Critical Fire Weather Patterns in Drought Monte Oaks Fire Weather Program Leader NWS Austin/San Antonio TX DEM Conference April 29, 2011

NWS Austin/San Antonio

Synoptic Scale Patterns for the South Central United States NWS Austin/San Antonio Western US ridge/ Eastern US trough: –Common pattern for dry (Polar) cold fronts –Can lead to persistent dry conditions (late winter/early spring) –NW flow storms in late spring

Synoptic Scale Patterns Continued…. NWS Austin/San Antonio Western US trough/ Eastern US ridge: –Results in dry SW flow off the higher terrain to the SW of Texas –Greatest impact on the NW half of TX

NWS Austin/San Antonio Strong zonal flow across the US: –Common producer of extremely Critical fire weather conditions over West TX –Disturbances in this flow can be a South Plains Wildfire Outbreak Pattern Synoptic Scale Patterns Continued...

Research by T. Todd Lindley, Jared L. Guyer, Gregory P. Murdoch, Seth R. Nagle, Kenneth J. Schneider, and Gary D. Skwira

NWS Austin/San Antonio

South Plains Wildfire Outbreak Pattern: Cross Plains, TX Dec 27, 2005 Weather: SPWOP - eastward moving dry-line followed by a prefrontal trough; strong westerlies aloft mixed down Fuels: heavy loading of cured grasses; also brush (juniper) Rates of spread: up to 5 mph

NWS Austin/San Antonio

Wilderness Ridge Fire Feb 28, 2009 Bastrop County Weather - post frontal winds Primary fuels-Loblolly Pine with an understory of Yaupon Rates of Spread 1-2 mph in the forest, (then faster the adjacent grass field)

La Nina Impacts: SPWOP = Tornado Outbreak Pattern?

Entering Summer: ENSO Forecast

La Nina Impacts Carry into Summer: Fire Patterns Plume Dominated Fire Environment Dry Microburst Patterns Sea Breezes Tropical Storms

Plume Dominated Fires Typically large long- duration fires that generate their own spread characteristics in a light wind environment High mixing heights, Haines Index 5-6 Pyrocumulonimbus possible: dangerous downdrafts in already poor visibility; firewhirls NWS Austin/San Antonio

Dry Microbursts Occurs when mid-level moisture and instability exists in an otherwise dry, hot, and stable environment Lightning starts without rain Strong to severe downdraft winds possible

September 5, 2000: Plume fires and dry lightning Large fire in Kerr County during this period

Sea Breezes Expect drier “post- frontal” conditions and less rain this year Fire spread could increase and change directions Typical impact on fire 1-3 hours

Tropical Storms “Near critical fire weather conditions”, especially on the west side of a cyclone Long duration fire impact (Several hours to 1 day) Complications from evacuations?

Influence of Rita: RH<50% Winds at or above 10 mph La Grange RAWS (winds measured at 20-FT) A 150 Acre Fire occurred in Fayette County during this time

Describing Fire Weather Conditions “Fire Weather Conditions” communication style is driven by the Storm Prediction Center and IMETs in the interest of not overlapping phrases used by land management agencies General categories of “elevated”, “near critical”, “critical”, “extreme”

Other Considerations: In addition to variances in wind and RH based Red Flag criteria for TX, not all NWS offices forecast and verify Red Flag Warnings based on the same duration Elevated and near critical fire weather conditions imply that a forecaster is not ready to issue a Fire Weather Watch or Red Flag Warning…however, other products and graphicasts may address these concerns, and a headline statement is typically used in the Fire Weather Planning Forecast

Elevated Fire Weather Conditions Fuels are moist, but near critical or critical fire weather conditions are expected Fuels are very dry, but either winds or RH values are expected to be well above criteria Most vaguely defined of the categories –Example: South winds reaching critical levels, but RH minimums expected to be 10 percent higher than Red Flag criteria (Note: Fuels typically assessed by TFS based Fire Danger and Fuel Dryness maps)

Near Critical Fire Weather Conditions Fuels are not quite dry enough for a RFW, but critical fire weather conditions are expected Critical fire weather conditions are possible a few days out, but confidence is too low for a Fire Weather Watch Fuels are very dry, but either winds or RH values are not quite expected to reach Red Flag criteria –Example: South winds reaching critical levels, but RH minimums expected to be 5 percent higher than Red Flag Criteria

Critical/Extreme Fire Weather Conditions Red Flag Warning or Fire Weather Watch is in effect or will be soon Critical fire weather conditions means red flag criteria for a given are is expected to be met Extreme fire weather conditions are issued for unique events that rival prior events of historical significance, and is intended to be the fire weather equivalent of the SPC’s High Risk for severe weather

Questions? NWS Austin/San Antonio