"Surface" temperature/wind doesnt show earth's surface values



  • Hi,

    when i set the "elevation slider" to surface, it doesn't show me the real parameters (temperature, wind f.e.) that i would observe on the surface (of the terrain) for the select place.
    But It shows me the parameters that i would see at this place at sea level, or some other defined level. Is that correct?

    Here is an example screenshot, temperature at Zugspitze, approx. 3000m AMSL:
    0_1516437784016_Capture.JPG

    In the city Garmisch-Partenkrichen next to it, approx. 700m AMSL it shows me the same temperature at surface.
    Because of the different elevation there should be a significant difference
    So in alpine areas i have to set the slider manualy to the elevation of earth's surface?
    Is that the intention, or a bug?

    Anyway, apart from that i really enjoy using your site, keep up the good work.

    Best Regards,
    Simon


  • Sailor

    @sphoenix
    Hi,
    The lack of temperature consistency is probably due
    to the resolution of the model. The resolution of ECMWF model is 9km, which means that in an area of 9 x 9km ( but it’s not a square) the temperature will the same. The distance between Garmirsch-Partenkirchen and Zugspitze is 10km, so...
    Furthermore the orographic resolution (ground surface modelling) is even more wider than 9km.


  • Sailor

    @sphoenix
    Then, if you look to figure 2 in this article, you will see that the temperature over the Alps cannot be very precise in mountains.
    https://www.ecmwf.int/en/newsletter/147/meteorology/new-model-cycle-brings-higher-resolution
    We have here the same problem, with -9ºC in Chamonix (1050m) and -11ºC on top of Mont-Blanc (4850m) !



  • @idefix37

    Hi, thx for the reply - this explanation makes sense.
    The "average elevation" of the models seems to raise very slowly, so at the main ridge of the Alps the temperature gets lower. While only single elevation peaks aren't mapped in these models accurate.

    But by combining these model results with high resultion terrain maps (like here at windy) there should be way to extract more accurate numbers from the model.
    Here's a snapshot from the meteoblue map for this area, which shows also the NEMS-4 model, but appearently maps the model results better on the terrain:
    0_1516527767482_Capture.JPG

    Or a simpler idea. It would already help to display the model surface elevation for a selected position. Than you could just calculate the delta from the real elevation to the model elevation and adjust the slider at the right side.

    Regards,
    Simon


  • Sailor

    @sPhoenix
    Hi
    NEMS-4 has a better resolution (4km) compared to ECMWF model. And also probably a better terrain resolution. But in Windy NEMS doesn’t show better temperature precision in mountain area. I don’t know why...
    If you want to know the temperature of a place whose altitude you know, just select the airgram close to this place.
    The altitude is given by the Atmospheric Pressure. For instance, at 700hPa (roughly 3000m) you get a best idea of the temperature than shown on the map.

    0_1516531979074_E9DD05DC-1EFA-4CFE-8C10-6D96BF63C8FA.jpeg

    Rgds
    Alain







  • @idefix37

    Hi,
    sorry i didnt mention that i also selected the NEMS4 model at windy. And i made the observation that it shows completely different surface values than other weather websited that use the same models - in alpine areas.

    This was very evident during the past days with strong winds. The windity map just didnt show these high gusts speed that you'd expect on mountains - while other weather websites with same models delivered far better results.

    The Airgram helps here - like the elevation slider, but it doenst show the elevation of the model data for this position. In fact, it seems that the pressure scale is hard coded? Otherwise it wouldnt make sense that the air pressure scale f.e. at Mont-Blanc starts at 1000hpa. I'd first need to calculate the current air pressure at the real surface level there.

    I just felt the urge to give this feedback. Because despite the really nice frontend, the great usability of windy.com and the state-of-the-art weather models this is quite a weakness if you look for forecasts in mountain areas.

    Regards,
    Simon



  • @meteo-gr

    Thanks for the link. That's exactly the same issue in fact



  • @sphoenix
    The actual altitude for Garmisch is 707m, but the ECMWF's reference altitude for G-P is 1369 m !
    0_1516538698852_5b78575a-800a-4bba-b110-616060444413-εικόνα.png

    Also for Zugspitze (actual=2962 m , model's reference alt.=1700m).
    Difference 1262m, temp. adjustment - 4 C (aprox).



  • @meteo-gr
    Thanks for this info.
    It would be great if these adjustment (model - actual) would be included at windy.com



  • I correct:
    Also for Zugspitze (actual altitude=2962 m , model's reference alt.=1700m).
    Difference 1262m, temp. adjustment - 8,2 C
    (as 6.5/1000 = 8.2/1262)


  • Sailor

    @meteo-gr
    Hi,
    Could we know where do you find these graphics ?


  • Sailor

    @sphoenix
    Yes it is a weakness in mountain areas, but ECMWF and GFS are global models designed to provide weather forecasts covering the globe, difficult to ask them for a better resolution. At least NEMS-4 must be more precise in alpine area... as claim Meteoblue. But difficult to see a difference with ICON-7. The best should be COSMO-1 (1.1km) covering the alpine arc, or AROME (1.3km) covering France and a little more.
    My concern is more about the Freezing Altitude which is considered « above the ground » but not above the sea (amsl) by ECMWF and ICON. In mountain, in Germany, what is the Freezing Altitude reference, local ground or amsl?
    Rgds
    Alain



  • @idefix37
    From ECMWF's application named "Forecaster" but it is not for public use,
    you have to log in.
    .


  • Sailor

    @meteo-gr
    thanks



  • @idefix37
    You said: "We have here the same problem, with -9ºC in Chamonix (1050m) and -11ºC on top of Mont-Blanc (4850m) !".

    I made a small research and I provide you the data and conclusions
    (for ECMWF model).
    Chamonix: model's "surface" =2137m, elevation=1036m (Δ= 1101)
    Mont-Blanc:model's "surface" =2265m, elevation=4808m (Δ= - 2543)
    Temperature adjustment
    Chamonix: +7,1C
    Mont-Blanc: -16,5 C.
    Those "adjustments" take into account Standard Atmosphere's lapse rate (6,5/1000m).
    In the real world, the lapse rate may vary from 9,8 °C/km in dry air
    to around 5 °C/km for moist air (into clouds).

    Hope it helps



  • ... in the same way (adjustments in ºC) ...
    for Vienna: +0,2 Innsbruck:+3,9 Praha: +0,4
    Olympus Mt.peak (2917m), Greece: -10



  • @meteo-gr

    Wouldn't it be even more accurate to use the result of the model for the exact elevation?

    So for example Mont Blanc: The delta between ECMWF model elevation and real elevation:1101m:

    So to get the estimated temperature/wind at the summit: use the closest calcuated value to 1101m above model surface. That's certainly also not 100% correct, because it doesn't take surface effects into account, but maybe more accurate than to assume ISA.
    It don't have access to the ECMWF data, but here a snapshot from NEMS4 sounding for Mont blanc:
    0_1516617214983_Capture.JPG
    The NEMS4 model surface seems to be at ca 3200m according to this sounding, temperature around -5°C.
    At 4800m it shows like -15°C. So a delta of -10°C in this case.

    Regards,
    Simon



  • @sphoenix
    For Mont Blanc the Δ is 2543m


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