Good morning everyone! It's a cold start this morning over western Washington, with temperatures in the 20s for much of the area with freezing fog causing slick spots on the roads. Our series of cold mornings and chilly, but mostly sunny, afternoons will continue unabated over the next few days as high pressure remains locked in place aloft. But, wow, what a difference a month makes!

Last month, Stormtracker radar worked overtime: we saw a record number of days, for the month of December, with measurable precipitation at SeaTac (at least 0.01"). This month? It's been nearly a full week without a drop of rain at SeaTac and the next shot at rain is still almost another full week away. Why the abrupt change?

Pattern Shift: Last month featured a zonal, or west to east, jet stream. A zonal jet stream pattern helps feed a nearly continuous stream of moisture from the Pacific toward the coast. This onshore flow keeps storms moving toward the coast at least every other day. This month, the jet stream pattern is more what we call meridional: the jet stream is oriented more north-to-south.

To understand the large scale weather pattern, you need to look at the upper level pattern at many spots across the globe. The most important locations for us are the central/western Pacific, northern Canada, and the northwest Atlantic Ocean. In the western Pacific, a persistent trough of low pressure has developed -- this generally supports a corresponding ridge, or high, in the eastern Pacific. In the northwest Atlantic, the jet stream is also pushing a bit farther north than usual, and this generally favors a dip in the jet stream over the east. Meantime, a big ball of cold air -- a polar vortex -- is descending southward from Hudson Bay, sending the jet stream farther south into the eastern United States and bringing a mountain of cold air with it.

Add all these things together, and you end up with persistent high pressure along the west coast with the jet stream/storm track well to our north into British Columbia. This pattern will continue through the weekend; in fact, the high will only get stronger as it moves right over western Washington late this weekend. High pressure will finally weaken in advance of our next storm late Tuesday and Wednesday, but not before...

Second Longest January Dry Streak on Record: The longest stretch of dry days at SeaTac for the month of January was during the second half of January 1963 (15). If rain does not fall until after midnight Wednesday, that will make this streak 12 straight days, marking the second longest January dry streak on record. If rain falls before midnight Wednesday (Tuesday night), this would be the third longest January dry streak on record. Either way, it's been a very unusual pattern!

Have a great day. I'm going to be blogging a few days a week now so, if you have any weather questions you'd like me to tackle or any blog ideas, please feel free to drop me a line at bmonahan@kirotv.com.