The weather can affect phone signals. However, there seems to be little research available on the subject, most likely because there is little you can do when weather conditions interfere with phone signals. Still, it may save some frustration with your cell carrier if you know the real reason your calls are suddenly being dropped.
The amount of water vapour suspended in the air is the aspect of the weather that can have the most significant effect on your phone signal. The high frequency radio signals used by cell towers travel best through air that is neither too dry or too damp. If the ambient humidity shifts too far in either direction, signal strength can suffer.
Cellphone signals are actually beams of invisible light, which means that they cannot be affected by wind. The extreme amount of precipitation brought by rain or snow storms can interfere with signals and make it more difficult for your phone to transfer voice and data streams.
Not all weather effects are negative. A 2008 study by the University of Leicester in the United Kingdom found that the atmosphere over the ocean can effectively amplify cell signals. Especially in the late afternoon and early evenings of the spring and summer, signals can travel much further than normal over the open ocean.
While it may seem like it would, the temperature has no effect on cell signal strength. Extreme cold can, however, damage your phone's battery and screen. It is best to keep your phone warm by moving it to an interior pocket if you have to take it outside in the winter.