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Winds Created by Terrain by Terrain 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. 1 2 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.JYJOHSBUJP HLH explained Gap Winds 4LFX5-PH1%JBHSBN "#- $PQZSJHIU¥CZ3PMBOE4UVMM Conditions needed: strong synoptic- 'SFFDPQJFTPGUIJTQBHFQFSNJUUFE GSPN by short-gap wind eq. based i.FUFPSPMPHZGPS4DJFOUJTUTBOE&OHJOFFST SE scale winds, layer of cold air under &EJUJPOu$&/("(&-FBSOJOH on Froude Number = 1: R R 5 r4UBUFMJOFTBSFUIJO 8 warm (often in winter.) r1SPDFTTMJOFTBSF UIJDL BOEBSFMBCFMFE XJUIUFNQFSBUVSFXIFSF UIFZDSPTT1L1B 13 R XFUCVMCQPUFOUJBMUFNQ $ 14 8 R Bora . Foehn = Chinook. $ 4 $NPJTUBEJBCBU rain 8 R R x x $ESZBEJBCBU Winds Modified by Terrain Downslope Winds 3 3 YouTube Search: Föehn effect - Bora on Feb 05th 2008 Cold, Fast 5m$JTPUIFSN http://www.youtube.com/watch?v=9pDVMv2hT7g Winds )FJHIU LN 1SFTTVSF L1B HLHJTPIVNF HLH 2. x LCL HLH For HW12 Warm, Fast Winds HLH Warm, Dry 1 Winds x Conditions needed: strong Conditions needed: strong synoptic- m m synoptic-scale winds, layer of cold scale winds, humid air causing 5FNQFSBUVSF $ air under warm (often in winter.) upslope precip. (often in winter.) 15 16 .JYJOHSBUJP HLH 4LFX5-PH1%JBHSBN "#- $PQZSJHIU¥CZ3PMBOE4UVMM 'SFFDPQJFTPGUIJTQBHFQFSNJUUFE GSPN i.FUFPSPMPHZGPS4DJFOUJTUTBOE&OHJOFFST SE &EJUJPOu$&/("(&-FBSOJOH R R 5 r4UBUFMJOFTBSFUIJO 8 r1SPDFTTMJOFTBSF UIJDL BOEBSFMBCFMFE XJUIUFNQFSBUVSFXIFSF UIFZDSPTT1L1B R XFUCVMCQPUFOUJBMUFNQ $ 8 R $ 4 $NPJTUBEJBCBU 8 R R x $ESZBEJBCBU Mountain Waves = Lee Waves 5m$JTPUIFSN )FJHIU LN 1SFTTVSF L1B HLHJTPIVNF 5 5 HLH HLH HLH 6 6 x x ∆θ/∆z = ∆T/∆z + Γd m m 5FNQFSBUVSF $ 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.
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