Saint Peters weather in September

In September, Saint Peters sees average daytime highs of 79°F and overnight lows near 59°F, with 3.2 in of rain across 7.6 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 8th-wettest month of the year here.

Highs ease over the month, from about 84°F in the first days to 75°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 36 min by month's end. Set against the rest of the year, September is Saint Peters's 1st-clearest and 10th-windiest month. For the whole year in context, see Saint Peters's year-round climate.

Daytime high
79°
4th warmest
Overnight low
59°
9th coldest
Rainfall
3.2 in
7.6 wet days
Daylight
12 h 12 min
5:49 AM – 6:04 PM
Cloud cover
45%
1st clearest
Wind
6 mph
10th windiest
Solar energy
4.75 kWh/m²
Travel score
7.1
out of 10

Saint Peters is city in Missouri.

Density
908/km²
people per km²
Founded
1910

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 84°F in the first days to 75°F by the end.

A typical September day in Saint Peters reaches about 79°F in the afternoon and slips back to 59°F overnight — a 20°F spread between the day's warmth and the night's chill. On most days the high lands between 69°F and 89°F. Set against its neighbours, September runs about 7°F cooler than August and about 12°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18465
28465
38364
48364
58364
68363
78263
88262
98262
108162
118161
128061
138060
148060
157960
167959
177859
187858
197858
207858
217757
227757
237756
247656
257656
267655
277555
287554
297554
307454

How September really feels in Saint Peters

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.

Saint Peters weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 8th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan40° / 24°2.57.739.60.0
Feb44° / 28°2.47.62.910.50.8
Mar55° / 37°3.610.61.411.73.5
Apr66° / 47°4.511.30.2135.8
May75° / 57°4.913.3014.16.3
Jun84° / 66°4.011.1014.75.5
Jul87° / 70°3.29.9014.44.6
Aug86° / 67°3.09.2013.55.2
Sep79° / 59°3.27.6012.37.1
Oct67° / 48°3.38.50116.6
Nov54° / 37°3.58.30.89.93.5
Dec43° / 28°2.47.72.29.30.6

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 (%)
16535
26535
36634
46634
56634
66634
76535
86535
96535
106436
116436
126337
136238
146139
156040
166040
176040
185941
195941
206040
216040
226139
236139
246337
256337
266337
276535
286535
296535
306535

Chance of precipitation in September

Any precipitation

Saint Peters gets around 3.2 in of rain over 7.6 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 26% and peaks near 27% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
126
226
326
426
526
626
726
826
926
1026
1126
1227
1327
1427
1527
1627
1727
1827
1927
2027
2126
2226
2325
2425
2524
2624
2723
2823
2922
3022

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 35% of days. Sticky, muggy-or-worse air turns up on roughly 25% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
11016252919
21117252818
31218262717
41418262615
51519262514
61720262413
71921262312
82021262210
9222226219
10242225208
11262225208
12272224197
13292223196
14312223195
15332222185
16352221184
17372220184
18392119173
19412118173
20432118162
21452017162
22472016152
23491915151
24511915141
25541814131
26541814131
27561813121
28591713110
29601712110
30621612100

Wind in September

Winds average 6 mph in September.

Across September, daily wind ranges from about 5 mph on the calmest days to 6 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
15calm
25calm
35calm
45calm
55calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
306calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 54 min at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 78 minutes over September. Sunrise moves from 5:36 AM to 6:03 AM, and sunset from 6:29 PM to 5:41 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:366:29
212.85:376:27
312.85:376:26
412.85:386:24
512.75:396:22
612.75:406:21
712.65:416:19
812.65:426:18
912.55:436:16
1012.55:446:14
1112.55:456:13
1212.45:466:11
1312.45:476:09
1412.35:486:08
1512.35:486:06
1612.25:496:04
1712.25:506:03
1812.25:516:01
1912.15:525:59
2012.15:535:58
2112.05:545:56
2212.05:555:54
2311.95:565:53
2411.95:575:51
2511.95:585:49
2611.85:595:48
2711.86:005:46
2811.76:015:44
2911.76:025:43
3011.66:035:41

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.75 kWh/m².

For context, solar energy here swings from a low near 1.92 kWh/m² to a high of 6.42 kWh/m² in June across the year — September's 4.75 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.3Bright
25.2Bright
35.2Bright
45.1Bright
55.1Bright
65.1Bright
75.0Bright
85.0Bright
95.0Bright
104.9Bright
114.9Bright
124.8Bright
134.8Bright
144.8Bright
154.7Bright
164.7Bright
174.7Bright
184.6Bright
194.6Bright
204.6Bright
214.5Bright
224.5Bright
234.5Bright
244.5Bright
254.4Bright
264.4Bright
274.4Bright
284.3Bright
294.3Bright
304.3Bright
Planning a trip in September

Is September a good time to visit Saint Peters?

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

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

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

What to pack for Saint Peters in September

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

In September, Saint Peters sees daytime highs around 79°F and nights near 59°F. Worth packing: light clothes and sun protection. About 8 days see rain.

light clothessun protection

UV index in Saint Peters 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 Saint Peters peaks around June 22 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 at about 2 (low).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateJun 22UV 9Jan 1UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr7High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep7High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Saint Peters 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 Saint Peters is worst in July — around 17 µg/m³ PM2.5 (moderate), about 2.3× the cleanest month (October, 7 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1616 µg/m³Oct 237 µg/m³
PM2.5 (µg/m³)Level
Jan9Good
Feb11Good
Mar11Good
Apr10Good
May13Moderate
Jun14Moderate
Jul17Moderate
Aug14Moderate
Sep11Good
Oct7Good
Nov7Good
Dec8Good
Location & terrain

Where is Saint Peters?

Saint Peters sits at 38.8°N, 90.6°W, 440 ft above sea level, in United States. The nearest listed city is O'Fallon, 3.7 mi away.

Topography around Saint Peters

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

Within 2 miles, the terrain around Saint Peters has only modest variations in elevation — a maximum elevation change of 167 ft around an average of 469 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 469 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 978 ft.

The land around Saint Peters is covered by artificial surfaces (32%), trees (26%) and cropland (26%) within 2 miles, trees (36%) and cropland (27%) within 10 miles, and trees (51%) and cropland (32%) within 50 miles.

2 miles
167 ft
10 miles
469 ft
50 miles
978 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: O'Fallon 3.7 mi · Saint Charles 8.1 mi · Chesterfield 9.9 mi · Maryland Heights 12 mi · Wentzville 12 mi · Hazelwood 14 mi · Creve Coeur 15 mi · Ballwin 15 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 Saint Peters (38.8003°, -90.6265°, elevation 440 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).