Posted: May 27, 2026

Wildfires can start suddenly, grow rapidly, and quickly threaten entire communities when weather and vegetation (fuel) conditions align. Flammable fuels like dry brush, grasses, and trees plus high winds and low relative humidities can set the stage for catastrophic fire behavior.

One way to reduce the amount of accumulated fuel is to conduct prescribed burning - controlled fires set on purpose with the intent of accomplishing specific objectives. Recognizing the importance of this approach, the National Cohesive Wildland Fire Management Strategy recommends a strategic increase in the pace and scale of prescribed burning to reduce wildfire hazard in the United States.

Prescribed burns are conducted by a variety of groups: local, state, Tribal, and federal agencies; private companies, community-based organizations, and individual landowners. Burn practitioners use two main types of prescribed burning: pile and broadcast. In pile burning, they collect and burn woody debris in multiple individual piles. In contrast, broadcast burning allows a fire to spread over a predetermined area in a manageable way. Regardless of the type, practitioners must extensively plan the fire and conduct it only when conditions are favorable.

To reduce risk, burn practitioners create a detailed burn plan that outlines exactly how they will carry out the burn. This includes specifying the burn type, the necessary equipment and human resources, and the multiple weather and fuel conditions required. Together these factors define a “burn window,” the timeframe in which practitioners can safely and effectively conduct the prescribed burn.

Knowing and understanding burn windows is critical to prescribed burning but, until now, research has not characterized the local- and large-scale weather patterns that determined past “go-burn” days. A “go-burn” day is when all conditions are favorable to carry out a prescribed burn.

A new study led by the NOAA Physical Sciences Laboratory’s Rochelle Worsnop does just that. By looking at past burn data and documenting the accompanying environmental patterns in Northern California, the team gained a better understanding of what constitutes a suitable burn window and identified areas and times of year most favorable for prescribed burns. This information can help improve prescribed burn planning and operations across many high wildfire-risk areas.

“What’s unique about our retrospective approach is that we didn’t have to make assumptions about what counts as a suitable burn window,” said Worsnop. “We effectively learned this from thousands of burn practitioners based on when they decided it was an opportune time to place fire on the landscape. This data-driven insight from the experts enabled us to give a more tailored estimate of potential broadcast and pile burn windows throughout the year.”

The approach

• The team defined separate burn-prescription criteria for pile and broadcast burns using the information from more than 15,000 burn permits issued to government agencies, private companies, and individuals in the Northern California Geographic Area Coordination Center’s region (ONCC) from 2011 to 2024, as well as accompanying environmental data.
• The ONCC was selected because it contains the greatest number of high-risk firesheds. A wildfire that ignites in these areas is highly likely to result in catastrophic wildfire impacts to nearby communities.
• The team defined the burn-prescription criteria based on a fire-danger indicator along with variables related to fire weather, fuel moisture, and smoke, for two elevation bands (above and below ~3200 feet) and three primary landcover types (forests, croplands, and grass/savanna/shrub).
• Since the data correspond with actual burn decisions, the criteria inherently captured the preferences of burn practitioners for past “go-burn” days.
• By applying these prescription criteria, the team better estimated the expected number of burn days available throughout the ONCC each month.
• Additionally, the team identified the average large-scale weather patterns linked to each burn type over the Pacific Ocean and North America. Because weather models can capture these broad patterns further in advance than localized conditions, they offer potential to forecast upcoming burn windows.

The results

Burn type matters

• The researchers observed that past broadcast burns occurred most frequently in June and October, whereas past pile burns occurred most frequently in November and December.
• Regardless of month, burn practitioners generally preferred to burn piles in cooler and wetter conditions. Because piles burn hotter, they can be burned when adjacent fuels are too wet to burn, helping ensure the fires do not spread.
• In cooler months, burn practitioners generally conducted broadcast burns when warm and dry conditions existed several days beforehand. This ensured fuels were more receptive to burning in an otherwise cool and moist time of year for the ONCC.

Time of year matters

• Because practitioner preferences for weather and fuel conditions differed between broadcast and pile burns, the number of burn windows for each burn type varies throughout the year. Across the ONCC, October broadcast-burn windows are three times more numerous than pile-burn windows on average. Conversely, February pile-burn windows are twice as numerous as February broadcast windows.

Certain weather patterns are associated with each burn type

• Atmospheric high-pressure centers (ridges) often coincide with warmer, drier conditions. These conditions favor broadcast burns in the regions underneath and downstream of the ridge from December through May, ensuring receptive fuels during an otherwise typically cool and moist season. Conducting burns from January through April requires even stronger ridge patterns to persist for about seven days before ignition.
• Atmospheric low-pressure centers (troughs) often coincide with cooler, wetter conditions with clouds and potential rainfall. These conditions favor pile burns in the regions underneath and downstream of the trough in May, October, and November. However, because pile burns often produce higher-intensity fires and larger flame lengths than broadcast burns, achieving the right cool and moist conditions in October and November requires stronger troughing patterns.

There are many burn windows every month

• The researchers identified on average more than 15 weather-appropriate burn days per month across the ONCC, including in high-risk firesheds, with the specific month determining whether opportunities exist for broadcast burns, pile burns, or both. The team also found that by slightly expanding the criteria, available safe burn days could increase to 25 days per month, especially from October through May.

Insights

Weather pattern monitoring

• Weather models predict ridges and troughs days to weeks in advance, though these forecasts become less certain further out. By monitoring for the favorable large-scale patterns for the preferred burn type and month, practitioners could potentially better anticipate opening or closing burn windows.

Burn-type flexibility

• The researchers found potentially unrealized opportunities to conduct both broadcast and pile burns, as weather conditions present more “go-burn” days than practitioners currently use. Each month has many different opportunities, but they vary widely by burn type. Some years will have more burn windows than others due to regional climate variability, so flexibility is key.

Late-spring opportunity

• While June has been the most popular month for broadcast burning in the ONCC, May actually has more burn windows to implement either burn type, based on weather and available fuel. Taking advantage of these early burn windows could enable practitioners to reduce fuels more strategically ahead of peak wildfire season, especially in high-risk areas.

What's next

The study highlights the benefit in analyzing meteorological factors from past prescribed “go-burn” days to learn when practitioners decided conditions were suitable to put fire on the landscape. This novel approach to define burn criteria enables a more tailored estimate of potential burn windows for a particular area, which can aid in future prescribed fire planning and operations.

While this study focused on Northern California, future research could focus on characterizing the typical prescribed burn patterns in other regions to help improve prescribed burn management and burn window estimation throughout the country.

Worsnop and team are not done either: “For our team, we’re thinking about prediction next. We’re working on developing forecasting algorithms with the goal of providing advanced notice of potential burn windows in order to help practitioners implement their burn plans in the future.”

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