Monday, 17 November 2003: 3:30 PM
Comparison of Local Wind and Stability Fields with Synoptic-Scale Observations and Forecast Products at Fort Ord, California
Current weather forecasting for prescribed burns relies on synoptic-scale data and forecast products, and the forecasterís experience with local conditions to determine burn days at least three to five days in advance. In complex meteorological situations, such as those found in the land/sea interface, and/or in complex terrain, experience has shown this task to be very difficult at best. At Fort Ord, located in Monterey County on the Central California Coast, approximately 150 miles south of San Francisco, the influences of the local land/sea interface, complex terrain, and a large nearby population, combine to limit the number of burn days to only three to five annually. Bridging the gap between the available synoptic-scale weather patterns and the corresponding weather patterns in the burn zone to improve the ability to correctly forecast these events with sufficient time to assemble the necessary assets requires the development of signature profiles that relate changes, over time, of the local-scale winds and atmospheric stability to the corresponding synoptic-scale weather patterns. The goal of this study was to collect local-scale data for comparison with the synoptic-scale flow regimes and meso-scale model output, as a preliminary step in the development of signature profiles for local weather condition forecasting, and the eventual modification of existing models or the development of new models for this purpose. The measurements of the three-dimensional wind, temperature, and humidity fields were taken at six locations in and around the former Fort Ord Military Reservation on six successive days. An A.I.R., Inc. ADAS Tethersonde/Kitesonde system was used to collect the data at each location. The measurement period was chosen to correspond with a period of little large-scale pattern change so that the temporal differences in the measurements would not impact the area-wide analyses. The measurements were taken hourly at each location during daylight hours, in accordance with Federal Aviation Administration (FAA) requirements. This paper describes the process of performing the field measurements, the data validation, processing, and analysis procedures used to determine the three-dimensional wind and stability fields, and the comparison of these data with the corresponding synoptic-scale data and forecast products, and MM5 model runs. The results were used to determine the variability between the synoptic-scale weather data and forecast products, and the MM5 model run results with the with the tethersonde/kitesonde data to demonstrate the difficulty of using synoptic- and meso-scale data, and model output to forecast conditions in the Fort Ord area. Results from this limited study indicate a need to perform an expanded study to collect three-dimensional wind and stability data continuously over a longer period of time. This additional data are required to characterize the local-scale flow and stability regimes under synoptic-scale situations that include those conditions related to favorable burn days, and to support the modification of existing models, or the development of new models for use in forecasting favorable burn conditions in complex environments.