SIGMET / AIRMET

[Dirk Schepmann]

I'm really wondering why the shapes of the SIGMETs are not simplified per se.

After all, the SIGMETs are based on weather model outputs and they are not very accurate. The GFS model has a resolution of 28 km, for example. In my opinion it would make much more sense to highlight the areas with a simplified (and slightly oversized) rectangular shape.

[Hardy Heinlin]

Around the globe I see very different individual styles of "boundary drawings". Maybe there are different "schools". Some guys often draw just rectangles, some others often draw very fine "Mona Lisas" with many details down to the mile -- partially or entirely along the entire boundary hundreds of miles long. Especially in the Brazil area there are often pretty complex artworks :-) The area between Brazil and West Africa generally displays a great gallery of many large and complex SIGMET areas (mostly thunderstorms).

I don't think that all SIGMETs are based on weather models. Some are inflight reports. And I guess some are ground or radar observations. Some phenomena like dust or ash may be automatically reported by satellite systems.


|-|

[James H]

Hi Hardy,

Can PSX parse tropical cyclone SIGMETs in the format below? I only ask because SkyVector can't. I suspect it has something to do with the "WI 280NM OF TC CENTRE" element.

WCAU01 ABRF 071910
YBBB SIGMET D02 VALID 071915/080115 YBRFYBBB BRISBANE FIR TC SANDRA PSN S1500 E15600 CB
OBS AT 1800Z WI 280NM OF TC CENTRE TOP FL500 MOV NE
07KT INTSF =

James.

[Hardy Heinlin]

Hi James, no problem parsing "... NM OF TC". It's a standard phrase.

(Click on pic to enlarge)




Regards,

|-|ardy

[James H]

Outstanding!

[Dirk Schepmann]

That's fantastic ... can't wait to see it in action. 😊

[cagarini]

Around the globe I see very different individual styles of "boundary drawings". Maybe there are different "schools". Some guys often draw just rectangles, some others often draw very fine "Mona Lisas" with many details down to the mile -- partially or entirely along the entire boundary hundreds of miles long. Especially in the Brazil area there are often pretty complex artworks :-) The area between Brazil and West Africa generally displays a great gallery of many large and complex SIGMET areas (mostly thunderstorms).

I don't think that all SIGMETs are based on weather models. Some are inflight reports. And I guess some are ground or radar observations. Some phenomena like dust or ash may be automatically reported by satellite systems.


|-|

We use at most 8 points, convex polygons. Our models are WAFCs ( 120km ), ECMWF ( 20 Km ) and AROME can also be used with res down to 2,5 Km. Information is complemented, among other sources, by AIREP.

[Hardy Heinlin]

Here's a nice example of different "drawing styles".

The boundary of SBBS 17 looks extraordinarily detailed. Is this polygon human made or machine made? Look at its "nose tip" to the left: There's an additional tiny little leg inserted to make the nose round. Or look at its northern part: There's a small round bulge consisting of five short legs; they're just some miles apart. When someone paints such details, it's true love ...




|-|

[cagarini]

Indeed Hardy - that's "Aviation Weather Art" !

Congratulations for being able to display it so well in the PSX Map !

I guess that just as with tropical cyclones in the example further above in this thread, these shapes are automatically drawn.

And, btw:  Today's EDUU creativity :-)

WSDL34 EDZF 241400
EDUU SIGMET 1 VALID 241400/241800 EDZF-
EDUU RHEIN UIR SEV TURB FCST W OF LINE N4948 E00632 - N5029 E00647
FL200/350 MOV E 05KT NC=



In some cases the rather complex form is also associated with the limits of the FIR / UIR. For instance here in Portugal the Lisbon FIR is delimited over mainland to the East and North by the "complex" geographical frontier with Spain. When a SIGMET starts to the West and South of this lines, the represented resulting SIGMET well have those contours, unless a polygon is designed that intercepts the Spanish FIRs.

The recommendations are well defined, within EUR, by ICAO EUR DOC 014 ( Edition 2, 2010 - rev 29Oct2018 ), with some interesting examples in Appendix G.

The base recommendations is actually that otherwise the polygongs should be defined by no less than 4 points and no more than 7.

[Hardy Heinlin]

PSX has no FIR database.

For "[direction] OF LINE [points]" formats within a FIR, PSX ignores the political FIR borders and sets a polygon whose one side is defined by that published "LINE [points]" and whose other side is defined by "[direction] OF". The distance to the other side is set by a typical average value. This works very well.

When an area is defined by "ENTIRE FIR", PSX uses a rectangle defined by the airport database; e.g. an FIR ID starting with the letters LP will be defined by the westernmost, easternmost, northernmost, and southernmost locations of all airports whose ICAO codes start with LP.

In most cases this agrees very well with the political borders. We're speaking of fuzzy weather areas. Weather doesn't stop at political borders. Even when the borders disagree a little more, the neighbour states will publish a similar SIGMET in their area and so the areas will overlap anyway. Same weather phenomenon, just different governments. And if the neighbours don't publish a SIGMET even though they should, it won't hurt if the simulator's fuzzy weather area goes a little bit into their area as well. It's realistic and plausible. Weather effects ending exactly at political borders are not realistic.


|-|

[torrence]

"Your SIGMET is encroaching on our sovereign airspace - we demand immediate WXEXIT!"

Sorry - couldn't resist 

[Hardy Heinlin]

Interestingly, a Florida SIGMET is encroaching on European/African airspace.

USA SIGMETs define boundary points by navaids. And this Florida SIGMET includes "MIA".

There are multiple MIA navaids on the planet. The USA SIGMET algorithm in PSX takes the nearest relative to the center of the USA.

The MIA navaid at Miami is not a VORTAC, not a VORDME, not a VOR, not an NDB.

It's a VOT.

VOTs are test VORs at airports. They are not included in the navigational database. So PSX picks the MIA NDB at the Spanish city Melilla at the coastline of Morocco.

Why do they use this TEST VOR of all nice VORs within the Miami terminal area? In flight, one cannot even use these MIA bearing/distance values published in that SIGMET.


Sigh,

|-|ardy

[cagarini]

Hardy,

your approach to the SIGMET areas is perfectly adequate and actually agrees with some of the recommendations / examples in the above mentioned ICAO EUR doc 014 :-)

Those americans are really weird .... ( sorry :-) )

[Jeroen Hoppenbrouwers]

Another theory: it is not even a VOT. It's the airport. Of course it should have been KMIA but hey, who cares? It's always "K". I really never had even heard of the existance of MIA VOT. Dolphin, Virginia Key, that's it.

You may want to add a hack: if you don't find a plausible navaid within x miles in the USA, prefix K and scan the airports database. Or, simply always includes the airports.

Hoppie

[Jeroen Hoppenbrouwers]

Weather doesn't stop at political borders.

Climate does, though.


Hoppie

[Hardy Heinlin]

KMIA, I had thought so too. But then I returned to the original idea that the purpose of all this traditional navaid/bearing/distance format is to provide GPS-less radio pilots with useful navaid references. You get no radial and DME signal from KMIA when you are in IFR weather. In VFR you may refer to visual references and the compass to find KMIA ...

If this happens one more time at another airport, I'll add an airport checker.

(I wanted this format to be as universal as possible, so that it can be used outside the USA as well.)


|-|

[Jeroen Hoppenbrouwers]

Do pilots navigate SIGMET areas that precisely? I would guess that they avoid SIGMET areas before taking off by flight planning, and after takeoff, by eyeballing. Not by skirting an imaginary line in the sky between essentially arbitrary points on the globe. Over land you have ATC radar backup, too. And lastly, IFR still means you know pretty well where you are, GPS or not. I vote for the theory that SIGMETs reference "easy points on aeronautical maps" and airports are as easy as navaids.


Hoppie

[Hardy Heinlin]

Well, sometimes Australian SIGMETs use airport ICAO codes to define points. This won't work either because they also use very small airports that are not in the 747 database.

I find the navaid method more useful, even if you plan your route in advance. You can set one of your VOR instruments to a radial that indicates a SIGMET line. SIGMETs can also update during your flight and can be checked on the COM radio.


|-|ardy

[Britjet]

If the sigmet was significant I used to put the coordinates in RTE 2 - then you had a pictorial presentation on the ND while flying.
Peter.

[Hardy Heinlin]

KMIA ...

If this happens one more time at another airport, I'll add an airport checker.

OK, today we have something with "TLH" which is not a navaid. But if I search for KTLH I get the point.

I'll add an airport checker :-)


|-|