Weather Radar

Our radar page brings together live data from all 12 weather radars of the Finnish Meteorological Institute (FMI). You can browse through the latest scans, switch between different radar products, and compare two views side by side.

Getting started

Pick a radar site from the dropdown at the bottom to see the latest velocity scan. Click and drag on the map to pan, scroll to zoom. The timeline at the bottom lets you step back through recent scans — use the arrow buttons or drag the slider.

The main view shows radial velocity by default. The smaller panel on the right shows reflectivity. You can swap them with the ⇄ button, or use the dropdown to pick a different product for either panel.

Products

Radial Velocity (V)

Velocity shows how fast precipitation is moving toward or away from the radar. Green-to-blue means motion toward the radar, yellow-to-red means away. Gray means near-zero velocity (crosswind).

This is your primary tool for spotting rotation in storms. A tight couplet of green next to red — especially if it persists across several scans — indicates a mesocyclone and potential tornado threat. Strong inbound/outbound couplets along a line suggest damaging straight-line winds.

The scale goes from −32 to +32 m/s. Values above the radar’s unambiguous range (typically around 7–8 m/s on single-PRF scans) may appear folded — you’ll see them wrapped around to the other side of the scale. Dual-PRF scans have a much higher range (~32 m/s) and show the full picture.

Reflectivity (Z_H)

Reflectivity is the classic radar view — it shows where rain and hail are and how intense they are. The scale goes from dark blue (light rain) through green, yellow, orange, and red to magenta (extreme precipitation).

Use reflectivity to locate thunderstorms, identify heavy rain cores, and estimate hail potential. Magenta cores (60+ dBZ) often contain large hail, especially when they’re elevated or have a distinct shape.

Differential Reflectivity (Z_DR)

Z_DR tells you about the shape of precipitation particles. Raindrops are oblate (flattened) as they fall, so they return stronger horizontal than vertical signals, giving positive Z_DR. Hail tumbles and is more spherical, giving Z_DR near zero or even slightly negative.

Purple shades indicate negative Z_DR — a sign of tumbling hail. Blue-to-green indicates typical raindrops. Yellow-to-red means large or highly oblate drops, often found in the inflow region of a supercell where strong updrafts sort particles by size.

A Z_DR column — a vertical tower of enhanced values — can mark the location of the main updraft.

Specific Differential Phase (K_DP)

K_DP measures how much the radar signal is slowed down by liquid water along the path. It’s great at cutting through hail contamination — unlike reflectivity, which gets confused by large hailstones, K_DP stays sensitive to the liquid water content underneath.

Dark blue means little liquid water. Greens and yellows indicate moderate rain. Orange-to-red suggests heavy rain, and magenta points to extreme liquid water content — often associated with flooding potential or hail cores wrapped in water.

The scale goes from 0 to 2 °/km. Values above 1 °/km usually indicate very heavy rain.

Correlation Coefficient (ρ_HV)

Rho_HV measures how similar the horizontal and vertical radar signals are. “Pure” precipitation like rain gives values close to 1.0 (blue). Mixed-phase precipitation, hail, or debris gives lower values (yellow to red).

This is your best tool for distinguishing meteorological from non-meteorological targets. A region of low rho_HV (red/orange) collocated with a reflectivity echo could mean hail, while the same signature outside precipitation suggests insects, birds, or chaff.

During tornado events, a rho_HV “debris ball” — a small area of very low values (red) surrounded by higher values — confirms debris lofted by the tornado.

A note on Korpo

Korpo is located in the archipelago and occasionally shows radial streaks in reflectivity and dual-pol products, most often around the 10 o’clock position. This is interference from marine radar on ships — not actual weather. FMI’s own display shows the same artifact.

Keyboard shortcuts

• 1, 2, 3 — Cycle products in the main view
• ← / → — Previous / next scan
• Space — Swap panels

Data source

All data is provided by the Finnish Meteorological Institute and updated every 1–5 minutes. The composite overlay combines all 12 radar sites into a single national view, with each site’s data blended at 85 % opacity.