Williamsport weather in September

In September, Williamsport sees average daytime highs of 72°F and overnight lows near 54°F, with 4.6 in of rain across 9.5 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 77°F in the first days to 68°F by the end. The sky is clear or mostly clear about 33% 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 Williamsport's 1st-clearest and 10th-windiest month. For the whole year in context, see Williamsport's year-round climate.

Daytime high
72°
4th warmest
Overnight low
54°
9th coldest
Rainfall
4.6 in
9.5 wet days
Daylight
12 h 18 min
5:54 AM – 6:10 PM
Cloud cover
58%
1st clearest
Wind
5 mph
10th windiest
Solar energy
4.08 kWh/m²
Travel score
6.8
out of 10

Williamsport is city in and county seat of Lycoming County, Pennsylvania, United States.

Density
1,196/km²
people per km²
Founded
1769

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 77°F in the first days to 68°F by the end.

A typical September day in Williamsport reaches about 72°F in the afternoon and slips back to 54°F overnight — a 18°F spread between the day's warmth and the night's chill. On most days the high lands between 63°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)
17759
27759
37758
47658
57658
67658
77657
87557
97557
107456
117456
127456
137355
147355
157354
167254
177254
187253
197153
207153
217152
227052
237051
246951
256951
266850
276850
286849
296749
306749

How September really feels in Williamsport

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.

Williamsport 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
Jan33° / 20°3.210.16.39.40.0
Feb36° / 21°2.79.15.610.30.0
Mar46° / 29°3.9114.411.71.1
Apr58° / 40°4.111.81.213.14.1
May68° / 49°4.013.2014.35.8
Jun77° / 58°4.211.9014.96.4
Jul81° / 63°3.711.5014.76.2
Aug80° / 62°3.710.5013.76.5
Sep72° / 54°4.69.5012.36.8
Oct60° / 43°3.9100.310.94.9
Nov48° / 34°3.591.49.71.8
Dec38° / 26°3.510.14.69.10.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 33% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 51%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15149
25248
35149
45149
55149
65050
75050
84951
94951
105050
114951
124852
134852
144852
154951
164852
174951
184852
194852
204951
214951
224951
234951
244951
255050
265050
274951
284951
294951
305050

Chance of precipitation in September

Any precipitation

Williamsport gets around 4.6 in of rain over 9.5 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 31% and peaks near 33% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
130
230
330
430
530
630
730
830
930
1029
1129
1229
1329
1430
1530
1630
1730
1831
1931
2031
2132
2232
2332
2433
2533
2633
2733
2833
2933
3033

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 52% of days. Sticky, muggy-or-worse air turns up on roughly 9% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1312823163
2322822153
3342822143
4352821142
5362821132
6382720122
7392720122
8402720112
9422619112
10432619102
11452519101
1246251891
1348241891
1449241891
1551231781
1652231780
1754221770
1856211670
1958201660
2059191660
2160191650
2262181550
2364171540
2465171440
2566171430
2668161330
2768161330
2870151320
2971151220
3072141220

Wind in September

Winds average 5 mph in September.

Across September, daily wind ranges from about 5 mph on the calmest days to 5 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
135calm
145calm
155calm
165calm
175calm
185calm
195calm
205calm
215calm
225calm
235calm
245calm
255calm
265calm
275calm
285calm
295calm
305calm

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 5:39 AM to 6:09 AM, and sunset from 6:37 PM to 5:46 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:396:37
212.95:406:35
312.95:416:33
412.85:426:32
512.85:436:30
612.75:446:28
712.75:456:26
812.65:466:25
912.65:476:23
1012.65:486:21
1112.55:496:19
1212.55:506:18
1312.45:516:16
1412.45:526:14
1512.35:536:12
1612.35:546:10
1712.25:556:09
1812.25:566:07
1912.15:576:05
2012.15:586:03
2112.05:596:02
2212.06:006:00
2311.96:025:58
2411.96:035:56
2511.86:045:54
2611.86:055:53
2711.86:065:51
2811.76:075:49
2911.76:085:47
3011.66:095:46

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.08 kWh/m².

For context, solar energy here swings from a low near 1.56 kWh/m² to a high of 5.98 kWh/m² in June across the year — September's 4.08 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.7Bright
24.6Bright
34.6Bright
44.5Bright
54.5Bright
64.5Bright
74.4Bright
84.4Bright
94.3Bright
104.3Bright
114.3Bright
124.2Bright
134.2Bright
144.2Bright
154.1Bright
164.1Bright
174.0Bright
184.0Bright
194.0Moderate
203.9Moderate
213.9Moderate
223.9Moderate
233.8Moderate
243.8Moderate
253.7Moderate
263.7Moderate
273.6Moderate
283.6Moderate
293.5Moderate
303.5Moderate
Planning a trip in September

Is September a good time to visit Williamsport?

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

6.8
Sightseeing
1st-best month of the year
4.9
Beach & pool
4th-best month of the year

September is a reasonable time to visit Williamsport for sightseeing.

What to pack for Williamsport in September

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

In September, Williamsport sees daytime highs around 72°F and nights near 54°F. Worth packing: light clothes and rain gear. About 10 days see rain.

light clothesrain gear

UV index in Williamsport 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 Williamsport peaks around June 23 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 21 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 23UV 9Dec 21UV 1
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May8Very high
Jun9Very high
Jul9Very high
Aug6High
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Williamsport 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 Williamsport is worst in July — around 15 µg/m³ PM2.5 (moderate), about 2.4× the cleanest month (November, 7 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1415 µg/m³Nov 127 µg/m³
PM2.5 (µg/m³)Level
Jan9Good
Feb10Good
Mar11Good
Apr11Good
May13Moderate
Jun14Moderate
Jul15Moderate
Aug13Moderate
Sep11Good
Oct7Good
Nov7Good
Dec8Good
Location & terrain

Where is Williamsport?

Williamsport sits at 41.2°N, 77.0°W, 518 ft above sea level, in United States. The nearest listed city is Back Mountain, 53 mi away.

Topography around Williamsport

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

Within 2 miles, the terrain around Williamsport has significant variations in elevation — a maximum elevation change of 1,148 ft around an average of 686 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 1,585 ft; within 50 miles, large variations in elevation — a maximum elevation change of 2,228 ft.

The land around Williamsport is covered by trees (48%) and artificial surfaces (29%) within 2 miles, trees (68%) within 10 miles, and trees (79%) within 50 miles.

2 miles
1,148 ft
10 miles
1,585 ft
50 miles
2,228 ft
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Back Mountain 53 mi · State College 55 mi · Hazleton 57 mi · Wilkes-Barre 58 mi · Elmira 60 mi · Harrisburg 67 mi · Lebanon 70 mi · Scranton 70 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 Williamsport (41.2412°, -77.0011°, elevation 518 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).