Rocky Mountains insulating us from storms
Considering that the Northern Plains have already experienced two blizzard events this season, and record-low temperatures in the single digits have already visited parts of the Northeast, we can say that the weather has been pretty quiet around here so far this fall.
There are two basic reasons we haven’t really seen the snow so far this season. When it has been wet, it has been warm; and when it’s been dry, it has also been cold.
We can thank the Rocky Mountains for insulating us from at least a couple of early winter blasts this season. When strong high pressure builds over north central Canada, chilly air begins to stream southward. This shallow arctic air pushes through the Northern Plains and Great Lakes Region, making its way as far south as Oklahoma and eastward through the Ohio Valley. It is often said in states like Nebraska, that nothing but cows stand in the way of the bitter cold flowing down from the north.
Across the Inland Northwest, however, we do have something in the way, in the form of a significant mountain range. Unless the Arctic air is very deep, it is unable to spill southwestward over the mountains, and we are spared from the deep freeze. Of course there are other roads that cold air can travel to infiltrate our region, when for example, high pressure sets up off the coast of British Columbia. Clockwise circulation around the high brings a northerly flow from Canada into Eastern Washington and Northern Idaho, though the terrain makes for less than an open highway like what is seen across the Plains states.
Coming up in December, we will continue to see shorter days and longer nights, with average temperatures continuing to fall. Though the shortest day will be on the winter solstice on Dec. 21, the coldest average temperatures will lag, occurring in January.
Average December snow is nearly 20 inches in Coeur d’Alene and 13.7 inches for Spokane.