1. 452 Precipitation

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

5. Orographic precipitation enhancement

7. Annual Precipitation

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

9. Rainshadow

12. Rainshadow in westerly flow

13. Annual Precipitation

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

15. Sequim: roughly 15 inches per year..

16. 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.

23. Progress in Precipitation Prediction in Terrain

24. NGM, 80 km, 1995

25. NGM, 1995

26. 2001: Eta Model, 22 km

27. 36-km 12-km

28. NWS WRF-NMM (12-km)

29. 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.

30. 2007-2008 4-km MM5 Real-time

35. 10-km Smaller Scale Terrain Modulates Precipitation

36. 12-km 4-km

38. 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

39. Annual Climatologies of MM5 4- km domain

40. Verification of Small-Scale Orographic Effects

41. 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.)

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

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

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

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

46. 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.

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

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

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

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

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

52. Precipitable Water

53. 500 mb height

54. SLP

55. 850 mb Temp

56. 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.

57. 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.

58. Predicting Clouds Zero-order approach: use relative humidity 70% 1000-500 mb RH often corresponds with thicker, middle-level clouds that have a serious impact on radiation. 700 and 850 mb RH is also used by some.

64. Direct Use of Model Clouds All modern models predict clouds, specifically mixing ratios of cloud liquid water and cloud ice. The quality varies…and keep in mind there are serious deficiencies of even the best microphysical schemes. And problems with other physical parameterizations: boundary layer turbulence or radiation can also mess up model clouds.

65. Direct Use of Model Clouds Most problematic: stratus, stratocumulus, and FOG. Remember, some models have spin-up issues: precipitation and clouds improve during the first 3-9 hours. Particularly true of UW WRF which is now cold-started (no clouds at initialization!)

69. Cloud/Precip Forecasting Strategy Very short-term (0-3 hr): temporal extrapolation (informed by human judgement) is HARD to beat. Nowcasting. –Use radar and satellite animation. Models generally not that useful. –New data assimilation/modeling systems: e.g., EnKF, RUC/RR/HRRR may be viable soon and eventually will take this on successfully.

70. Strategy Short-term (2-6 hr): Satellite extrapolation becomes central. Model becomes more dominant at the end Daily (6-24 h): Satellite extrapolation and model, weighing model more at longer range. Remember model spin up issues.

71. Strategy A wise forecaster ALWAYS evaluates model’s initial moisture fields—often a failure mode and a good indicator of potential model failures. How? Compare initial model fields and RH to satellite imagery.

72. 850 700

73. Strategy Know regional precip/cloud climatology –Diurnal and geographic features tend to be very repeatable, particularly during the warm season –Example: front range convection

74. Human Forecaster Issues Precipitation is a parameter where in general forecasters add the least skill compared to objective guidance. There are examples: like Monday’s convection in eastern WA/OR Psychological issues for high and low precip probabilities

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

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

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

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

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

80. 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” Rain Psychology

81. Humans Help with Heavier Precipitation

89. The End

91. Bias scores for the (a) 1.33- and (b) 4-km model simulations for 1400 UTC 13 Dec 2001 through 0800 UTC 14 Dec 2001.

95. Puget Sound Convergence Zone

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