Every instrument on this page forecasts rather than simply records, and almost all of them do it from one measurement: barometric pressure. Pressure is the weight of the atmosphere above you, measured in hectopascals or the identical millibars, and it averages 1,013 hPa at sea level. Falling pressure means air is being lifted, which produces cloud, rain and wind. Rising pressure means air is sinking, which suppresses cloud and settles the weather.
What matters is not the reading but the change. A barometer sitting steadily at 1,000 hPa tells you far less than one that has dropped eight hectopascals since breakfast. This section covers traditional aneroid barometers, digital pressure instruments and electronic forecast stations that turn the pressure trend into a symbol on a screen.
How a barometer forecasts weather
A traditional barometer is a mechanical instrument. Inside is a sealed metal capsule, called an aneroid cell, with most of the air removed. As atmospheric pressure rises the capsule is squeezed and flexes inwards; as pressure falls it expands. A lever train multiplies that tiny movement and drives the needle. No liquid, no mercury, no maintenance.
The forecasting comes from reading the trend, which is what the second, manually set pointer on the glass is for. You align it with the needle when you look, and next time you check, the gap between the two tells you which way the pressure has moved and by how much. A steady or slowly rising needle means settled weather holding. A slow fall over a day suggests a front approaching within twelve to twenty-four hours. A fall of more than 3 hPa in three hours indicates a rapidly deepening low, and that is when to expect strong wind rather than merely rain.
The words printed on old dials — Stormy, Rain, Change, Fair, Very Dry — are a rough guide only, and they were calibrated for a temperate maritime climate at sea level. The needle movement is the useful part.
Setting up a barometer correctly
Pressure falls with altitude by roughly 1 hPa every 8 metres, so a barometer must be set to your own elevation or it will read consistently low and every forecast will be pessimistic. Adjust it against a known local sea-level pressure — a nearby airfield or Met Office observation — using the small screw on the back, then leave it alone. Hang it indoors on an interior wall, away from direct sun, radiators and draughts. Pressure is the same inside and out, so there is no advantage to mounting it outdoors.
How electronic forecast stations work
A digital station replaces the aneroid cell with a piezoresistive or capacitive MEMS pressure sensor, which is a silicon diaphragm whose electrical properties change as it flexes. The station samples pressure continuously, builds a rolling history, and applies an algorithm to the shape and rate of the trend to produce a twelve to twenty-four hour outlook, usually shown as sun, cloud, rain or snow icons.
These forecasts are genuinely useful for the immediate area and the immediate future, and typically right around three times in four. They are not a substitute for a numerical model forecast, because your station has one data point where a model has millions. What it does have is your exact location, which is why local pressure often beats a regional forecast at telling you whether this afternoon is worth risking.
Radio-controlled time and forecast displays
Many forecast stations also set their own clock from the MSF radio time signal broadcast from Anthorn in Cumbria, which carries UTC plus British Summer Time information. That means the display corrects itself for the clock change and never needs setting. Reception is best overnight and near a window, away from other electronics.
What we recommend
For a traditional instrument, the Brass Barometer 11.5cm is the simplest starting point, the Oak Banjo Barometer 39cm is the classic English hall piece, and the FCC Brass Barometer Mounted on Mahogany is a serious 17cm movement. For digital forecasting, the Technoline WS 9130 Weather Forecast Station and TFA HORIZON 35.1155 Weather Forecast Station both give pressure trend plus forecast icons, and the TFA View 35.1142.01 Wireless Weather Forecaster adds a wireless outdoor sensor. For a forecast built from your own full sensor suite rather than pressure alone, the TechnoLine WS 2816 Complete Weather Station and the internet-connected Bresser Wi-Fi 4CAST MD with 7-Day Forecast combine local measurement with a wider outlook.
Related measurements
The complete traditional range is in Barometer Range, with electronic instruments in Digital Barometers and the banjo-cased pieces in Banjo Barometers. Dedicated forecast consoles are in Weather Forecasters and entry-level complete stations in Basic Home Weather Stations. Rapid pressure falls are a storm signal, so see Storm & Lightning. Combined barometer and clock pieces are in Clocks, the wider decorative range is in Traditional Weather Instruments, and the other elements are indexed under Elements.