Terrain is one of the quiet architects of weather. Even when the larger weather pattern is set by fronts, pressure systems and the jet stream, hills, valleys and mountain ranges can decide where clouds form, where rain falls, where wind accelerates and where cold air lingers long after sunrise.

Short-term weather decisions often depend less on what might happen tomorrow and more on what is already unfolding now.

Every year on 23 March, the global meteorological community celebrates World Meteorological Day, recognising the vital role of weather and climate services in society.

In the first part of this guide, we explored how numerical weather prediction models simulate the atmosphere, from observational data and data assimilation to model grids and parameterisation. Modern forecasting goes further by combining global and regional models, ensemble systems and advanced computational techniques to better predict weather and its uncertainty.

Weather forecasts influence decisions every single day. They guide aviation routes, protect infrastructure, support agriculture, optimise renewable energy production and help individuals plan their routines. Behind every temperature value, rainfall icon or wind warning stands a sophisticated scientific system: the numerical weather model.

On a calm winter evening, the contrast between city and countryside can be striking. Frost may cover open fields while snow settles over rural landscapes, yet the city centre stays a few degrees warmer. Streets turn wet instead of white, and freezing rain replaces snow. These differences are not random – they are shaped by the urban climate.

Climate change is not unfolding evenly across the globe. Nowhere is this more evident than in the Arctic, which is warming far more rapidly than any other region on Earth. This phenomenon, known as the Arctic amplification, has become one of the most striking and consequential indicators of modern climate change.

Why do some winter cold spells last for weeks instead of days? Learn how large-scale atmospheric patterns trap cold air, suppress weather changes, and contribute to long-lasting winter conditions.

On a cold winter day, the number shown on a thermometer rarely tells the full story. Add wind to low temperatures, and conditions can feel significantly colder – sometimes dangerously so. This effect is known as wind chill, and it plays an important role in how the human body experiences cold weather.

High above our heads, at roughly the cruising altitude of commercial aircraft, a powerful river of air is constantly shaping the weather we experience at the surface. This river is known as the jet stream, and during winter it plays a particularly important role in determining whether we see storms, frost, or prolonged calm.