Gaithersburg weather in September

In September, Gaithersburg sees average daytime highs of 78°F and overnight lows near 60°F, with 4.5 in of rain across 9.3 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 82°F in the first days to 73°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 Gaithersburg's 2nd-clearest and 9th-windiest month. For the whole year in context, see Gaithersburg's year-round climate.

Daytime high
78°
4th warmest
Overnight low
60°
9th coldest
Rainfall
4.5 in
9.3 wet days
Daylight
12 h 18 min
5:56 AM – 6:11 PM
Cloud cover
56%
2nd clearest
Wind
6 mph
9th windiest
Solar energy
4.28 kWh/m²
Travel score
6.9
out of 10

Gaithersburg is city in Montgomery County, Maryland, United States; suburb of Washington, D.C..

Density
2,518/km²
people per km²
Founded
1802

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 82°F in the first days to 73°F by the end.

A typical September day in Gaithersburg reaches about 78°F in the afternoon and slips back to 60°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 68°F and 87°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)
18365
28265
38265
48264
58264
68164
78163
88163
98063
108062
118062
127962
137961
147861
157860
167860
177760
187759
197759
207659
217658
227558
237557
247557
257457
267456
277456
287356
297355
307355

How September really feels in Gaithersburg

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.

Gaithersburg 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
Jan41° / 27°3.18.63.19.60.1
Feb44° / 29°2.88.43.210.50.8
Mar53° / 36°3.810.22.311.73.0
Apr65° / 46°3.410.40.2135.7
May73° / 55°3.811.5014.16.5
Jun83° / 64°3.610.8014.75.7
Jul87° / 69°4.011.3014.54.6
Aug85° / 67°3.410.5013.55.3
Sep78° / 60°4.59.3012.36.9
Oct66° / 49°3.47.80116.4
Nov55° / 38°3.07.70.39.93.7
Dec45° / 32°3.58.81.99.31.1

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 17% of September, with mostly cloudy or overcast conditions the remaining 48%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15248
25248
35248
45248
55248
65248
75248
85347
95347
105347
115347
125248
135248
145248
155248
165149
175050
185050
195050
204951
214951
224951
235050
245050
255248
265248
275347
285347
295446
305545

Chance of precipitation in September

Any precipitation

Gaithersburg gets around 4.5 in of rain over 9.3 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 31% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
129
229
329
429
529
629
729
829
928
1028
1128
1228
1328
1428
1528
1628
1729
1829
1930
2030
2131
2231
2331
2431
2531
2631
2731
2831
2930
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 36% of days. Sticky, muggy-or-worse air turns up on roughly 22% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
11821242512
21921232511
32021222411
42222222411
52322212310
62422212310
7262320229
8272320219
9282320218
10302320217
11312220206
12322220206
13332220195
14352220194
15362221184
16372221173
17382121163
18392121163
19412121152
20422121142
21432120142
22442120132
23462120131
24472019121
25492019121
26502018111
27511918111
28521917111
29541817101
30551816101

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
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 5:42 AM to 6:09 AM, and sunset from 6:35 PM to 5:47 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:426:35
212.95:436:34
312.85:436:32
412.85:446:31
512.75:456:29
612.75:466:27
712.65:476:26
812.65:486:24
912.65:496:22
1012.55:506:21
1112.55:516:19
1212.45:526:17
1312.45:536:16
1412.35:546:14
1512.35:556:12
1612.35:566:11
1712.25:576:09
1812.25:576:07
1912.15:586:06
2012.15:596:04
2112.06:006:02
2212.06:016:01
2311.96:025:59
2411.96:035:57
2511.96:045:56
2611.86:055:54
2711.86:065:52
2811.76:075:51
2911.76:085:49
3011.66:095:47

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.28 kWh/m².

For context, solar energy here swings from a low near 1.91 kWh/m² to a high of 6.15 kWh/m² in June across the year — September's 4.28 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
224.0Bright
234.0Bright
244.0Moderate
253.9Moderate
263.9Moderate
273.9Moderate
283.9Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Is September a good time to visit Gaithersburg?

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
6.3
Beach & pool
4th-best month of the year

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

What to pack for Gaithersburg in September

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

In September, Gaithersburg sees daytime highs around 78°F and nights near 60°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Gaithersburg 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 Gaithersburg 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
Jan2Low
Feb3Moderate
Mar5High
Apr6High
May8Very high
Jun9Very high
Jul9Very high
Aug7High
Sep6High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Gaithersburg 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 Gaithersburg 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 Gaithersburg?

Gaithersburg sits at 39.1°N, 77.2°W, 502 ft above sea level, in United States. The nearest listed city is Montgomery Village, 2.5 mi away.

Topography around Gaithersburg

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

Within 2 miles, the terrain around Gaithersburg has only modest variations in elevation — a maximum elevation change of 259 ft around an average of 453 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 912 ft; within 50 miles, large variations in elevation — a maximum elevation change of 2,375 ft.

The land around Gaithersburg is covered by trees (52%) and artificial surfaces (34%) within 2 miles, trees (67%) within 10 miles, and trees (60%) within 50 miles.

2 miles
259 ft
10 miles
912 ft
50 miles
2,375 ft
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Montgomery Village 2.5 mi · Redland 3.1 mi · Germantown 4.3 mi · Rockville 5.0 mi · North Potomac 5.6 mi · Olney 7.5 mi · North Bethesda 8.1 mi · Aspen Hill 8.1 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 Gaithersburg (39.1434°, -77.2014°, elevation 502 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).