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HPC Experimental PQPF: Method, Products, and Preliminary Verification

HPC Experimental PQPF: Method, Products, and Preliminary Verification. David Novak HPC Science and Operations Officer Based on work by: Keith Brill (Technique) Chris Bailey (Product Generation) Mark Klein (Web Design) Additional contributions from Ed Danaher, Robert Kelly, and Mike Eckert.

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HPC Experimental PQPF: Method, Products, and Preliminary Verification

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  1. HPC Experimental PQPF: Method, Products, and Preliminary Verification David Novak HPC Science and Operations Officer Based on work by: Keith Brill (Technique) Chris Bailey (Product Generation) Mark Klein (Web Design) Additional contributions from Ed Danaher, Robert Kelly, and Mike Eckert 1

  2. Learning Objectives • At the end of this module, you will be able to: • Explain the method used to generate the HPC PQPF • List two experimental HPC PQPF products • Identify at least one way in which the PQPF product can be used in your operations 2

  3. Motivation Singled-value QPF is not the whole story 3

  4. Providence: March 30, 2010 Nashville: May 1, 2010 Atlanta: Sept. 21, 2009 Seattle: Jan 7, 2009 Motivation Recent high-profile flood events highlight the need for expressing and quantifying low probability, yet high impact events. 4

  5. Method 5

  6. Ensemble Spread (SREF+GEFS+ NAM+GFS+ECMWF) Probability QPF HPC “most likely” deterministic value HPC PQPF Method Modifies ensemble distribution such that HPC deterministic QPF is the mode, while allowing skew Based on Bi-Normal Method – Toth and Szentimrey (1990) 6

  7. HPC PQPF Method Modifies ensemble distribution such that HPC deterministic QPF is the mode, while allowing skew Based on Bi-Normal Method – Toth and Szentimrey (1990) Probability QPF HPC “most likely” deterministic value 7

  8. HPC PQPF Method HPC PQPF provides full distribution consistent with the HPC deterministic forecast Probability QPF HPC “most likely” deterministic value 8

  9. Products 9

  10. 50th Probability 25th 75th 10th 90th 5th 95th QPF PQPF at HPC • PQPF available in 6 h increments out to 72 h • Probability of Exceedance • Percentile Products updated synchronously with issuance of HPC deterministic QPF Available in graphical (web) and gridded format (ftp) 10

  11. Web Products Probability of Exceedance http://www.hpc.ncep.noaa.gov/pqpf_6hr/conus_hpc_pqpf_6hr.php 11

  12. Web Products Percentile http://www.hpc.ncep.noaa.gov/pqpf_6hr/conus_hpc_pqpf_6hr.php 12

  13. HPC Percentile AWIPS GFE Hydrologic Model 60 h 24 h 48 h RFC Gridded Products Exceedance probabilities and percentile products available in grib2 format: ftp://ftp.hpc.ncep.noaa.gov/pqpf/conus/pqpf_6hr Gridded percentile products for hydrologic applications * 13

  14. Applications Probabilistic and contingency hydrologic modeling Graphics for use in decision support briefings Situational awareness of reasonable worst case scenarios 14

  15. Tennessee Example 12 UTC 1 May – 12 UTC 3 May Observed HPC Deterministic (Issued 12 UTC 1 May) 15

  16. Tennessee Example 12 UTC 1 May – 12 UTC 3 May Observed 95th percentile 16

  17. Preliminary Verification 17

  18. Preliminary Verification • Four Methods considered: • HPC PQPF • SREF uncalibrated relative frequency • MDL High-Res QPF MOS (Charba 2009) • Tulsa Method applied to HPC QPF (Amburn and Frederick 2006) • 6 h PQPF at F12 and F24 verified over CONUS using RFC Stage IV (MPE) analysis (remapped to 32 km) • Skill quantified in terms of Brier Skill Score and Reliability (relative to sample climatology) • IMPORTANT CAVEATS • Short period: February 1 – May 15, 2010 • Mainly Spring season • Over CONUS • Verification continuing 18

  19. Preliminary Verification Feb 1 - May 15, 2010 Day 1 Brier Skill Score • HRMOS and Tulsa approaches best at lower thresholds while HPC best at higher thresholds • HPC generally has higher score than ensemble 19

  20. 0.50” Reliability Preliminary Verification Feb 1 - May 15, 2010 0.25” Reliability Perfect No Skill 20

  21. Summary • HPC issuing experimental Probabilistic QPF • Modifies ensemble distribution such that HPC deterministic QPF is the mode • Graphical and gridded probability of exceedance and percentile products available • Preliminary verification shows that the product is at least as skillful as ensemble guidance • Additional adjustments to method and product format may be made • Interested in your feedback: Edwin.Danaher@noaa.gov 21

  22. Resources • Webpage Description: http://www.hpc.ncep.noaa.gov/pqpf_6hr/navigating_6hr_pqpf.shtml • Charba, 2009: Hi-res gridded MOS 6-h QPF guidance. 23rd Conf on Wea. Analysis and Forecasting/19th Conf on NWP, 17B.2, Omaha, NE, AMS • Amburn, S., and J. Frederick, 2006: Probabilistic quantitative precipitation forecasting. P2.21, 18th Conf. on Probability and Statistics, Atlanta, GA, Amer. Meteor. Soc. • Toth, Z., and T. Szentimrey, 1990: The binormal distribution: A distribution for representing asymmetrical but normal-like weather elements. J. Climate, 3, 128-136. 22

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