1. The November 2002 Pineapple Express:
Orographic Ups and Downs

2. Major rain event affected area Nov. 18-20, 2002.
Large range in storm total precipitation amounts.
Consider influence of terrain on precipitation enhancement and suppression.

3. Early in storm much of Lower Mainland in rainshadow area.
Strong increase in rain intensity as North Shore Mountains approached.

4. XSI 0.5° beam about 1600 m above sea level for North Shore mountains.
Radial winds confirm flow towards mountains greater than 15 m/s.

5. A day later flow has veered and is more west-southwesterly now.

6. Reflectivity field confirms rainshadow influence is not as far east.

7. WUJ radar confirms variable position for southwestern edge of precipitation.
Persistent sharp gradients in weather conditions create different perceptions among general public.
Public education required for perceived forecast credibility.

8. Storm Total Precipitation Amounts
Burnaby Mountain
166 mm
South Burnaby
127 mm
Kitsilano
98 mm
YVR
54 mm
South Richmond
44 mm
Victoria Gonzales
26 mm
Hope
39 mm

9. Summary
Sharp increases in rainfall amounts near the mountains with a suitably strong upslope flow.
Rainshadow influences may extend well into the Lower Mainland.
Persistence of rainshadow boundaries leads to large rainfall gradients even over flat terrain.