Overview

Note: WindWizard is no longer supported by the Missoula Fire Sciences Lab as the underlying software is not readily available. Much of the Computational Fluid Dynamics (CFD) modeling within the WindWizard framework will be added to WindNinja within the next two years.

WindWizard is a Gridded Wind Model - Gridded wind is a method that can provide information about the effect of topography on local wind flow at the 100-300 ft scale. Wind information at this detail is not available from the weather service. The wind simulations are not forecasts but rather simulations of what the wind flow would be under different general (synoptic) wind speed and direction scenarios.

Users can essentially pick the scenario they want to simulate; it might be based on forecasts, local observations or historical weather patterns. This high resolution wind information has been used to identify areas and/or conditions that may produce high fire intensity and spread rates and for identifying locations where fire spotting might occur. It also increases the accuracy of FARSITE predictions.

How is it produced?

The process of producing the gridded wind data is straight forward. It occurs in three steps. First detailed information about the terrain is needed. This is obtained in the form of digital elevation model (DEM) files.

It is useful to think of the next step as the process of building a box. The DEM file forms the floor of the box and represents the terrain surface for an area 10 to 40 miles square. The sides of the box are 3 to 5 miles high and the roof of the box represents the atmosphere 3 to 5 miles above the earth’s surface. The sides and roof of the box allow air flow into and out of the box. The box or domain is then divided into small cubes or cells that are 100 to 300 feet long on each side. The result is a big box made up of approximately one million small boxes.

The final step is to simulate the flow of air through the domain. The user specifies the general flow and direction of air into the box and using the laws of physics the software calculates the flow everywhere within the box. The result from this set of calculations is a predicted wind speed and direction in every cell from which a map of surface wind speed and direction can be produced.

WindWizard or WindNinja?

Users are often confused about which wind model they should use: WindWizard or WindNinja. Each of these models has certain advantages and disadvantages and the best choice will depend on the particular situation. Below is a list of advantages and disadvantages of each model to help make the right choice:

WindWizard

• Advantages
  • more accurate during moderate to strong winds in the lee areas of hills/mountains where recirculation zones are likely to occur
    
    
• Disadvantages
  • no longer available
  • not free
  • slower (30 min to 2 hours per run)
  • no diurnal slope model
  • assumes flow is of neutral or near-neutral stability

WindNinja

• Advantages
  • free
  • fast (8-45 seconds depending on hardware and simulation settings)
  • diurnal slope flow model
  • accounts for non-neutral atmospheric flows
    
    
• Disadvantages
  • less accurate during moderate to strong winds in the lee areas of hills/mountains where recirculation zones are likely to occur

In general, WindWizard will be more accurate for stronger winds (since diurnal slope flow effects are small, and WindWizard more accurately simulates momentum effects) and WindNinja will be more accurate for weaker winds (especially when diurnal slope flows significantly affect the wind patterns). If WindWizard is unusable for high winds (because of cost, licensing, or long simulation times), WindNinja can be used for all cases.