You might check your heater core / heater core hoses.

I experienced a similar problem in my 242. It wasn't related to the rain, but more to changes in temperature outside.

There was a pin hole leak in one of the heater core hoses. When it would get cold, it would allow a tiny bit of coolant to seep out, and it would make the entire car fog up. Similar to what you described, the only clear part of the window was directly above the vents.

In my 245, there was a leak in the heater core it self. This was a much bigger leak, and it would make fog shoot out of the vents!

You might try cracking the window a bit when it gets bad. It should help.

My 122 doesn't clear the windows as quickly as my 240s do, but it has no trouble keeping the window clean once it's warmed up (and living in the Pacific Northwest, we get tons of rain).

Water or coolant is getting in somewhere.
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Formerly 'HearToTemptYou'