Frederick weather in September

In September, Frederick sees average daytime highs of 78°F and overnight lows near 59°F, with 4.2 in of rain across 9.2 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 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 Frederick's 2nd-clearest and 9th-windiest month. For the whole year in context, see Frederick's year-round climate.

Daytime high
78°
4th warmest
Overnight low
59°
9th coldest
Rainfall
4.2 in
9.2 wet days
Daylight
12 h 18 min
5:56 AM – 6:12 PM
Cloud cover
56%
2nd clearest
Wind
5 mph
9th windiest
Solar energy
4.28 kWh/m²
Travel score
6.9
out of 10

Frederick is city in Frederick County, Maryland, United States.

Density
1,156/km²
people per km²
Founded
1745

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 Frederick reaches about 78°F in the afternoon and slips back to 59°F overnight — a 18°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)
18364
28264
38264
48263
58263
68163
78162
88062
98062
108061
117961
127961
137960
147860
157860
167859
177759
187758
197658
207658
217657
227557
237556
247456
257456
267455
277355
287355
297354
307254

How September really feels in Frederick

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.

Frederick 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
Jan40° / 26°3.18.73.39.50.0
Feb43° / 27°2.78.53.610.50.6
Mar52° / 35°3.810.22.511.72.8
Apr64° / 45°3.510.20.2135.6
May73° / 54°3.711.8014.16.4
Jun82° / 64°3.410.8014.75.8
Jul87° / 68°3.610.5014.54.8
Aug85° / 67°3.09.9013.55.4
Sep78° / 59°4.29.2012.36.9
Oct66° / 47°3.47.90116.3
Nov54° / 37°3.07.90.49.83.4
Dec44° / 30°3.48.82.29.30.8

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%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15248
25347
35347
45347
55347
65347
75347
85347
95347
105347
115347
125347
135347
145248
155149
165149
175149
185050
195050
205050
214951
224951
235050
245050
255050
265149
275248
285248
295248
305446

Chance of precipitation in September

Any precipitation

Frederick gets around 4.2 in of rain over 9.2 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
728
828
928
1028
1127
1227
1327
1427
1527
1627
1728
1829
1929
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 40% of days. Sticky, muggy-or-worse air turns up on roughly 19% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1212421268
2232421258
3242420258
4252419248
5272419237
6282418227
7302418226
8312418216
9322418215
10342418205
11352418204
12362418193
13372418183
14392318182
15402318172
16412318162
17422318151
18432319141
19442319131
20452218131
21472218121
22482218111
23492218110
24522117100
25522117100
2654201790
2754201790
2855191790
2958181680
3058181680

Wind in September

Winds average 5 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
175calm
185calm
195calm
205calm
215calm
225calm
235calm
245calm
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 6:10 AM, and sunset from 6:37 PM to 5:48 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.95:426:37
212.95:436:35
312.85:446:33
412.85:456:32
512.75:466:30
612.75:476:28
712.65:486:27
812.65:496:25
912.65:506:23
1012.55:516:22
1112.55:526:20
1212.45:536:18
1312.45:536:17
1412.35:546:15
1512.35:556:13
1612.35:566:12
1712.25:576:10
1812.25:586:08
1912.15:596:06
2012.16:006:05
2112.06:016:03
2212.06:026:01
2311.96:036:00
2411.96:045:58
2511.96:055:56
2611.86:065:55
2711.86:075:53
2811.76:085:51
2911.76:095:50
3011.66:105:48

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 1.86 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
283.8Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Is September a good time to visit Frederick?

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 Frederick for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Frederick in September

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

In September, Frederick sees daytime highs around 78°F and nights near 59°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Frederick 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 Frederick peaks around July 10 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 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 10UV 9Dec 20UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May8Very high
Jun9Very high
Jul9Very high
Aug7High
Sep6High
Oct3Moderate
Nov2Moderate
Dec2Low

Air quality in Frederick 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 Frederick is worst in July — around 17 µg/m³ PM2.5 (moderate), about 2.1× the cleanest month (November, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1317 µg/m³Nov 138 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb11Good
Mar12Moderate
Apr12Moderate
May15Moderate
Jun16Moderate
Jul17Moderate
Aug14Moderate
Sep12Good
Oct9Good
Nov8Good
Dec9Good
Location & terrain

Where is Frederick?

Frederick sits at 39.4°N, 77.4°W, 285 ft above sea level, in United States. The nearest listed city is Ballenger Creek, 3.1 mi away.

Topography around Frederick

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

Within 2 miles, the terrain around Frederick has only modest variations in elevation — a maximum elevation change of 482 ft around an average of 312 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 1,791 ft; within 50 miles, large variations in elevation — a maximum elevation change of 2,756 ft.

The land around Frederick is covered by artificial surfaces (41%), trees (28%) and grassland (23%) within 2 miles, trees (47%), grassland (25%) and cropland (22%) within 10 miles, and trees (59%) and grassland (20%) within 50 miles.

2 miles
482 ft
10 miles
1,791 ft
50 miles
2,756 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Ballenger Creek 3.1 mi · Damascus 14 mi · Germantown 18 mi · Montgomery Village 20 mi · Gaithersburg 22 mi · Leesburg 22 mi · Hagerstown 23 mi · Redland 24 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 Frederick (39.4143°, -77.4105°, elevation 285 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).