@Paul
500mbar (= 500hPa) thickness is available as isolines (Geopotential height isolines) but unfortunately not as a chart.
Here shown with Wind layer and Temperature layer
[image: 1589445783986-6a99e33b-03f0-4e9f-a270-385580aba7b8.jpeg]
Press More layers... in the right Menu and select Geopot. height. Then adjust the altitude slider at 500hPa
[image: 1589446373538-capture-d-e-cran-2020-05-14-a-10.48.00.png]