Pattern Change Leads to a Much Cooler End to October

The month of October has, so far, been a relatively average month. It was off to a very rainy start, but things have dried out since the first week and a half. Temperatures are expected to warm briefly heading into Wednesday but then tumble again Thursday and Friday. We'll likely see another warm up Saturday, and possibly Sunday, before the pattern really changes the last couple of days of October and for the beginning of November.

A strong ridge of high pressure will develop over Alaska late this week and weekend. It is forecast to dislodge quite a bit of cold front from the north, sending it down across the lower 48 next week. The problem, however, is trying to figure out when exactly that cold air is expected to arrive. This type of pattern change - strong ridging over Alaska - is a result of the Eastern Pacific Oscillation, which is a variation in the flow pattern across the Eastern Pacific, as well as Alaska. 

It has both a negative and positive phase, where the positive phase keeps the more mild, Pacific air flowing into the middle of the country and the cold air locked to the north. The negative phase, the phase we look to be heading towards next week, develops a strong ridge of high pressure over Alaska, pushing the colder air to the south.

Whether or not this pattern change will bring our first chance of seeing any snow is yet to be seen, but as we get closer to November we tend to have a higher chance for seeing at least some snow as the temperatures drop. 

Our average first trace of snow usually occurs around November 2nd, with the first tenth of an inch of snow occurring around November 20th and the first inch of snow typically within the first week of December. Of course we know it can happen at any time - and not even in the winter season. Just be prepared for the colder air, and likely colder Halloween, and we'll keep on the lookout for the chance for any snow.