The map¶
The Map tab fills the screen. A floating control panel sits on the left, a layer menu at the top right, and a legend appears once you choose a layer.
Choosing what to show¶
The control panel has four dropdowns. Choosing a layer in one clears the others: one layer is shown at a time.
Forcing: the downscaled weather¶
The weather that drives the snow model, after it has been adjusted to the terrain (how). Values are daily.
| Layer | Unit | Daily value |
|---|---|---|
| Temperature | °C | mean air temperature, 2 m |
| Precipitation | mm | total, rain + snow as water |
| Rainfall | mm | liquid part |
| Snowfall | cm | solid part, as fresh snow depth |
| Direct SW / Diffuse SW | W/m² | mean incoming sunshine on the slope, direct beam and diffuse sky |
| Longwave | W/m² | mean incoming thermal radiation |
| Wind Speed | m/s | mean wind (not gusts) |
| Relative Humidity | % | mean |
| Pressure | hPa | mean surface pressure |
Model: the snowpack¶
Output of the snow model (how).
| Layer | Unit | Meaning |
|---|---|---|
| SWE | mm | snow water equivalent: water you would get by melting the pack |
| Snow Depth | cm | height of the snowpack |
| Runoff | mm | water leaving the bottom of the snowpack or soil surface: melt plus rain |
| Snowmelt | mm | melt part of runoff (where available) |
| Albedo | – | how reflective the surface is (fresh snow ~0.85, bare ground ~0.2) |
| Surface Temp | °C | temperature of the snow or ground surface |
| Soil Temp | °C | shallow soil temperature |
Runoff is not melt
Runoff includes rain that falls on bare ground or passes through the snowpack. In rain-dominated seasons a large runoff value says nothing about melt. Use Snowmelt where the board offers it.
Anomaly (vs climatology)¶
How unusual the value is for this place and this date. See Anomalies.
Satellite¶
Shown where satellite data are available:
- MODIS fSCA: fractional snow-covered area seen by the MODIS satellite (daily, 500 m, gap-filled for cloud).
- Model fSCA: the same quantity from the model, for comparison.
- Model-DA fSCA: the model after data assimilation (where used).
- Satellite image: …: a Sentinel-2 true-colour scene (10–20 m) for selected areas.
See Satellite and data assimilation.
The time controls¶
- Date slider: one step per day. It opens on today; a marker shows today's position.
- ▶ (Animate): plays the days in sequence. Press again to stop.
- Opacity: from 0.1 to 1. Lower it to see the terrain under the layer.
Deterministic and Ensemble¶
Where an ensemble forecast exists, a Deterministic | Ensemble switch appears at the top of the
panel. Ensemble mode replaces the dropdowns with a forecast-only panel of percentiles and
accumulations. See Forecasts and the ensemble.
DA Corrected¶
Where the region assimilates satellite or station data, a DA Corrected switch appears (on by default). Off shows the open-loop model, without the correction.
Layer menu (top right)¶
Basemaps: Satellite, OpenStreetMap, DEM Hillshade.
Overlays (each listed only where the data exist):
| Overlay | Shows |
|---|---|
| Boundaries & Labels | country borders and place names. Disputed borders are dashed |
| Stations | weather or snow stations; click one for its panel |
| Glaciers | glacier outlines (RGI) |
| Snow line | modelled snow line for the day |
| Freezing level | modelled zero-degree level |
| Admin areas | administrative boundaries |
| Peaks | named summits |
| SNOWPACK sites | points with a detailed snowpack simulation; click for profiles |
Hover and click¶
- Hover: the tooltip shows
Layer: value unit │ lat, lon. - Click on the map: opens the meteogram.
- Click on a station: opens the station panel.
- Click on a SNOWPACK site: opens the SNOWPACK panel.
Why the map looks blocky in places¶
Each map pixel belongs to one of about 10 000 terrain units, and all pixels of a unit share its value. Two neighbouring pixels on the same slope therefore show the same number, while a ridge splits sharply into a sunny and a shady value. This is by design: see Terrain and spatial units.