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    Description of weather overlays

    Frequently Asked Questions
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    • sonnigekerstin
      sonnigekerstin @alecloudenback | Premium last edited by

      @alecloudenback Me neither. I was searching for a manual to find out about the meaning of the different colors,graphs,pictograms etc....

      edneff 1 Reply Last reply Reply Quote 11
      • J
        joalb @TZ last edited by

        @tz What height does surface refer to? There would technically be no wind at the surface, so it must be some standard height above the ground (whatever the common reading instrument height is). What is that height? (i.e. 2m, 10m, 20m?). I'd like to use the data to estimate wind shear at a given location and using surface (0m) is not valid.

        Gkikas LGPZ 1 Reply Last reply Reply Quote 1
        • Gkikas LGPZ
          Gkikas LGPZ Moderator @joalb last edited by

          @joalb
          Surface wind refers to 10m above model's surface.
          Surface temperature refers to 2m.

          For ECMWF datasets, see https://www.ecmwf.int/en/forecasts/datasets/set-i
          For ICON, see chapter 6 (Global output fields) in
          "Database Reference Manual for ICON"
          https://www.dwd.de/SharedDocs/downloads/DE/modelldokumentationen/nwv/icon/icon_dbbeschr_aktuell.html

          Gkikas LGPZ 1 Reply Last reply Reply Quote 2
          • Gkikas LGPZ
            Gkikas LGPZ Moderator @Gkikas LGPZ last edited by

            .... or scroll on top of this page

            1 Reply Last reply Reply Quote 2
            • J
              jwh @ivo last edited by

              @ivo From Leilani Estates Big Island Hawaii: what is the source of SO2 data? Satellite only? Any way to include data from ground monitors such as: http://weather.hawaii.edu/vmap/hysplit/ ?

              Gkikas LGPZ 2 Replies Last reply Reply Quote 1
              • Gkikas LGPZ
                Gkikas LGPZ Moderator @jwh last edited by

                @jwh
                For the source of SO2 data ....click ...
                0_1527573931458_69a4c7f2-385d-472b-a661-fe6d2ca57ea3-εικόνα.png

                1 Reply Last reply Reply Quote 2
                • Gkikas LGPZ
                  Gkikas LGPZ Moderator @jwh last edited by

                  @jwh
                  https://community.windy.com/topic/5982/so2-actual-time-or-predicted

                  1 Reply Last reply Reply Quote 0
                  • IgorXXXmirror
                    IgorXXXmirror last edited by

                    What does it mean in lightning l / km ^ 2?

                    IXMfoxPrower^_^;;

                    Gkikas LGPZ 1 Reply Last reply Reply Quote 0
                    • Gkikas LGPZ
                      Gkikas LGPZ Moderator @IgorXXXmirror last edited by

                      @igorxxxmirror
                      lightnings per square kilometer.

                      1 Reply Last reply Reply Quote 3
                      • T
                        TomSlavkovsky API developers last edited by

                        @Gkikas-LGPZ @IgorXXXmirror There is a mistake pointed out by ECMWF - it should be flash/km2/day.

                        idefix37 1 Reply Last reply Reply Quote 1
                        • idefix37
                          idefix37 Sailor Moderator @TomSlavkovsky last edited by

                          @tomslavkovsky
                          If the unit is flash/km2/day, why does the map changes every 3 hours? Is it a sliding average over 24 hours? Looking to the way how thunderstorms move on the map every 3 hours, it seems surprising

                          Gkikas LGPZ 1 Reply Last reply Reply Quote 1
                          • Gkikas LGPZ
                            Gkikas LGPZ Moderator @idefix37 last edited by Gkikas LGPZ

                            @idefix37
                            ECMWF definitions:
                            https://software.ecmwf.int/wiki/display/FCST/45r1+new+parameters%3A+lightning+flash+density

                            I think windy uses "Averaged total lightning flash density in the last 3 hours (litota3)"
                            with unit conversions.

                            P.S. as the model's grid is 9x9 km, I propose to keep the original ECMWF density
                            (units of flashes per 100 sq. km per hour).
                            Windy converted values down to 1 sq. km,
                            but this is a "very small" area for lightning forecast
                            and maybe it is prone to larger errors.

                            idefix37 1 Reply Last reply Reply Quote 2
                            • idefix37
                              idefix37 Sailor Moderator @Gkikas LGPZ last edited by

                              @gkikas-lgpz
                              Thanks for this information. However, I still can’t understand how the thunderstorm maps can change every 3 hours step if the parameter used is « per day » (which is the case of the 4 parameters described in the ECMWF document). These parameters are probably useful for statistical comparisons, but not for forecast.
                              And it’s what is explained in this document :

                              0_1530607573507_57905F25-5384-441D-A09E-CB90F43D6D74.jpeg

                              So the ECMWF provide probably data to Windy in [ flashes / 100km2 / hour].... to be confirmed

                              Gkikas LGPZ 1 Reply Last reply Reply Quote 0
                              • Gkikas LGPZ
                                Gkikas LGPZ Moderator @idefix37 last edited by Gkikas LGPZ

                                @idefix37
                                I don't know how windy computes the lightnings parameters provided on the picker.
                                Maybe is "flashes / 100km2 / hour", multiplied by 100 (to provide flashes per sq. km),
                                multiplied by 3 (to provide flashes in 3 hr timesteps).
                                Windy's developers know!

                                I have also to mention that flashes per sq. km per day, is a UNIT, not a parameter.
                                Think about "rain rate" (or intensity):
                                in a stormy day we may have (for a small time period) a "rain rate" of 500 mm/hr
                                but the total rainfall may be only 50 mm /24 hrs.

                                idefix37 1 Reply Last reply Reply Quote 1
                                • idefix37
                                  idefix37 Sailor Moderator @Gkikas LGPZ last edited by

                                  @gkikas-lgpz
                                  I understand perfectly what does mean a rate of rain, or flashes density, per hour, or per day, or per 3 hours per day...
                                  What bother me is the discrepancy between map displays and units supposed to be used.
                                  In the screenshots below the weather picker (for the same place) shows:
                                  At 17h, 0.04 l/km2
                                  At 20h, 2.22 l/km2
                                  At 23h, 0 l/km2

                                  0_1530721438639_C6BDB437-8D54-4117-B23E-820862FC5B14.jpeg

                                  Showing such a variation, I can’t imagine that these values are expressed per day.

                                  And as you said, Windy’s Developers must know which units are really used.

                                  Gkikas LGPZ 1 Reply Last reply Reply Quote 2
                                  • Gkikas LGPZ
                                    Gkikas LGPZ Moderator @idefix37 last edited by

                                    @idefix37
                                    This is a new product and we don't know much about it.
                                    Personaly, I use it as an "light-moderate-heavy" indication
                                    rather than arithmetic values.

                                    1 Reply Last reply Reply Quote 2
                                    • katesisco
                                      katesisco @Gkikas LGPZ last edited by

                                      @gkikas-lgpz
                                      I have trouble using Windy.com
                                      I was able to just click on carbon monoxide and see but that ceases as the choice for CO is no longer there. What happened or what am i doing wrong?
                                      katesisco@yahoo.com

                                      Gkikas LGPZ 1 Reply Last reply Reply Quote 0
                                      • Gkikas LGPZ
                                        Gkikas LGPZ Moderator @katesisco last edited by

                                        @katesisco
                                        Press "more layers"
                                        0_1531834033951_87158022-a15e-4bc2-84a9-44e7e8797408-εικόνα.png

                                        and then activate "CO concentration".
                                        0_1531834169952_02844908-7363-4cb0-9f8f-5489a54a8c23-εικόνα.png

                                        1 Reply Last reply Reply Quote 0
                                        • M
                                          Meridies @Eand last edited by

                                          @eand said in Description of weather overlays:

                                          @ivo

                                          Could you explain difference between:

                                          • wawes
                                          • swell 1
                                          • swell 2
                                          • swell 3
                                          idefix37 V 2 Replies Last reply Reply Quote 0
                                          • idefix37
                                            idefix37 Sailor Moderator @Meridies last edited by idefix37

                                            @meridies
                                            @Eand

                                            As you probably know the shape of waves, in a given place, is a mix of different kind of waves:

                                            • The windsea (also called wind waves) is produced by the local wind.

                                            • The main swell is produced by a strong wind far away.

                                            • Secondary swells are produced also by winds far away but in other places.

                                            All of them have different heights, come from different directions and show different periodes (which is the time between 2 wave crests)
                                            Swell 1 is the main swell, swell 2 and 3 are secondary swells (the swell classification 1, 2, 3 depends on their respective heights)
                                            In this example below, Wind gives the direction of windsea. Swell 1 has a height of 0.6m and a period of 9 seconds.

                                            0_1532433836586_C4D96B18-4CD9-49E4-8BCE-75D80F835ACE.jpeg

                                            The best surf conditions correspond to a strong swell with weak windsea and secondary swells.

                                            A cross sea thrown up by a strong wind and a strong swell whose directions make an angle close to 90º gives hard conditions for navigation.

                                            1 Reply Last reply Reply Quote 5
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