The moral of the story is Be Careful of What You Post in The Deep End since it's where I can feel free to be me (and that's pretty geeky)

Seriously, there are lots of things that just aren't fully explained, but as anyone who's followed a bunch of what many members working together have figured out, it's worth it. It's like a puzzle with each of us contributing to see the full picture.

For my two cents.... I think alot has to do with the air currents and where the storm forms. A storm that forms in Western NY (just west of me) seems to be "dirtier" than a storm that forms a thousand miles away. It's like the storm cleans the air when it first forms and all that stuff is in the rain that falls in the first hour or so. Also the wind that blows from the west or southwest seems to be the 'dirtiest" when the storm forms closeby and rain starts.

I measured the rain water once for PH and it was a lot lower than my min of 6.8 that I could measure.

Anyhow, in northern NY we have a few lakes that are dead from acid rain.

There is no doubt that lots of organics get swept into my pool when it rains - we have a lot of close in trees and the runoff from those definitely has dust and such. Even 1" of rain in a 20x40 pool is a LOT of water (I calculate ~ 520 gallons (20x40/12 * 7.) - if the organic load is high, that might be like having 10 or 20 uninvited guests partying in the pool for hours - no one would question whether that might be considered a "chlorine needed event". Plus, like others have said, creatures seem to move when it rains, we get tons of worms & millipedes committing hari-kari everytime we get a significant rain.

Way back when, on Poolforum I believe, we discussed this in relation to SWG PH rise, which seems very regional. In my case, I measured the PH of rain water and suggested that it might be a counteracting factor since I had seen no PH rise with my SWG. I still believe this is at least partly true, earlier in the summer when we had no rain, I did have to add acid. Lately, with a lot of rain, no rise - no acid.