Northwest Oregon Dry Easterlies (NODE Index)

Technical Details for Version 3.2

   

Northwest Oregon Dry Easterlies (NODE) Index is designed to give people a “heads up” as to when dry east winds are likely to occur in northwestern Oregon. It is dimensionless with an arbitrary scale from 0 to 100. The NODE Index combines forecast relative humidities, wind directions and wind speeds into a single index. Higher indices indicate stronger east winds and/or lower humidities. When the NODE Index is high this is a signal for fire personnel to carefully read the entire weather forecast to see how potential dry east winds could affect their areas of interest.

The NODE index is computed as follows:

 
  function compute_node($wind_dir, $wind_speed, $rh){
    $wind_component = 0;
   
    if($wind_dir>180){
      $wind_component = 0;
    }elseif($wind_dir>0 and $wind_dir<=90){
      $wind_component = .3333*$wind_dir + min(2*$wind_speed, 30);
    }elseif($wind_dir>90 and $wind_dir<180){
      $wind_component = .3333*(180-$wind_dir) + min(2*$wind_speed, 30); 
    }
   
    if(trim($rh)==''){
      $rh_component=0; 
    }else{
      $rh_component=(100-$rh)*.4;
    }
	
    if(1*$wind_component==0){
      $node=0;
    }else{
      $node= $wind_component + $rh_component;
    }
	
    if($wind_dir>0 and $wind_dir<=90){
      $node = $node*($wind_dir/90);
    }elseif($wind_dir>90 and $wind_dir<180){
      $node = $node*((180-$wind_dir)/90);


    }
 
    return round($node);	
 }
 

The NODE matrix uses forecasts from the National Weather Service’s National Digital Forecast Database (NDFD). A server script downloads values of wind direction, speed, and relative humidity for each location in the matrix. Hourly values are examined for each hour from 18Z (11am PDT) to 03Z (8pm PDT). The NODE Index is computed using the highest hourly value for wind component and the lowest hourly value for relative humidity.A server script builds the matrix graphic, formats the html for the web page and also formats a plain-text version for e-mailing to the NODE mailing list.