Yes, global warming, which means average annual temperatures are rising each year, is causing all kinds of freak weather around the world. Global warming destabilizes normal weather patterns, bringing us extremes. This includes droughts, floods, record heat, record cold, and very intense storms. It is responsible for unusual snowfall, such as what happened in Portland.
1990-- the last really cold December recorded in Portland. Coldest day had high of 20 and low of 12. 1983-- but Christmas-time 1983 will long be remembered as much worse than 1990. For many days the east winds whistled at consistent 40-50 mph, while episodes of rain, snow and fog messed up all transportation. Temperatures for the 12-14 days of the cold wave were not quite as cold as what would occur in 1989, but with the extreme winds were brutal, eg. Dec. 23 with a high of only 19, a low of 12, and winds gusting to 48 mph! This cold wave featured a terrible ice storm that began on Christmas Day and lasted for the next several days.
Every major storm now is frequently followed up with someone citing global warming. Humans really think they know more than they do. We may have a better grasp for weather patterns, but to be able to definitively tie one major snow storm to global warming is far beyond human mental capacity.
The average daily high in Portland, Oregon is 47 degrees during the month of January; the average low is about 36 degrees; which is too warm for significant snowfall. The eight-12 inches recently recorded in Portland overnight were the exception - the ninth-snowiest day in the city since 1940 - rather than the rule.