It's peak fire season in Vermont. Here's what to know.

It’s officially spring in Vermont, and residents have started to swap their winter coats for short sleeves and the occasional rain jacket.

But don’t be fooled by mild temperatures. Spring is peak fire season in the Green Mountain State, with 75% of fires happening in April and May each year.

What makes April and May such flammable months? The National Weather Service in South Burlington says these months take place during “pre-greenup” season, when multiple weather conditions – sunshine, wind, warm temperatures, extended periods of little or no rain and low relative humidity – are most likely to co-occur and heavily dry out grasses, leaves and twigs.

Such debris, called as dry or fine fuels, “can be easy to ignite and cause fires to spread very quickly,” NWS Burlington said this week as part of its annual Open Burning Weather Awareness Campaign.

What’s the biggest culprit of wildfires?

In Vermont, the leading cause of wildland fires is open burning.

“With dry fuels and warm, windy weather, it would not take much for any open burning to quickly get out of control,” NWS Burlington said in their awareness campaign.

This is why opening burning requires a permit from a local fire warden.

To practice safe open burning, follow these guidelines:

• Remove dry fuels from your burn pile.

• Keep water and other tools around to contain the fire.

• Burn only “natural, untreated materials.”

What’s peak fire season looking like for Vermont this year?

This spring, NWS Burlington predicts “near to slightly above normal” fire activity, similar to 2016’s peak season as the current El Nino weather pattern fades to Neutral. NWS Burlington anticipates a couple of active fire days before early May, moving from southern to northern Vermont as snow disappears and debris dry.

As of April 17, Vermont’s risk for fire danger is moderate, according to the Department of Forests, Parks and Recreation.

How is fire danger determined?

Vermont’s department of forests and parks and rec gauge fire danger by analyzing weather data and observing how wet or dry fuels debris is throughout the state. This combined information helps predict how easily a fire might start, how quickly it could spread, how hard it could be to control the fire and the fire’s level of severity.

The five levels of fire danger include:

• Low: Fires are slow to start and spread and require minor effort to contain. Spotting – when the wind carries away embers and increases fire risk – is also unlikely.

• Moderate: Fires can occur from most catalysts and are moderately strong.

• High: Fires spark easily and quickly from most catalysts. Brush fires and campfires are likely to spread. Short-distance spotting is frequent.

• Very High: Fires begin and spread promptly and are hard to predict or control. Spotting is a persistent risk.

• Extreme: Same as the previous category, except all extreme-level fires pose a grave safety risk.

If danger levels reach very high or extreme, or Vermont is facing a drought, fire wardens may issue a statewide burn ban.

If NWS Burlington believes there’s a chance for dangerous fire conditions to occur – also known as a red flag event – they will issue a fire weather watch notification 12 to 48 hours before the possible event. If a red flag event is expected, NWS Burlington will announce a red flag warning 24 hours beforehand.

For fire weather forecasts and other information, visit weather.gov/btv and weather.gov/btv/firewx.

Megan Stewart is a government accountability reporter for the Burlington Free Press. Contact her at mstewartyounger@gannett.com.

This article originally appeared on Burlington Free Press: Vermont's peak fire season lasts April to May