Wind Channeling in the St. Lawrence River Valley: Synoptic Patterns, Local Conditions, and Operational Forecasts

The Eleventh Northeast Regional Operational Workshop4-5 November 2009Albany, New York

Alissa Razy, Eyad Atallah, John Gyakum Department of Atmospheric & Oceanic Sciences

McGill University

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

YUL: Observed Winds (DJF 1979-2002)

Observed Wind & Geostrophic Wind

1 histogram per 22.5° range of geostrophic winds

Pairing a

Pairing b

{{

Pairing a

(northeasterly surface winds)

n = 210

Pairing b

(southeasterly surface winds)

n = 207

Pairing bspeed

- Pairing aspeed

= 5.3 knots

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

Pairing a: NE sfc winds (red) & Pairing b: SE sfc winds (blue)

stability = ϴ925

– ϴ1000

Pairing bstab

- Pairing astab

= -2.6 K

Pairing c

Pairing d{

{

Pairing c

(northeasterly surface winds)

n = 52

Pairing d

(southeasterly surface winds)

n = 192

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

Pairing c: NE sfc winds (red) & Pairing d: SE sfc winds (blue)

stability = ϴ925

– ϴ1000

Pairing dstab

- Pairing cstab

= -2.5 K

Summarysouth-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