Round Lake Beach weather in September

In September, Round Lake Beach sees average daytime highs of 72°F and overnight lows near 58°F, with 2.9 in of rain across 9 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 7th-wettest month of the year here.

Highs ease over the month, from about 76°F in the first days to 67°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 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Round Lake Beach's 1st-clearest and 9th-windiest month. For the whole year in context, see Round Lake Beach's year-round climate.

Daytime high
72°
4th warmest
Overnight low
58°
9th coldest
Rainfall
2.9 in
9 wet days
Daylight
12 h 18 min
5:38 AM – 5:55 PM
Cloud cover
50%
1st clearest
Wind
9 mph
9th windiest
Solar energy
4.41 kWh/m²
Travel score
6.9
out of 10

Round Lake Beach is village in Lake County, Illinois, United States of America.

Density
2,061/km²
people per km²

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 76°F in the first days to 67°F by the end.

A typical September day in Round Lake Beach reaches about 72°F in the afternoon and slips back to 58°F overnight — a 14°F spread between the day's warmth and the night's chill. On most days the high lands between 62°F and 82°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)
17764
27764
37663
47663
57662
67662
77562
87561
97561
107461
117460
127460
137359
147359
157359
167258
177258
187158
197157
207157
217056
227056
236955
246955
256955
266854
276854
286753
296753
306753

How September really feels in Round Lake Beach

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.

Round Lake Beach weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 7th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan30° / 19°2.39.16.49.30.0
Feb33° / 20°2.07.25.310.30.0
Mar42° / 29°2.69.73.211.60.6
Apr53° / 40°4.412.21.213.12.9
May64° / 51°4.112.3014.45.3
Jun76° / 62°3.611.40156.5
Jul80° / 67°3.310.8014.86.4
Aug79° / 66°3.610.7013.76.7
Sep72° / 58°2.99012.36.9
Oct60° / 46°3.39.50.110.84.8
Nov46° / 35°2.68.51.49.61.4
Dec35° / 25°2.48.84.590.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 42% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 15% of September, with mostly cloudy or overcast conditions the remaining 43%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16040
26040
36040
46040
56139
66139
76139
86139
96139
106139
116040
126040
135941
145842
155842
165743
175743
185644
195644
205545
215545
225545
235446
245347
255347
265347
275347
285248
295248
305248

Chance of precipitation in September

Any precipitation

Round Lake Beach gets around 2.9 in of rain over 9 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 31% and peaks near 32% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
128
228
328
428
528
629
729
829
929
1030
1130
1231
1331
1432
1532
1632
1732
1832
1932
2032
2132
2232
2332
2432
2532
2632
2732
2831
2931
3030

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 46% of days. Sticky, muggy-or-worse air turns up on roughly 13% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1182625228
2202725218
3222725207
4232725186
5252724176
6272724165
7292724154
8312724144
9332723143
10352623133
11372622123
12392522122
13412421112
14432421112
15452320101
16472319101
1749221991
1850221891
1953211781
2055211680
2158201570
2259201470
2362191360
2463191260
2566181150
2667181050
276818950
287017940
297117840
307316740

Wind in September

Winds average 9 mph in September.

Across September, daily wind ranges from about 8 mph on the calmest days to 10 mph at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
139light breeze
149light breeze
159light breeze
169light breeze
179light breeze
189light breeze
199light breeze
209light breeze
219light breeze
229light breeze
239light breeze
249light breeze
259light breeze
269light breeze
279light breeze
289light breeze
299light breeze
3010light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours 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 84 minutes over September. Sunrise moves from 5:22 AM to 5:54 AM, and sunset from 6:22 PM to 5:30 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:226:22
213.05:236:21
312.95:246:19
412.95:256:17
512.85:266:15
612.85:276:13
712.75:286:12
812.75:296:10
912.65:316:08
1012.65:326:06
1112.55:336:04
1212.55:346:02
1312.45:356:01
1412.45:365:59
1512.35:375:57
1612.35:385:55
1712.25:395:53
1812.25:405:51
1912.15:425:50
2012.15:435:48
2112.05:445:46
2212.05:455:44
2311.95:465:42
2411.95:475:40
2511.85:485:39
2611.85:495:37
2711.75:505:35
2811.75:525:33
2911.65:535:31
3011.65:545:30

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.41 kWh/m².

For context, solar energy here swings from a low near 1.56 kWh/m² to a high of 6.4 kWh/m² in June across the year — September's 4.41 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
15.0Bright
25.0Bright
34.9Bright
44.9Bright
54.8Bright
64.8Bright
74.8Bright
84.7Bright
94.7Bright
104.6Bright
114.6Bright
124.5Bright
134.5Bright
144.5Bright
154.4Bright
164.4Bright
174.3Bright
184.3Bright
194.2Bright
204.2Bright
214.2Bright
224.1Bright
234.1Bright
244.0Bright
254.0Moderate
263.9Moderate
273.9Moderate
283.9Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Is September a good time to visit Round Lake Beach?

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
4.9
Beach & pool
4th-best month of the year

September is a reasonable time to visit Round Lake Beach for sightseeing.

What to pack for Round Lake Beach in September

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

In September, Round Lake Beach sees daytime highs around 72°F and nights near 58°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

Sea temperature near Round Lake Beach in September

The nearest coast averages about 67°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 11 mi away) is warmest in August at about 71°F and coldest in March near 36°F.

It's comfortable for a long swim from Jul 18 to Sep 8 — about 1.7 months when the water holds above 68°F.

30°40°50°60°70°80°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmcomfortable to swim
Sea temperature (°F)Comfort
Jan38Bracing
Feb36Bracing
Mar36Bracing
Apr38Bracing
May43Bracing
Jun55Bracing
Jul68Refreshing
Aug71Refreshing
Sep67Cool
Oct57Bracing
Nov47Bracing
Dec42Bracing

UV index in Round Lake Beach in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Round Lake Beach 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 1 (low).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJun 22UV 9Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar4Moderate
Apr6High
May7Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Round Lake Beach 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 Round Lake Beach is worst in July — around 21 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (October, 10 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodJul 921 µg/m³Oct 2410 µg/m³
PM2.5 (µg/m³)Level
Jan12Moderate
Feb15Moderate
Mar18Moderate
Apr19Moderate
May20Moderate
Jun21Moderate
Jul21Moderate
Aug18Moderate
Sep15Moderate
Oct10Good
Nov10Good
Dec11Good
Location & terrain

Where is Round Lake Beach?

Round Lake Beach sits at 42.4°N, 88.1°W, 764 ft above sea level, in United States. The nearest listed city is Round Lake, 1.2 mi away.

Topography around Round Lake Beach

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

Within 2 miles, the terrain around Round Lake Beach has only modest variations in elevation — a maximum elevation change of 151 ft around an average of 784 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 318 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 827 ft.

The land around Round Lake Beach is covered by trees (34%), artificial surfaces (33%) and grassland (22%) within 2 miles, trees (36%) and grassland (29%) within 10 miles, and water (30%), cropland (26%) and trees (20%) within 50 miles.

2 miles
151 ft
10 miles
318 ft
50 miles
827 ft
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Round Lake 1.2 mi · Grayslake 3.1 mi · Mundelein 8.7 mi · Libertyville 9.3 mi · McHenry 9.3 mi · Gurnee 9.3 mi · Vernon Hills 12 mi · Lake Zurich 12 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 Round Lake Beach (42.3717°, -88.0901°, elevation 764 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).