If you’re tracking wildfires or the weather conditions that make them possible, you may have come across some terms you don’t recognize. Here’s what they mean.
Watches and Warnings
Fire watches and warnings are issued by the 122 local National Weather Service forecast offices across the United States. Forecast offices maintain criteria specific to their areas of coverage that are developed in consultation with land and fire managers, the federal, state or other bodies — such as the U.S. Forest Service — that study a particular place’s vulnerability to fire.
The criteria used to determine whether a local forecast office issues a watch or a warning can include, among other factors, the likelihood of lightning (which can ignite a fire), high winds and low humidity.
Watches and warnings don’t predict wildfires, but they do predict the conditions that are conducive to their formation or spread. They can take two forms:
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Fire weather watch: This alert is issued when there is a “high potential for the development of a Red Flag event” in 18 to 96 hours. “The overall intent of a fire weather watch is to alert users at least a day in advance for the purpose of resource allocation and firefighter safety,” according to Weather Service policy.
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Red flag warning: This more serious alert describes an “impending, or occurring Red Flag Event,” indicating “a high degree of confidence that weather and fuel conditions consistent with local red flag event criteria will occur in 48 hours or less.” The term has been used by the Weather Service and the National Oceanic and Atmospheric Administration since the 1960s, according to a NOAA fact sheet.
Fire weather watches and red flag warnings can be issued several times a year, in some cases in quick succession during a single weather event, in fire-prone areas, said Robyn Heffernan, a fire weather services senior adviser at the National Interagency Fire Center.
Much more rarely, forecasters can advise of a “particularly dangerous situation” within a forecast, she added. This kind of description is made “if an office feels like this is an extreme event where the criteria for issuance is greatly exceeded, or we’re near record levels or at record levels,” Ms. Heffernan said.
Before this fire season, the Weather Service’s Los Angeles office had used that designation only twice, both for warnings in 2020. Since November, it has issued them four times.
Fire Weather Outlooks
The Storm Prediction Center, a part of the National Weather Service that monitors for severe weather events like thunderstorms, tornadoes and winter weather, also identifies areas where there is a “significant threat for the ignition and/or spread of wildfires” in the near future, according to a description of its products published by NOAA. Fire weather outlooks are broader in scope and are intended to provide guidance for forecasters and to “aid land management agencies in determining large-scale areas of fire danger risk,” according to Weather Service policy. They are not warning products, Ms. Heffernan said.
The Storm Prediction Center describes five kinds of fire risk. For the center to label an area with a given risk level, the area must satisfy several criteria for weather and the potential for fueling fires. The first three pertain to how actively a fire may burn:
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Fire weather risk is described as “elevated” when “we know that the fuels are dry and that the weather is conducive for fire activity,” Ms. Heffernan said.
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Fire weather risk is described as “critical” when “we know that if a fire starts in that area, it is going to be difficult to contain,” she said.
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Fire weather risk is described as “extremely critical” when “there are going to be very limited fire tactics that are going to be able to be employed on that fire because the weather is so overwhelming,” such as during a Santa Ana wind event, she said.
There are also two risk levels that pertain to the potential for a new fire to be ignited (it would be rare, though not impossible, for the two types of fire risk to coincide, Ms. Heffernan said):
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An outlook of “isolated dry thunderstorms” is issued based on the whether a potential fire has fuel to spread (determined through drought, rainfall and vegetation data, for example) and the presence of isolated cloud-to-ground lightning strikes, according to Weather Service directives. This is equivalent to an elevated fire weather threat.
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An outlook of “scattered (critical) dry thunderstorms” is issued based on a potential fire’s fuel conditions and the presence of scattered-to-numerous cloud-to-ground lightning strikes. This is equivalent to a critical fire weather threat.
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