1. Mid-Mountain (a.k.a Harvey’s) Clouds at Whistler, BC, Canada Ruping Mo Environment Canada

2. Whistler Mountain

3. Mid-Mountain (Harvey’s) Clouds Harvey Fellowes 1040 PST 2010-02-14

4. Mid-Mt. Clouds (Mosaic)

5. Impact of Alpine clouds 11 February 2010, Whistler

6. Diurnal visibility Occurrence frequency 5 Feb – 21 Mar 2010

7. Mid-mountain cloud 2010-02-16 1100 – 1340 PST

8. Mid-mountain cloud Thermal impact: Thermally forcing up-slope flow interacting with inversion in the morning (Mo et al. 2012) Late-morning tendency

9. Mid-mountain cloud 2010-02-16 1100 – 1340 PST A Case Study

10. Mid-mountain cloud A Case Study: Morning (1000 PST, 16 Feb 2010 )

11. Mid-mountain cloud A Case Study: Afternoon (1600 PST, 16 Feb 2010)

12. Mid-mountain cloud Whistler (WAE) Sounding

13. Mid-mountain cloud

14. Dry layer (cloud top)

15. Model Prediction (1 km resolution) Meteograms at mid-mountain (VOL, 2010-02-16) Low visibility Cloudy No high cloud

16. Model Prediction (1 km resolution) Meteograms at mid-mountain (VOL, 2010-02-16) Cloudy No high cloud Gusty SW winds

17. Observation vs Prediction

18. Page 18 – March 4, 2016 Observed Predicted

19. Model Prediction 1 km resolution model Visibility forecast

20. Model Prediction 1 km resolution model Valid at 2010-02-16 1100 PST (1900 UTC)

21. 1 km resolution model Valid at 2010-02-16 1100 PST (1900 UTC) (Vertical velocity) Model Prediction

22. Conceptual Model Valley inflow drives up-slope flow and gives rise to clouds Leeward subsidence of elevated flow traps the clouds Late-morning tendency is thermally driven

23. Page 23 – March 4, 2016 Another Case

24. Oscillation on mountain slope 2010-02-27, 1100 – 1500 PST

25. Oscillation on mountain slope 2010-02-27, 1100 – 1500 PST Possible mechanisms: Cloud-top evaporative instability

26. Oscillation on mountain slope 2010-02-27, 1100 – 1500 PST Possible mechanisms: Cloud-top evaporative instability Slope-flow induced gravity waves

27. Page 27 – March 4, 2016

28. Page 28 – March 4, 2016

29. Summary Mid-mountain clouds at Whistler are common in Winter Mid-Mt clouds form most frequently late in the morning Mid-Mt clouds form under stably stratification, usually post-frontal, when moderate valley inflow prevails Mid-Mt clouds form on the leeward slope, when weak to moderate leeward subsidence is expected Mid-Mt clouds could experience oscillations with 1-3 hr periods Mid-Mt clouds have significant impact on downhill skiing competitions Demonstrate value of web cams, 1 km model