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Climatology of Precipitation Extremes in the United States

Explore precipitation patterns and extremes in the U.S., factors influencing climate, statistical properties, and the PRISM modeling system. Get insights from SNOTEL data and PRISM-derived products for accurate climatic analysis.

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Climatology of Precipitation Extremes in the United States

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  1. Climatology of Precipitation and Precipitation Extremes in the United States Greg Johnson Applied Climatologist USDA-NRCS National Water and Climate Center Portland, Oregon

  2. Characteristics of the Mean Precipitation Climate • The principal controlling factors are the availability of atmospheric moisture and lifting mechanisms • Moisture controlled by flow from or proximity to large water bodies • Propensity for lifting influenced by topography, convergence zones (seabreeze, etc.), preferred storm tracks (jet dynamics)

  3. Orographic Precipitation Enhancement Factors • Wind Direction (relative to topography) • Wind Speed • Atmos. Moisture (precipitable water) • Elevation Rise • Slope Angle

  4. Issues of Scale(Spatial and Temporal) • Over long averaging times (say, the 30 year normal maps), only the most important and consistent meteorological factors are evident • Progressively shorter time spans reveal ever-increasing nuances of the atmospheric system

  5. July normal Precipitation (top) versus July 1993 Precipitation (bottom)

  6. Statistical Properties of Precipitation • Persistence, or lack thereof • Average amount of precipitation • Variability in precipitation amount, and theoretical maximum • Frequency of precipitation • Duration of precipitation

  7. Annual Mean of P10 (x1000), Southwest Idaho

  8. Standardized PrecipitationIndex (SPI)

  9. A Spatial Climate Modeling System • PRISM (Parameter-elevation Regressions on Independent Slopes Model) • Statistical/Dynamical/Topographic approach • Uses point data, a DEM and a coordinated set of rules, decisions and calculations, designed to mimic an “expert” climatologist • Developed by Dr. Chris Daly of the Spatial Climate Analysis Service, Oregon State University

  10. PRISM • Originally developed for precipitation only, now expanded to temperature, dewpoint, solar radiation and many derived variables such as HDD’s/CDD’s, GDD’s, frost dates, snowfall, snow water equivalent, etc. • Most commonly applied in monthly or annual time increments, but also applied to events

  11. PRISM Model from OSU’sSpatial Climate Analysis Service • Funded primarily by the NRCS-NWCC since 1993 for development of spatial climate products for the U.S. • 4 km horizontal resolution raster data, and ARC polygon coverages both available • Most commonly applied in monthly or annual time increments, but also applied to events

  12. PRISM • Any given grid cell value is determined by a linear regression of station values against elevation • Stations assigned weights • Combined weight of a station is a function of many factors

  13. SNOTEL • Large Automated Climate Network • Began in 1978 • Over 650 remote site • Generally in high elevation areas • Located in the 12 Western States and Alaska • Utilizes meteor burst communication technology to telemeter data

  14. Typical SNOTEL Site

  15. SNOTEL Coverage

  16. PRISM-derived Products • Mean Mon. and Ann. Precipitation • Mean Mon. and Ann. Temps (mx/mn) • Frost dates and freeze-free season • Extreme winter min. temps & probs. • Growing, heating, cooling degree days • Snow-water equivalent

  17. Cartographic-quality Map of Mean Annual Precipitation for Idaho Produced at the USDA-NRCS NCGC

  18. Annual Precipitation Map of Elmore County, Idaho Produced by the NRCS NCGC “Cut-out” of State Map

  19. PRISM - SWE Map - Oregon

  20. PRISM Product Dissemination • Web Sites: OSU: www.ocs.orst.edu/prism/prism_new.html (Raster and polygon coverages of practically everything produced to date (Arc, GRASS); documentation; metadata; DEM’s) NRCS: www.ftw.nrcs.usda.gov/prism/prism.html (U.S., Regional and State mean annual precipitation cartographic products)

  21. http://www.ftw.nrcs.usda.gov/prism/prism.html: • Cartographic state mean annual precipitation maps • Full repository of “official” NRCS PRISM layers

  22. PRISM Product Dissemination • Compact Discs: All precipitation layers for all of the U.S. 3 CD’s (East, Central, West) of the lower 48 states. Includes Arc Explorer viewing software, and all documentation. Available from the NRCS-NCGC: 800-672-5559

  23. PRISM Product Dissemination • Hardcopy maps: Cartographic-quality, walls-size maps of mean annual precipitation for each state Available from the NRCS Climate Data Liaison in each state

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