Come on lets go on the record with what we see in our magic 8 ball!
Winter 2017-18 Forecast
The winter of 2016-17 was one of the coolest in recent memory. Most locations along the I-5 corridor experienced at least one significant snowfall. The cold anomalies were focused in December and January, with February closer to normal, and March above average SLE and points south. Precipitation was normal to slightly below the first half of the winter after record setting fall rains. February and March however, were anomalously wet. There were several modified intrusions of arctic air, but no significant regional arctic blasts. Temperatures in W. Oregon were about 3-4 degrees below normal in December and 5-8 degrees below normal in January.
I view December as a true wildcard month for the upcoming winter with equal chances for a wide variety of outcomes. I have very low confidence in my December forecast. Overall though I think the most likely outcome for December 2017 is something along the lines of December 2007, 2010, or 2011. I see the biggest chances for cold anomalies being toward the beginning of the month and then the week after Christmas. I think there is a high likelihood we see some kind of atmospheric river event in December, followed by either ridging or a split flow. The latter would likely lead to an inversion setup in the lowlands. Overall I expect the month to have near normal to slightly above normal precipitation. With temperatures near to slightly above normal. As for snowfall, I would say chances for valley snow are about as they would be in a typical year. The mountains should see slightly below normal snowfall.
Regionally last January was the coldest since at least 1993. Will this year top that? It is possible, but probably not. For analogs January 1968 and 2008 were weighed heavily. I do think we could potentially see more amplification upstream than those years however, leading to a much better potential outcome for cold weather lovers. I see precipitation being normal to above normal. I believe temperatures regionally will be below average in January, though I believe the flow will be much more progressive than last January, leading to a few mild periods interspersed. Therefore, I would expect cold anomalies more in line with Dec 2016, than Jan 2017. There should be quite a bit of cold onshore flow which could bring snow levels to the surface at times. I think there is a better than 50% chance we see a significant arctic outbreak during the month. I expect at least one widespread accumulating snowfall in the inland valleys during the month. Snowfall in the mountains should be above average.
I believe February will be our coldest month regionally in relation to the long term average. I expect near normal precipitation across the NW. I think there is a high likelihood of arctic air, especially early in the month. Later in the month likely some periods of cold onshore flow. Expect the coldest February since at least 2011. I think the inland valleys have a greater than 50% of at least one accumulating snowfall with above average mountain snow.
March should be cool and wet early in the month. Trending drier and milder as we get toward the end of the month as is typical. I expect temperatures to be slightly below normal for the month overall with above normal precipitation. There will likely be some foothills snow, but I do not expect accumulating snow at the lowest elevations. The mountain snowpack should continue to be healthy.
Overall I expect another cooler than average winter. Most valley locations will likely see accumulating snowfall at least once. Precipitation should be normal to above average, with a healthy mountain snowpack. I expect at least one regional arctic outbreak in the Dec-Feb period.