Weather basics

Why do windows fog up? Condensation, dew point and ice

Learn why glass fogs on the inside or outside, how dew point controls condensation and when moisture can turn into ice.

Anabatic and katabatic winds: why air rises by day and drains at night

Mountain slopes create a daily cycle of upslope and downslope winds. Learn how it forms, when it breaks down and what it means outdoors.

Advection fog: how coastal fog forms and how long it can last

Advection fog develops when moist air moves over a colder surface. Learn how to identify it, why it can persist and what it means for coastal travel.

Radiation fog: why it often thickens around sunrise

Clear, humid nights with light winds favour radiation fog. Here is how it forms, pools in valleys and eventually clears after sunrise.

Solar and lunar halos: how they form and what they really mean

Learn to identify the 22° halo, sundogs and coronas, understand the role of ice crystals, and avoid turning a sky sign into a false forecast.

Kelvin-Helmholtz clouds: why the sky can look like breaking waves

Fluctus clouds resemble breaking waves and rarely last long. Here is how wind shear creates them and what they really indicate.

Mammatus clouds: how they form and what they really mean

The pouches beneath some clouds look dramatic, but they do not predict tornadoes on their own. Here is how they form and how to read the sky.

Rainbows: how they form, why they are circular and when a double bow appears

A rainbow has no fixed position: it depends on sunlight, water droplets and the observer. Here is why its colours form an arc and sometimes double.

Cold fronts: what they are and how the weather changes as they pass

A cold front is not a wall of air and does not automatically mean a cold wave. Learn to read its cloud, rain, wind and temperature changes.

Upper-air troughs: what they are and why they favour rain and storms

An upper-air trough is an elongated dip of colder air and relatively low heights. Learn how to identify it, what weather it can support and why it is not the same as a cut-off low.

Atmospheric pressure in hPa: how to read a barometer and isobars

Understand hPa readings, compare barometers correctly and use pressure trends and isobars without jumping to conclusions.

Virga: why rain sometimes evaporates before reaching the ground

Virga forms when precipitation falls from a cloud but evaporates or sublimates before reaching the surface. Learn how to identify and interpret it.

Saharan dust haze: what it is and how to read the maps

Why Saharan dust can wash out the sky, and which maps show dust aloft, surface concentrations or reduced visibility.

Cloud cover percentage: what it means and how to read it

Learn what cloud-cover percentage measures, how it relates to oktas, and why it does not by itself predict rain, sunshine duration or visibility.

How to read a weather map: isobars, fronts, highs and lows

A step-by-step guide to synoptic charts and what they can — and cannot — tell you about pressure, wind, cloud and rain.

How fog forms: types, visibility and why it can appear suddenly

The conditions that create fog, how its main types differ and why visibility can change over just a few metres.

Weather Alerts: official warnings, 7-day forecast, rain radar and weather station

A complete WeatherAlerts guide to EU weather warnings, the seven-day forecast, live rain radar and data from your personal weather station.

Atmospheric pressure: what hPa mean and how to interpret changes

Learn what atmospheric pressure measures, why it is shown in hPa, and how to combine its trend with charts, forecasts and warnings.

Relative humidity and dew point: how to interpret both

Relative humidity changes with temperature; dew point helps reveal how much water vapour is present and when condensation may begin.

Chance of rain: what the percentage really means

Learn how to interpret a 30%, 60% or 90% chance of rain, distinguish probability from amount, and combine forecasts with radar and warnings.