What POLRAD is
IMGW-PIB runs a network of ten Doppler radars — Brzuchania, Gdańsk, Legionowo, Pastewnik, Poznań, Ramża, Rzeszów, Świdwin, Użranki and Gdańsk-Sadki — and publishes the national composite of them every five minutes, free and without a key, in ODIM HDF5. That is a standards-conformant scientific radar product, not a picture of one, and very few European services publish theirs at all.
Two products are drawn here:
- CMAX — column-maximum reflectivity in dBZ. The highest echo anywhere in the vertical above each point, so it shows a storm's core rather than what has reached the ground. It is the field to read for where the convection is.
- SRI — surface rainfall intensity in mm/h, the reflectivity near the ground converted to a rain rate. Read this one for how hard it is actually raining. It is always weaker than CMAX, and that difference is the storm's vertical structure.
It is on the model's frame, on purpose
POLRAD's own raster is an azimuthal-equidistant grid centred on 19.09°E, 52.35°N — a point in the fields near Piątek, the geographical centre of Poland. This site resamples it onto the same Web Mercator box every model is drawn in.
That costs one resample per frame and buys the thing worth having: in the explorer you can put the last five minutes of real radar over COSMO's next hour with the Radar toggle, and the map does not move between them. Verifying a model against reality should not require re-finding your town.
Reading it honestly
A radar composite is a measurement of the atmosphere, not of the ground. Three things it will show you that are not weather:
- Rings and spokes near a site. Ground clutter and beam blocking. The concentric rings that sometimes appear around Legionowo or Gdańsk are the radar seeing itself.
- Bright band. A ring of enhanced echo where snow melts into rain, typically a few hundred metres below the freezing level. It reads as heavier rain than is falling. Compare with the freezing level.
- Overshooting at range. The beam climbs with distance, so at 200 km it is sampling 3 km up and can miss shallow winter drizzle entirely. Poland's corners — the Bieszczady, the far north-east — are the worst served.
For the official product with IMGW's own quality control, see meteo.imgw.pl.