When painting in cold weather, always follow the manufacturer's recommendations. Most traditional latex-based paints won't cure at temperatures below 60 degrees Fahrenheit (15.6 degrees Celsius). If you paint in colder weather, the paint may change colors, "blush or "bloom" (appear milky, blotchy or cloudy), lose its glossiness in some areas, run or drip.
Keep in mind that even if the weather is warmer than 60 degrees Fahrenheit (15.6 degrees Celsius) when you're painting, the temperature will drop and dew will form once the sun goes down. If the paint isn't dry when the temperature drops, the paint will stop curing and when dew forms, moisture will get into the paint. This can shorten the life expectancy of the paint and cause adhesion problems, surface leaching or mildew growth.
While the temperature should ideally be within the manufacturer's suggested temperature range for 48 hours after painting, most alkyd- and latex- based paints require a minimum of four hours to dry before allowing moisture to settle on the surface; consequently, be sure to stop painting early enough in the day to allow sufficient drying time before dark. Other helpful tips include keeping your paint in a warm room so it won't be cold when you start painting and warming the painting surface before you begin.
If you absolutely must paint in cold weather, there are some paints on the market that can be used in temperatures as low as 35 degrees Fahrenheit (1.7 degrees Celsius). You can also use a heat gun to systematically dry the paint. Paint a small area, then dry it with the heat gun and move on to the next area. This is tedious, and you have to be careful to dry it long enough and to use the appropriate temperature. Put your heat gun on a low setting of 86 to 266 degrees Fahrenheit (30 to 130 degrees Celsius) when drying paint. Heat guns are used on high settings for removing paint, so don't set the temperature too high! However, when at all possible, it's preferable to wait until the temperature is appropriate for painting to ensure the best quality paint job.