Glassy coating on inside of lid

The shiny coating that develops on the inside of the WSM lid has been mentioned many times in the past. This morning, after several days of heavy rains, I took the cover off my WSM to see if any water had accumulated inside (only a little had, no problem) but I was surprised to see that the coating on the inside of the lid had apparently somehow been converted to a very light, brittle, puffy ash material (about the consistency of the outside of a burned marshmallow). After removing this stuff, and a light brushing with a wire brush, I was practically down to the bare porcelain. Here's a poor quality photo of the ash:

It's so brittle that picking up the large piece by one edge would result in its breaking under its own weight. Has anyone else ever seen this?

We recently received alot of rain, 5" over a 2 day period..
My Performer was covered, but the moisture loosened up the same looking stuff from inside the lid.
Thankfully it fell on the grate before the meat went on.

Interesting. I've never seen that on mine. I get a light rusty looking coating in my lid. It's probably the result of some after cook condensation. I clean much of it out by rubbing it with some balled up newspaper. I don't try to clean it all out, but there's a lot less remaining come smoking time. I think some soap and water might do it though.

FWIW, I clean my WSM after every use and store it in the garage intact and covered.