Zones of Wind Shear

Discussion in 'Flight Following' started by Richard, Oct 4, 2010.

  1. Richard

    Richard Final Approach

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    Hypothesis: There are zones more inclined to experience wind shear than other areas. These zones may be non-mountainous areas.

    Physical observation: Ground based observer views SCT022 layer hauling ass from the north-north east. Simultaneously a BKN layer at 050 is hauling out of the SSW. Similar observations have been made each day for the previous two week period. Sightings include morning, noon, and twilight observations.

    Example: Cape Cod, Massachusetts

    Winds aloft for Boston and Nantuckett, the two closest wx stations 52 nm and 27 nm respectively.
     
    Last edited: Oct 4, 2010
  2. Richard

    Richard Final Approach

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    Opinions expressed by various pilots including local experienced CFIs support the hypothesis that over Cape Cod there exists a fairly permanent zone of shear. The layer of shear may exist between 020 and 060.
     
  3. DutchessFlier

    DutchessFlier Line Up and Wait

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    Shear over coastal environments usually the result of land-breeze/sea-breeze components near the surface and upper air components above. Can happen anytime of the year, and sometimes is a pretty localized event, sometimes enhanced by an approaching frontal system.
     
  4. JohnSBA

    JohnSBA Pre-takeoff checklist

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    So in flight is this experienced as an abrupt shear or a layer of turbulence? I've flown through layers of less dramatic shear and not even noticed anything other than a gradual but dramatic change in ground speed.
     
  5. Richard

    Richard Final Approach

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    Both. Usually the latter.

    As yet, I'm uncertain if this is mechanical due to landforms or caused by the confluence of water on three sides of the peninsula which is Cape Cod. I suspect the latter given the upper altitudes of the layer and the absence of significant elevation changes of the terrain.

    Being in Santa Barbara perhaps you are familiar with the coastline from Pt Conception to Avila/Port San Luis (Pt Buchon) in the north. There there are coastal range and the venturi effect most notably at Pt Sal and Pt Buchon. This occurs with winds 260 to approx 030. The venturi is more pronounced as the winds veer more north of the prevailing 330 winds. Even with the prevailing winds, the wind is onshore/offshore/onshore as they pass the prominence of the points. The turb layer ranges from 1,400 to 5,000.
     
  6. Richard

    Richard Final Approach

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    Scott, as always, your input is highly appreciated. Your responses are like candy to a child.

    However, I should say there were a couple days several weeks ago that cloud observations were similar to the conditions which were the basis of this thread. That was before the recent period of high humidity and temps.

    I will be watching how the next few days develop. It looks very interesting.
     
    Last edited: Oct 5, 2010
  7. Richard

    Richard Final Approach

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    Scott, nothing personal but I'm going to be looking for observations to prove your synoptic picture incorrect (as reason for local observations).

    I'll be looking to define if this "shear" is a result of geography and not short-term weather patterns, seasonal wx inclusive.

    EDIT: This reminds me of the convergence zone in the PNW and a similar zone in the mid-eastern region of the Los Angeles basin. These zones exist throughout the year (although seasonally pronounced) and are a result of geography.
     
    Last edited: Oct 5, 2010
  8. JohnSBA

    JohnSBA Pre-takeoff checklist

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    Thanks for the reply. Glad I didn't encounter that while flying in that area!
    Wish you could see my enigmatic smile. Actually though most of my encounters with wind shear and mountain wave have been on the East-West portion of coast between Carpinteria and Pt. Conception. Sometimes just making the 10 minute hop from SBA to IZA can be a bit harrowing. Several times I've returned from a long, placid flight elsewhere to be greeted by hot air crossing the mountains into SBA, and cool air two minutes later on the ground. Needless to say, those two minutes can be interesting. Often the shear layers are gradual, and sometimes there's not even much turbulence. Worst I've commonly encountered is between El Capitan and Point Conception, and when I see lenticular clouds out there my flight plans on local scenic flights are elsewhere. The coast from the point to VBG is on pretty much permanent restricted status, so I've never been closer than two miles of shore. Seems to me the stretch of East-West coast and mountains has the worst shear issues due to the upper level winds commonly being North and sometimes South, while lower level are more West and sometimes East.
     
  9. Richard

    Richard Final Approach

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    FYI: that moisture sucked up last week from the disturbance off FLA warmed the local water in Nantucket Sound and Cape Cod Bay. The surface temps rose from 60 to 65 in two days.

    In coastal central California, of which I am most familiar, such a rise in sea surface temps while rare would deepen the marine layer. The marine layer is stratus therefore as smooth as butter.

    How such a rise in sea surface temps surrounding Cape Cod would impact winds aloft I haven't a clue.
     
  10. Richard

    Richard Final Approach

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    John, it is not uncommon to see an air temp difference of 50*F in the summer months 'tween IZA and SBA. Or Morro Bay and Atascadero, which I am most familiar with.