Ice layer not rendering low-concentration data #40
Description
Description
The ice layer fails to render in regions with low sea ice concentration (e.g., Baltic Sea in late February). Even after lowering the alpha cutoff from 10% to a gradual fade-in starting at 1%, the layer remains effectively invisible.
Root Cause
CMEMS sea ice data for the Baltic peaks at ~8% concentration in late winter. The canvas overlay color LUT maps these low values to near-transparent pixels invisible against the dark basemap.
The ice color ramp (ICE_RAMP) starts at [0.00, 0, 100, 255] (dark blue at 0%) which blends with the ocean basemap at low alpha.
Reproduction
- Open Weather tab, select Ice layer
- Enable timeline, navigate to Baltic/Nordic region (55-70N, 15-35E)
- Ice layer appears completely empty despite data existing in DB
Data Evidence
- DB has 10 ice frames (0h to 216h, daily resolution)
- Frame 168 (Day 7): 8522 non-zero values out of 26741 total
- Value range: min=0.0001, max=0.0789, mean=0.0161
- All values below 8% concentration
Suggested Fix
- Use a brighter, more contrasting color ramp for low ice concentrations (white/cyan tones visible against dark basemap)
- Consider rendering ice as a distinct overlay (hatching/stippling) for concentrations below 15%
- Review whether CMEMS siconc is the right source for Baltic ice -- dedicated Baltic products (e.g., SMHI) may provide better coverage
Environment
- Branch: dev at 9e388fe
- CMEMS ice source: cmems_ice (siconc parameter)
- Affected file: frontend/components/WeatherCanvasOverlay.tsx (lines 27-30, 89-91)