1. Wind Channeling in the St. Lawrence River Valley: Synoptic Patterns, Local Conditions, and Operational Forecasts The Eleventh Northeast Regional Operational Workshop 4-5 November 2009 Albany, New York Alissa Razy, Eyad Atallah, John Gyakum Department of Atmospheric & Oceanic Sciences McGill University

2. Data • hourly surface data (winds) recorded at YUL • North American Regional Reanalysis (NARR) dataset • developed by the National Centers for Environmental Prediction (NCEP)‏ • 32 km horizontal resolution • 45 vertical layers • analyses performed every 3 hours

3. YUL: Observed Winds (DJF 1979-2002)‏

4. Observed Wind & Geostrophic Wind

6. 1 histogram per 22.5° range of geostrophic winds

7. { Pairing a { Pairing b

8. Pairing a (northeasterly surface winds)‏ n = 210 Pairing bspeed - Pairing aspeed = 5.3 knots Pairing b (southeasterly surface winds)‏ n = 207

9. Difference Fields: Pairing b (SE) - Pairing a (NE) MSLP (contours) & 1000-500mb thickness (shading)

10. Pairing a: NE sfc winds (red) & Pairing b: SE sfc winds (blue)‏ stability = ϴ925 – ϴ1000 Pairing bstab - Pairing astab = -2.6 K

11. { Pairing d { Pairing c

12. Pairing c (northeasterly surface winds)‏ n = 52 Pairing d (southeasterly surface winds)‏ n = 192

13. Difference Fields: Pairing d (SE) - Pairing c (NE) MSLP (contours) & 1000-500mb thickness (shading)

14. Pairing c: NE sfc winds (red) & Pairing d: SE sfc winds (blue)‏ stability = ϴ925 – ϴ1000 Pairing dstab - Pairing cstab = -2.5 K

15. Summary south-southeasterly to south-southwesterly geostrophic winds • northeasterly surface winds • low/high couplet • weaker gradients • weaker upper-level pattern • stronger stability • warm air advection • southeasterly surface winds • low/high couplet • tighter gradients • more saturated • stronger upper-level pattern • larger amplitudes • smaller wavelengths • lower stability • less suppressed mixing