In the Graphs section it's difficult to see the precipitation amount when it rains several hours. The numbers overlap. Also there is no Y-axis for precipitation. Have you done any thinking about that?
I know that. The “full” graph are not that good, i did the graph initially as daily as it gives more width per timestep and also fits better on narrow screens. Whole “EWN-forecast” design was made with mobile screens in mind.
Would it be possible to have the days at the X-axis, not only the time? It would make it easier to get an overview of each day.
It would if the days fits. The problem are narrow screens and how to (auto)detect if days fits or not
I don't quite get how the buttons on the bottom of the graps work? When I enter Graphs, Forecastgraph is marked and the graph is shown. Pressing Show whole forecastperiod shows that graph, but now both buttons are marked. Pressing Forecastgraph now nothing happens. Pressing Show whole forecastperiod switches between the 2 graph each second time.
The left button are actually a leftover from the orginal and could be removed from the WXSIM-version as it do nothing.
Legends for Dewpoint and Feels Like are greyed out. Do you plan to show them?
I see you figured them out 
I left them hidden as default to keep the initial look clean.
Do you mean this to be a replacement for the 3-in-1 script? I don't see 3-in-1 on your site anymore.
Yes, i think so. Actually, my own WXSIM have had (and still have) problems with its accuracy with MAE’s well above 3C as worst, and it have came in mind a couple of times to scrape whole WXSIM from my site (and then discontinue my WXSIM-related scripts). So the interest about it haven’t been the best. But but…That haven’t happen yet 