Guide 01 · Method
How to read Japan’s climate normals before planning a trip
A climate normal is a long-term reference, not a prediction for a particular journey. That distinction is the starting point for every comparison in this Atlas.
What the numbers summarize
The values shown here come from the Japan Meteorological Agency’s 1991–2020 climatological normals. For each observatory and month, the Atlas organizes mean temperature, typical daily high and low, precipitation total, and sunshine duration. A January normal for Tokyo of 5.4°C, for example, is a summary of many January observations over that 30-year period. It does not say that a future January day will be 5.4°C.
That makes normals useful for one specific job: comparing broad seasonal patterns between named observatories. They are less useful for deciding what will happen on a particular flight day, whether transport will be disrupted, or whether a place will feel comfortable to an individual visitor.
Read the five measures together
| Measure | What it describes | What it does not describe |
|---|---|---|
| Mean temperature | Average monthly thermal context | A future day’s temperature |
| Daily high / low | Long-run monthly average of daily extremes | The range on a specific itinerary |
| Precipitation | Monthly total over the normal period | Which days will be wet |
| Sunshine duration | Monthly hours of recorded sunshine | Cloud cover or daylight on a chosen day |
Use a city comparison, then check current information
Japan covers wide geographic variation. A single national “Japan weather in June” statement hides much of that. Compare the selected observatories first—such as Tokyo and Sapporo or Tokyo and Naha—then use official forecasts and local guidance close to departure for time-sensitive planning.
Source and limits. Values used in this Atlas are organized from the Japan Meteorological Agency, Tables of Climatological Normals (1991–2020). This is an independent reference, not a JMA product, and it is not a forecast.