Description of weather overlays

[sonnigekerstin]

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

[joalb]

@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]

@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]

.... or scroll on top of this page

[jwh]

@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]

@jwh
For the source of SO2 data ....click ...

[Gkikas LGPZ]

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

[IgorXXXmirror]

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

[Gkikas LGPZ]

@igorxxxmirror
lightnings per square kilometer.

[TomSlavkovsky]

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

[idefix37]

@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]

@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]

@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 :

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

[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]

@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

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]

@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.

[katesisco]

@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]

@katesisco
Press "more layers"

and then activate "CO concentration".

[Meridies]

@eand said in Description of weather overlays:

@ivo

Could you explain difference between:

• wawes
• swell 1
• swell 2
• swell 3

[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.

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.