Marion weather in September

In September, Marion sees average daytime highs of 81°F and overnight lows near 61°F, with 2.9 in of rain across 7.5 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 11th-wettest month of the year here.

Highs ease over the month, from about 85°F in the first days to 76°F by the end. The sky is clear or mostly clear about 49% of the time in September, and the air most often feels dry.

Daylight stretches from about 12 h 54 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Marion's 1st-clearest and 10th-windiest month. For the whole year in context, see Marion's year-round climate.

Daytime high
81°
4th warmest
Overnight low
61°
9th coldest
Rainfall
2.9 in
7.5 wet days
Daylight
12 h 12 min
5:43 AM – 5:57 PM
Cloud cover
45%
1st clearest
Wind
6 mph
10th windiest
Solar energy
4.78 kWh/m²
Travel score
6.9
out of 10

Marion is city in and the county seat of Williamson County, Illinois, United States.

Density
412/km²
people per km²
Founded
1839

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 85°F in the first days to 76°F by the end.

A typical September day in Marion reaches about 81°F in the afternoon and slips back to 61°F overnight — a 19°F spread between the day's warmth and the night's chill. On most days the high lands between 71°F and 90°F. Set against its neighbours, September runs about 6°F cooler than August and about 12°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18567
28567
38566
48566
58466
68465
78365
88364
98364
108364
118263
128263
138262
148162
158162
168061
178061
188060
197960
207960
217959
227859
237858
247858
257758
267757
277757
287656
297656
307656

How September really feels in Marion

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.

Marion weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 11th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan42° / 28°3.492.39.70.3
Feb47° / 31°3.18.12.310.51.5
Mar57° / 39°4.211.40.911.74.0
Apr68° / 49°5.011.4012.96.0
May76° / 60°4.612.60146.3
Jun85° / 68°3.610.6014.65.2
Jul88° / 72°3.510.2014.34.5
Aug87° / 69°2.88.1013.55.1
Sep81° / 61°2.97.5012.36.9
Oct69° / 50°3.57.60116.9
Nov56° / 39°3.88.70.5103.9
Dec46° / 31°3.38.91.89.41.2

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 49% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 14% of September, with mostly cloudy or overcast conditions the remaining 37%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16436
26337
36436
46436
56436
66436
76436
86436
96337
106337
116337
126139
136139
146139
156139
166040
176040
186040
196139
206139
216139
226337
236436
246436
256535
266535
276634
286634
296733
306733

Chance of precipitation in September

Any precipitation

Marion gets around 2.9 in of rain over 7.5 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 25% and peaks near 27% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
124
224
324
424
524
624
724
824
924
1024
1124
1224
1325
1425
1525
1626
1726
1827
1927
2027
2127
2227
2326
2426
2525
2624
2723
2822
2922
3021

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 31% of days. Sticky, muggy-or-worse air turns up on roughly 28% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
11015223122
21116223120
31217223119
41318223017
51419223015
61520222914
71621222812
81822222811
9192223279
10202223268
11222323257
12232323246
13252323236
14262323225
15282223215
16302223204
17322223194
18342123194
19362122183
20382022173
21411921163
22431920163
23451819152
24471719142
25501718132
26511618132
27531617122
28561517111
29571516111
30591416101

Wind in September

Winds average 6 mph in September.

Across September, daily wind ranges from about 6 mph on the calmest days to 7 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
16calm
26calm
36calm
46calm
56calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
307calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 54 min at the start of September to 11 h 42 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 72 minutes over September. Sunrise moves from 5:30 AM to 5:55 AM, and sunset from 6:21 PM to 5:35 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:306:21
212.85:316:19
312.85:326:18
412.75:326:16
512.75:336:15
612.75:346:13
712.65:356:12
812.65:366:10
912.55:376:08
1012.55:386:07
1112.45:396:05
1212.45:396:04
1312.45:406:02
1412.35:416:00
1512.35:425:59
1612.25:435:57
1712.25:445:56
1812.25:455:54
1912.15:465:52
2012.15:465:51
2112.05:475:49
2212.05:485:48
2311.95:495:46
2411.95:505:44
2511.95:515:43
2611.85:525:41
2711.85:535:40
2811.75:545:38
2911.75:545:36
3011.75:555:35

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.78 kWh/m².

For context, solar energy here swings from a low near 1.93 kWh/m² to a high of 6.45 kWh/m² in June across the year — September's 4.78 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.3Bright
25.3Bright
35.2Bright
45.2Bright
55.2Bright
65.1Bright
75.1Bright
85.0Bright
95.0Bright
105.0Bright
114.9Bright
124.9Bright
134.9Bright
144.8Bright
154.8Bright
164.7Bright
174.7Bright
184.7Bright
194.6Bright
204.6Bright
214.6Bright
224.5Bright
234.5Bright
244.5Bright
254.5Bright
264.5Bright
274.4Bright
284.4Bright
294.4Bright
304.3Bright
Planning a trip in September

Is September a good time to visit Marion?

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

6.9
Sightseeing
1st-best month of the year
7.1
Beach & pool
2nd-best month of the year

September is a reasonable time to visit Marion for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Marion in September

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

In September, Marion sees daytime highs around 81°F and nights near 61°F. Pack light clothes. Worth having: sun protection. About 8 days see rain.

light clothessun protection

UV index in Marion in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 7 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Marion peaks around June 23 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 at about 2 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateJun 23UV 9Dec 22UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar5High
Apr7High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep7High
Oct4Moderate
Nov3Moderate
Dec2Moderate

Air quality in Marion 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 Marion is worst in July — around 19 µg/m³ PM2.5 (moderate), about 2.4× the cleanest month (November, 8 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1318 µg/m³Nov 128 µg/m³
PM2.5 (µg/m³)Level
Jan8Good
Feb11Good
Mar12Moderate
Apr11Good
May14Moderate
Jun17Moderate
Jul19Moderate
Aug14Moderate
Sep12Good
Oct8Good
Nov8Good
Dec8Good
Location & terrain

Where is Marion?

Marion sits at 37.7°N, 88.9°W, 423 ft above sea level, in United States. The nearest listed city is Carbondale, 16 mi away.

Topography around Marion

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

Within 2 miles, the terrain around Marion has only modest variations in elevation — a maximum elevation change of 148 ft around an average of 446 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 331 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,030 ft.

The land around Marion is covered by trees (32%), grassland (26%) and artificial surfaces (24%) within 2 miles, trees (51%), grassland (21%) and cropland (20%) within 10 miles, and trees (46%) and cropland (40%) within 50 miles.

2 miles
148 ft
10 miles
331 ft
50 miles
1,030 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Carbondale 16 mi · Mount Vernon 40 mi · Cape Girardeau 43 mi · Paducah 48 mi · Sikeston 69 mi · Henderson 74 mi · Evansville 77 mi · Belleville 79 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 Marion (37.7306°, -88.9331°, elevation 423 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).