Aviation Winds Aloft on Airgram



  • love the app and the website. im a pilot and love the wind/radar/metar/taf's etc.
    in the airgram detailed forecast the winds aloft are given in Hpa. in aviation we use MSL for winds aloft. pilots would need to do a complicated conversion every 100 NM to be accurate especially when crossing frontal boundaries or areas of large pressure changes. 800hpa isnt always 6400ft MSL and 900hpa isnt always 3000ft msl. some places that you click on...lets say a mountainous area...3000ft (900hpa) is under the ground but the chart is still showing a wind barb for that altitude.

    The same thing goes for the wind overlay where you can select a pressure setting (altitude) and it shows the wind streams with color coded velocity

    this could be a smaller issue than im thinking it is because a lot of pilots are saying how awesome this site is.
    any light that could be shed on this would be greatly apriciated...because i could just be way over thinking this

    thanks



  • Ok so looks like all MSL altitudes for winds aloft are based on Standard atmosphere so abovee FL180 it won’t make a difference because we set our altimeters to standard and below FL180 it will be just a few hundred ft off or so....so no big deal I guess...??

    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



  • @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


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