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452 Precipitation

452 Precipitation. Rainshadow. Rainshadow in westerly flow. Annual Precipitation. SW Olympic Slopes-Hoh Rain Forest: 150-170 inches yr -1. Sequim: roughly 15 inches per year. Puget Sound Convergence Zone. Progress in Precipitation Prediction in Terrain. NGM, 80 km, 1995. NGM, 1995.

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452 Precipitation

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  1. 452 Precipitation

  2. Rainshadow

  3. Rainshadow in westerly flow

  4. Annual Precipitation

  5. SW Olympic Slopes-Hoh Rain Forest: 150-170 inches yr-1

  6. Sequim: roughly 15 inches per year. .

  7. Puget Sound Convergence Zone

  8. Progress in Precipitation Prediction in Terrain

  9. NGM, 80 km,1995

  10. NGM, 1995

  11. 2001: Eta Model, 22 km

  12. 36-km 12-km

  13. NWS WRF-NMM (12-km)

  14. 2007-2008 12-km UW MM5 Real-time 12-km WRF-ARW and WRF-NMM are similar December 3, 2007 0000 UTC Initial 12-h forecast 3-hr precip.

  15. 2007-2008 4-km MM5 Real-time

  16. Smaller Scale Terrain Modulates Precipitation 10-km

  17. 12-km 4-km

  18. Small-Scale Spatial Gradients in Climatological Precipitation on the Olympic Peninsula Alison M. Anders, Gerard H. Roe, Dale R. Durran, and Justin R. Minder Journal of Hydrometeorology Volume 8, Issue 5 (October 2007) pp. 1068–1081

  19. Annual Climatologies of MM5 4-km domain

  20. Verification of Small-Scale Orographic Effects

  21. Flow over terrain can be highly 3D and complex

  22. Convective Precipitation • Need at least 2-4 km resolution to get most convection even half right. • If grid spacing is more coarse must have cumulus parameterization--Kain-Fritsch is used for MM5/WRF. • Convection is least skillful precipitation in virtually all models. • High resolution models can potentially give a heads on type of precipitation a day ahead (squall line, supercell, etc.)

  23. Real-time WRF 4 km BAMEX Forecast Valid 6/10/03 12Z 4 km BAMEX forecast 36 h Reflectivity 4 km BAMEX forecast 12 h Reflectivity Composite NEXRAD Radar

  24. Real-time 12 h WRF Reflectivity Forecast Valid 6/10/03 12Z 4 km BAMEX forecast 10 km BAMEX forecast 22 km CONUS forecast Composite NEXRAD Radar

  25. Hurricane Isabel Reflectivity at Landfall 18 Sep 2003 1700 Z 41 h forecast from 4 km WRF Radar Composite

  26. Most West Coast heavy precip events are associated with “atmospheric rivers”, a.k.a. the“Pineapple Express” A relatively narrow current of warm, moist air from the subtropics…often starting near or just north of Hawaii.

  27. Associated with extraordinarily narrow filaments of moisture Precipitable Water From Mike Warner

  28. A Recent Devastating Pineapple Express: November 6-7, 2006

  29. November 6-9, 2006 Dark Green: about 20 inches

  30. We know quite a bit about atmospheric rivers and heavy NW precipitation events, although there are still gaps in our knowledge

  31. Synoptic Set-Up for Top Fifty Events at ForksCourtesy of Michael Warner

  32. Precipitable Water

  33. 500 mb height

  34. SLP

  35. 850 mb Temp

  36. Extreme Precipitation Events • The current of warm, moist air associated with atmospheric rivers are found in the warm sector, parallel, near, and in front of the cold front. • Thus, atmospheric rivers are closely associated with the jet core and the region of large baroclinicity.

  37. Orographic Enhancement • Upslope flow greatly increases precipitation rates on terrain. • Thus, wind speed and angle of attach can greatly modify the extreme nature of the precipitation.

  38. Human Versus Objective Skill for Precipitation Forecasts: NWS Offices Around the US

  39. Prob. Of Precip.– Cool Season(0000/1200 UTC Cycles Combined)

  40. Brier Scores for Precipitation for all stations for the entire study period.

  41. Brier Score for all stations, 1 August 2003 – 1 August 2004. 3-day smoothing is performed on the data.

  42. Precipitation Brier Score for all stations, 1 August 2003 – 1 August 2004, sorted by geographic region.

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