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TEMSI weather charts guide

The french produce the (apparently) highly informative TEMSI charts but I’ve been unable to find a good reference on how to actually read those charts. Anyone has a link that might be useful ?

I fear the information out there is only available in French. On Aeroweb, there is the highly informative aviation weather guide and a good summary of the TEMSI depiction can be found here.

These appear similar to the old SigWx – example:

It’s a useful presentation.

One thing to watch out for is what rules are applied when producing the chart as to what information is left out when specific information is not left out.

For example the SigWx used to show fronts, but some years ago ICAO mandated their removal, which immediately made them a lot less useful. Then, a bit later, most (all?) information on the vertical extents of any weather was removed if CBs (even FEW) are forecast (in any of the scalloped areas) which made them even less useful.

One can understand that in the context of jet traffic and particularly AOC operating manuals and instructions therein specifying what weather determines what fuel reserves and alternate planning, but it makes them almost useless for GA flying in the lower airspace (FL200 and below) without onboard weather radar.

Accordingly, vertical extent of IMC was never shown directly – despite the “suggestion” of it being depicted by e.g. vertical extents of icing and turbulence. One example is area #10 above. That is again OK for jet traffic with bleed air anti-ice systems, where the leading edges are hot enough to vapourise the droplets, so flight in some level of icing (below severe) can be done for as long as is ever necessary in the normal context of AOC ops (i.e. you might be in a hold until approaching reserves and then you must divert and land, declaring a mayday if necessary) but this is of little use to light GA where – in IFR – convective wx avoidance is done by climbing to VMC on top and avoiding it visually. In VFR it is done by flying below the cloudbase

I stopped using the SigWx years ago because they are basically useless. I keep looking at them, and sometimes drop them into my trip writeups for amusement, but they continue to be useless – IMHO.

Another thing to check is what data they are produced from. I know for a fact that some commercial wx services use GFS data in some of their products because their national wx body charges too much money for the data GFS is good (practically all of the many free wx websites use GFS) but it has limitations, specifically in its [in]ability to forecast vertical extents of non-convective cloud.

Administrator
Shoreham EGKA, United Kingdom

Thanks for the info.

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