So I failed with picking the weather for Saturday.
Initially the wind was actually from the NW (which is not good for winching), and the cloudbase on the deck. After standing around looking at the windsocks for 3hrs at 1pm the cloudbase was at 1700ftasl and the wind still NW so we made the decision to abandon winching for the day
At 2:30pm the wind was still NW (and not good for winching), Dave Marriot arrived in the Sportstar, so we were back in business. Cloud base was still only 3000ftasl but there was a strong convergence line above the airfield (at least I got that bit right).
If you are interested in knowing what I got wrong with the forecast here goes:
1) I underestimated how much water there would be lying on the ground in the morning (it had rained a little overnight). This pushed the blue line to the right and added more moisture(and thus cloud) to the system than I had accounted for.
2) The upper air was unstable, which meant that once a cloud formed the top of the cloud kept growing taller and many of the clouds grew into towering cumuli (and the tall clouds block more sunlight from falling on the ground) (see attached photo). This was predicted in the high confidence RASP issued this morning, but either it was not there, or more likely I missed it, when looking at the low confidence RASP that was issued on Thursday.
3). The combination of more and taller clouds, meant that much less sunlight reached the surface pushed the red dot (surface temperature) to the left and this meant that the day took much longer to get going, and when it finally did get going(around 2pm) was not as
strong as forecast and had a much lower (3000ftasl cloudbase)..
The resulting late afternoon convergence line was still very useable, and it was possible to climb in the convergence above cloudbase up the side of the towering cumuls (see photo).
I'm still picking Sunday to be a boomer day, strong thermals, high (6500ftasl) cloudbase, light NW wind, and a strong convergance energy line setting up overhead Stratford in the afternoon but unfortunately no TGC flying Sunday as I have not been able to secure an instructor or a winch driver.
(Sunday was a bit better but the rest of the week has produced some days with high cloud-bases. Ed.)
Nice work if you can get it. 4000ft and at a bit under 50 knots. I believe they could have winched into it. But it also shows that you should never write the day off too early.
.jpg "Running the Convergence line(copy)")