Forest Fire Weather Information and Danger Explanations

Fire Weather Forecasts  |  Forest Fire Danger Rating  |  Forest Fire Seasons  |  Special Fire Weather Statements  |  Fire Danger Listserve

Fire Weather Forecasts

Starting in early spring, the CT Division of Forestry begins monitoring the weather as it relates to Fire Danger. During the spring and fall fire seasons and at other times of the year when the fire danger is high or above, we broadcast daily predictions for fire danger for 1:00 PM. The predictions are normally out before 8:00 AM. You can subscribe to the Forest Fire Danger listserv.

Forest Fire Danger Rating

The DEEP Division of Forestry issues Forest Fire Danger Ratings for Connecticut. A National Fire Danger Rating system that utilizes two indexes is used in Connecticut. The "spread" of a fire is predicted with the Spread Index, which is a measure of the effect of weather on the relative rate of forward movement of surface fires. Actual rates of spread are additionally influenced by fuel type, topography, and aspect.

Connecticut also uses a Build Up Index that tracks fuel moisture. It is a relative scale that is based upon past precipitation.

The 5 Forest Fire Danger Ratings or Class Days are: 

Rating or Class Days

Spread Index

Build Up Index














> 40

> 75

In addition, three vegetative conditions that may exist.:

  • The first stage is a cured stage, meaning the fuels are in a cured state, exposed to full sunlight (early springtime).
  • The second stage is a transition stage (late spring/fall), meaning the upper tree canopy is partially leafed out.
  • The third stage indicates full leaf out (summer).

Three very important weather factors affect fire start, spread, and the fire weather danger.

  1. Wind - the most important factor; it dries out fuels and drives the fire.
  2. Relative humidity - affects fuel moisture.
  3. Precipitation.


Forest Fire Seasons in Connecticut

Spring Fire Season: Normally Mid-March to Mid-May

After the snow melts in the northeastern part of the U.S., we enter into a traditional spring fire season. This is the time of year when deciduous trees are bare and the warm spring sun heats up the forest fuels. Forest fuels are made up of anything that burns; typically grasses, leaves, twigs, branches, and decaying material in the soil. As the days grow longer and the sun gets hotter, the fuels that are most exposed dry out very fast. Grasses, twigs, and very small branches are called "1-hour fuels". That is, they can take on atmospheric conditions within an hour. Consequently, we can receive precipitation and, if the sun comes out and a breeze picks up, the fine fuels can be available for burning within an hour. Larger fuels take longer to dry out. Typically, fires that start this time of year burn just the surface leaves and can spread very fast. Generally, they cause little, long-term damage to the forest.

During the spring, the Spread Index usually drives the fire danger. Wind is most critical.

Summer Fire Season: Normally Mid-May through September

After the trees are fully leaved out, we enter a different fire season. The Build Up Index is the driving factor with past precipitation (drought) being critical. Forest fuels dry slowly because of lower temperatures in the shaded woods with corresponding higher humidity. Remember, temperature and relative humidity have an inverse relationship. The vegetation is growing and sucking moisture from the soil. When the woods become dry enough and a fire starts, the fire tends to grow more slowly than a spring fire, but burns deeper into the ground. Fires that burn deeper into the ground burn organic matter in the soil (including tree roots), are more difficult to suppress, and cause extensive mortality to vegetation.

Fall Fire Season: Normally October through Snow Fall

Fall fire season takes on some of the characteristics of both the spring and summer. Falling leaves are dry but not quite cured. We go back to the "transition stage" in fire danger predictions. The sun is getting lower and is diminishing in drying capacity. Fires can spread rapidly.


Special Fire Weather Statements

Red Flag Warnings

Red Flag Warnings are issued by the National Weather Service (NWS), which predicts weather and forecasts warnings nationwide. Connecticut is divided between three different National Weather Service stations. Predictions for Hartford, Tolland, and Windham counties are made in Taunton, MA; predictions for Litchfield County are made in Albany, NY; and predictions for Fairfield, New Haven, Middlesex, and New London counties are made in Brookhaven, NY.

A Red Flag Warning is a warning to the fire fighting community that if there is a fire, the weather conditions can be expected to cause erratic fire behavior. Red Flag Warnings are not a fire danger rating and they are not synonymous with High, Very High, or Extreme fire danger. Red Flag Warnings are issued when winds will be sustained or there will be frequent gusts above a certain threshold (normally 25 mph). In addition, relative humidity needs to be below 30% and precipitation for the previous 5 days has to have been less than 1/4-inch.


Receive Forest Fire Danger Information by E-mail

If you would like to receive notification regarding Connecticut's wild fire danger by e-mail, please subscribe to the Forest Fire Danger listserv.

To subscribe to the listserv:

Compose an e-mail to from the e-mail address you wish to have added.

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You will then receive an e-mail that you have successfully subscribed to the listserv.

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Content last updated in March 2022.