Rialto weather in September

In September, Rialto sees average daytime highs of 85°F and overnight lows near 62°F, with 0.3 in of rain across 1.8 wet days and about 12.2 hours of daylight. It is the 3rd-warmest and 11th-wettest month of the year here.

Highs ease over the month, from about 88°F in the first days to 82°F by the end. The sky is clear or mostly clear about 87% of the time in September, and the air most often feels dry.

Daylight stretches from about 12 h 42 min at the start of September to 11 h 42 min by month's end. Set against the rest of the year, September is Rialto's 2nd-clearest and 10th-windiest month. For the whole year in context, see Rialto's year-round climate.

Daytime high
85°
3rd warmest
Overnight low
62°
10th coldest
Rainfall
0.3 in
1.8 wet days
Daylight
12 h 12 min
5:38 AM – 5:50 PM
Cloud cover
15%
2nd clearest
Wind
3 mph
10th windiest
Solar energy
6.24 kWh/m²
Travel score
7.0
out of 10

Rialto is city in San Bernardino County, California, United States.

Density
1,780/km²
people per km²
Founded
1911

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 88°F in the first days to 82°F by the end.

A typical September day in Rialto reaches about 85°F in the afternoon and slips back to 62°F overnight — a 23°F spread between the day's warmth and the night's chill. On most days the high lands between 75°F and 94°F. Set against its neighbours, September runs about 4°F cooler than August and about 8°F warmer than October.

60°80°100°151015202530
Avg high (°F)Avg low (°F)
18865
28865
38865
48865
58765
68764
78764
88764
98664
108663
118663
128663
138562
148562
158562
168562
178561
188461
198461
208461
218460
228460
238360
248360
258360
268359
278359
288259
298258
308258

Rialto weather by month

How September compares with the rest of the year at a glance. September is the 3rd-warmest and 11th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan60° / 41°2.96.10.6105.5
Feb61° / 42°3.66.81.110.75.5
Mar64° / 45°2.26.20.811.76.6
Apr69° / 48°1.13.90.312.87.7
May74° / 53°0.52.6013.78.6
Jun82° / 59°0.10.7014.28.2
Jul87° / 65°0.52.60146.0
Aug89° / 66°0.42.8013.35.5
Sep85° / 62°0.31.8012.27.0
Oct77° / 54°0.72.4011.18.7
Nov67° / 46°1.03.10.210.27.7
Dec60° / 41°2.250.49.85.6

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 87% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 6% of September, with mostly cloudy or overcast conditions the remaining 7%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
1937
2937
3937
4946
5946
6946
7946
8946
9946
10955
11955
12946
13946
14946
15946
16946
17946
18937
19937
20937
21928
22928
23928
24928
25919
269010
279010
289010
299010
309010

Chance of precipitation in September

Any precipitation

Rialto gets around 0.3 in of rain over 1.8 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 6% and peaks near 9% on the wettest days.

0%10%20%30%151015202530
Rain chance (%)
19
29
39
49
59
68
78
87
97
106
116
125
135
145
155
165
174
184
194
204
214
224
234
244
254
265
275
285
295
305

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 77% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)
16128101
26227101
36326101
46326101
5652591
6662491
7672391
8702280
9712270
10722170
11742060
12761950
13771850
14791740
15811630
16821530
17821530
18841420
19841420
20841420
21851320
22851320
23851320
24851320
25851320
26861220
27871210
28871210
29881110
30881110

Wind in September

Winds average 3 mph in September.

Across September, daily wind ranges from about 3 mph on the calmest days to 3 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
183calm
193calm
203calm
213calm
223calm
233calm
243calm
253calm
263calm
273calm
283calm
293calm
303calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 12 h 42 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 60 minutes over September. Sunrise moves from 5:27 AM to 5:48 AM, and sunset from 6:12 PM to 5:30 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.75:276:12
212.75:286:10
312.75:286:09
412.65:296:07
512.65:306:06
612.65:306:05
712.55:316:03
812.55:326:02
912.55:336:00
1012.45:335:59
1112.45:345:57
1212.45:355:56
1312.35:355:54
1412.35:365:53
1512.25:375:52
1612.25:385:50
1712.25:385:49
1812.15:395:47
1912.15:405:46
2012.15:405:44
2112.05:415:43
2212.05:425:41
2312.05:435:40
2411.95:435:38
2511.95:445:37
2611.85:455:36
2711.85:465:34
2811.85:465:33
2911.75:475:31
3011.75:485:30

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 6.24 kWh/m².

For context, solar energy here swings from a low near 3.02 kWh/m² to a high of 8.25 kWh/m² in June across the year — September's 6.24 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
16.7Intense
26.7Intense
36.7Intense
46.6Intense
56.6Intense
66.6Intense
76.5Intense
86.5Intense
96.5Intense
106.5Intense
116.4Intense
126.4Intense
136.4Intense
146.3Intense
156.3Intense
166.3Intense
176.2Intense
186.2Intense
196.1Intense
206.1Intense
216.1Intense
226.0Intense
236.0Bright
245.9Bright
255.9Bright
265.8Bright
275.8Bright
285.7Bright
295.7Bright
305.7Bright
Planning a trip in September

Is September a good time to visit Rialto?

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

7.0
Sightseeing
6th-best month of the year
8.9
Beach & pool
1st-best month of the year

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

What to pack for Rialto in September

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

In September, Rialto sees daytime highs around 85°F and nights near 62°F. Pack light clothes and sun protection.

light clothessun protection

UV index in Rialto in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 8 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Rialto peaks around June 23 at about 11 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 16 at about 3 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 11 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highExtremeVery highHighModerateJun 23UV 11Dec 16UV 3
UV index (midday)Level
Jan4Moderate
Feb5Moderate
Mar5High
Apr8Very high
May8Very high
Jun11Extreme
Jul11Extreme
Aug11Extreme
Sep8Very high
Oct6High
Nov4Moderate
Dec3Moderate

Air quality in Rialto 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 Rialto is worst in September — around 40 µg/m³ PM2.5 (poor), about 5.4× the cleanest month (December, 7 µg/m³).

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

010203040JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateModerateGoodSep 1437 µg/m³Dec 207 µg/m³
PM2.5 (µg/m³)Level
Jan8Good
Feb9Good
Mar11Good
Apr10Good
May8Good
Jun19Moderate
Jul12Moderate
Aug20Moderate
Sep40Poor
Oct10Good
Nov8Good
Dec7Good
Location & terrain

Where is Rialto?

Rialto sits at 34.1°N, 117.4°W, 1,257 ft above sea level, in United States. The nearest listed city is Bloomington, 3.1 mi away.

Topography around Rialto

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

Within 2 miles, the terrain around Rialto has only modest variations in elevation — a maximum elevation change of 335 ft around an average of 1,250 ft above sea level; within 10 miles, very significant variations in elevation — a maximum elevation change of 4,675 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 11,417 ft.

The land around Rialto is covered by artificial surfaces (82%) within 2 miles, artificial surfaces (50%) within 10 miles, and shrubs (27%) and artificial surfaces (20%) within 50 miles.

2 miles
335 ft
10 miles
4,675 ft
50 miles
11,417 ft
treesshrubsgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Bloomington 3.1 mi · Fontana 3.7 mi · Colton 3.7 mi · San Bernardino 4.3 mi · Loma Linda 7.5 mi · Rubidoux 8.1 mi · Glen Avon 9.3 mi · Highland 9.3 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 Rialto (34.1064°, -117.3703°, elevation 1,257 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).