Northwest Oregon Dry Easterlies
(NODE Number)


Northwest Oregon Dry Easterlies (NODE) Number 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 Number 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 Number 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 Number is computed using the highest hourly value for wind component and the lowest hourly value for relative humidity. A server script formats the html for the web page, which includes a link to a plain-text version for your viewing pleasure.