Avalanche Weather Forecasting

• Introduction
  • Glory Bowl Avalanche Incident
  • Avalanche Impacts
  • Avalanche Weather Forecasts
  • About the Module
• Basic Avalanche Information
  • Introduction
  • Avalanche Climate
  • Types of Avalanches
  • Avalanche Paths
  • Avalanche Terrain
  • Avalanche Triggers
  • Avalanche Sizes
  • Avalanche Development
  • Sliding Surfaces
  • Stable vs. Unstable Snowpacks
  • Snow Bonding
• Avalanche Weather Forecast Process
  • Overview
    • The Forecast Process
    • Forecasting Guide and Data Form
  • Pre-forecast Preparation
    • Overview
    • Avalanche Climate
    • Avalanche Terrain
    • Weather History
    • Recent Avalanches
  • Current Weather
    • Overview
    • Precipitation
    • Wind
    • Temperature
    • Cloud Cover & Solar Radiation
  • Future Weather
    • Overview
    • Precipitation
    • Wind
    • Temperature
    • Cloud Cover & Solar Radiation
  • Making the Avalanche Weather Forecast
• Forecast Exercises
  • Introduction
  • Case 1
  • Case 2
  • Case 3
  • Case 4
  • Case 5
• Summary and Resources
  • Summary
  • Resources

Cloud Cover & Solar Radiation

Forecast cloud cover amount for each 6- to 12-hour interval, noting daytime vs. nighttime cloudiness. Some models provide explicit cloud cover forecasts. If not, you can use relative humidity (RH) forecasts at various pressure levels to estimate the cloud cover expected over the area. You may need to analyze RH at all significant pressure levels at or above the elevation for which you are forecasting, for example, 850, 700, 500, and 300 mb. Meteograms depicting model forecasted RH vs. time at all atmospheric levels are excellent graphical tools for evaluating model results with respect to RH and possible cloudiness.

Note that model forecasted RH values greater than 60% typically imply some amount of cloud cover.

Real-time satellite imagery can also be very helpful for short-term cloudiness forecasts. By extrapolating cloud areas (using thermal infrared imagery) or moisture layers (using water vapor imagery) upstream of the forecast area, you can generate rough estimates of cloud cover for short-range (12- to 18-hour) forecasts. Even longer extrapolations of synoptic weather features, such as storm systems, frontal cloudiness, and short wave troughs, can provide a first approximation of possible cloud conditions as much as a day in advance.

Pay particular attention to long durations of clear skies at night and clear or thin overcast skies during the day. The former is a precursor to weak layer formation, the latter still allows direct solar insolation to melt the snow surface.