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    Description of weather overlays

    Frequently Asked Questions
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    • RaniR
      Rani @ivo | Premium
      last edited by

      @ivo

      When using wave overlay, I see a color key indicating wave height and also boxes with values in them with either- or~ before the value. These numbers never match the color key .

      Please explain.

      1 Reply Last reply Reply Quote 2
      • AtalantiaA
        Atalantia
        last edited by

        What means the 330 before 64km/h? 0_1507996931412_WindyScreen.png

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

          @Atalantia
          wind direction 330 degrees (coming from NorthWest)

          M 1 Reply Last reply Reply Quote 4
          • jmdsJ
            jmds
            last edited by

            @ivo said in Description of weather overlays:

            Rain rate:

            I cannot see RAIN RATE in the settings ....

            1 Reply Last reply Reply Quote 2
            • alecloudenbackA
              alecloudenback | Premium
              last edited by

              Is there an overview of the meteograms that Windy displays for the forecasts? I am not sure of what some of the background colors and charts mean.

              sonnigekerstinS 1 Reply Last reply Reply Quote 10
              • sonnigekerstinS
                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....

                edneffE 1 Reply Last reply Reply Quote 12
                • 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 LGPZG 1 Reply Last reply Reply Quote 1
                  • Gkikas LGPZG
                    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 LGPZG 1 Reply Last reply Reply Quote 3
                    • Gkikas LGPZG
                      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 LGPZG 2 Replies Last reply Reply Quote 1
                        • Gkikas LGPZG
                          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 LGPZG
                            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
                            • IgorXXXmirrorI
                              IgorXXXmirror
                              last edited by

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

                              IXMfoxPrower^_^;;

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

                                @igorxxxmirror
                                lightnings per square kilometer.

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

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

                                  idefix37I 1 Reply Last reply Reply Quote 1
                                  • idefix37I
                                    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 LGPZG 1 Reply Last reply Reply Quote 1
                                    • Gkikas LGPZG
                                      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.

                                      idefix37I 1 Reply Last reply Reply Quote 2
                                      • idefix37I
                                        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 LGPZG 1 Reply Last reply Reply Quote 0
                                        • Gkikas LGPZG
                                          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.

                                          idefix37I 1 Reply Last reply Reply Quote 1
                                          • idefix37I
                                            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 LGPZG 1 Reply Last reply Reply Quote 2
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