Best posts made by idefix37

@ivo
Vote 2: AROME

AROME is available as free data. Very interesting along coastline, in mountain zone and for local forecasts (thunderstorms, large towns effect...)

The dust of the Sahara desert raised by the wind can cross the oceans. Using NASA satellite imagery, scientists have shown that this transport by upper tradewinds reaches the Amazon basin and contributes to the supply of nutrients to the Amazon rainforest. Part of this dust comes from the Bodélé depression, which is an ancient lake that covered part of Chad at the time when the Sahara was green, several thousand years ago. It has disappeared, and the current Lake Chad is somehow a remnant.

The bottom of the Bodélé depression, located approximately 17°N and 17°E, is rich in dust from the microorganisms that lived in this ancient lake. This region, between the mountains of Tibesti and Ennedi, experiences violent local winds in winter that lift clouds of dust.

The transport of this particular dust is a source of nutrients needed by plants especially phosphorus, but also potassium, soluble iron... Thus the largest desert feeds the largest rainforest in the world.

This dust from the Sahara can also reach the Amazon rain forest, the Caribbean zone and even the southern part of United States.

In spring and summer, SW currents frequently bring mineral dust from central Sahara to Western Europe. The early spring that we know this year in this part of Europe because of the blocked high pressure is causing a rise in temperatures and the transport of dust from the Sahara as shown by this map from Windy. The southern flow on the west flank of the anticyclonic ridge carries this dust over Spain, the west of France, Great Britain and Ireland, up to Norway.

https://www.nasa.gov/content/goddard/nasa-satellite-reveals-how-much-saharan-dust-feeds-amazon-s-plants

https://www.windy.com/annotation/5ca33262ade88d001cd025d5

Cover image: Sea near Marseille when Mistral blows

Next Sunday, May 5, all models predict a storm at sea, or at least a strong gale weather, with average winds of 9 Bf (40kt, 75 km/h) and gusts of more than 75kt (130km/h). This type of storm is quite common in this region and it is linked to the typical conditions that cause these violent winds.

The French coast of the Mediterranean Sea is surrounded by mountains that change the speed and direction of the winds when high pressure is established on the near Atlantic. The northwesterly flow at ground level is deflected by 3 mountains, the Alps, the Massif Central and the Pyrenees.
The Mistral blows in the narrow valley of the Rhone to the coast, in Provence and in Languedoc. It is a strong and gusty wind, usually cold, which is feared in the summer for the risk of forest fires.

Northwestern Tramontane causes sudden storms in the Gulf of Lion. Both are accelerated by the upper flow crossing the mountains with a foehn effect providing gusting conditions and a typical blue sky.

In addition to the pressure gradient, a dynamic low in the Gulf of Genoa results from the divergent upper flow after the passage over the Alps. This depression in the Ligurian Sea can move and it is its position that actually controls the direction of the winds at sea, between Corsica, Sardinia and the Balearic Islands.
  At sea, sailors generally fear deep depressions, but in this region, the high pressures that settle in the west or the north of France resulting in mistral or tramontane storms, mariners rather watch the anticyclones!

Large commercial vessels use poorly refined heavy fuel containing sulfur compounds. These boats release large amounts of sulfur dioxide SO2 which is a source of acidification for the environments (oceans, forests ...). Due to local regulations on the US coasts, the Baltic Sea, the North Sea and the English Channel, these vessels must switch locally to a more refined fuel with a limited content of sulfur compounds, similar to the diesel fuel. Elsewhere they can use this heavy fuel, even in the Mediterranean where there is a lot of traffic.

In addition to SO2, these ships produce a lot of nitrogen oxides, such as NO2, to the point that coastal areas may become highly polluted areas. One can imagine pollution in cities with car traffic or near certain industrial sites. But at sea, people think that the air is clean, which is not the case everywhere.

The Windy maps that present these pollutants, SO2 and recently NO2, speak for themselves: they make it possible to highlight and monitor this pollution along the trade routes of the Atlantic, the Mediterranean and the Indian Ocean ... The comparison of these traces of pollutants at sea with the main shipping routes shows an obvious correlation.

However, these big boats remain the least expensive and even the least polluting means per ton of freight transported. If it were necessary to transport the same quantities of goods by truck, plane or even diesel train, the pollution would be worse!

@ivo
Great idea to mix the layer of rain and lightning

@ivo
I’ve just changed the colors of this layer, considering White for 0°C.
Then I have kept the default colors for positive temperatures, except for the highest. I have replaced the Black by White, because I keep the image of a piece of steel that you heat. It takes successively these colors: Red-brown, red, light red and finally white, with no risk for me to confuse with the 0°C color.
For the negative colors I have changed the default colors too. There are OK near the ground but in high altitude e.g. at 500hPa, I would like more color changes. Just need to work on it.

@WXcycles
Excellent! You should write articles here. Windy team would be pleased !!

@robbrooks33
Fronts are NOT drawn by numerical weather forecast models, but by skill weather forecast meteorologists.
As Windy shows maps directly and automatically issued from weather forecast models, there is no way to show fronts.

In addition, what brings the plot of fronts? The position of the air masses? The changes of direction, and the eventual strengthening, of the wind? The type of weather, cloud systems, precipitation? All of this you find it in detail on Windy. The fronts were imagined in the 1930s, at the time when this synthetic and graphic presentation allowed a simplified representation of current and forecasted weather. Today's weather models provide much more detailed forecasts, even if they are not able to offer drawings of fronts.

Personnaly, I use to look at Temperature layer at 850hPa which gives a rough idea of the location of the different fronts...

Until now it was only possible to display Geopotential isolines from ECMWF model. That was not possible with GFS. Today these isolines work perfectly with these 2 models ! Many thanks for the repair !!
Even more it works with ICON too. But instead of levels expressed in metres, they seem to be in decimetres, ....or if they are in metres that corresponds to stratospheric altitude :)
At 500hPa, Geopotential heights are around 5500m.
With ICON layer, figures are around 55000 ??

By the way Geopotential heights (isohypses) are often in decametres (dam) and 5500m=550dam.

And now a nice future feature would be to add a Geopotential height layer, not only as isolines.

@gkikas-lgpz
There are different thickness of flash symbol as it can be seen on this zoomed view on a thunderstorm area in North Dakota this morning at 9h00 UTC. They correspond roughly to the lightning density.

In winter is it possible to have snow precipitation and thunderstorm at the same place? Then it could give some display trouble?

@phil-lay58
The seastate that you can observe in a given place, is a mix of different type of waves:

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

• The main swell is produced by a strong wind in a remote place. The swell travels great distances to where you observe it.

• Secondary swells are produced also by winds in other remote places.

All of them have different heights, come from different directions and show different periods (i.e. 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

You find this detail on Windy by pressing the amber arrow on the picker.

@tz
Hi, here you find some information and data sources about wildfires over the world.

https://firms.modaps.eosdis.nasa.gov/map/#z:6;c:-3.2,14.4;d:2018-10-10..2018-10-11

https://firms.modaps.eosdis.nasa.gov/web-services/

The colour palette used for the wind layer can be optimized for navigation at sea.
Most sailors know and use the Beaufort scale. Each degree of this scale corresponds to a range of wind and to a sea state. Therefore it is useful to calibrate the wind speed range according to the Beaufort scale. In this way, at a glance, it is possible to know which are the areas concerned by a certain wind force.
These settings are based on the following considerations:

• Light winds are displayed by light colors while strong winds are shown by denser, darker colours for an intuitive approach. However beyond 64 kt i.e. 12 Bf or Hurricane force, rather than being darker, the colours become very clear « like LED lights ».
• Each wind range is represented by a uniform colour without shading or smoothing, with only a small mixing transition.
• From 64 kt, colours are chosen according to degrees used by NHC (Cat.1, Cat.2...)
• Choice of colours has been mainly based on GREEN when conditions are the best for sailing (4Bf - 5 Bf), ORANGE when conditions become tougher (6Bf) and RED when a coastal cruising sailboat must find a shelter (7Bf - 8Bf).

HOW TO APPLY THESE COLOUR SETTINGS ?

Go to Settings
Choose Modify colours
Select overlay: Wind
At bottom of page find the line For developers
Click on [show gradient] to open a window pop up
Delete the text code in this window
Copy the code here below and paste it in the window
Then press [Import Gradient]
Press Save
Note that you must be login to apply these settings in your Windy cloud.

[[1.5,[134,163,171]],
[2.5,[126,152,188,256]],
[4.12,[110,143,208,256]],
[4.63,[110,143,208,256]],
[6.17,[15,147,167,256]],
[7.72,[15,147,167,256]],
[9.26,[57,163,57,256]],
[10.29,[57,163,57,256]],
[11.83,[194,134,62,256]],
[13.37,[194,134,63,256]],
[14.92,[200,66,13,256]],
[16.46,[200,66,13,256]],
[18,[210,0,50,256]],
[20.06,[215,0,50,256]],
[21.6,[175,80,136]],
[23.66,[175,80,136]],
[25.21,[117,74,147]],
[27.78,[117,74,147]],
[29.32,[68,105,141,256]],
[31.89,[68,105,141]],
[33.44,[194,251,119,256]],
[42.18,[194,251,119,256]],
[43.72,[241,255,109,256]],
[48.87,[241,255,109,256]],
[50.41,[256,256,256,256]],
[57.61,[256,256,256,256]],
[59.16,[0,256,256,256]],
[68.93,[0,256,256,256]],
[69.44,[256,37,256,256]]]

Try to use these new colours during at least one week. If you like them, keep them. If you don’t like, you can come back to the default Windy settings by pressing Load defaults

If you keep them, you can use the wind speed units that you like ...kt...km/h...mph...m/s

WIND SPEEDS EASY TO IDENTIFY BY COLOURS :

EXAMPLE OF WIND FIELD WITH NEW COLOUR SETTINGS :

@marianpoara
Hi,
Of course there are huge differences in mountainous regions between models.
Some are global models covering the whole globe, like GFS and ECMWF model, so they have a coarse horizontal and vertical resolution. For instance the temperature calculated by GFS is supposed to be the same on an area of 22x22km (and then interpolated between each grid points). It gives a very coarse « image » of temperature in Switzerland.
Limited area models like ICON, NEMS and AROME offer a better resolution, so the temperature at a location is much more in relation with altitude.

Temperature over Switzerland - modified colours

The resolution of the model has a high influence on temperature forecasts in mountains, same for the limit between rain and snow, and also for precipitation. They all depend on the orography.
However, global models are useful for medium term forecasts at a synoptic scale.

@svenson
Weather radars show rain/snow in the near past. The wind overlay is forecasted wind ... in the futur. So difficult to mix them.
At least you can select Reported wind and Radar, you will have both rain and wind, but not sure at the same time.

By dragging slowly the time slider near the limit of 2 consecutive days, the displayed days and hours are:

.... Day 1 - 23:00 ... Day 1 - 0:00.... Day 2 - 0:00 ... Day 2 - 1:00

Day 1- 0:00 should not appear.

@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.

@wxcycles

Before « selling » your own color settings, it should be better first to show what they look like, with few screenshots ! Don’t you think so?

@flarkey
What should be the benefit of land and sea in different color? Most of layers like Wind, Temperature, Pressure ... cover completely the map, so you could not see what is below.
Then Rain being in blue, above the sea it would be quite difficult to distinguish where it’s raining or not.

@svsecondchance
That’s absolutely normal. The arrows are in the same direction of the « particule animation ». In the conventional way to show the wind direction i.e. with the arrows type called « wind barbs », these arrows are also in the same direction of the wind flow and not from where it come.