The only thing I came up with that meets all your needs is the
Earthcam 802.11B at webcamstore.com. Unfortunately, the price is
around two grand. The one on eBay and the D-Link give a lot of bang
for the buck. As others have pointed out, you'd have to come up
with your own weatherproofing scheme. However, outdoor camera
housings are readily available.

Living near the ocean, where low overcasts and fog are frequent,
I have long wanted a way to determine what the weather is like at
the airport from a distance (likely quite different than where I
am). Amazingly, I have found one near (but not on) the airport I
am now using - and I do use it for that purpose. You can check it
out at www.sunnyfortuna.com/fortunacam/ Look at the Riverlodge
camera, which alternately looks North, South, East and West.

Let us know what you settle on.