	8.8	0.2
Feb	48° / 32°	0.9	6.2	1.3	10	2.0
Mar	58° / 38°	0.9	5.9	0.4	11.6	4.6
Apr	68° / 44°	0.7	4.9	0	13.3	6.9
May	77° / 52°	0.7	4.5	0	14.7	7.6
Jun	84° / 58°	0.5	2.8	0	15.5	6.6
Jul	93° / 64°	0.1	1	0	15.2	3.9
Aug	92° / 62°	0.2	1	0	14	4.5
Sep	81° / 54°	0.3	1.8	0	12.3	7.7
Oct	66° / 44°	0.9	5	0	10.7	6.7
Nov	50° / 35°	1.1	7.3	0.7	9.2	2.4
Dec	41° / 29°	1.4	8.4	2.4	8.5	0.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 60% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 24%. Skies tend to cloud over as the month goes on.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Clearer (%)	83	83	83	81	81	80	80	78	78	76	76	75	75	74	73	73	73	73	73	73	73	73	73	74	74	73	73	73	73	71
Cloudier (%)	17	17	17	19	19	20	20	22	22	24	24	25	25	26	27	27	27	27	27	27	27	27	27	26	26	27	27	27	27	29

	Clearer (%)	Cloudier (%)
1	83	17
2	83	17
3	83	17
4	81	19
5	81	19
6	80	20
7	80	20
8	78	22
9	78	22
10	76	24
11	76	24
12	75	25
13	75	25
14	74	26
15	73	27
16	73	27
17	73	27
18	73	27
19	73	27
20	73	27
21	73	27
22	73	27
23	73	27
24	74	26
25	74	26
26	73	27
27	73	27
28	73	27
29	73	27
30	71	29

Chance of precipitation in September

Any precipitation

Tri-Cities gets around 0.3 in of rain over 1.8 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 6% and peaks near 8% on the wettest days.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Rain chance (%)	4	4	4	4	4	4	5	5	5	6	6	6	6	6	7	7	7	7	7	7	7	7	7	7	7	7	7	8	8	8

	Rain chance (%)
1	4
2	4
3	4
4	4
5	4
6	4
7	5
8	5
9	5
10	6
11	6
12	6
13	6
14	6
15	7
16	7
17	7
18	7
19	7
20	7
21	7
22	7
23	7
24	7
25	7
26	7
27	7
28	8
29	8
30	8

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the dry band about 98% of days. It rarely turns muggy — the humid and sticky bands barely register.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Dry (%)	99	99	99	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	98	99	99	99	99
Comfortable (%)	1	1	1	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	1	1	1	1

	Dry (%)	Comfortable (%)
1	99	1
2	99	1
3	99	1
4	98	2
5	98	2
6	98	2
7	98	2
8	98	2
9	98	2
10	98	2
11	98	2
12	98	2
13	98	2
14	98	2
15	98	2
16	98	2
17	98	2
18	98	2
19	98	2
20	98	2
21	98	2
22	98	2
23	98	2
24	98	2
25	98	2
26	98	2
27	99	1
28	99	1
29	99	1
30	99	1

Wind in September

Winds average 5 mph in September.

Across September, daily wind ranges from about 5 mph on the calmest days to 5 mph at its breeziest. It stays fairly steady from day to day.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Wind speed (mph)	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5
Feels	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm

	Wind speed (mph)	Feels
1	5	calm
2	5	calm
3	5	calm
4	5	calm
5	5	calm
6	5	calm
7	5	calm
8	5	calm
9	5	calm
10	5	calm
11	5	calm
12	5	calm
13	5	calm
14	5	calm
15	5	calm
16	5	calm
17	5	calm
18	5	calm
19	5	calm
20	5	calm
21	5	calm
22	5	calm
23	5	calm
24	5	calm
25	5	calm
26	5	calm
27	5	calm
28	5	calm
29	5	calm
30	5	calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 h 12 min at the start of September to 11 h 30 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 102 minutes over September. Sunrise moves from 5:22 AM to 6:00 AM, and sunset from 6:31 PM to 5:32 PM.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Daylight (h)	13.2	13.1	13.0	13.0	12.9	12.9	12.8	12.8	12.7	12.7	12.6	12.5	12.5	12.4	12.4	12.3	12.3	12.2	12.2	12.1	12.0	12.0	11.9	11.9	11.8	11.8	11.7	11.6	11.6	11.5
Sunrise (AM)	5:22	5:23	5:24	5:26	5:27	5:28	5:30	5:31	5:32	5:34	5:35	5:36	5:38	5:39	5:40	5:41	5:43	5:44	5:45	5:47	5:48	5:49	5:51	5:52	5:53	5:55	5:56	5:57	5:59	6:00
Sunset (PM)	6:31	6:29	6:27	6:25	6:23	6:21	6:19	6:17	6:15	6:13	6:11	6:09	6:07	6:05	6:03	6:01	5:59	5:57	5:55	5:53	5:51	5:48	5:46	5:44	5:42	5:40	5:38	5:36	5:34	5:32

	Daylight (h)	Sunrise (AM)	Sunset (PM)
1	13.2	5:22	6:31
2	13.1	5:23	6:29
3	13.0	5:24	6:27
4	13.0	5:26	6:25
5	12.9	5:27	6:23
6	12.9	5:28	6:21
7	12.8	5:30	6:19
8	12.8	5:31	6:17
9	12.7	5:32	6:15
10	12.7	5:34	6:13
11	12.6	5:35	6:11
12	12.5	5:36	6:09
13	12.5	5:38	6:07
14	12.4	5:39	6:05
15	12.4	5:40	6:03
16	12.3	5:41	6:01
17	12.3	5:43	5:59
18	12.2	5:44	5:57
19	12.2	5:45	5:55
20	12.1	5:47	5:53
21	12.0	5:48	5:51
22	12.0	5:49	5:48
23	11.9	5:51	5:46
24	11.9	5:52	5:44
25	11.8	5:53	5:42
26	11.8	5:55	5:40
27	11.7	5:56	5:38
28	11.6	5:57	5:36
29	11.6	5:59	5:34
30	11.5	6:00	5:32

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 5.04 kWh/m².

For context, solar energy here swings from a low near 1.26 kWh/m² to a high of 7.85 kWh/m² in July across the year — September's 5.04 kWh/m² falls in the middle.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Solar energy (kWh/m²)	5.9	5.9	5.8	5.8	5.7	5.6	5.6	5.5	5.4	5.4	5.3	5.3	5.2	5.1	5.1	5.0	4.9	4.9	4.8	4.8	4.7	4.6	4.6	4.5	4.4	4.4	4.3	4.3	4.2	4.1
Level	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright	Bright

	Solar energy (kWh/m²)	Level
1	5.9	Bright
2	5.9	Bright
3	5.8	Bright
4	5.8	Bright
5	5.7	Bright
6	5.6	Bright
7	5.6	Bright
8	5.5	Bright
9	5.4	Bright
10	5.4	Bright
11	5.3	Bright
12	5.3	Bright
13	5.2	Bright
14	5.1	Bright
15	5.1	Bright
16	5.0	Bright
17	4.9	Bright
18	4.9	Bright
19	4.8	Bright
20	4.8	Bright
21	4.7	Bright
22	4.6	Bright
23	4.6	Bright
24	4.5	Bright
25	4.4	Bright
26	4.4	Bright
27	4.3	Bright
28	4.3	Bright
29	4.2	Bright
30	4.1	Bright

Planning a trip in September

Is September a good time to visit Tri-Cities?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

7.7

Sightseeing

1st-best month of the year

8.1

Beach & pool

1st-best month of the year

September is one of the better times to visit Tri-Cities for general sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Tri-Cities in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Tri-Cities sees daytime highs around 81°F and nights near 54°F. Pack light clothes. Worth having: sun protection.

light clothessun protection

UV index in Tri-Cities in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 5 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Tri-Cities peaks around July 16 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 17 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
UV index (midday)	1	2	4	5	7	6	8	6	5	3	1	1
Level	Low	Low	Moderate	Moderate	Very high	High	Very high	High	Moderate	Moderate	Low	Low

	UV index (midday)	Level
Jan	1	Low
Feb	2	Low
Mar	4	Moderate
Apr	5	Moderate
May	7	Very high
Jun	6	High
Jul	8	Very high
Aug	6	High
Sep	5	Moderate
Oct	3	Moderate
Nov	1	Low
Dec	1	Low

Air quality in Tri-Cities in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Tri-Cities is worst in August — around 27 µg/m³ PM2.5 (moderate), about 3.1× the cleanest month (December, 9 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
PM2.5 (µg/m³)	10	11	14	11	9	10	13	27	21	12	11	9
Level	Good	Good	Moderate	Good	Good	Good	Moderate	Moderate	Moderate	Moderate	Good	Good

	PM2.5 (µg/m³)	Level
Jan	10	Good
Feb	11	Good
Mar	14	Moderate
Apr	11	Good
May	9	Good
Jun	10	Good
Jul	13	Moderate
Aug	27	Moderate
Sep	21	Moderate
Oct	12	Moderate
Nov	11	Good
Dec	9	Good

Location & terrain

Where is Tri-Cities?

Tri-Cities sits at 46.2°N, 119.2°W, 348 ft above sea level, in United States. The nearest listed city is Kennewick, 3.7 mi away.

Topography around Tri-Cities

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Tri-Cities.

Within 2 miles, the terrain around Tri-Cities has only modest variations in elevation — a maximum elevation change of 197 ft around an average of 400 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 1,677 ft; within 50 miles, large variations in elevation — a maximum elevation change of 3,894 ft.

The land around Tri-Cities is covered by artificial surfaces (32%) and grassland (28%) within 2 miles, grassland (38%) and cropland (28%) within 10 miles, and grassland (51%) and cropland (42%) within 50 miles.

2 miles

197 ft

artificial surfaces 32%

10 miles

1,677 ft

grassland 38%

50 miles

3,894 ft

grassland 51%

treesgrasslandcroplandartificial surfacesbare terrainwater

← August Tri-Cities year-round climate October →Best places to visit in September

September weather nearby: Kennewick 3.7 mi · Pasco 4.3 mi · Richland 5.0 mi · Hermiston 29 mi · Sunnyside 39 mi · Walla Walla 43 mi · Pendleton 44 mi · Moses Lake 62 mi

United States travel facts

Power plugs: Type A / B; 120 V · 60 Hz
Prices: ≈ 100% of US; price level, 2025
GDP per capita: $90,027; 2025
Happiness: 6.8 / 10; World Happiness, 2025
Safe drinking water: 98%; of population, 2024
Homicide rate: 5.8; per 100k, 2023
Road deaths: 12.7; per 100k/yr, 2019
Income group: High; World Bank
Religion

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Tri-Cities (46.2454°, -119.1962°, elevation 348 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).

	Avg high (°F)	Avg low (°F)
1	87	58
2	86	58
3	86	58
4	86	57
5	85	57
6	85	57
7	85	56
8	84	56
9	84	56
10	83	56
11	83	55
12	83	55
13	82	55
14	82	55
15	81	54
16	81	54
17	81	54
18	80	53
19	80	53
20	79	53
21	79	52
22	79	52
23	78	52
24	78	51
25	77	51
26	77	51
27	76	50
28	76	50
29	75	50
30	75	49

	Clearer (%)	Cloudier (%)
1	83	17
2	83	17
3	83	17
4	81	19
5	81	19
6	80	20
7	80	20
8	78	22
9	78	22
10	76	24
11	76	24
12	75	25
13	75	25
14	74	26
15	73	27
16	73	27
17	73	27
18	73	27
19	73	27
20	73	27
21	73	27
22	73	27
23	73	27
24	74	26
25	74	26
26	73	27
27	73	27
28	73	27
29	73	27
30	71	29

	Rain chance (%)
1	4
2	4
3	4
4	4
5	4
6	4
7	5
8	5
9	5
10	6
11	6
12	6
13	6
14	6
15	7
16	7
17	7
18	7
19	7
20	7
21	7
22	7
23	7
24	7
25	7
26	7
27	7
28	8
29	8
30	8

	Dry (%)	Comfortable (%)
1	99	1
2	99	1
3	99	1
4	98	2
5	98	2
6	98	2
7	98	2
8	98	2
9	98	2
10	98	2
11	98	2
12	98	2
13	98	2
14	98	2
15	98	2
16	98	2
17	98	2
18	98	2
19	98	2
20	98	2
21	98	2
22	98	2
23	98	2
24	98	2
25	98	2
26	98	2
27	99	1
28	99	1
29	99	1
30	99	1

	Avg high (°F)	Avg low (°F)
1	87	58
2	86	58
3	86	58
4	86	57
5	85	57
6	85	57
7	85	56
8	84	56
9	84	56
10	83	56
11	83	55
12	83	55
13	82	55
14	82	55
15	81	54
16	81	54
17	81	54
18	80	53
19	80	53
20	79	53
21	79	52
22	79	52
23	78	52
24	78	51
25	77	51
26	77	51
27	76	50
28	76	50
29	75	50
30	75	49

	Clearer (%)	Cloudier (%)
1	83	17
2	83	17
3	83	17
4	81	19
5	81	19
6	80	20
7	80	20
8	78	22
9	78	22
10	76	24
11	76	24
12	75	25
13	75	25
14	74	26
15	73	27
16	73	27
17	73	27
18	73	27
19	73	27
20	73	27
21	73	27
22	73	27
23	73	27
24	74	26
25	74	26
26	73	27
27	73	27
28	73	27
29	73	27
30	71	29

	Rain chance (%)
1	4
2	4
3	4
4	4
5	4
6	4
7	5
8	5
9	5
10	6
11	6
12	6
13	6
14	6
15	7
16	7
17	7
18	7
19	7
20	7
21	7
22	7
23	7
24	7
25	7
26	7
27	7
28	8
29	8
30	8

	Dry (%)	Comfortable (%)
1	99	1
2	99	1
3	99	1
4	98	2
5	98	2
6	98	2
7	98	2
8	98	2
9	98	2
10	98	2
11	98	2
12	98	2
13	98	2
14	98	2
15	98	2
16	98	2
17	98	2
18	98	2
19	98	2
20	98	2
21	98	2
22	98	2
23	98	2
24	98	2
25	98	2
26	98	2
27	99	1
28	99	1
29	99	1
30	99	1

	Avg high (°F)	Avg low (°F)
1	87	58
2	86	58
3	86	58
4	86	57
5	85	57
6	85	57
7	85	56
8	84	56
9	84	56
10	83	56
11	83	55
12	83	55
13	82	55
14	82	55
15	81	54
16	81	54
17	81	54
18	80	53
19	80	53
20	79	53
21	79	52
22	79	52
23	78	52
24	78	51
25	77	51
26	77	51
27	76	50
28	76	50
29	75	50
30	75	49

	Clearer (%)	Cloudier (%)
1	83	17
2	83	17
3	83	17
4	81	19
5	81	19
6	80	20
7	80	20
8	78	22
9	78	22
10	76	24
11	76	24
12	75	25
13	75	25
14	74	26
15	73	27
16	73	27
17	73	27
18	73	27
19	73	27
20	73	27
21	73	27
22	73	27
23	73	27
24	74	26
25	74	26
26	73	27
27	73	27
28	73	27
29	73	27
30	71	29

	Rain chance (%)
1	4
2	4
3	4
4	4
5	4
6	4
7	5
8	5
9	5
10	6
11	6
12	6
13	6
14	6
15	7
16	7
17	7
18	7
19	7
20	7
21	7
22	7
23	7
24	7
25	7
26	7
27	7
28	8
29	8
30	8

	Dry (%)	Comfortable (%)
1	99	1
2	99	1
3	99	1
4	98	2
5	98	2
6	98	2
7	98	2
8	98	2
9	98	2
10	98	2
11	98	2
12	98	2
13	98	2
14	98	2
15	98	2
16	98	2
17	98	2
18	98	2
19	98	2
20	98	2
21	98	2
22	98	2
23	98	2
24	98	2
25	98	2
26	98	2
27	99	1
28	99	1
29	99	1
30	99	1