The rain that has not fallen yetis already in the sky. We weigh it.
Every GNSS signal is slowed by the water vapour it passes through. Forty-five public base stations, from Hokkaido to Okinawa, let us turn that delay into millimetres of water standing over each station, every 30 seconds. This page shows where the sky is loaded now, and how it moved over the last three days.
Each dot is a station. Colour is the amount of water over it; a ring marks a station that rose more than 3 mm in the last three hours. Click a dot to open that station's detailed values.
All stations in order of longitude, from Kyushu and Okinawa on the left to Hokkaido on the right. Moisture usually enters Japan from the south-west; when the western bars stand higher than the eastern ones, it is on its way.
Millimetres of precipitable water. One line per station.
A high value is a condition for heavy rain, not a prediction of it. Whether it rains depends on what lifts the air and where the moisture converges, which one station cannot see. A fast rise at several stations at once is what to notice.
Each row is a JMA announcement of a band-shaped rain system, with what this network measured at that time. Not a forecast: two facts side by side.
When the Japan Meteorological Agency announces a band-shaped rain system anywhere in Japan, the network's values at that moment are written here and drawn as a line.
From a satellite signal to a millimetre of water.
Each base station streams its raw satellite observations. From the last eight hours we compute the extra time the atmosphere added to the signals, subtract the part due to dry air using the nearest barometer, and convert what remains to water. Every value carries its time, the products and observation points used, and the constants. Where an observation is missing, nothing is filled in.
Every value, open.
One file per station and UTC day at /api/pwv/{station}/{YYYY-MM-DD}, 30-second values with delay, pressure and temperature. The three-day summary is /api/pwv/latest. Free, no key. Please cite KUON GEO and the sources above.
Stations: community NTRIP casters (geortk.jp, ntrip1.bizstation.jp). Orbits and clocks: Wuhan University WUM0MGXRTS via IGS. Positioning: PRIDE PPP-AR (Wuhan University). Pressure and temperature: JMA AMeDAS 10-minute values. Satellite image: JMA Himawari-9. Method: Saastamoinen 1972; Bevis et al. 1992, 1994.