Fire-Effective Return Flow Regimes: A Critical Fire Weather Pattern on the Southern Great Plains (0)

Barry R. Bowers, National Weather Service, Norman, Oklahoma

T. Todd Lindley, National Weather Service

Steven R. Cobb, National Weather Service

Gregory P. Murdoch, National Weather Service

Drew Daily, Oklahoma Forestry Services



During the Southern Plains' fire season, veering and strengthening low-level flow in response to surface pressure falls can enhance the potential for wildfires. This effect appears most prevalent in the Cross Timbers of central and eastern Oklahoma, where the slow equilibrium response of large diameter vegetative fuels is juxtaposed with frequent open burning. At the onset of return southerly flow, moisture advection is typically insufficient to preclude problematic fire spread, and a brief period of dry and windy conditions favorable for outbreaks of initial attack fire activity can occur. The 2017 fire season brought significant challenges in providing strategic decision support during these atypical fire episodes. Past research-to-operations efforts to develop climatology and composite patterns for southern Great Plains wildfire outbreaks have improved the ability of forecasters to recognize these particularly dangerous events, and this awareness has led to mitigating responses by state forestry agencies. A similar understanding is needed for fire-effective return flow regimes, which tend to be difficult to identify in advance and are heavily influenced by the ambient state of vegetative fuels. We will explore synoptic and mesoscale characteristics of fire-effective return flow events with the goal of recognizing these challenging fire episodes and how they contrast with more commonly known critical fire weather patterns.