Jan_Olieslagers wrote:
Am I right in interpreting the Gramet?
Yes.
As Peter says, it’s very early yet. Looking at the surface pressure charts it’s a trough, not a front. And it’s moving away from your route.
Could well end up that the weather isn’t all that bad, or that it improves during the day, and a later departure works better.
Anyway, too early to make any no-go decision. That should be kept for the morning of departure if possible, and the evening before if not possible to leave to the morning of departure. Anything further in advance is just an educated guess.
Hi Jan, in my opinion the GRAMET is of little use for VFR flying.
Sometimes it shows clear skies while in reality there is a layer of low clouds which prevents a VFR departure.
I have also seen situations where the GRAMET predicted low clouds while in reality the cloudbase was fine for VFR.
It’s a great planning tool for IFR because it shows a rough picture of what to expect. Since one can fly in cloud, the accuracy of the model is less important.
I find the forecasted wind and icing level quite accurate. The cloud tops can be a couple of thousand feet off.
Remember, it’s just a model so you need to always check the actuals.
I would check the METAR/TAF’s on Thursday morning and take your GO/NOGO decision based on that.
And the cloud layer could be at 2500ft or 5k. It just isn’t that accurate.
Jan, did you have a peek at this page ?
https://router.euroga.org/wiki/gramet/
I found it was very useful in helping to interpret the GRAMETs
As others said already it will certainly change and it is a model, so not really 100% accurate
in my opinion the GRAMET is of little use for VFR flying
Very much agree.
VFR flight is IMHO best done by a quick and dirty look at the MSLP chart – I think I have posted this “expert analysis” before
and then the tafs and metars on the morning of the flight.
Never cancel until the morning of the flight.
If at all possible, fly as early in the day as possible.
I have found GRAMET (both the one from Achim’s site and the original one from the Univ of Granada) to be of almost no use for forecasting stratified cloud, and convective cloud is usually pretty obvious from the MSLP chart. For high altitude (Eurocontrol IFR) I use the IR images for cloud tops – much written on this here previously.
For forecasting cloud bases the GRAMET is almost totally useless. Just use TAFs for a string of airports along the route. These are done by people who are paid for it. You will never beat them (except by pure luck).
I concur with Peter, especially about flying early in the morning – this year it has been true like rarely before.
On the other hand, even a nasty frontal weather may sometimes be less dangerous than it seems – you may have to fly through heavy rain but you will still have the surface in sight.
Except of course Jan is flying a minimalist ultra light and I can understand him being risk adverse when it comes to flying through weather
Thanks for thinking along – I am postponing the go/no go decision, but it seems less and less likely I will be flying.
Some of the responses will be well remembered for the future.
The Ogimet one might be more optimistic ;)
The Autorouter one marks cloud with a 25% coverage, Ogimet needs 50% (according to the Autorouter GRAMET interpretation docs).
How unreasonable would speculation that when the Autorouter GRAMET shows clouds but the Ogimet one does not, there is a reasonable chance the clouds will be avoidable. Especially when all TAFs along the route are CAVOK.
