Wind Systems of the Mountain West: Project Overview Jebb Q. Stewart Undergraduate Research Assistant NOAA Cooperative Institute for Regional Prediction and Department of Meteorology University of Utah Faculty Advisors: Jim Steenburgh, University of Utah C. David Whiteman, Pacific Northwest National Laboratory

The complex topography of the western United States produces a wide variety of thermally- and dynamically-driven mesoscale wind systems. Historically, knowledge and understanding of such systems has been limited by a variety of factors, including limited observational data.

Over the past few years, data from a variety of meteorological observing networks has been collected as part of the Utah Mesonet, a collaborative project between the University of Utah/NOAA Cooperative Institute for Regional Prediction and National Weather Service Salt Lake City Forecast Office. Presently, data is collected from over 25 observing networks and 1300 surface stations over the Mountain West.

The primary objective of this project is to produce a climatology of Mountain West wind systems using observations collected by the Utah Mesonet. Wind roses, vector winds, and hodographs are presently available for several regions and seasons. Additional high resolution analyses for areas such as the Tooele Valley, Salt Lake Valley, Truckee Basin, and Las Vegas basin will be added in the near future.

Data and Methods

Using computer modem dialout and anonymous ftp, the Utah Mesonet collects data from meteorological networks maintained by a variety of government agencies and commercial firms, with data stored at the University of Utah in GEneral Meteorology PAcKage (GEMPAK) format. Because each network is designed to meet the needs of the operating agency or firm, there is considerable variance in the reporting intervals, station density, and meteorological equipment in each network. Since real-time quality control algorithms for wind observations are presently under development, a relatively simple scheme was implemented for this project to eliminate grossly erroneous data. This involved removing missing data reports, observations of calm conditions or the same wind speed and direction for more than three successive observations times, and the removal of reports with high unlikely wind speeds (i.e., 75 m/s). At a given location vector-averaged winds, wind roses, and hodographs were generated for each season at hourly intervals using all reports within 15 minutes of the top of the hour, provided a minimum of 60 observations were available. Cumulative and individual winter (DJF) and summer (JJA) season statistics were generated using data from Dec 1997 through Aug 1999.

Wind roses were generated by segregating wind direction observations at 22.5 degree intervals (for the 16 compass points) and wind speed observations at 2.5 m/s intervals. Vector-averaged winds were calculated by breaking down the wind into U and V components and determining the mean for each component. Thus, the vector-averaged wind magnitude is typically lower than the mean wind speed due to vector cancellation (e.g., a north and south wind of the same magnitude average to calm conditions). Hodographs were created using the vector-averaged wind at 3-h intervals, with the hodograph vector pointing from the tip of the wind vector at time t to the tip of the wind vector at time t+3.

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