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Snow or thunder on the pass

· 3 min read
Massimo Di Stefano
Massimo Di Stefano
FastGIS author

The weather timeline could tell you how much rain, how hard the wind and how cold. It could not tell you the two things that actually decide a mountain day: whether the 3 mm/h at 2 °C on the pass falls as rain or snow, and whether there is thunder in the hours ahead. From today it does both, on the same rain frames, with nothing new to switch on.

Rain or snow​

Where the rain layer shows precipitation, it now shows its phase too. Snow pulls the colour halfway to a pale blue-white under a fine diagonal hatch; sleet is a lighter tint with a sparser hatch; freezing rain keeps its colour under a red hatch. The rain colours themselves have not moved — your eye is trained on them — and where nothing falls, nothing is drawn. The legend strip under the bar shows the three swatches (❄ 🌨 🧊), and when you plan a route, each stop's line reads ❄ 2.1 mm/h instead of 🌧 2.1 mm/h where it is going to snow at your arrival time.

The phase comes from the forecast model's own split of precipitation into snow and rain (DWD ICON-EU, pan-Europe, with its present-weather code marking freezing rain), and in the Nordics from MET Norway's 1 km snow-phase probability — the same file the timeline already reads for the 1 km detail. Snow is snow from a 70 % share; between 30 and 70 % it is sleet.

Thunder​

Thunderstorm cells are drawn on the rain frames as small yellow ⚡ marks (orange when hail is forecast with them), spaced so they read as a hazard rather than a wash — and drawn even where the rain colours are transparent, because a storm cell is a hazard whether or not the frame shows rain under it. The source is the model's present-weather code across Europe and MET's 1 km thunder probability in the Nordics.

The bar itself now knows about thunder at your position: whenever the rain timeline loads, the app asks the server what your own spot on the map sees at each forecast hour, and the hours that answer "thunder" get a yellow tick on the track and a ⚡ before the time while you are on them. Plan a route and the stop lines carry ⚡ (or 🌩 with hail) after the rain value at that stop's arrival time.

Nothing else changed​

Same frames, same tile URLs, same manifests: the phase and the hazards are two extra bands inside the frames the timeline already draws, so an older build of the app keeps working and simply does not see them. The frames from before today render exactly as they did.