1. 452 Precipitation

2. Rainshadow

5. Rainshadow in westerly flow

6. Annual Precipitation

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

8. Sequim: roughly 15 inches per year.

9. Puget Sound Convergence Zone

10. Progress in Precipitation Prediction in Terrain

11. NGM, 80 km, 1995

12. NGM, 1995

13. 2001: Eta Model, 22 km

14. 36-km
12-km

15. NWS WRF-NMM (12-km)

16. 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.

17.
4-km MM5
Real-time

22. Smaller Scale Terrain Modulates
Precipitation
10-km

23. 12-km
4-km

24. 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

25. Annual Climatologies of MM5 4-km domain

26. Verification of Small-Scale Orographic Effects

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

29. 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.)

30. 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

31. Composite NEXRAD Radar
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

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

33. 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.

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

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

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

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

38. Synoptic Set-Up for Top Fifty Events at Forks Courtesy of Michael Warner

39. Precipitable Water

40. 500 mb height

41. SLP

42. 850 mb Temp

43. 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.

44. 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.

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

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

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

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

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

51. Reliability diagrams for period 1 (a), period 2 (b), period 3 (c) and period 4 (d).

52. Rain Psychology
More than a day out….Human Forecasters Tend to Overpredict 10-30%
--exaggerating the threat of rain when it is not likely.
“Its probably not going to rain…but I will throw in 10-30% anyway to cover myself”
And underpredict rain when it is fairly definite. “Well it looks like it will rain…but I am unsure…so I will knock down the probabilities to 60-80% to cover myself”

53. Humans Help with Heavier Precipitation

60. The End

62. Bias scores for the (a) and (b) 4-km model simulations for 1400 UTC 13 Dec 2001 through 0800 UTC 14 Dec 2001.