The Haines Index is computed by evaluation of temperature and humidity differences between layers in the upper atmosphere. Weather balloons launched twice daily at various locations throughout the United States gather this upper atmospheric data and transmit it to weather offices around 5 am and 5 pm PDT during the fire season. The Haines Index is a quick and easy way to combine two important atmospheric factors into one simple value. If upper atmospheric data is available, the Haines Index is quite easy to compute. The Haines Index can then be calculated for daily operational use or for historical weather research.
Informal studies suggest similar results in the central and eastern parts of Oregon and Washington.
So it appears that on days with Haines Index 6, problem wildfires are possible. With this in mind, the Portland NWS office uses Haines Index 6 as a Red Flag Warning criteria. Drawbacks The Haines Index does not take wind into account at all. It is possible to have a mild Haines Index value while the wind is creating a hazardous fire situation. The Haines Index does not take into account fuel moisture.