Here in December a similar pattern of freezing minimum record temperatures is repeated. It is interesting to note that there is no corresponding pattern of peaking high temperatures. Here in the PNW, especially in the Portland area with our maritime influence our high temps are often dampened while the lows show a response pattern tied to the colder continental air mass which sometimes drops down out of Canada and attacks us from the east. Normally there is a mixing of our air in winter, preventing the buildup of stagnant layers of cold air which can occur in other Valley areas.