Surface Wind & Weather System Issues

Weather Menu

There are a couple of problems concerning the way Asobo has approached the calculation of surface winds. I’m not talking about live weather here, the manual weather system is working very odd with regard to winds. Although you can see the wind layer is labelled WIND - ground in the examples below, the wind entered is NOT actually the ground wind. Turns out MSFS uses the wind you punch in as the geostrophic wind (wind above the friction layer) and modifies it to produce a ground wind. This means that anything you enter here is cut in half. In the examples below a wind of 295 degrees with 60 kts, gusting 80 kts is entered.

Ground Level:

Wind 295 degrees with 30 kts, gusting 40 kts.

At 100 ft AAL:

Wind 295 degrees with 38 kts, gusting 50 kts

At 200 ft AAL:

Wind 295 degrees with 45 kts, gusting 59 kts

At 500 ft AAL:

Wind 295 degrees with 50 kts, gusting 67 kts

At 1000 ft AAL:

Wind 295 degrees with 60 kts, gusting 80 kts.

At 2000 ft AAL:

Wind 295 degrees, with 60 kts, gusting 80 kts.

The wind according to ATC and ATIS:

292 degrees 101 (?!) kts. No idea where that is coming from.

I quickly punched something in excel and it looks like this, above 1000 ft there is no change in wind direction and speed unless you add multiple wind layers.

image

Geostrophic versus Ground Wind

It seems that Asobo borrowed a page out of some meteorology book, rough rule is indeed that the ground wind is half the geostrophic wind over land. Weirdly they for some reason decided to implement the change of wind speed accross the friction layer but not to implement the veering / backing of the wind, which is a little bit a half baked approach if you ask me.

Problems with the current Wind Model

There are a multitude of problems caused by this implementation. First of all, what you are really interested in using a simulator is direct and accurate control over the ground wind, I’m not that interested in what the wind at 1000 ft is doing as a result of the ground wind I’ve entered. If I want to practice a crosswind landing, and I punch in 20 kts crosswind, gusting 30 kts, then I want the wind to be exactly that at the surface and not 10 gusting 15 kts. The weather menu even states WINDS - ground, which is clearly not the case, even though the wind layer is put at ground level the selected wind is really the geostrophic wind and not the ground wind.

The rules they have implemented are rough rules of thumb and would probably work fine for light to moderate winds, I have checked this the past week in real life by keeping an eye on the FMS wind readout on approach and during landing, and this rule of thumb works kind of. I found the wind at 1000 ft indeed around twice the reported ground wind in most cases (and veered in direction). For stronger winds and inversions this does NOT work though. If the wind is 25 kts, gusting 35 kts at ground level, there is no way the wind is 70 kts (?!) at 1000 ft AGL (maybe is some limited cases but normally not) This rules starts to fall apart as wind speed increases.

When simulating gusts this implementation causes big problems, if you want to simulate a gust of 10 kts above the steady wind at ground level, you’ll need to enter a gust of 20 kts above the steady wind in the weather menu. For example, for a surface wind of 20 kts, gusting 30 kts, you’ll need to select a wind of 40 kts, gusting 60 kts in the weather menu. Modelling the wind this way is fundamentally wrong, most gusts and turbulences are precisely caused by obstructions within the friction layer. In real life its often less turbulent and gusty above the friction layer, subsequently it become more and more turbulent and gusty during approach to landing. In orde to simulate a strong, gusty crosswind in MSFS you’ll end up with the opposite situation, namely extreme winds and gusts at altitude, becoming less gusty and turbulent during approach.

Another bug in the weather menu, if you change the steady wind by typing a number in the window instead of using the slider, the gust moves to maximum (150 kts).

Correct Implementation

Asobo should have approached it the other way around, the wind you punch in is the actual ground wind, from that the geostrophic wind should be calculated (x2 and 30 degrees veered in Northern Hemisphere, 30 degrees backed in Southern Hemisphere), the selected gusts should be slowly faded out as altitude increases. Wind in aviation is normally measured at 10 m above the surface, so the actual wind during flare might be slightly lower than the reported surfaces wind, although I have kept an eye on the FMS wind readout recently and I have not found any significant difference between the wind at 10 m (30 ft) and the wind during flare in the real world, so I guess you could safely use the reported surface wind as actual ground wind.

Live Weather

I haven’t checked if the live weather behavior is correct with regards to surface winds, anybody?

Crosswind Landings

Work in progress, check back later.

Please Asobo, you don’t want to open up the weather system to 3rd party devs, at least make it right then! Which means direct and precise control over the surface wind, visibility / RVR and cloud base / ceiling. Again also interesting design choices here, who thought it would be a great idea to implement it this way? Have real world professionals (including pilots?) been involved with these design choices? I find it hard to believe.

Nice write up and as a meteorological observer and aviation meteorologist in my early working life, I came to exactly the same conclusion. Obviously surface drag (and turbulence) is a product of terrain etc. but even if they just applied the rules of thumb you state, things would be a big improvement.

Once they get all the bugs sorted out, I do hope they eventually capitulate and open up access to the weather systems.

They did use this rule of thumb, just the wrong way around :sweat_smile: :joy:

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Thank You for the type up.

Thank you! I filed a bug report with the link to this thread.

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The additional issue here, as I have found today, is that if you set the default ground layer wind and gusts, then add another layer above that with different values (at 3000ft or whatever), the speed and direction of the ground wind including gusts instantly changes to half the speed of the second layer. So it doesn’t seem possible to do it.

So you either get a ground wind with gusts, that is half the value of what it is at 1000ft when it reaches the full values you’ve entered and that remains a constant from then on up (gusts at 12000 ft :thinking:), or you set a second layer (for example with an increased wind speed but no gusts) and that instantly overwrites the ground layer parameters. :man_shrugging:

Then there’s the issue of the update frequency of the wind gusts. Currently it’s rapidly changing across the gust range at approx and random 0.2 second intervals, so it’s like 23…18…29…23…17…19…16…20…16…26…23…27…19…25…18. That’s 3 seconds worth.

It’s almost like is should ebb and flow high to low speed more naturally and in a more linear fashion instead of this back and forth between extremes at rapid intervals i.e. 22…23…24…25…26…25…24…23…22…21…20…21…26…26…27…28…28

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You can change this gusts per second slider I guess, does that make it respond more realistic? I’ve never touched the slider so far.

I reduced the gusts per minute slider back from 5 to 2 and it’s less frantic, but still showing those big swings in speed rapidly. This image from the following clip is what makes sense to me, rather than what the sim is currently doing and showing:

Mount Washington observers see strongest wind gust in decades - YouTube

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For custom, non-live weather, they should allow highly experienced users like Nijntje91 to set whatever they want, whenever they want, wherever they want, instead of adding extra stuff to it that some might or might not find useful, such as the one this case. In other words, it should be 100 percent custom, be it visibility, wind, gusts, clouds, temperature, pressure, dewpoint and everything else at various altitudes. For beginners, the sim already offers pre-made presets, therefore accessibility for newbies won’t be affected even with the existence of such highly advanced and customisable weather options. Voted.

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Thanks for highlighting the specific issues. This has come up a number of times since launch, and probably in the alpha even if I remember correctly. Maybe a rough approximation of a friction layer was just a feature on the TODO list, and the devs, not being sim pilots or weather geeks, didn’t realize that when you set the lowest wind layer, you expect winds of about that value at the field (not for the sim to manipulate the wind speed again after they’re set). Or this is the default handling of the terrain induced wind fields, and it just conflicts with the preset weather. Either way, it needs to get fixed as the modeling is not correct. This overly simplified rule of half winds until 1000 feet applies everywhere, whether you’re in the hills and trees, or out in the middle of the ocean where the effects of friction would be vastly different.

And as pointed out above, the problem is much more apparent with higher wind speeds. There’s nothing like trying to practice pattern work with a strong crosswind, and then unavoidably also being dealt really strong wind shear as your wind speed doubles at pattern altitude. I tried to negate this effect by setting additional wind layers, but since the wind speed change with height is not linear, doing this by hand is not feasible or it’s just impossible.

It also apparently affects the METAR injectors. I’ve heard users reporting that the winds they’re seeing readout in the sim are half of what the METAR showed, while other folks just shrug. Since the METAR injectors use the same basic controls of the weather menu and the preset weather system, they’re going to be subject to the same limitations.

This was also affecting Live Weather a few months ago until there was a loud enough outcry that the surface winds were consistently too low. They correctly disabled this effect for Live Weather, as the Meteoblue numerical forecast model should already be taking into consideration things like friction induced wind speed and direction changes, boundary layer turbulence and mixing, orographic influences, etc. If the sim tries to start modeling its own weather, the two will conflict.

The fix here I think is to have the sim backward compute how the other weather variables need to change in order to fit what users are setting in the weather menu. Not start with the weather menu settings, and change it from there.

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I don’t know whether this is related, but I’m practising flying a Cub around the Inner Hebrides (Oban and the Isle of Mull) and I’m finding a strange issue setting custom weather to get the conditions I want.

The first problem is that to get any kind of breaking waves on the sea I have to set at least 15 knots of wind, which seems a little high, the waters around the Hebrides are generally pretty choppy in any wind at all. But that’s fine I don’t mind flying in a bit of wind.

The next issue though is that with 15 knots of wind set, if I have gusts set to even 1 knot the gusts are almost strong enough to knock me out of the sky. So I fly with gusts set to 0.57 knots, which still gives some nice buffetting, but having to set the gusts so low gives the impression that something in the modelling is not at all correct.

The other issue I have is that after setting the wind in the map, and verifying the wind on the airfield icon on the map, I click Fly and when the game loads the winds are set back to default, and I have to enter them in the game again, what’s going on there?

ok soo im getting 3 different wind reporting which one is right ?

I don’t know where the wind in the ATIS is coming from, it never makes any sense when using manual weather for some reason.

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interesting, if you set gusts to 0 the Garmin displays the correct information for wind speed

I’ll make an uneducated guess and say that the stronger the wind, the smaller the friction layer, and the lower the wind fall off. Even so, Asobo should work it out in reverse: start from the ground wind and work out the wind higher up.

All these things seems like rushed decisions. Like someone implemented this rule, and then someone else decided to call it “ground wind”.

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I wonder why this bug has not been logged yet? We can’t describe it better than you did @Nijntje91

The windspeed should be less stable on groundlevel not 50% if we not standing right behind a building or something as a cover.

Looks like they fixed this in SU7 when i read the fix list. Still downloading.

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I’m going to have a peek in dev. mode shortly to see.

@N6722C I guess they did fix it after all! :slight_smile:

Wind set to 6kts due North:

The data looks like I do have 6kts at ground level now, where before I believe it would have shown 3. According to the following image, and what I thought, the first white segment should be raised a little more but its very close:

Screenshot 2021-11-20 174636

15kts is a little off too, looking a little more like 9-10 kts:

Last time I checked (prior to SU7), if the wind was set to say 15 knots, it was being reported as about 25 ( which is 15 knots in ft/sec)

Note : The important wind speed is what the Windsock is showing, and what the ground based weather Instrumentation is reading and being reported at the airport, not what is happening at 1000ft AGL !!

Notice in your screen shot, the WIND is for the marker at Ground level !!!

OK, just checked out SU7

Big Surprise, One step forward, two steps back.

Wind is now correct, in Knots, and the wind set in the Weather Panel is now the GROUND wind at the airport (not the wind @ 1000ft)
Plane sees the wind as correct airspeed if headwind

SO FAR SO GOOD … but now ATC/ATIS cannot read the wind !!! Totally wrong, which probably means it gets the runway incorrect as well.

atis

Note wind is set to 1 deg @ 40 knots
Airspeed shows 40 knots (approx)
Windsock is correct ? (may still be a true/mag error, difficult to tell at KDCA, should try again in South NZ where magvar is BIG !! )

Simvars (not shown) are Correct

But ATIS, which should be saying 40 at 360 is saying 012 at 135

actually, should it not be direction at speed ?? !!!
ie 360 at 40 - same order as Metar

You really cannot make this Stuff UP !!!

I don’t know “WEATHER” to laugh or cry

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