Analyzing Extreme Weather in Complex Terrain Across the Western United States

The frequency of occurrence of rapid temperature falls and rises in basins and mountain valleys across the western US as a result of strong fronts, cold pools, and thermally and dynamically driven flows are investigated. A spatially dense and temporally rich dataset of surface observations exists in the western United States as a result of efforts to aggregate and make available the data from existing and rapidly growing networks. The Synoptic Data API service provides access to data from over 12,000 stations across the western United States, which simplifies applying data mining and analysis techniques to the data. Derived products from historical data and the real-time quality controlled data stream can be used to identify and flag the occurrence of extreme weather events in the varied and complex terrain of the western United States.

To summarize the extensive amount of data, discrete percentile values from the probability density distributions of the near-surface variables (temperature, pressure, wind speed, etc.) are computed from the station records with sufficient length and quality. The variability of these percentiles is examined as a function of location, latitude and elevation. Similarly, percentiles of the hourly rates of change of temperature and pressure are computed. Spatial checks are used to identify spurious values or rates of change. Individual observations or entire station records are ranked relative to these percentile values to identify extreme events and locations where relatively extreme events are common. Typical intensities and magnitudes of the most extreme events are then contrasted across the western United States. As might be expected, interior basins tend to have larger numbers of rapid temperature rises and falls than coastal areas or nearby mountainous regions.