Clouds would surely be a hinderance to satellite snooping, and the weather did seem pretty bad during AVP. However, the thermal imaging would still be able to penetrate (because, they y'know, did during the movie (new tunnel vs. old tunnel stuffs). However, the Queen, which is the primary source of potential weirdness visible wouldn't be, since Aliens don't show up on heat scanners, and the Predator would probably just look like a big dude. There is the matter of the Predator ship, but one could assume that the Preds have been flying circles around human sensor tech just as long as we've had it, so, again, nada.
The only positive note is that surely Weyland Industries would have their satellite in the area and looking; after all, their CEO was heading down there personally, and on a fact-finding mission to boot. They wouldn't miss a chance to see anything that went on, to capture any data. Unfortuatnely, there probably just wouldn't have been much to catch.
Of course, there was a hollowed out alien skull and tail-tip laying around in the snow. Makes me think of the end of the first Terminator.
-Pax
