Arlington weather in September

In September, Arlington sees average daytime highs of 67°F and overnight lows near 50°F, with 3.4 in of rain across 8.8 wet days and about 12.4 hours of daylight. It is the 3rd-warmest and 9th-wettest month of the year here.

Highs ease over the month, from about 70°F in the first days to 64°F by the end. The sky is clear or mostly clear about 42% 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 Arlington's 3rd-clearest and 9th-windiest month. For the whole year in context, see Arlington's year-round climate.

Daytime high
67°
3rd warmest
Overnight low
50°
9th coldest
Rainfall
3.4 in
8.8 wet days
Daylight
12 h 18 min
5:52 AM – 6:13 PM
Cloud cover
49%
3rd clearest
Wind
4 mph
9th windiest
Solar energy
4 kWh/m²
Travel score
6.5
out of 10

Arlington is city in northern Snohomish County, Washington, United States.

Density
790/km²
people per km²
Founded
1903

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 70°F in the first days to 64°F by the end.

A typical September day in Arlington reaches about 67°F in the afternoon and slips back to 50°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 60°F and 76°F. Set against its neighbours, September runs about 6°F cooler than August and about 10°F warmer than October.

40°50°60°70°80°151015202530
Avg high (°F)Avg low (°F)
17153
27053
37053
47052
57052
66952
76952
86952
96952
106952
116851
126851
136851
146851
156751
166751
176750
186750
196650
206650
216649
226549
236549
246549
256549
266448
276448
286448
296348
306347

How September really feels in Arlington

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
0
heat index over the day's high
Days feeling ≤ 32°F
0
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.

Arlington weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 9th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan44° / 36°9.319.15.38.60.6
Feb47° / 36°6.115.54.59.91.2
Mar51° / 38°7.619.63.711.61.9
Apr56° / 42°5.616.4113.43.2
May62° / 47°3.812.10.114.95.0
Jun66° / 51°2.89.8015.86.0
Jul72° / 55°1.35.2015.57.8
Aug73° / 55°1.65.5014.17.8
Sep67° / 50°3.48.8012.46.5
Oct57° / 44°7.214.9010.63.7
Nov48° / 38°10.419.22.291.4
Dec43° / 35°9.319.26.18.20.4

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 42% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 15% of September, with mostly cloudy or overcast conditions the remaining 43%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16139
26139
36139
46238
56238
66238
76139
86139
96139
106040
115941
125842
135842
145743
155644
165644
175545
185545
195545
205545
215446
225446
235446
245446
255545
265446
275446
285347
295347
305248

Chance of precipitation in September

Any precipitation

Arlington gets around 3.4 in of rain over 8.8 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 30% and peaks near 33% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
126
226
327
427
527
627
728
828
929
1029
1130
1230
1331
1431
1531
1631
1731
1831
1932
2032
2132
2232
2332
2432
2532
2631
2731
2832
2932
3033

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 83% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)
17624
27624
37723
47723
57822
67822
77921
87921
97921
108020
118020
128119
138119
148119
158218
168218
178317
188317
198416
208515
218515
228614
238713
248812
258911
268911
279010
28919
29928
30937

Wind in September

Winds average 4 mph in September.

Across September, daily wind ranges from about 4 mph on the calmest days to 4 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
14calm
24calm
34calm
44calm
54calm
64calm
74calm
84calm
94calm
104calm
114calm
124calm
134calm
144calm
154calm
164calm
174calm
184calm
194calm
204calm
214calm
224calm
234calm
244calm
254calm
264calm
274calm
284calm
294calm
304calm

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 5:31 AM to 6:13 AM, and sunset from 6:45 PM to 5:43 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.25:316:45
213.25:336:43
313.15:346:41
413.15:356:39
513.05:376:37
612.95:386:35
712.95:406:33
812.85:416:30
912.85:426:28
1012.75:446:26
1112.65:456:24
1212.65:476:22
1312.55:486:20
1412.55:506:18
1512.45:516:15
1612.35:526:13
1712.35:546:11
1812.25:556:09
1912.25:576:07
2012.15:586:04
2112.06:006:02
2212.06:016:00
2311.96:025:58
2411.96:045:56
2511.86:055:54
2611.76:075:52
2711.76:085:49
2811.66:105:47
2911.66:115:45
3011.56:135:43

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4 kWh/m².

For context, solar energy here swings from a low near 0.83 kWh/m² to a high of 6.16 kWh/m² in July across the year — September's 4 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.7Bright
24.6Bright
34.6Bright
44.6Bright
54.5Bright
64.5Bright
74.4Bright
84.4Bright
94.3Bright
104.3Bright
114.2Bright
124.2Bright
134.1Bright
144.0Bright
154.0Moderate
163.9Moderate
173.9Moderate
183.8Moderate
193.8Moderate
203.7Moderate
213.6Moderate
223.6Moderate
233.5Moderate
243.5Moderate
253.5Moderate
263.4Moderate
273.3Moderate
283.3Moderate
293.2Moderate
303.2Moderate
Planning a trip in September

Hazard calendar for Arlington

In seasonPeak

None of Arlington's seasonal hazards are active in September. The full-year calendar below shows when the rainy season, cyclone risk and dust haze do peak.

Arlington's rainy season runs October–April, when most of the year's rain falls.

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

Is September a good time to visit Arlington?

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

6.5
Sightseeing
3rd-best month of the year
3.1
Beach & pool
3rd-best month of the year

September is a reasonable time to visit Arlington for sightseeing.

What to pack for Arlington in September

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

In September, Arlington sees daytime highs around 67°F and nights near 50°F. Worth packing: rain gear. About 9 days see rain.

rain gear

Sea temperature near Arlington in September

The nearest coast averages about 53°F in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 35 mi away) is warmest in August at about 53°F and coldest in February near 46°F.

The water stays below 68°F all year — cool enough that most swimmers want a wetsuit.

45°50°55°JanFebMarAprMayJunJulAugSepOctNovDecbracing
Sea temperature (°F)Comfort
Jan46Bracing
Feb46Bracing
Mar47Bracing
Apr48Bracing
May50Bracing
Jun52Bracing
Jul53Bracing
Aug53Bracing
Sep53Bracing
Oct50Bracing
Nov49Bracing
Dec47Bracing

UV index in Arlington in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 4 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Arlington peaks around July 17 at about 8 (very high) — sunscreen and a hat are worth it in the middle of the day. It bottoms out near December 18 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 7 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 17UV 8Dec 18UV 1
UV index (midday)Level
Jan1Low
Feb1Low
Mar4Moderate
Apr5Moderate
May7High
Jun6High
Jul8Very high
Aug6High
Sep4Moderate
Oct3Moderate
Nov1Low
Dec1Low

Air quality in Arlington 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 Arlington is worst in August — around 20 µg/m³ PM2.5 (moderate), about 3.1× the cleanest month (December, 6 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodGoodModerateGoodModerateGoodAug 2119 µg/m³Dec 157 µg/m³
PM2.5 (µg/m³)Level
Jan8Good
Feb10Good
Mar12Moderate
Apr12Good
May13Moderate
Jun11Good
Jul10Good
Aug20Moderate
Sep18Moderate
Oct11Good
Nov7Good
Dec6Good
Location & terrain

Where is Arlington?

Arlington sits at 48.2°N, 122.1°W, 115 ft above sea level, in United States. The nearest listed city is Marysville, 11 mi away.

Topography around Arlington

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

Within 2 miles, the terrain around Arlington has only modest variations in elevation — a maximum elevation change of 479 ft around an average of 157 ft above sea level; within 10 miles, large variations in elevation — a maximum elevation change of 3,297 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 10,755 ft.

The land around Arlington is covered by trees (51%) and grassland (32%) within 2 miles, trees (76%) within 10 miles, and trees (66%) and water (21%) within 50 miles.

2 miles
479 ft
10 miles
3,297 ft
50 miles
10,755 ft
treesgrasslandcroplandartificial surfacesbare terrainsnow and icewater
September weather nearby: Marysville 11 mi · Lake Stevens 13 mi · West Lake Stevens 14 mi · Everett 16 mi · Mount Vernon 18 mi · Mukilteo 19 mi · Eastmont 21 mi · Silver Firs 23 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
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

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 Arlington (48.1987°, -122.1251°, elevation 115 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. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. 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).