Thursday, December 10, 2015

Pacific Northwest Weather Patterns

Issued 12-10-2015

Some of the early forecast models were suggesting that this fall and early winter the Northwest would have above normal temperatures and below normal precipitation.
Bottom part is forecast for Oct through Dec 2015

These extended forecast from the Climate Predication Center (CPC) are usually heavily weighted on past weather patterns that the Pacific Northwest "normally" gets during a strong El Nino event. When we have a strong El Nino the Northwest "usually" gets above normal temperatures and below normal precipitation. We certainly have  a strong El Nino now with much above normal sea-surface temperatures off the equatorial coast of South America.

Well the good news is we have been getting the much needed precipitation especially given the extremely warm and dry conditions from the summer of 2015. So this falls above normal precipitation is very welcome indeed.

Here is a list rainfall totals in inches through 12-9-2015 with (yearly normal  rainfall). As you can see many locations are already close to normal or above normal: Sea-Tac 39.58 (36.55), Bellingham 28.97 (36.29), Wenatchee 10.29 (9.09), and Spokane 11.86 (16.52). If one looked at the rainfall totals at the end of summer most locations were well below normal.

What are the longer term outlooks?  Well let's start with this weekend and into early next week. A trough of low pressure will swing inland this weekend for some rainfall but certainly not the totals that were recorded earlier this week. Also of note the air mass will be colder with freezing levels close to 5000 feet early in the weekend then 2500 feet later on Sunday and Monday. That's good news as we will get some mountain snow and not heavy rainfall in the mountains that we recorded earlier this week with freezing levels at 8000 to 9000 feet.

Extended outlook for the winter? I issued a forecast earlier this fall and compared other "strong El Nino events: The winter of 1982-83 and 1997-98. In this smaller sample size the data shows that the snowfall  generally ran about 80% of normal for many location. The graph below reflects this: Snowfall for 1982-82 and 1997-98: Snoq Pass was 78% and 84% of normal and Paradise at Mt. Rainier was 105% and 104% of normal.
We will keep you appraised of the patterns.

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