ATSC 201 - Meteorology of Storms Week 12 Day 5

Learning Goals Discussion Points & Demos Local Winds: Topic: West-coast Weather & Local / 1. Discussion & interaction on topics Winds created by the terrain. Regional Winds from readings (bring your clicker). Winds modified by the terrain. At the end of this section, you should be able to: 1. Synthesize all aspects of the general 2. Look at transparencies from case- circulation, air masses, fronts, midlatitude study West Coast extratropical cyclone. view is looking toward the northeast cyclones to explain why we get the weather we do. 2. Demonstrate the UBC NWP forecast North Shore Mtns. 2. Describe west-coast weather phenomena web page. Howe including: pre-frontal jets, the pineapple Sound express, outflow & gap winds, the cyclone Burrard Inlet graveyard, orographic precipitation, instant occlusions upon landfall, mountain waves, polar lows, etc. UBC 3. Access web-based weather, satellite, radar, and numerical weather forecast info on current and future weather. 4. Describe and explain these local winds: anabatic wind, katabatic wind, mountain and valley winds, sea breeze, gap winds, coastally trapped jet, mountain waves, Bora, Foehn (Chinook) winds.

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Scales of Motion Rossby wave Winds Created by

L Midlatitude Cyclone Terrain

Hurricane ... by differential heating of different terrain features.

Thunderstorm

Boundary-layer Thermals

3 4 Winds Created Winds Created by Terrain by Terrain

Daytime. Mountain Nighttime. Mountain slopes heated by slopes cool by IR sunlight. radiation to space.

Warm updrafts called Cold downdrafts anabatic winds hug called katabatic the slopes. Conditions needed: light synoptic- winds hug the slopes. Conditions needed: light synoptic- scale winds, mostly clear, sunny skies. scale winds, mostly clear skies.

5 6 Katabatic Wind Speed Winds Created by Terrain Sea Breeze

Daytime. Sun- heated land warmer than neighboring water.

Conditions needed: light synoptic- scale winds, mostly clear, sunny skies.

∆θv = θv environ. – θv kat.air Hint: if you are not given a humidity, then assume Tv = T.

7 8 Winds Created by Terrain Sea Breeze Sea Breeze

9 10

Winds Modified by Cold Air Terrain

... when synoptically-driven winds hit mountains, etc.

11 12 Winds Modified Strong gap winds by Terrain (known locally as For HW12 Squamish winds) flowing toward the south in Howe Sound hydraulic damaged BC jump Ferry. (Short) Winds were well.JYJOH

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Winds Modified by Terrain Downslope Winds 3 3 YouTube Search: Föehn effect - Bora on Feb 05th 2008

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17 18

Brunt-Väsäilä frequency (from Ch 5) Mountain Waves = Lee Waves

Froude Number =

= natural wavelength / (2· Mtn.Width) Stronger static stability creates a stronger restoring force, giving a faster oscillation.

Oscillation + wind = mountain wave

19 20 Coastally-trapped Low-level Jet (Barrier Jet) Lenticular clouds, at the crests of Synoptic mountain waves set-up

21 22 Coastally-trapped Low-level Jet Long-gap Winds

23 24 Cold Air

west winds Cool Sea-Surface Temperature CAPE

25 26

Satellite View cyclone fully occluded graveyard in cyclones of Fronts in Gulf of Alaska Typical (cinnamon roll) NE Pacific Winter fronts in NE occluded warm front disappear over front Pacific mtns. L T-shaped orographic occluding precip. (m) cyclone pre-frontal jet cold front warm-front Pineapple stub Express

27 28 Heavy orographic Zooming in. precipitation Winter. Book by Cliff Mass, 2008: “The Weather of the Rain shadow Pacific Northwest”, Univ. Washington Press. cA airmass -> Channeling of very cold Demo of UBC Weather Forecast web pages. wind through outflow from gaps Fraser Canyon Q: Look at current weather maps, and pick out mP airmass - Olympic Mtn features. (Perhaps Questions on the fly.) > Mild convergence temperatures zone winter & summer

29 30