I could see cold affecting a GPS if it sucking the batteries dry. Fresh batteries give me better readinags than almost dead ones.

Winter caching I carry hand warmers in my coat pocket to keep the gps warm.

How Does Weather Affect GPS?
The GPS system is designed to be unaffected by the weather, with the 1575.42MHz frequency chosen as it is not affected by rain, snow or clouds. In bad weather, there may be slight signal degradation, but this should not prevent a GPS receiver from receiving satellite data. Although GPS signals can penetrate rain, a coating of water on the receiver can block the signal, so you should keep the GPS receiver itself dry to ensure optimum performance. Unlike Earth-based weather systems that do not affect GPS, space weather events such as solar flares or radio bursts can temporarily degrade the performance of the GPS system.

Other Considerations
As GPS requires an unobstructed line of sight to four satellites, any obstructions such as tall buildings or forest canopies can block the signal and prevent the GPS receiver from calculating your location. In these cases, changing your location to an area with no obstructions will allow your GPS receiver to obtain a signal. The power supply to the GPS receiver also plays a part in its operation, especially with mobile GPS receivers using batteries. In cold weather, or if the battery power is getting low, it can be harder to receive a good signal. For this reason, you should carry a spare set of batteries for the GPS receiver.

Read more : http://www.ehow.com/info_12106197_weather-affect-gps.html