Probabilities of an Extended Summer and Moderate Transition to Fall 2017

Fall Colors are coming

Many people are wondering about the potential for an extended summer season that would continue our warm and dry weather into October and possibly longer.  I will start out by saying it is certainly more likely this year than it was in 2016.  You may recall that the day the calendar turned from summer to fall last year (September 21) we were done with summer and began one of the coolest winters in 30 years.  It was also one of the wettest and most prolonged cool periods we have seen in the Pacific Northwest in a long time.

Right now is a time of conflicting climate themes.  On one hand, the winter of 2016 -2017 was one of the coldest and wettest in decades that lasted through May, and, conversely, the summer of 2017 was almost as hot and dry as the drought of 2015.  These extremes occurred in the same Water Year (see definition of Water Year at the end).

Here are some numbers to sum up where we are as we head into Water Year 2018 (Starts October 1st 2017).

One of the Wettest and Coldest Fall, Winter, and Spring temperatures in 30 Years

  • Average of 10 – 15 degrees F below normal temperatures September 2016 through May 2017. The closing months of a record El Nino did not help us dodge a nasty fall and winter as predicted.
  • Currently we have recorded almost 71 inches of rain for the 2017 Water Year (remember a Water Year differs from the calendar year because it is measured from October 1st 2016 to September 30th 2017).
  • That is 20 inches above the average of 51 inches we typically receive, and ranks in the top five wettest years since 1897.
  • Groundwater levels may remain high into the upcoming wet season. They have remained slightly elevated throughout the summer- but not at record levels.

At the Same Time:

One of the driest summers in 30 years

  • The summer of 2017 was a close rival of the drought of 2015 in its duration and temperature.  The difference was all of the rain we received in the spring kept the soils a bit wetter longer into the summer.  For the record we received 2.54” of rain between June 1, 2017 and September 25, 2017 – that’s almost four months with less than 2 ½ inches of rain!
  • July 2017 we received a scant 0.01”of rain (many spots received no rain) and the average high temperature was 82 degrees F. It was consistently above average temp and below average precip.
  • August 2017 was warmer than July with the average high temperature 84 degrees F and 0.15” of rain. Also consistently above average temp and below average precip.
  • September 2017 had an average high temperature of 78 degrees F and > 1” of rain. Again above average temp and below average precip.
  • Air quality alerts for smoke were issued for a total of 16 days because of huge wild fires.  Some of these fires were burning as far away as Northern British Columbia and Southern Oregon.  That is about 500 miles from Olympia yet they caused persistent air quality problems locally- including minor ash fall.  Many fires closer to Olympia in the Columbia River Gorge and near Mt. Rainier also added greatly to air quality problems. The wet spring and dry summer combined to provide lots of dry fuel for these fires to exploit.
  • The snow pack that was about 120-150 percent above average melted very fast and by the end of August many of the local peaks were bare again.

The Olympics are almost completely bare as seen from the Olympia waterfront in late September.

Here’s the Prediction for Fall and Winter

Official

Looking at the National Weather Service Climate Prediction Center prognosis for the fall and winter of 2017 into 2018, they indicate we will have a warmer and about average precipitation fall and winter.  This holds true for the one two and three month prognosis as of September 25th.  Some local publications indicated that a La Niña would give us a cooler and wetter fall and winter but this is contrary to the current climate model consensus.  The watch issued for a La Niña is that a very weak one is possible, forming by late fall 2017.  There are many other factors that have a more profound impact on our local winter weather than either the La Niña, or its warmer than average counterpart, El Niño.  Keep in mind that one of the strongest El Niño patterns in history (2015 -2016) did not prevent the coldest winter in 30 years for our area.  Local sea surface temperatures off the coast of North America and arctic jet stream fluctuations are more likely to moderate our short term seasonal weather.  The processes that goes into these models and the complexity of the calculations is mind boggling so this is why forecasters like to simply use the La Niña or El Niño as a sufficient predictor of upcoming climate. The models will be updated in mid-October so we will get a bit more specific guidance then.

Unofficial (Mine)

My prediction, based on the persistent pattern we have seen over the Eastern Pacific Ocean off the Washington and Oregon coast is that we will not have a particularly cold winter and it will transition into fall more gradually than we saw last year.  It will likely follow the trend we have been experiencing over the past five to seven years during the winter – with the winter of 2016 being an anomaly in the warming trend.

Some cold periods at the end of November and in January are likely – but not like 2016 near record low temperatures (I reached 13 deg F a couple times in January 2017).  The high pressure that has been residing off of the North American West Coast seems relatively stable for now and the sea surface temperatures are above average off the coast as well.  Looking at the National Weather Service models mixed with my observations, I am making the prediction that we will experience average or slightly below average precipitation.  I do not think we will have a wet fall, winter, and spring like we had in 2016-2017.

There are likely to be two or three strong windstorms that get an added kick from the warm water off the west coast.  The presence of this reservoir of warm water allows ordinary storms to intensify very rapidly right off the coast.  They are hard to predict because of their ability to explode within a 6-12 hours of making landfall.

We will see in 2018 if I can pat myself on the back or try to analyze myself out of a bad prediction.

1The Water Year is defined as beginning October 1 and running through September 30 of the following year.  It is intended to capture all of the wet months so as not to split the wet winter months arbitrarily in the middle as is the case of the calendar year.