Climate averages 1991–2020
Seosan weather
by month.
See how the year changes. August has the highest average daily maximum; January has the lowest average monthly rainfall.
Pleasant-weather months by our simple rule: MayJuneSeptemberOctober
Long-term climate patterns, not a forecast for a particular trip.
Across the year Seosan averages a daytime high of 15.9°C and a nighttime low of 9.5°C, with about 1,087 mm of rain on roughly 91 days. August is the warmest month (average high 27.9°C) and January the coolest (2.5°C). July is the wettest month with 245 mm; January is the driest with 22 mm.
Months with pleasant weather by a simple rule (average high between 18°C and 29°C, average low of at least 5°C and at most 8 rain days): May, June, September and October. This looks at temperature and rain only, not humidity, wind, sea temperature or crowds.
The annual picture
A year in Seosan
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Seosan climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 2.5°C-2.8°C | -2.8°C | 22 | 4.8 | 9.910 h |
| February | 4.4°C-1.9°C | -1.9°C | 28 | 4.3 | 10.811 h |
| March | 9.0°C1.7°C | 1.7°C | 41 | 5.6 | 11.912 h |
| April | 15.1°C6.8°C | 6.8°C | 69 | 6.8 | 13.113 h |
| May | 20.3°C12.2°C | 12.2°C | 79 | 7.0 | 14.114 h |
| June | 24.6°C17.3°C | 17.3°C | 116 | 7.7 | 14.615 h |
| July | 27.0°C21.9°C | 21.9°C | 245 | 14.8 | 14.414 h |
| August | 27.9°C22.9°C | 22.9°C | 225 | 13.7 | 13.614 h |
| September | 24.2°C18.4°C | 18.4°C | 133 | 7.5 | 12.512 h |
| October | 18.6°C12.3°C | 12.3°C | 55 | 5.3 | 11.311 h |
| November | 11.7°C5.7°C | 5.7°C | 49 | 7.2 | 10.210 h |
| December | 5.0°C-0.5°C | -0.5°C | 26 | 6.1 | 9.710 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
Nearby cities
- HongseongSouth Korea · 28 kmHigh 17.0°C · Low 8.8°C · 1,155 mm rain a year
- AsanSouth Korea · 49 kmHigh 17.0°C · Low 8.3°C · 1,109 mm rain a year
- BoryeongSouth Korea · 50 kmHigh 16.4°C · Low 9.9°C · 1,166 mm rain a year
- Hwaseong-siSouth Korea · 57 kmHigh 15.1°C · Low 9.1°C · 1,215 mm rain a year
- PyeongtaekSouth Korea · 61 kmHigh 16.8°C · Low 8.1°C · 1,103 mm rain a year
- CheonanSouth Korea · 62 kmHigh 17.3°C · Low 8.4°C · 1,158 mm rain a year
- Ansan-siSouth Korea · 69 kmHigh 15.8°C · Low 8.5°C · 1,215 mm rain a year
- OsanSouth Korea · 69 kmHigh 16.6°C · Low 7.9°C · 1,120 mm rain a year
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsWhat do the high and low temperatures mean?
We average the daily maximum and daily minimum for each calendar month over 1991–2020. They are not record extremes, a forecast range or temperatures at a fixed time of day.
How is a rain day counted?
A local calendar day (standard time, UTC+9, no daylight saving) with at least 1 mm of total precipitation counts as one rain day. We count these for each year and month, then average across 30 years. The average does not predict which days will be wet.
Where do the numbers come from?
ERA5-Land (temperature) and ERA5 (precipitation) reanalysis from the Copernicus Climate Change Service, read from the Open-Meteo open-data archive. Temperature comes from the 0.1° model cell at 36.80°, 126.50° (5 km from the city centre), adjusted up by 0.3°C for the difference between the city's elevation (33 m) and the cell's (79 m). Rain comes from the 0.25° cell at 36.75°, 126.50°. These are model estimates, not weather-station readings; coast, hills and city streets can differ.
Does this page show sunshine, humidity or sea temperature?
No. The data used here contain air temperature and precipitation only. Daylight hours are calculated from the city's latitude (sunrise to sunset), not measured sunshine.