I sought out this topic because I’m new to using custom weather and thought I’d done something wrong.
Evidently the problems discussed here are still problems.
I planned a flight to KDCA – which is near sea level – and wanted to try the published visual approach to runway 19 (River Visual).
The wind in LIVE WEATHER favored north operations so I set up a custom scenario with southerly winds and cloud bases (I thought) at about 3,500 ft AGL.
When I descended to the recommended altitude for the first fix of 3000 ft. I was still in cloud.
No visual landmarks / IRL request an IAP. But this is the sim so I decided to guesstimate my position and continue…
At 1,800, the recommended altitude for the next fix… still in cloud.
Finally at 900 ft. and 3 nm from the airport I could see the ground but I was way out of position for the approach. 
Next flight I’ll try this again with different settings, but can someone who uses custom weather and knows the correct values to put in for cloud heights advise the correct numbers for a ceiling of 3,500 ft. at a sea level airport?