wind channeling in the st. lawrence river valley: synoptic patterns, local conditions, and...
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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