Analysis of delayed sea breeze onset for Fort Ord prescribed burning operations

Abstract

The U.S. Army conducts prescribed burns at Fort Ord, in Monterey County, California, and is reliant upon forecasting a delayed sea breeze for successful smoke management. This has been previously associated with opposing synoptic scale flow, static stability, and weakened thermal gradients. Evolution of the sea breeze in the complex coastline and topographic structure of the Monterey Bay area is the focus of this study. The CFSR and 12 km NAM combined with local observations in a multiquadric data assimilation system was used to characterize synoptic and mesoscale flow evolutions. Eight case studies were analyzed to better understand background synoptic flow and mesoscale response, characterize primary sensitivities, and develop rules of thumb. All case studies had delayed sea breeze onset until approximately 2000 UTC. A 5 knot delayed sea breeze is triggered by a 5° cross-sectional thermal gradient in the presence of a 2–3 knot offshore synoptic scale component over Fort Ord regardless of synoptic flow strength or direction. A weaker 2 knot delayed sea breeze developed when strong static stability reduced vertical motion or in the absence of a background cross-coast thermal gradient. These factors suggest key forecast parameters to anticipate sea breeze delay effectively lengthening a burn window.