Manassas weather in September

In September, Manassas sees average daytime highs of 79°F and overnight lows near 61°F, with 4.4 in of rain across 9.1 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 83°F in the first days to 74°F by the end. The sky is clear or mostly clear about 35% 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 Manassas's 3rd-clearest and 9th-windiest month. For the whole year in context, see Manassas's year-round climate.

Daytime high
79°
4th warmest
Overnight low
61°
9th coldest
Rainfall
4.4 in
9.1 wet days
Daylight
12 h 12 min
5:57 AM – 6:12 PM
Cloud cover
56%
3rd clearest
Wind
6 mph
9th windiest
Solar energy
4.29 kWh/m²
Travel score
6.7
out of 10

Manassas is independent city in Virginia, United States.

Density
1,623/km²
people per km²
Founded
1975

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 83°F in the first days to 74°F by the end.

A typical September day in Manassas reaches about 79°F in the afternoon and slips back to 61°F overnight — a 18°F spread between the day's warmth and the night's chill. On most days the high lands between 70°F and 89°F. Set against its neighbours, September runs about 7°F cooler than August and about 11°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18466
28466
38366
48365
58365
68265
78264
88264
98264
108163
118163
128063
138062
148062
157961
167961
177961
187860
197860
207860
217759
227759
237658
247658
257658
267557
277557
287456
297456
307456

How September really feels in Manassas

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.

Manassas 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
Jan43° / 29°3.08.62.89.60.6
Feb47° / 30°2.88.32.510.51.4
Mar55° / 37°3.810.51.711.73.6
Apr67° / 47°3.4100136.0
May75° / 56°3.711.2014.16.5
Jun84° / 65°3.411.1014.75.3
Jul88° / 70°3.711.8014.44.2
Aug86° / 69°3.310013.55.0
Sep79° / 61°4.49.1012.36.7
Oct68° / 49°3.37.60116.7
Nov56° / 39°2.97.60.29.94.2
Dec47° / 32°3.48.81.89.31.6

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 35% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 18% of September, with mostly cloudy or overcast conditions the remaining 47%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15248
25347
35446
45446
55545
65545
75545
85545
95545
105545
115446
125446
135446
145347
155347
165248
175149
185050
195050
204951
214951
224951
235050
245050
255149
265248
275248
285446
295446
305545

Chance of precipitation in September

Any precipitation

Manassas gets around 4.4 in of rain over 9.1 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 29% and peaks near 30% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
129
230
330
430
530
630
729
829
929
1029
1129
1228
1328
1428
1528
1628
1728
1829
1929
2029
2129
2230
2330
2429
2529
2628
2728
2827
2927
3027

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 34% 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 (%)
11519252715
21619242615
31720242514
41820232414
52020232413
62121232313
72221232212
82421222111
92521222110
102621222010
11282122209
12292122198
13302123197
14322123196
15332123186
16342023185
17352023184
18372023174
19382022173
20392022173
21411921162
22421921162
23431920162
24451820151
25461819151
26481819141
27491719141
28511718131
29521618131
30541617121

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
135calm
145calm
155calm
165calm
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 5:43 AM to 6:10 AM, and sunset from 6:36 PM to 5:49 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:436:36
212.85:446:35
312.85:456:33
412.85:466:31
512.75:476:30
612.75:486:28
712.65:496:27
812.65:496:25
912.55:506:23
1012.55:516:22
1112.55:526:20
1212.45:536:18
1312.45:546:17
1412.35:556:15
1512.35:566:13
1612.25:576:12
1712.25:586:10
1812.25:596:08
1912.16:006:07
2012.16:006:05
2112.06:016:03
2212.06:026:02
2311.96:036:00
2411.96:045:58
2511.96:055:57
2611.86:065:55
2711.86:075:53
2811.76:085:52
2911.76:095:50
3011.66:105:49

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.29 kWh/m².

For context, solar energy here swings from a low near 1.99 kWh/m² to a high of 6.15 kWh/m² in June across the year — September's 4.29 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.8Bright
24.8Bright
34.8Bright
44.7Bright
54.7Bright
64.7Bright
74.6Bright
84.6Bright
94.6Bright
104.5Bright
114.5Bright
124.5Bright
134.4Bright
144.4Bright
154.3Bright
164.3Bright
174.3Bright
184.2Bright
194.2Bright
204.1Bright
214.1Bright
224.1Bright
234.0Bright
244.0Moderate
254.0Moderate
263.9Moderate
273.9Moderate
283.9Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Is September a good time to visit Manassas?

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

6.7
Sightseeing
1st-best month of the year
6.6
Beach & pool
2nd-best month of the year

September is a reasonable time to visit Manassas for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Manassas in September

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

In September, Manassas sees daytime highs around 79°F and nights near 61°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Manassas 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 Manassas peaks around July 11 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 19 at about 2 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 9 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateLowJul 11UV 9Dec 19UV 2
UV index (midday)Level
Jan2Moderate
Feb3Moderate
Mar5High
Apr6High
May8Very high
Jun9Very high
Jul9Very high
Aug7Very high
Sep6High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Manassas 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 Manassas is worst in July — around 17 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (November, 9 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1317 µg/m³Nov 129 µg/m³
PM2.5 (µg/m³)Level
Jan11Good
Feb12Moderate
Mar13Moderate
Apr13Moderate
May15Moderate
Jun16Moderate
Jul17Moderate
Aug15Moderate
Sep12Moderate
Oct9Good
Nov9Good
Dec10Good
Location & terrain

Where is Manassas?

Manassas sits at 38.8°N, 77.5°W, 305 ft above sea level, in United States. The nearest listed city is Manassas Park, 2.5 mi away.

Topography around Manassas

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

Within 2 miles, the terrain around Manassas has only modest variations in elevation — a maximum elevation change of 194 ft around an average of 272 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 768 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 4,157 ft.

The land around Manassas is covered by trees (54%) and artificial surfaces (32%) within 2 miles, trees (71%) within 10 miles, and trees (68%) within 50 miles.

2 miles
194 ft
10 miles
768 ft
50 miles
4,157 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Manassas Park 2.5 mi · Buckhall 2.5 mi · Sudley 3.1 mi · Linton Hall 5.6 mi · Centreville 6.8 mi · Chantilly 9.9 mi · Lake Ridge 11 mi · Fairfax 11 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 Manassas (38.751°, -77.4753°, elevation 305 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).