Fire Weather, Patterns and Processes


Brushfires in Central Texas are inevitable. With the current ongoing drought affecting our region, another season of dangerous wildfires seem to just stare us right in the face. Fires enhanced by atmospheric processes have an effect on all of us in some shape or form from economical to emotional.

Weather that can enhance the chances for fires to spread quickly and out of control is a common occurrence during the spring and summer seasons here in Central Texas. There are a number of components that make our region so susceptible to fire outbreaks. Our geographic makeup is the foremost parameter when dealing with these situations. The Austin metro area is positioned in a physical transition zone that lies between the coastal plain and the hill country. Two physical processes in this region, the Balcones Escarpment and the Edwards Plateau, aid in giving the area distinct elevation changes that ultimately contribute to significant wind patterns that aid in fire outbreaks.

Like most in the Great Plains, the spring season is our time to start seeing some pretty intense weather changes. Stronger, deeper fronts that are mP in nature make their surge from the Pacific northwest and have a tendency to modify their moisture content as they pass the Rockies. As these dry fronts approach the Central Texas region, the pressure gradient tightens and winds begin to increase in speed. The dry northwesterly flow at the surface inhibits any moisture flow from the Gulf of Mexico, thus allowing relative humidities to significantly decrease, at times to the single digits. Wind speed and relative humidity are the two basic weather conditions that are required for the National Weather Service Austin/San Antonio office (KEWX) to release a wide array of fire weather information products, which we'll take a look at next.

Local NWS offices release what is known as a Fire Weather Planning Forecast (FWF). This information is intended for those that deal with any sort of land management. They are issued at least once a day, with certain offices modifying the products throughout the day as far as updates are concerned. Each contains a title describing the changing conditions, a discussion that breaks down the key elements of the forecast, and a forecast up to at least 5 days describing conditions such as temperature, humidity and wind.

Another product that is more well-known to the general public is the Red Flag Program (RFW). This program works in conjunction with certain land management agencies such as the Texas Forest Service (TFS) and the Texas Interagency Coordination Center (TICC). All parties work together to obtain information about current moisture content in vegetation, topographic makeup of the land and the distance these locations are from the Gulf of Mexico.

Within the RFW are a brand of watches and warnings that are released to the public with regards to imminent or changing weather conditions. A Fire Weather Watch is issued to inform various fire and land management agencies of pending conditions that could reach Red Flag status, which will be discussed shortly. This watch is released anywhere from 12-48 hours ahead of the expected conditions, but can be issued as far out as three days, dependent upon the confidence of the forecasting meteorologist.

If the Fire Weather Watch is upgraded, it is considered a Red Flag Warning. Each of the 13 NWS offices that represent their CWFA have different variations of what meets red flag criteria. These variations are dependent upon various parameters such as geography, topographic makeup and proximity to water. Our criterion for the Austin/San Antonio area is as follows:

*20ft wind speeds of 15mph or greater with daytime minimum RH <25%
*20ft wind speeds of 15mph or greater with nighttime minimum RH <60%
*Presence of dry lightning
*Expected dry wind shifts and/or extremely low humidity
*Presence of ongoing wildfires in South Central Texas

Causes for wildfire outbreak are statistically more human based than nature. Even though broadcast media has so many outlets to convey information to the general public, instances still arrive where human error is the key factor that ignites this issue. Burning embers from lit smoking products are what most fire officials suspect is the main cause of wildfire outbreak. A local battalion chief with the Austin Fire Department is referenced during a recent interview about fire safety, saying that another growing cause is purely accidental. Vehicles traveling down rural roads may pull to the side of an overgrown patch off the pavement or asphalt. The excessive heat being generated by the catalytic converter and exhaust manifold is just enough to ignite the brush and grass, coupled with the excessive wind speed and low moisture content in the air is a perfect combination for wildfire.

One specific case is the East Amarillo Complex wildfire of March 2006. From the initial start date on March 12th to the contain/control date on March 18th, this fire had burned a final size of 907,245 acres, making it the largest area burned in one fire season in the state of Texas. The atmospheric setup preceding this event was pretty characteristic.

Since early fall of 2005, drought conditions already had a stranglehold on the southwestern US. Winter temperatures were above the climatologically norm, which in turn brought about early spring conditions. A surface low pressure system amplified due to an approaching jet stream from the southern branch of the Rockies. Surface pressure gradients began to tighten, and in turn wind speeds increased to 35mph, gusting to 50+mph from the south/southwest. As the surface low ejected the Midwest with the aid of the polar jet, an accompanying cold front brought dry and brisk winds back around from the north/northwest.

Relative humidities during this time frame were drastic. Preliminary climatological data confirms that between the 12th and the 18th of March, RH values were between 7% and 10%. Winds were confirmed at an average between 16 and 23mph, with gusts of up 45pmh during the one week time frame. The next approaching storm system following the East Amarillo Complex wildfire brought 1.25" of rain at the official reporting station (KAMA), thus suppressing and containing the fire.

Informing the public is key to better containing these destroying wildfires. Even though the media can alert everyone from TV, radio and internet mediums, it's ultimately up to the individual to do their part on salvaging millions and millions of dollars in tax revenues and general funds from being portioned towards firefighting and rebuilding efforts.

Reference Citations

Preliminary Local Climatological Data for KAMA, March 2006
Surveillance of Mortality During the Texas Panhandle Wildfires, March 2006
"The Dryline" (official newsletter of the NWS Amarillo), Spring/Summer 2006
National Interagency Coordination Center 2006 Summary and Statistics Report
Texas Fire Weather Operating Plan 2005-2006