Offshore flow as a proxy for thermal trough analysis

Thermally induced pressure troughs (commonly referred to as “thermal troughs”) are recognized as a critical weather pattern in the Pacific Northwest. The development of a trough along the coast introduces a period of downslope flow and hot, dry conditions on the east side of the Cascade Mountains. The eventual transition of the trough across the ridge of the Cascades brings fluctuating winds and chaotic fire behavior on the eastern slopes.

Operationally, thermal troughs are usually hand-analyzed and mapped. Preliminary attempts to analyze them from numerical models in the Northwest showed mixed results. High resolution WRF output produced complicated, difficult to interpret trough “axes.” Based on these attempts, the use of offshore flow across the ridge as a proxy for trough development was proposed. In this presentation, we describe the use of this offshore flow during the summer of 2014, along with comparison to fire growth during the season. Refinements and possible improvements are discussed.