Air pressure map
Pressure reduced to sea level, in hectopascals. The lines are isobars every 4 hPa, and the letters H and L mark the centres of highs and lows. They decide whether sunshine or rain is on its way.
ECMWF · CC BY 4.0
A high (H) usually means calm, dry weather: heat in summer, frost and fog in winter. A low (L) brings cloud, rain and wind. In the northern hemisphere air circulates anticlockwise around a low and clockwise around a high.
Pressure is reduced to sea level so that places at different altitudes can be compared. A barometer in the mountains will read lower unless it also converts to sea level.
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FAQ
What is normal air pressure?
Average sea-level pressure is about 1013 hPa. Above 1020 hPa we usually talk about a high, below 1000 hPa about a marked low.
What do tightly packed isobars mean?
A big pressure difference over a short distance, and therefore strong wind. Tight lines around a low over the ocean often mean a storm.
Can I see weather fronts on this map?
Fronts are not drawn, but you can spot them indirectly: a front usually sits in a kink of the isobars, where the wind direction and temperature change.
Where the data comes from
The forecast is computed by the European Centre for Medium-Range Weather Forecasts (ECMWF) and published as open data under the CC BY 4.0 licence. A new model run arrives 4 times a day and the map picks it up automatically.
We reduce the model grid from 0.25° to 0.5°, roughly 55 km, so the map loads quickly on a phone too. That is why it shows weather systems well, while very local details, like a storm over a single town, can get smoothed out.
This service is based on data and products of the European Centre for Medium-Range Weather Forecasts (ECMWF). Source: www.ecmwf.int. Licence: CC BY 4.0. Data modified (resampled to 0.5°, smoothed, rounded to 8-bit values). ECMWF does not accept any liability whatsoever for any error or omission in the data, their availability, or for any loss or damage arising from their use. Map: OpenFreeMap © OpenMapTiles © OpenStreetMap contributors.