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Downslope Windstorms in Howe Sound: Two Case Studies

This study examines the rare downslope windstorms in Howe Sound through two significant cases. Analyzing climatological data from Pam Rocks (1995-2012), we identify predictors for these unusual Southeast wind events. The major case on January 18, 2010, demonstrated a robust pressure difference of over 6.5 hPa, leading to accurate forecasting, while the minor event on February 12, 2010, during the Olympics, revealed forecasting challenges. Our findings suggest the orographic effects and critical layers influence the wind patterns, presenting hazards for mariners and road users, especially on the Sea-to-Sky Highway.

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Downslope Windstorms in Howe Sound: Two Case Studies

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  1. Downslope Windstorms in Howe Sound: Two Case Studies Ruping Mo, Paul Joe National Lab for Coastal & Mountain Meteorology, Environment Canada Johnson Zhong, Cindy Yu, Ken Kwok, and Michel Gélinas Pacific Storm Prediction Centre, Environment Canada 15th Conf. Mountain Meteorology 20–24 August 2012, Steamboat, CO, USA

  2. Outline • Geography and windstorm climatology • Rules of thumb for the freak windstorms • Case studies: • 18 January 2010 – A major event • 12 February 2010 – A minor event • New heuristic rule • Conclusions Test test test test

  3. Howe Sound

  4. Where is Howe Sound? Howe Sound Pam Rocks Metro Vancouver

  5. Winds in Howe Sound – Climatology • Data: Pam Rocks (WAS)– Jan to Mar, 1995 to 2012 (18 years)

  6. Winds in Howe Sound – Climatology Sustained winds at Pam Rocks (WAS) Hourly, Jan – Mar, 1995 – 2012

  7. Unusual/Freak Southeast Windstorms ??? ???

  8. Freak Southeast Windstorms 30 14 Hourly, Jan–Mar, 1995–2012 (18 yrs)

  9. Heuristic Rule/Rules of thumb • Pre-frontal • Strong Southeasterlies in the Strait of Georgia PYVR−PYQQ > 6.5 hPa Pressure Difference

  10. Case 1: 18 Jan 2010 04:00 PST (12:00 UTC) PYVR−PYQQ> 6.5 hPa (MAX Pdif = 11.9 hPa) SE wind warning issued at 20:00 PST 17 Jan

  11. Case 1: 18 Jan 2010 • Predicted by 1-km model (GEM-LAM-1km) WAS S2S Hwy

  12. Case 1: 18 Jan 2010 • Predicted by 1-km model (GEM-LAM-1km) • Southwest wind aloft • Possible critical layer for wave breaking • Induced convective instability over water Possible Critical Layer for SEly WAS

  13. Case 2: 12 Feb 2010 (1st day of 2010 Olympics) Wind dir. unknown 04:00 PST (12:00 UTC) PYVR−PYQQ> 6.5 hPa (MAX Pdif = 8.1 hPa) SE wind storm was not predicted. Forecast amended after the fact.

  14. First Day of Olympics PYVR−PYQQ > 6.5 hPa (MAX Pdif = 8.1 hPa) SE wind storm was not predicted. Forecast amended after the fact.

  15. Case 3: 12 Jan 2010 • Predicted by 1-km model (GEM-LAM-1km)

  16. WSK Wind Profile New rules of thumb • Pre-frontal • Strong Southeasterlies in the Strait of Georgia PYVR−PYQQ > 6.5 hPa • Winds shift to southwest aloft!

  17. Potential hazard on Sea-to-Sky HWY

  18. Conclusions • Southeast windstorm in Howe Sound is a rare event • It has quite an impact on mariners, but is difficult to predict • It is likely related to a downslope windstorm due to orographic wave breaking • Orographic effect leads to Wind shifting from SE to SW above mountain, which provide a possible critical layer aloft for orographic wave breaking • Downslope windstorm could be a hazard on the Sea2Sky Hwy as well • The development of LAM-1km model was accelerated for the Olympics and this is a serendipitous benefit of that

  19. Thank You! Michael O’Toole’s “Storm Over Howe Sound”

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