It worth thinking about autoexposure like this...

I magine that the camera takes all the pixels, adds them together and works out an "average" value. This value should be a mid grey. If there is a lot of bright sky (or snow) in the picture, then there are a lot of bright pixels. When the camera works out an "average" these bright pixels make the average a "light grey" and the camera compensates by reducing the exposure.
Unfortunately, in doing so, it makes the sky correctly exposed and anything else underexposed.

What you need to do is either switch off the autoexposure when the camcorder is pointing slightly downwards so that it remains on that setting (that way it doesn't overcompensate when the sky comes in to frame) or press the "backlight" button when a large expanse of sky comes into the picture.

With a consumer camcorder, getting the exposure right in situations like yours, isn't at all easy.