It all has to do with the temperature of the central and eastern Pacific Ocean. When the surface is warmer than usual, that is known as El Nino (Little Boy). When it is colder, that is known as La Nina (Little Girl).
This Year... it's La Nina's Turn
Because of the colder than normal temperatures of the Pacific ocean, the Northern Jet Stream is stronger during the winter months. This means more precipitation in north-west North America. More rain on the West Coast, more snow in the Rocky Mountains.
The Good and The Bad
More snow means more powder and that means some of the best skiing can be found during these La Nina events roughly every 7 years.
Don't love the snow? Go to Florida! Wet cold winters in the North West means, warmer, drier winters in the south eastern states. Spread your wings snow birds!
More rain on the coast and more snow towards the mountains always means more hazardous driving conditions on most highways. Usually we see accidents related to weather increase during these winters.
More precipitation means more clouds and less sunlight. During a La Nina people often get less Vitamin D which can lead to forms of depression. Take your multi-vitamins!