View Full Version : Forecasting Thermals

Phil Cater
18th July 2016, 14:51
Hi there all,

This is a pertinent forum to ask this question (!):

Does anyone know where one can access a reliable forecast of just how thermic any given day is likely to be, preferably with some kind of scale guidance? Glider pilots in particular no doubt know of a likely interweb link....

Many thanks,


Wally Hayward
18th July 2016, 15:42
Not being facetious, but the good ole "Mark1 eyeball" works on the day....... after a long period of getting it wrong... and also remembering what works for your particular site:-)

But for a "forecast"


Maybe also worth reading this:

After some 70 years of "KNOWING" everything about it....my best ever soaring flight here, was 4 years ago when it "should" have been absolute and utter "cr***P"......
a total distance of some 80 miles in the Shadow (engine on tickover.. no electric start) with thermals of 1300 to 1500 feet per min UP to 5000 feet cloudbase........................... (never went in... honest)
better climb than normally with full power engine on....
then decided I needed a cup of tee and a P............
so enjoyed throwing it all away as fast as possible:-)

Just go out in the Shadow and "ave a go".. (assuming you are intending to soar and not trying to avoid them!!!) she will do you proud. when you get it wrong... the engine will help although mine did not have electric start at that time... now "corrected" as SSDR!!:-)!!

If ONLY the weather would co-operate:-(

19th July 2016, 08:52
I think that you'll find this interesting


The further you delv into the site the more good info you can garner

Phil Cater
20th July 2016, 08:50
Thanks all.....the reason for asking is that I've got a nervous (potential) passenger to take aloft who really wants to go up on a nice clear, sunny day when it's not at all 'bumpy' (quote).....she's convinced that she's going to throw up if it is - which might be a self-fulfilling prophesy!

Short of waiting 'til a sunny winter's day, I was hoping that there'd be a website which rated the coming week day by day on a scale from 'silky smooth' to 'OMG, what a rollercoaster' as it were....



Martin Watson
20th July 2016, 09:27
In the summer if its a "nice clear, sunny day" there will pretty much always be thermals, even if they are not going high enough to generate cumulus clouds. What I would do is pick a nice day but wait til the evening to do the flight - a couple of hours or so before sunset the heating effect of the sun drops and the air will be much smoother - its an ideal time to take first time passengers.

Wally Hayward
24th July 2016, 11:02
I would add... keep up continuous conversation with her.. explain every little thing you are going to do.. including the various "strange noises" she may hear!! and then again just before you do it.... in the same way as if you are a good Instructor!!....... that should help her relax and help stop her nausea.

Although not common in the UK.. a period of stable temperature helps reduce thermals............ cold.. good... hot .. bad:-)

If she feels that worried, possibly a good idea to fly yourself first to determine if you think it suitable on that day

Phil Cater
25th July 2016, 21:25
Yep, all your suggestions are already a given but what I was really after was: if she asked me to pick any day of the next week, say, to earmark for a flight, which website might be able to give me a fairly accurate indication of likely turbulence day by day so's I could choose the best one.....it's certainly a good idea to make it an evening flight regardless though.

I suppose I'm just going to have to deduce it myself based on forecast temperatures/lapse rates/winds/fronts/dewpoints/pressures etc for the week ahead. I was just being lazy and hoping some professional person out there on the interweb had already worked it out for me to access. Your links might prove useful for that Ginge, thanks.

Happy landings,


3rd August 2016, 07:58
No need to deduce it yerself! Click here (http://rasp.inn.leedsmet.ac.uk/RASPtableGM/RASPtableGM.html).
Find your place on the map. Note the coloured scale at the bottom showing the updraft velocity from 150fpm to 600fpm. Then click through the days at the top left to show the forecast. Just be sure to reference to other weather factors as well. A day may not be thermic, but there could be fog to the ground!

Phil Cater
31st August 2016, 23:18
David, that link was right on the money!

Many, many thanks, you're a star!!

Best regards,


Martin Watson
2nd September 2016, 07:58
"for cloudless thermals. Updraft strengths will be stronger than this forecast if convective clouds are present"

So you cant just look at that one page on RASP. You also need to know if there are thermally generated (convective) cumulus clouds on the day in question.

That said, RASP is a fantastic resource - all the answers are there, but it will take a bit of ferreting around actually to answer the question.