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452 Precipitation

452 Precipitation. Prob. Of Precip.– Cool Season (0000/1200 UTC Cycles Combined). Orographic precipitation enhancement. Annual Precipitation. Orographic Enhancement of Precipitation. Upper-level frontal band. Convective precipitation. Upslope site (elev. 1067m). Surface frontal rainband.

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452 Precipitation

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  1. 452 Precipitation

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

  3. Orographic precipitation enhancement

  4. Annual Precipitation

  5. Orographic Enhancement of Precipitation Upper-level frontal band Convective precipitation Upslope site (elev. 1067m) Surface frontal rainband Pre-frontal precipitation Valley site Precipitation Rate (mm/hr) Post-frontal convection Distance (km)

  6. Rainshadow

  7. Rainshadow in westerly flow

  8. Annual Precipitation

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

  10. Sequim: roughly 15 inches per year. .

  11. Rainshadows Shift with Approaching Flow Directions and Depend on Stability • As the flow approaching a barrier changes direction, so does the orientation of the rain shadow. • Less rainshadow during warm frontal period, more post-frontal.

  12. Progress in Precipitation Prediction in Terrain

  13. NGM, 80 km,1995

  14. NGM, 1995

  15. 2001: Eta Model, 22 km

  16. 36-km 12-km

  17. NWS WRF-NMM (12-km)

  18. 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.

  19. 2007-2008 4-km MM5 Real-time

  20. Smaller Scale Terrain Modulates Precipitation 10-km

  21. 12-km 4-km

  22. 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

  23. Annual Climatologies of MM5 4-km domain

  24. Verification of Small-Scale Orographic Effects

  25. 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.)

  26. 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

  27. 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

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

  29. Atmospheric Rivers • Meridional flow of moisture is often limited to relatively narrow currents of moisture and usually warm temperatures.

  30. 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.

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

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

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

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

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