Cold temperatures cause finger resistance on  iPad screen
I've had similar issues, and my guess has been that it's due to poor circulation when the temperature drops.

The solutions I've come up with are to buy either:


a stylus
a pair of gloves with conductive tips (like these)
something like the GloveTips 3-Piece Touchscreen Texting Glove Tips (which you can apply to an existing pair of gloves).