Description of weather overlays
Rani | Premium last edited by
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 .
Atalantia last edited by
What means the 330 before 64km/h?
wind direction 330 degrees (coming from NorthWest)
jmds 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.
sonnigekerstin | 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....
@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.
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"
.... or scroll on top of this page
For the source of SO2 data ....click ...
IgorXXXmirror last edited by
What does it mean in lightning l / km ^ 2?
lightnings per square kilometer.
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
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.
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 :
So the ECMWF provide probably data to Windy in [ flashes / 100km2 / hour].... to be confirmed
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.
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
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.