Wildfires

Many wildfires begin unnoticed and spread very quickly in grassy or wooded areas. Wildfires can create a dense smoke that fills the area for miles surrounding the actual fire. Wildfires can be caused by lightning or volcano eruptions, but 80% are caused by arsonists or by people who are careless. Wildfires can occur at any time of the year, generally when there is no rain or snow. They typically occur when it is windy and the humidity is in the 30’s or lower.

Depending on the weather, wildfires can occur suddenly and spread rapidly. That is why it is very important that families prepare before, and know what to do during, a wildfire. To prepare your family, download our Wildfire Safety Guide.

Fire Weather Forecasts

According to the National Weather Service, the elements that make up the criteria of a “Red Flag Warning” for New England are a combination of current meteorological conditions (winds, relative humidty), longer term dryness (rainfall amounts, Keetch-Byram Drought Index) and the vegetation status.

The Keetch-Byram Drought Index is an index used to determine wildfire potential. It is a mathematical model based on a daily water balance, where a drought factor is balanced with precipitation and soil moisture. The index ranges from 0-800, with 0 representing no drought and 800 extreme drought.

Red Flag Criteria

Red Flag Criteria

  • When in Vegetative Stage I and II (Spring/Fall):
    • Winds sustained or frequent gusts at or above 25 mph
    • Relative Humidity at or below 30%
    • Rainfall amounts for the previous 3 days of less than 0.25"
  • When in Vegetative Stage III (Summer):
    • Winds sustained or with frequent gusts at or above 25 mph
    • Relative Humidity at or below 30%
    • Rainfall amounts for the previous 5 days of less than 0.25"
    • Keetch-Byram Drought Index values of 300 or greater

Forecasters may issue watches or warnings if the criteria are close to being met.

Fire Weather Watch

Fire Weather Watch

When predicted fire weather conditions appear to be elevated in the 12 to 48 hour time frame, a Fire Weather Watch may be issued when confidence of reaching the above criteria is 50% or greater.

Red Flag Warning

Red Flag Warning

Red Flag Warnings will be issued to warn of the onset of critical weather conditions, which could lead to extensive wildfire occurrences. A warning implies that conditions are imminent or occurring and confidence in the above criteria being met must be 80% or higher. 

Red Flag conditions authorize the prohibition of activities that pose a high risk of accidentally starting a wildfire, such as could occur from any form of open burning.