Lombardy rain forecast: how to choose between ICON-2I and ECMWF
The map lets you see both observed rain and forecast rain. In the future part of the timeline you can choose ICON-2I or ECMWF and compare what they predict for the same hour. This guide explains how to switch models, how to read differences between them and what it means when a forecast hour is unavailable.
Open forecasts and compare ICON-2I with ECMWFAlways check the source timestamp: radar and weather-station data are observations, while ICON-2I and ECMWF provide model forecasts. Experimental nowcasting does not replace official weather warnings.
Start by separating OBSERVED radar from FORECAST rainfall
Below the map the timeline shows OBSERVED frames before NOW and FORECAST frames after it. Radar shows precipitation echoes that were actually detected; the future section shows hourly precipitation calculated by either ICON-2I or ECMWF.
Moving the slider beyond NOW is not a continuation of radar scans into the future. The source and physical quantity change, and the map's information card identifies the currently selected frame as either an observation or a forecast.
A forecast frame represents a modelled scenario valid for a given hour: it is not a ground measurement or proof of rainfall at one precise point. Predictions at longer lead times may differ from conditions eventually observed.
ICON-2I or ECMWF: how to choose
When you are in the FORECAST part of the timeline you can switch between ICON-2I and ECMWF. They are two independent forecasts, and comparing them is especially useful when you want to understand how uncertain the weather situation may be.
When you change model, the map tries to stay on the same hour and the same area so you can compare them directly. Wait until loading has finished before judging the colours.
If the models show rain in different places or at different times, it does not automatically mean one is wrong. It means the forecast is less certain and may still change.
Open the next available forecast and browse its valid times
Use the Rainfall forecast shortcut on the homepage, the map link below or the slider's future section. Once forecast metadata have loaded, the page opens the first available future frame from the active source; you can then switch models to compare ICON-2I and ECMWF at the same valid time when both are available.
Press ▶ to play through available frames, or move the time slider to inspect a particular hour and pause whenever you need. Actual forecast coverage and the number of available hours depend on the provider data for the current model run.
NOW returns to the latest available observed radar scan, not to the forecast model's initial time or the exact minute on your own clock. Observed radar remains usable even when the forecast model is unavailable.
The umbrella button: jump to the next forecast rain
The umbrella beside the timeline searches both ICON-2I and ECMWF for the earliest future hour with meaningful rainfall in the available forecast period. If the models point to different times, the site uses the earliest valid event it finds and switches to the model that produced it.
An umbrella icon appears beside NOW on both phones and larger screens. It is a shortcut to the earliest meaningful rainfall found across the currently available forecasts from both models.
When enabled, tap the umbrella to jump to the forecast hour and model where the first rain was found. A grey, disabled umbrella may mean the check is still running, forecast data are unavailable, or neither model found meaningful rain in the available period; it does not guarantee dry weather.
The search concerns the monitored forecast area and map-visible rain rather than a guaranteed point forecast for one address. ICON-2I and ECMWF may legitimately place rainfall at different times and locations.
How to read the forecast time
Each future image refers to a specific hour. If you select 15:00, for example, you are looking at the rainfall expected for that period rather than an exact snapshot of what must happen at precisely 15:00.
To understand the trend, it is usually better to look at several consecutive hours instead of focusing on a single moment. Rain areas may move, strengthen or weaken from one hour to the next.
Forecasts are updated regularly, so rainfall position and intensity can change when newer information becomes available.
What the forecast colours mean
The colours help show where the model expects lighter or heavier rain. In the future part of the timeline they represent a forecast; in the OBSERVED part they show what radar actually detected.
Magenta or red forecast pixels indicate relatively stronger modelled precipitation than blue areas on the map's scale, not rain already measured by a gauge at that location. Do not convert a colour to an observed millimetre total for a particular street or garden.
The model represents a gridded weather field: zooming in does not create a separate, highly precise forecast for each building. To inspect actual ground rainfall, return to observed frames and check nearby ARPA rain gauges with their own timestamps.
Using Play without losing the past/future boundary
Playback lets you see how precipitation areas change across available frames. In the observed portion of the timeline you can follow detected echo movement; in the future portion you see changes predicted by the selected model, not radar motion already confirmed by observations.
Pause near NOW and check the selected-frame label before interpreting an approaching coloured band. Playback can contain both kinds of frames in one sequence, but you still need to check which timeline phase is selected.
If one image fails to load, the map may keep the previous complete raster while the slider remains on the requested time and reports that the new frame is unavailable. The retained image is not the missing hour's forecast.
Why observed rain gauges are hidden on future frames
ARPA rain gauges provide ground observations, and the Rain metric reconstructs accumulation for the selected observed radar hour. Future forecast hours cannot yet have ground measurements, so the map hides observed station values while you view ICON-2I future precipitation.
This prevents a gauge measurement from 14:00 from looking like a reading already taken at 17:00. To compare radar and rain gauges, return to an observed frame and check the timestamp of the individual station.
ARPA temperature, humidity and wind are also observations with their own timestamps. They are not predictions of future temperature, humidity or wind supplied by this ICON-2I precipitation timeline.
If a forecast hour is unavailable
Sometimes one of the two models does not have a forecast available for a particular hour yet. The map tells you when this happens: missing data do not mean that dry weather is forecast.
You can try the other model, choose a nearby hour or press NOW to return to the latest observed radar image.
If the map is still loading, wait for the loading indicator to disappear before interpreting it. For warnings or hazardous weather, always rely on official alerts.
Walkthrough: forecast rain during the next few hours near a town
Suppose you want to compare the latest observed precipitation near a town with the modelled rainfall in the next three hours. The useful information is the sequence of properly timestamped frames, not a single colour assumed to apply to the entire town.
The diagram values are invented and not a weather bulletin for any city. Forecast rain location, timing and intensity can change after the next model run, and an individual pixel does not determine precisely what will happen on one street.
The separate experimental nowcasting layer can estimate short-term geometric movement of recent intense observed radar cells. That is a different analysis and does not make a future ICON-2I or ECMWF frame a confirmed observation.