Aviation Winds Aloft on Airgram



  • @andrew2213 said in Aviation Winds Aloft on Airgram:

    ...Still don’t understand why there is wind info given for the surface and then 2000/3000 ft MSL etc in areas where the elevation of the ground is like 5000 or 10000MSL etc in like Colorado or mountainous areas.

    I would love to hear a good explanation for this question. I live in Colorado, and there are wind barbs on the airgram at hPa corresponding to an approximate elevation of several hundred feet beneath the dirt I'm standing on. Also, I wonder about that sam issue as related to the map display, when you can set altitude based on pressure. Just skip the 850-1000 hPa range?

    P.S. I think when I finally have all this sorted out well enough, I'm going to post a very thorough "explainer" with a bunch of screenshots so nobody gets as confused as me again (⊙.☉)7





  • @TChilli
    .... Aspen, CO has a 10.000 ft elevation (roughly 700 hPa)
    In the airgram the "fictionary" winds at lower levels are those given by the model
    as the pressure levels are terrain following
    95f24c0d-e120-4f5d-8f05-fb37e94a521a-εικόνα.png



  • @TChilli
    .... If you activate the "sounding" for Aspen ...
    282a5242-63c4-4fa9-8c10-10a1557cbca1-εικόνα.png

    ... you'll have a more realistic view (winds and temp/d.p. start from the ground, not from msl)

    18e24fec-f837-41b3-bd5f-eaf0be87777e-εικόνα.png



  • @Gkikas-LGPZ said in Aviation Winds Aloft on Airgram:

    @TChilli
    .... Aspen, CO has a 10.000 ft elevation (roughly 700 hPa)
    In the airgram the "fictionary" winds at lower levels are those given by the model
    as the pressure levels are terrain following...

    Thanks for that! I actually looked at those images in the other thread before, but something you said made it click this time ...I think.
    So, if I’m understanding you correctly, the isobaric surfaces are technically actually contiguous, but they are highly compressed at higher altitudes (functionally, to the point of being at the same plane, relatively speaking). As such, any barbs below your altitude on the airgram are still modeled, but can be ignored if they’re below x hPa (700 hPa in your example). [edit to insert for clarification: ok, not actually “ignored” completely, because they are functionally the surface winds at 700 hPa, but below that they are all pretty much the same direction & strength, so ignoring the bottom bit is fine].
    However, if I’m also understanding atmospheric pressure systems and the way they move, to be technically most accurate you can’t truly just say “Ignore everything below 700 hPa” and be done. This is because as pressure systems move, they also lower/raise the regional atmospheric pressure a bit, such that a really accurate statement would be more like, “Today, in a low pressure system, everything below 690 hPa can be ignored on the airgram.” Though, that sort of precision is largely superfluous and there is better information to be gleaned from understanding pressure systems and their movement. Additionally, if you want accurate surface wind speeds, the easiest thing to do is look at sounding. Let me know if I really missed the mark on that stuff. Otherwise, I think I finally got it :D.
    Thanks!



  • @TChilli
    Yes, you got it!
    Always keep in mind that complex terrain is a major source of inaccuracy in models.



  • @Gkikas-LGPZ
    Good deal. Glad to hear it. Thanks for the explanation. One more question, and I think I’ve got Windy sorted out...
    It appears as though the above is also true of the colorized map view of wind speeds, with two exceptions:

    1. “Surface” is actually a map of surface wind speeds (and not wind speeds at MSL)
    2. “100 m / 330 ft” is a map of wind speeds 100 m above surface (AGL).
      After those two, the local wind speeds are mapped based on the ‘fictional’ predicted speeds based on the models up to the hPa corresponding to the altitude at that location. That is to say, for Aspen, after “surface” and “100 m,” the locally displayed wind speed color shouldn’t change very much until 700 hPa (allowing for some variance within model).
      Is that the gist of the map, as well?
      If so, I’ll just go ahead now and say “thanks again for the help!” :)


  • @TChilli
    "Surface" is a map of wind (or temperature) at model's lowest atmospheric layer.
    Over the ocean (or open sea) it is the same with MSL.
    In complex terrain it may differ a lot from reality.

    466e782e-540c-4964-88d2-396d1d5895ec-εικόνα.png

    Also ...
    0d8776d0-91c5-40a7-968a-b51bd9be7a55-εικόνα.png

    Strong winds situations give even more innacurate forecasts near surface.
    c98a9a6c-ee2d-4ed3-ad7b-70d4e5ef2c80-εικόνα.png



  • @Gkikas-LGPZ said in Aviation Winds Aloft on Airgram:

    @TChilli
    "Surface" is a map of wind (or temperature) at model's lowest atmospheric layer.
    Over the ocean (or open sea) it is the same with MSL.
    In complex terrain it may differ a lot from reality.

    466e782e-540c-4964-88d2-396d1d5895ec-εικόνα.png
    ...

    Are those images from a book [in English or translated] that discusses specifics of weather models? If so, what’s the title/author?
    If not, do you have recommendations for other resources you might be able to offer?
    I’m serious about my plans to write up an “explainer” post for other people who might benefit from an “idiot’s guide” to Windy’s graphical displays, and I want to make sure I’m being accurate (but don’t want to pester you with every little question). Thanks!



  • @TChilli
    The images come from a paper named: "Wind Flow Models over Complex Terrain ..."
    source: https://www2.dmu.dk/atmosphericenvironment/cost/docs/COST710-4.pdf

    Also I propose you to sign up to MetEd (https://www.meted.ucar.edu/index.php)
    where you'll find a lot of educational resources in meteorological topics.
    You can use keywords (e.g. "NWP" for Numerical Weather Prediction)
    and skill levels (e.g. "1" stands for easy) to narrow your search.
    https://www.meted.ucar.edu/training_detail.php?topicSorting=15&languageSorting=1&module_sorting=skillLevelAsc


Log in to reply
 

Windyty, S.E. - all rights reserved. Powered by excellent NodeBB
NodeBB & contributors, OSM & contributors, HERE maps