The best temperatures for painting are 50 plus degrees during the day and 35 plus at night. Many paint manufactures have reformulated their paints for good cold weather drying.
These paints are often referred to as "Low-Temp" and they can be applied at temperatures of 35 degrees or above, this includes day and night.
Even with "Low Temp" acrylic paints it is important to keep an eye on the weather and stop applying 2-3 hours before any major moisture, rain or fog. Applying any paint at low temperatures over a moist or wet surface, or if the paint film is subjected to moisture before curing, could cause discoloration and drastically reduce the life of the paint film.