Mount Vernon weather in September

In September, Mount Vernon sees average daytime highs of 65°F and overnight lows near 51°F, with 3.9 in of rain across 9.5 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 68°F in the first days to 62°F by the end. The sky is clear or mostly clear about 40% 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 Mount Vernon's 3rd-clearest and 10th-windiest month. For the whole year in context, see Mount Vernon's year-round climate.

Daytime high
65°
3rd warmest
Overnight low
51°
10th coldest
Rainfall
3.9 in
9.5 wet days
Daylight
12 h 18 min
5:53 AM – 6:14 PM
Cloud cover
50%
3rd clearest
Wind
3 mph
10th windiest
Solar energy
4.02 kWh/m²
Travel score
6.1
out of 10

Mount Vernon is city in Skagit County, Washington, United States.

Density
1,050/km²
people per km²
Founded
1870

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 68°F in the first days to 62°F by the end.

A typical September day in Mount Vernon reaches about 65°F in the afternoon and slips back to 51°F overnight — a 14°F spread between the day's warmth and the night's chill. On most days the high lands between 57°F and 74°F. Set against its neighbours, September runs about 5°F cooler than August and about 10°F warmer than October.

40°50°60°70°80°151015202530
Avg high (°F)Avg low (°F)
16854
26854
36854
46853
56853
66753
76753
86753
96753
106753
116653
126652
136652
146652
156552
166552
176551
186551
196451
206451
216451
226450
236350
246350
256350
266349
276249
286249
296249
306149

How September really feels in Mount Vernon

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.

Mount Vernon 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
Jan42° / 34°10.219.19.58.60.2
Feb44° / 34°6.715.499.90.7
Mar48° / 37°8.119.79.811.61.4
Apr53° / 41°5.816.6413.42.5
May60° / 47°4.112.80.7154.4
Jun64° / 51°3.110.9015.85.5
Jul70° / 55°1.55.6015.57.4
Aug71° / 56°1.85.7014.17.5
Sep65° / 51°3.99.5012.46.1
Oct55° / 44°7.915.20.710.63.2
Nov46° / 37°11.419.47.791.0
Dec41° / 33°10.01912.28.20.1

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 40% 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 45%. Skies tend to cloud over as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15941
25941
35941
46040
56040
66040
75941
85941
95941
105842
115842
125743
135644
145545
155545
165545
175446
185446
195347
205347
215347
225248
235248
245347
255347
265347
275248
285248
295149
305050

Chance of precipitation in September

Any precipitation

Mount Vernon gets around 3.9 in of rain over 9.5 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 32% and peaks near 34% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
128
228
329
429
530
630
731
831
932
1032
1133
1234
1334
1434
1534
1634
1734
1834
1934
2034
2134
2233
2333
2433
2533
2632
2732
2832
2933
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 82% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)
17426
27525
37525
47624
57723
67723
77822
87822
97921
108020
118020
128020
138119
148119
158218
168218
178317
188317
198416
208515
218515
228614
238713
248812
258911
269010
27919
28928
29928
30937

Wind in September

Winds average 3 mph in September.

Across September, daily wind ranges from about 3 mph on the calmest days to 4 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
13calm
23calm
33calm
43calm
53calm
63calm
73calm
83calm
93calm
103calm
113calm
123calm
133calm
143calm
153calm
163calm
173calm
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 5:32 AM to 6:14 AM, and sunset from 6:46 PM to 5:44 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.25:326:46
213.25:336:44
313.15:356:42
413.15:366:40
513.05:376:38
612.95:396:36
712.95:406:34
812.85:426:32
912.85:436:29
1012.75:456:27
1112.75:466:25
1212.65:476:23
1312.55:496:21
1412.55:506:18
1512.45:526:16
1612.35:536:14
1712.35:556:12
1812.25:566:10
1912.25:586:08
2012.15:596:05
2112.06:006:03
2212.06:026:01
2311.96:035:59
2411.96:055:57
2511.86:065:54
2611.76:085:52
2711.76:095:50
2811.66:115:48
2911.66:125:46
3011.56:145:44

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.02 kWh/m².

For context, solar energy here swings from a low near 0.85 kWh/m² to a high of 6.27 kWh/m² in July across the year — September's 4.02 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.7Bright
24.7Bright
34.6Bright
44.6Bright
54.5Bright
64.5Bright
74.5Bright
84.4Bright
94.3Bright
104.3Bright
114.2Bright
124.2Bright
134.1Bright
144.1Bright
154.0Bright
164.0Moderate
173.9Moderate
183.8Moderate
193.8Moderate
203.7Moderate
213.7Moderate
223.6Moderate
233.6Moderate
243.5Moderate
253.5Moderate
263.4Moderate
273.4Moderate
283.3Moderate
293.3Moderate
303.2Moderate
Planning a trip in September

Hazard calendar for Mount Vernon

In seasonPeak

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

Mount Vernon'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 Mount Vernon?

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

6.1
Sightseeing
3rd-best month of the year
2.3
Beach & pool
3rd-best month of the year

September is a reasonable time to visit Mount Vernon for sightseeing.

What to pack for Mount Vernon in September

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

In September, Mount Vernon sees daytime highs around 65°F and nights near 51°F. Worth packing: rain gear. About 10 days see rain.

rain gear

Sea temperature near Mount Vernon 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 25 mi away) is warmest in August at about 54°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
Aug54Bracing
Sep53Bracing
Oct50Bracing
Nov49Bracing
Dec47Bracing

UV index in Mount Vernon 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 Mount Vernon 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 Mount Vernon 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 Mount Vernon is worst in September — around 18 µg/m³ PM2.5 (moderate), about 3.2× the cleanest month (December, 6 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodSep 1018 µg/m³Dec 176 µg/m³
PM2.5 (µg/m³)Level
Jan7Good
Feb9Good
Mar12Good
Apr12Good
May12Good
Jun11Good
Jul11Good
Aug18Moderate
Sep18Moderate
Oct12Good
Nov7Good
Dec6Good
Location & terrain

Where is Mount Vernon?

Mount Vernon sits at 48.4°N, 122.3°W, 95 ft above sea level, in United States. The nearest listed city is Anacortes, 14 mi away.

Topography around Mount Vernon

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

Within 2 miles, the terrain around Mount Vernon has significant variations in elevation — a maximum elevation change of 938 ft around an average of 89 ft above sea level; within 10 miles, very significant variations in elevation — a maximum elevation change of 4,045 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 10,755 ft.

The land around Mount Vernon is covered by trees (29%), grassland (28%) and artificial surfaces (27%) within 2 miles, trees (41%) and grassland (25%) within 10 miles, and trees (57%) and water (29%) within 50 miles.

2 miles
938 ft
10 miles
4,045 ft
50 miles
10,755 ft
treesgrasslandcroplandartificial surfacesbare terrainsnow and icewaterwetland
September weather nearby: Anacortes 14 mi · Oak Harbor 17 mi · Arlington 18 mi · Bellingham 24 mi · Marysville 27 mi · Lake Stevens 30 mi · Everett 31 mi · West Lake Stevens 32 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 Mount Vernon (48.4212°, -122.3341°, elevation 95 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).