During the past several years, San Jose State University has developed and applied practical mesoscale objective analysis techniques to the atmospheric boundary layer. The efforts began with the development of the Winds on Critical Streamline Surfaces (WOCSS) computer program. More recently, that PC-based wind analysis methodology has been expanded to include the analysis of boundary layer turbulence indices. The model's objective analysis scheme interpolates winds in complex terrain and then adjusts the initial estimates to meet mass and energy-conservation constraints. Low-level turbulence estimates are based on indices derived from gridded wind and temperature fields and similarity theory parameterizations.
The purpose of this Cooperative Project is to develop, test, and deliver a practical, user-friendly, computerized, objective mesoscale analysis and display system (termed the Real-time Mesoscale Analysis and Display System [RMADS]), based on the WOCSS software, that will meet many mesoscale analysis and forecast needs in the San Francisco Bay area and elsewhere. One such problem is the short-term prediction of surface wind fields affecting air traffic into San Jose (SJC) and San Francisco (SFO). Arrival scheduling is particularly difficult when SFO is under the influence of northerly winds at the same time SJC is experiencing southerly winds. RMADS could be used in this situation to construct local windfield analyses to provided monitoring of the wind field and its changes. Another short-term forecast problem is the occurrence of moderate and severe turbulence over the east Bay Hills during easterly flow. The turbulence, which is generally mechanical in nature, is a function of terrain size, shape, and orientation, and the wind velocity. RMADS could be used with a mechanical turbulence index to generate fields of turbulence intensity as a function of geographical location.
Beginning in October 1992, the RMADS was used operationally at the Redwood City WFO where the staff found it to be extremely useful in improving the short term forecasts of cloud cover and winds at and around the major airports in the San Francisco Bay Area. In particular, it has allowed the forecasters to better understand the mesoscale influences of wind, terrain, and sources of moisture on local terminal weather. Some of the specific findings include:
1) Light southwest winds into the approach zone of San Francisco allow for early clearing of stratus from the approach zone due to downslope drying off of the coastal mountains.
2) A strong west flow of air from the ocean eastward across San Francisco and Hayward into the Livermore Valley will keep stratus in over SFO and the approach zone longer than normal.
3) Easterly winds in the winter will bring fog from the San Joaquin valley into south San Francisco Bay via the Altamont Pass and Livermore Valley. Previously it was assumed this fog was only advected via the Carquinez Straits.