A New Approach to National Weather Service Fire Weather Support in the Southwestern United States

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Monday, 5 January 2015: 5:15 PM
221A-C (Phoenix Convention Center - West and North Buildings)
Valerie L. Meyers, NOAA/NWS, Phoenix, AZ

Since the 1990s, many wildland fires in the southwest United States have exhibited rapid “blow-up” conditions and unprecedented extreme fire behavior, often growing to immense proportions and threatening lives and property. Some of these wind-driven conflagrations in Arizona and New Mexico have consumed hundreds of thousands of acres (Rodeo-Chedeski 2002, Cave Creek Complex 2005, Wallow 2011, Los Conchas 2011, Whitewater-Baldy 2012), while others have had disastrous human impact, burning down and threatening communities, or claiming the lives of firefighters (Dude 1990, Yarnell Hill 2013). The Southwest Area (Arizona, New Mexico, and western Texas) fire season enters a unique phase during June and early July. During this period, high pressure builds and intensifies over the intermountain west, resulting in synoptic-scale winds that are generally weaker than what is seen in the spring. Temperatures become very hot, frequently warranting Excessive Heat Warnings for portions of the area. Over time, moisture is drawn into the region, setting the stage for thunderstorms that form during the North American Monsoon. The storms are a source of locally strong, gusty and erratic winds.

Throughout the fire season, land and fire management agencies rely on timely and accurate fire weather forecasts, warnings and other decision support services provided by the National Weather Service to know when critical conditions of strong wind and low humidity are forecast to occur. The current watch and warning thresholds are built around the early-season synoptic pattern, in which systems generate widespread strong winds and low humidity. In Arizona and New Mexico, the frequency of Fire Weather Watches and Red Flag Warnings is lower during June and early July due to the meteorological characteristics described in the previous paragraph. However, critical fire weather conditions still occur, and are influenced by the position and intensity of the upper-level ridge, surface temperatures, and changes in atmospheric stability. Essentially, the hotter the temperatures, the more unstable the atmospheric conditions will be, and the greater the potential for extreme fire behavior.

Once sufficient mid-level moisture is present in an unstable atmosphere featuring excessive heat in the lower levels, thunderstorms may develop. Any thunderstorm that forms will produce little rain but extremely strong outflow winds that can travel great distances. These conditions were present during the deadly Yarnell Hill and Dude fires. Similar conditions were also noted in fire documentation and reports over the last decade where blow-up conditions and observed fire behavior were totally outside the frame of reference of fire management experience.

In light of the costly, destructive and deadly fires that have occurred in the last several years, fire and land management agencies have stressed the need for communications and information sharing based on potential impacts rather than pre-existing thresholds. A desired outcome of this sharing will be a stimulation of critical thinking within all partner agencies, and a better utilization of decision support resources provided by the National Weather Service.

Since decision support services are based on a scientific foundation, continued forecaster research and training will be crucial in identifying critical conditions found in June and early July across the Southwest Area. Combining the science with our decision support channels such as conference calls, briefings, NWSChat, and graphical forecasts, we can help ensure that our fire and land management partners are well prepared for the dangers present during each fire season in the Southwest Area.