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San Francisco State University: "Adaptation and testing of an upper air diagnostics program to diagnose vertical motion fields in Pacific weather systems"

Final Report

In the last decade, much has been written on the basic controls of the synoptic-scale vertical motion and height fields. Sutcliffe's development theory is predicated on the near-geostrophic balance which characterizes most of the atmosphere and relates surface development to so-called dynamic effects and thermal effects. Such an approach is more complete than approaches which center on forecasting weather development merely on the basis of the vorticity advection in the mid-troposphere. This approach has been recently applied on an operational basis to diagnose the synoptic-scale vertical motion field. The omega equation is the basis of a number of such operational schemes, including one developed by Mike Foster of the Southern Region. This PC-based program diagnoses the forcing for the 700 mb and 500 mb vertical motion fields quasi-geostrophically. Its inputs are the NMC plot files. While it includes no topographic effects on the vertical motion field, there are numerous times when the verified qualitative aspects (location of centers and shape of fields) in California can be more accurately estimated by the diagnosed fields of the Foster program than by the numerical guidance which uses a highly smoothed and idealized topography.

One drawback to the use of the Foster program (or the Upper Air Diagnostics program) in California is that the grid extends only about 5 degrees longitude west of the coastline and allows manual input of only five "bogus" data points. As a result, the quality of the analyses and diagnoses can be rather poor for the data-sparse eastern Pacific. The purpose of this Partners Program, then, was to customize the Upper Air Diagnostics program so that it automatically ingests, not only the current plot files, but also bogus soundings created from NGM-gridded data for the eastern Pacific. Changes were also made so that the analysis and data grids could be shifted westward to at least 160 degrees longitude to make it useful for diagnosing fields for Pacific weather systems. Work on this project was not entirely completed, partially because the acquisition of PC-GRIDS software at the forecast office provided most of the fields that would have been available from the Upper Air Diagnostics program.

The university principal investigator also presented a seminar and workshop on the features of the SHARP workstation which can aid forecasters in anticipating tornadoes in California. Examples presented were drawn from the database prepared as part of the Outreach project.