Osan climate

Name: Osan
Address: KR

Osan is warmest in August, with average highs of 29 °C, and coldest in January, when nights average -5.8 °C. July is the wettest month (285 mm) and January the driest (20 mm). Figures are 1991–2020 climate normals.

Across a full year Osan averages 1,148 mm of rain, 100 days above 25 °C and 109 days below freezing.

South Korea · population 238,788 · 1991–2020 normals

Temperature below 0 °C to above 30 °C Rain band height is that month’s share of the wettest month

Warmest month August 29 °C
Coldest month January -5.8 °C
Driest month January 20 mm
Wettest month July 285 mm
Least cloud October 44 % cloud
Hottest on record August 38 °C
Coldest on record January -22 °C

What to expectOsan through the year

Osan has a clear annual cycle: average daily highs run from 2.0 °C in January to 29 °C in August, a swing of 27 °C in mean temperature across the year.

Counted across a normal year, 100 days a year reach 25 °C, 21 of them reach 30 °C, 109 nights drop below freezing. The warmest reading in the 1991–2020 record is 38 °C, in August.

Rain is strongly seasonal. July averages 285 mm against 20 mm in January — 14 times as much. Planning around the dry months matters more here than planning around temperature.

Month by month

Month	Avg high	Rainfall	Cloud
January	2.0 °C	20 mm	50 %
February	4.8 °C	28 mm	48 %
March	10.2 °C	38 mm	49 %
April	16.8 °C	69 mm	51 %
May	22.3 °C	90 mm	55 %
June	26.5 °C	126 mm	64 %
July	28.2 °C	285 mm	73 %
August	28.8 °C	243 mm	64 %
September	24.8 °C	125 mm	56 %
October	18.9 °C	55 mm	44 %
November	11.1 °C	46 mm	47 %
December	4.0 °C	23 mm	47 %

Temperature month by month

Month	Avg high	Avg low	Mean	Record high	Record low	Days above 25 °C	Days above 30 °C	Days below 0 °C
January	2.0 °C	-5.8 °C	-2.1 °C	14.7 °C	-22.0 °C	0	0	30
February	4.8 °C	-3.8 °C	0.1 °C	18.2 °C	-19.8 °C	0	0	25
March	10.2 °C	0.3 °C	4.9 °C	21.2 °C	-9.9 °C	0	0	16
April	16.8 °C	6.0 °C	11.1 °C	29.1 °C	-2.4 °C	0	0	1
May	22.3 °C	11.9 °C	16.8 °C	32.1 °C	4.6 °C	7	0	0
June	26.5 °C	17.3 °C	21.6 °C	33.7 °C	10.4 °C	22	3	0
July	28.2 °C	21.7 °C	24.6 °C	36.0 °C	14.9 °C	28	7	0
August	28.8 °C	22.2 °C	25.1 °C	38.4 °C	14.2 °C	28	10	0
September	24.8 °C	16.7 °C	20.5 °C	32.3 °C	7.5 °C	15	1	0
October	18.9 °C	9.5 °C	14.0 °C	27.1 °C	-1.4 °C	1	0	0
November	11.1 °C	2.4 °C	6.6 °C	23.9 °C	-11.2 °C	0	0	10
December	4.0 °C	-3.9 °C	-0.1 °C	15.3 °C	-18.7 °C	0	0	27

Rain, sun and wind month by month

Month	Rainfall	Wet days	Daylight	Cloud cover	Humidity	Wind
January	20 mm	4	9.9 h/day	50 %	62 %	16 km/h
February	28 mm	4	11 h/day	48 %	62 %	17 km/h
March	38 mm	5	12 h/day	49 %	67 %	18 km/h
April	69 mm	7	13 h/day	51 %	67 %	18 km/h
May	90 mm	7	14 h/day	55 %	70 %	16 km/h
June	126 mm	8	15 h/day	64 %	75 %	15 km/h
July	285 mm	15	14 h/day	73 %	84 %	15 km/h
August	243 mm	15	14 h/day	64 %	83 %	14 km/h
September	125 mm	8	12 h/day	56 %	77 %	13 km/h
October	55 mm	5	11 h/day	44 %	71 %	14 km/h
November	46 mm	7	10 h/day	47 %	70 %	15 km/h
December	23 mm	5	9.6 h/day	47 %	65 %	16 km/h

How Osan compares

The same four figures for nearby destinations, so the numbers above have something to be read against. Summer high is the warmest month's average high; winter low is the coldest month's average low.

Destination	Summer high	Winter low	Rain per year	Days above 25 °C
Osan	29 °C	-5.8 °C	1,148 mm	100
Suwon · South Korea	28 °C	-6.2 °C	1,146 mm	93
Pyeongtaek · South Korea	29 °C	-5.4 °C	1,132 mm	106
Hwaseong-si · South Korea	27 °C	-4.4 °C	1,224 mm	68
Gunpo · South Korea	28 °C	-6.1 °C	1,139 mm	85
Anyang-si · South Korea	28 °C	-6.1 °C	1,209 mm	84
Seongnam-si · South Korea	28 °C	-6.6 °C	1,294 mm	95

Planning a trip? See the best time to visit Osan.

QuestionsCommon questions about Osan’s climate

When is the best time to visit Osan?

That depends on what you want, so the honest answer is a comparison rather than a single month. May, June, September sit closest to 20 °C on average, August is the warmest month and January the driest. The month-by-month table above has the full picture.

How hot does Osan get?

In August, the warmest month, daily highs average 29 °C. About 21 days a year pass 30 °C. The highest value in the 1991–2020 record is 38 °C.

How cold does it get in winter?

Nights average -5.8 °C in January, the coldest month. A normal year has 109 nights below freezing.

Which month is wettest in Osan?

July, averaging 285 mm over 15 days with rain. The driest month is January with 20 mm. The year as a whole averages 1,148 mm.

Are these figures a forecast?

No. They are 1991–2020 climate normals: the average of thirty years, which describes what a month is usually like in Osan rather than what any particular week will bring. Individual years can differ substantially from the normal.

Data sources and method

ERA5 / ERA5-Land reanalysis — Copernicus Climate Change Service (C3S), ECMWF. Copernicus Licence
Open-Meteo — Open-Meteo.com. CC BY 4.0
NOAA OISST v2.1 — NOAA Physical Sciences Laboratory. Public domain
GeoNames — GeoNames.org. CC BY 4.0

Normal period: 1991–2020
Dataset version: era5-1991-2020-scores1.1
Last processed: 1 August 2026

Measured values come from ERA5 reanalysis and are reproduced unchanged. Calculated by us: monthly rankings, daylight hours, beach and comfort scores. Full formulas are on the methodology page.

Contains modified Copernicus Climate Change Service information 2026. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.