1. Oct. 26, 2005 Vertical Wind Shear
Robert’s Radar
Reminder
Oct. 26, 2005 Vertical Wind Shear
Vertical Wind Shear
Skookumchuck Rapids, September 2002.

2. Introduction Cold front moving across British Columbia Interior.
Not much moisture, especially in more southern districts.
Significant wind shears in speed and direction.

3. 500 hPa thickness
Significant ridge to the east and sharp trough to the west.

4. 850 hPa analysis
Still 40 knot southerly winds ahead of front at 850 hPa.

5. Surface analysis
Surface cold front at 0600Z shortly before passing over Prince George area.

6. GOES-10 IR
Considerable high cloud ahead of cold front, but not much moisture associated, especially in south. For radar imagery focus more on Prince George Radar.

7. PG surface observations
YXS SA M160 OVC /15.7/1.5/1710/AC10 UNOFF
YXS SA M120 BKN /14.6/1.7/1909/AC UNOFF
YXS SP M60 OVC 9SHRA- /8.3//3015G25/SC10 UNOFF
YXS SP M40 OVC 4SHRAPL /6.7//2915G25/SC10 UNOFF
YXS SA M30 BKN 60 OVC 4SHRA-RERA 986/6.2/0.7/2620G25/SC7SC3 RMK PK GUST 30 PAST HR PRESRR UNOFF
YXS SA M30 BKN 50 OVC 9SHRA- 009/5.9/-1.2/2509/SC9SC1 RMK PRESRR UNOFF
Surface winds southerly ahead of front become strong and gusty westerly behind front. Rapid temperature drop of over 8 degrees in one hour.

8. XPG 3.5 V LOOP
XPG 3.5 deg. scan shows low level westerlies deepening with time after cold frontal passage. Winds further aloft are still strong southerlies. Note characteristic Z-shaped pattern indicative of cold air advection.

9. XPG 3.5 V single frame
Westerly winds 24 m/s at 600 m agl; southerly winds 12 m/s at 1500 m agl. Yields vertical shear of 30 m/s / km (severe).

10. XSS 3.5 V single frame
Some shear evident from Mt. Silver Star Radar, but radar elevation higher (1880 m) and some rainshadowing to the west.

11. Summary
Satellite imagery indicates moisture somewhat limited with frontal system.
Upper air charts show significant winds aloft even at 850 hPa.
Prince George Radar 3.5° Doppler scan shows strong variation with height of wind speed and direction, facilitating analysis of severe vertical wind shear.
Vertical wind shear assessment using Silver Star Radar limited by higher elevation of radar and less moisture (further reduced by rainshadowing).
BC coastal radars: radar-level winds more affected by topography.