Bethlehem weather in September

In September, Bethlehem sees average daytime highs of 75°F and overnight lows near 56°F, with 4.3 in of rain across 8.8 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 1st-wettest month of the year here.

Highs ease over the month, from about 80°F in the first days to 70°F by the end. The sky is clear or mostly clear about 36% 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 Bethlehem's 2nd-clearest and 9th-windiest month. For the whole year in context, see Bethlehem's year-round climate.

Daytime high
75°
4th warmest
Overnight low
56°
9th coldest
Rainfall
4.3 in
8.8 wet days
Daylight
12 h 18 min
5:48 AM – 6:04 PM
Cloud cover
56%
2nd clearest
Wind
6 mph
9th windiest
Solar energy
4.19 kWh/m²
Travel score
7.0
out of 10

Bethlehem is city in Lehigh and Northampton counties, Pennsylvania, USA.

Density
1,487/km²
people per km²
Founded
1741

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 80°F in the first days to 70°F by the end.

A typical September day in Bethlehem reaches about 75°F in the afternoon and slips back to 56°F overnight — a 19°F spread between the day's warmth and the night's chill. On most days the high lands between 66°F and 85°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)
18061
28061
38061
47961
57960
67960
77860
87859
97859
107759
117758
127758
137657
147657
157657
167556
177556
187456
197455
207455
217354
227354
237354
247253
257253
267153
277152
287152
297051
307051

How September really feels in Bethlehem

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.

Bethlehem weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 1st-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan37° / 23°3.69.65.29.40.0
Feb40° / 24°3.18.94.610.40.1
Mar48° / 31°4.110.93.811.71.8
Apr60° / 42°3.910.70.5134.7
May70° / 51°3.711.4014.26.2
Jun79° / 60°4.111014.86.3
Jul84° / 65°3.610.2014.65.4
Aug82° / 64°3.79.8013.66.1
Sep75° / 56°4.38.8012.37.0
Oct63° / 45°4.18.70.210.95.7
Nov51° / 35°3.38.30.89.72.7
Dec41° / 28°4.19.93.49.10.3

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 36% 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 48%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15149
25149
35149
45149
55149
65149
75149
85149
95149
105149
115248
125248
135248
145248
155347
165347
175248
185248
195248
205248
215248
225347
235248
245248
255248
265248
275347
285347
295347
305347

Chance of precipitation in September

Any precipitation

Bethlehem gets around 4.3 in of rain over 8.8 wet days in September, the wettest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 28% and peaks near 31% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
125
225
326
426
526
626
727
827
927
1028
1128
1228
1328
1428
1528
1628
1728
1828
1929
2029
2130
2230
2330
2430
2531
2631
2731
2831
2931
3031

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 50% of days. Sticky, muggy-or-worse air turns up on roughly 14% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1322420204
2332419194
3342419194
4352418184
5362418184
6372417174
7382417174
8392417164
9402416154
10422316154
11432316144
12442216144
13462216133
14472117123
15492017123
16502017112
17521917102
18521917102
1955181791
2056171791
2157171781
2259161681
2361151671
2462151670
2564141660
2665141560
2766131560
2867131550
2967131550
3069121450

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
65calm
75calm
85calm
95calm
105calm
115calm
125calm
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 5:33 AM to 6:02 AM, and sunset from 6:30 PM to 5:39 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:336:30
212.95:346:28
312.95:356:26
412.85:366:25
512.85:376:23
612.75:386:21
712.75:396:19
812.65:406:18
912.65:416:16
1012.55:426:14
1112.55:436:13
1212.45:446:11
1312.45:456:09
1412.45:466:07
1512.35:476:06
1612.35:486:04
1712.25:496:02
1812.25:506:00
1912.15:515:58
2012.15:525:57
2112.05:535:55
2212.05:545:53
2311.95:555:51
2411.95:565:50
2511.95:575:48
2611.85:585:46
2711.85:595:45
2811.76:005:43
2911.76:015:41
3011.66:025:39

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.19 kWh/m².

For context, solar energy here swings from a low near 1.73 kWh/m² to a high of 5.99 kWh/m² in June across the year — September's 4.19 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.8Bright
24.7Bright
34.7Bright
44.6Bright
54.6Bright
64.6Bright
74.5Bright
84.5Bright
94.5Bright
104.4Bright
114.4Bright
124.3Bright
134.3Bright
144.3Bright
154.2Bright
164.2Bright
174.2Bright
184.1Bright
194.1Bright
204.0Bright
214.0Bright
224.0Moderate
233.9Moderate
243.9Moderate
253.8Moderate
263.8Moderate
273.8Moderate
283.7Moderate
293.7Moderate
303.6Moderate
Planning a trip in September

Is September a good time to visit Bethlehem?

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

7.0
Sightseeing
1st-best month of the year
5.8
Beach & pool
4th-best month of the year

September is one of the better times to visit Bethlehem for general sightseeing.

What to pack for Bethlehem in September

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

In September, Bethlehem sees daytime highs around 75°F and nights near 56°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Bethlehem 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 Bethlehem peaks around July 10 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 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 highHighModerateLowJul 10UV 8Dec 22UV 1
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May8Very high
Jun8Very high
Jul8Very high
Aug6High
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Bethlehem 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 Bethlehem is worst in July — around 18 µg/m³ PM2.5 (moderate), about 2.0× the cleanest month (November, 9 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1518 µg/m³Nov 149 µg/m³
PM2.5 (µg/m³)Level
Jan11Good
Feb13Moderate
Mar14Moderate
Apr14Moderate
May16Moderate
Jun17Moderate
Jul18Moderate
Aug15Moderate
Sep13Moderate
Oct10Good
Nov9Good
Dec10Good
Location & terrain

Where is Bethlehem?

Bethlehem sits at 40.6°N, 75.4°W, 358 ft above sea level, in United States. The nearest listed city is Allentown, 6.2 mi away.

Topography around Bethlehem

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

Within 2 miles, the terrain around Bethlehem has only modest variations in elevation — a maximum elevation change of 778 ft around an average of 358 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 1,024 ft; within 50 miles, large variations in elevation — a maximum elevation change of 2,516 ft.

The land around Bethlehem is covered by trees (43%) and artificial surfaces (36%) within 2 miles, trees (49%) and grassland (21%) within 10 miles, and trees (73%) within 50 miles.

2 miles
778 ft
10 miles
1,024 ft
50 miles
2,516 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Allentown 6.2 mi · Whitehall Township 7.5 mi · Easton 8.7 mi · Lansdale 27 mi · Limerick 29 mi · Pottstown 30 mi · Norristown 35 mi · Phoenixville 35 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 Bethlehem (40.6259°, -75.3705°, elevation 358 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).