Forecast methodology
How elevation forecasts, snowfall estimates and snowmaking calculations work.
Forecasts, observations and scenarios
A forecast describes expected weather; an observation is a measurement with a source and timestamp. Modelled values are calculations derived from inputs. A scenario starts with an assumption you choose. PisteWindow currently has no measured initial snowpack, so a scenario must not be read as actual snow depth or piste readiness.
Hourly coverage and altitude
We accept complete one-hour forecast intervals. Six-hour precipitation totals are not treated as hourly data. The overview shows available intervals in a 48-hour window starting at the next whole hour. Coverage can differ by altitude. Snowfall totals for 24, 48 or 72 hours appear only when the entire selected window is usable; missing intervals are not filled.
Snowfall as water equivalent
Solid precipitation is expressed in millimetres of water, not centimetres of fresh snow. The model assumes all precipitation is snow at a wet-bulb temperature of −1°C or below and none at +1°C or above, with a linear transition between. This is an uncalibrated assumption. Without a justified snow density, we do not convert water equivalent into snow depth.
Snowmaking weather
The displayed screening uses the Stull (2011) wet-bulb approximation from air temperature and relative humidity. It is not corrected for mountain air pressure. Hours at or below −2°C are counted as potentially suitable. Invalid or out-of-range inputs are unavailable. Tonight means remaining complete hours between 18:00 and 08:00 local time. Suitable weather does not confirm equipment operation, water supply or snow production.
The snow balance scenario
The scenario adds estimated snowfall water and subtracts temperature-based melt from an assumed starting snow water equivalent. Melt uses positive air temperature multiplied by the selected degree-day factor, divided by 24 per hour. The default factor is 3 mm per °C per day; the control spans 1–6. This is not a confidence interval. Radiation, wind redistribution, grooming and artificial snow are omitted. The result is an illustrative water balance, not a calibrated snowpack forecast.
Forecast changes and uncertainty
Comparisons align the same future hours, altitude, source and model version. Previous-update, daily and weekly comparisons use retained forecasts; missing history stays unavailable. We do not currently provide ensemble probabilities, validated accuracy scores or guarantees of snow conditions.
Reading lift reports
Lift states are provider reports, not independent observations by PisteWindow. Only explicit open states count as open; partial, preparation and unknown states stay separate. Missing sections are unknown, never closed. Retrieval is configured every 15 minutes. Current counts require verified source-time semantics and a timestamp with an explicit offset, no more than one hour old, and a successful retrieval within 30 minutes. Unconfirmed times, changed coverage or failed retrievals hide current counts. Older reports remain labelled in the saved-report view. These are product freshness limits, not a provider guarantee or confirmation of open ski pistes.
When a dated summary is shown
The official summary is labelled with its published date. Its counts appear only when that date matches today in Europe/Vienna, retrieval succeeded within the last hour and the latest attempt has not failed. At midnight, after a failed retrieval or when the stored copy becomes too old, the dated counts are hidden. We do not convert its unspecified timezone or treat its update time as an individual lift observation. Ski-area status is displayed alongside lift counts; operating lifts do not establish open ski pistes.