By Rod Hill on 2016-10-04
Before I announce my projection for the winter of 2016-2017, here is a quick word as to where we are coming from. Last winter was as expected, a strong El Nino pattern that produced a healthy snowpack on Mt. Hood, much above normal rainfall for the Willamette Valley in terms of the water year dating back to October 1st and ending Sept. 30th and above normal temperatures overall. Below are a few headlines for the water year:
1. Mt. Hood Test Site Snow Ending April 30th: 90" depth, 41.7" of water storage for 67% of normal.
2. Portland (PDX) Total Water Year Precipitation Oct. 1st - Sept. 30th: 47.02" / 10.99" above normal
3. Portland Season Snowfall: 1.3"
4. Highest Wind Gust (PDX) SW G 55 mph, December 21, 2015
5. Portland Temperature average: 2.5 degrees above normal mean temperatures.
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The strong El Nino of last winter weakened during the spring and Enso Neutral Conditions are in place. NOAA projects a 55-60% of Neutral conditions holding through the winter of 2016-2017. My forecast projection work is based on data sets showing Neutral condtions, dating back to 1950. I further examined Neutral seasons following a strong El Nino winter. My outlook is based on averages of the above mentioned data sets.
Here is my Winter Forecast for the Portland Metro Valley & Vancouver:
1. Temperatures likely to be near normal or above by no more than 2.0 degrees.
2. Rainfall: While a dry season is possible, odds favor rain totals near 37.90" / 1.87" above normal. November and December are likely to combine for a wet start to the rainy season.
3. Valley Snowfall: At least 1 or 2 mini-snow events dumping 3-6" of total snowfall are likely.
Also, I see an elevated chance to see an 8-12" snow event. The historical average for this winter's pattern is 6" of total season snowfall. However, odds are equal of seeing a big snow event as to seeing less than 3.00" for the year. The December snow of 2008 that dumped 19" and the winter of 2003-2004 that produced 12.6" are in the data set.
4. Windstorms: Odds are heightened for valley windstorms with south wind gusts reaching 50 mph or higher. The majority of Willamette Valley windstorms happen in Neutral and El Nino years. Most recently, Neutral years brought the windstorms of December 2014, when PDX had a 67 mph wind gust, the highest since 1981 and the storm of December 2006, which had a blow of 80 mph in Salem and 70 in downtown Portland, but 53 at PDX.
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Perhaps most important to many is the Mt. Hood Snow Outlook. My snow records for Mt Hood only go back to 2000. Of these years, I found 8 seasons in the data set matching this up-coming winter scenario and 6 of the years had solid snowpacks! The projected snowpack for this up-coming winter is 72% of average, which would be slightly higher than last winter. I do want to point out that the 2 bad seasons I looked at include the record low snowpack season of 2014-2015. In otherwords, there is reason to be cautious with the snow projection, but the best bet calls for a solid year with Timberline seeing more than 500" of total snowfall and Meadows more than 400 inches - both would be considered near normal. Also, odds favor a good start to the season with a decent snowpack build during the month of December.
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My Seasonal Foreast track record dates back to 2001 and has a 67% accuracy rate, including my 2016 summer prediction of 16 total 90 degrees at PDX. The airport hit 90 degrees, 14 times this past summer.
Industry standards for seasonal prediction is considered to be less than 50% for precipitation and 55% for temperature outlooks.
-Rod Hill
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