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Estimating Bounds on Extreme Precipitation Events A Brief Assessment (1994) / Chapter Skim
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Discussion
Pages 11-18

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From page 11...
... The standard PMP products from the NWS are "generalized" maps of PMP estimates for the United States, which allow variation only on a coarse scale. The NWS has updated its PMP estimates periodically.
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From page 12...
... Transposition is generally inappropriate to regions with greatly different orography or greatly different typical moisture levels. Some of the most difficult problems that have arisen with PMP assessments center around storm transposition and the implicit transposition that can result from the objective analysis step in which PMP estimates are mapped onto a national grid and contour lines are smoothed.
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From page 13...
... One distinction between the two types of PMP estimates is that generalized PMP estimates entail an additional smoothing step in the objective analysis procedure used to map local PMP estimates onto national (or regional) maps.
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From page 14...
... (For larger basins and longer durations, the values in the EPRI study were quite close to the NWS values.) The climatological raingauge network, which serves as the backbone of PMP analyses, is poorly suited for resolving rainfall accumulation gradients for small basins during short-duration precipitation events.
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From page 15...
... Comparisons of new radar data with concurrent traditional-style point measurements of precipitation, combined with the existing record of about a century's worth of stationbased time series, may allow greatly improved inferences concerning the probabilities of extreme precipitation events. Although the potential for radar is great, significant questions concerning the accuracy of radar rainfall estimates must still be resolved.
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From page 16...
... Visible and infrared satellite data have been utilized qualitatively for PMP analyses in recent years. Satellite imagery has proven especially useful in documenting the occurrence and characteristic life cycles of mesoscale convective complexes.
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From page 17...
... have demonstrated that atmospheric dynamics can have a significant effect on precipitation efficiency for severe convective storms. These model results have direct bearing on assessing the validity of moisture maximization assumptions that are part of PMP calculation procedures.
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From page 18...
... The question of probability-based analyses of extreme hydrometeorological events has been examined in detail in the report Estimating Probabilities of Extreme Floods (NRC 1988~. These statistical analysis techniques are a mature set of methodological procedures, and there is significant implementation experience.
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Key Terms

  • mountainous regions
  • moisture maximization
  • storm transposition
  • extreme precipitation
  • pmp analyses

  • precipitation events
  • heavy rainfall
  • flash flood
  • standard pmp
  • satellite data

  • extreme storms
  • precipitation efficiency
  • drop size
  • polarization diversity
  • numerical models

  • big thompson
  • rainfall products
  • objective analysis
  • regional pmp
  • western united

  • transposition step
  • pmp procedures
  • generalized pmp
  • observed moisture
  • field operations

  • standard approach
  • radar data
  • thompson storm
  • radar rainfall
  • maximization assumptions


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