After the sizzling summer of 2015, you may be wondering if this summer will be just as hot! Last year set the all-time record with 29 days reaching 90 degrees or warmer. The climate average is 11 days. In doing my research, I found that 5 of the 6 warmest summers in terms of 90 degree days were summer months leading into an El Nino pattern. This summer we will be leaving El Nino and heading toward either a neutral fall or a developing La Nina.
I further found that overwhelmingly, Portland's coldest and wettest summer months were tied to existing or developing La Nina patterns. It seems the current weakening El Nino leading into a weak, nearly neutral fall Enso pattern leaves the Northwest with no reason to expect extreme heat or cold as we head into summer.
Another topic I looked into is the apparent short-term rise of Portland's summer season temperature average. The number of 90 degree days according the climate average is 11, however, if you run the average since the year 2000, the average number of 90 degrees days is 14 and the average of hot days increases to 16 over the past 10 summer seasons.
The one part of my research that has me perplexed is the summer of 1983, following one of the strongest El Nino winters on record. That summer of '83 went on to only see three, 90 degree days due to wet weather in June, July and August! Throwing out 1983, my projection for 90 degree days is a range between 11 and 22 days and my rainfall projection is near normal.
I hope you found the above to be an interesting read. Below is my 2016 Summer Outlook for Portland:
1. TEMPERATURE: ABOVE NORMAL WITH 16, 90-DEGREE DAYS EXPECTED.
(The number would be roughly 1/2 of the record summer of 2015)
2. RAINFALL: NEAR NORMAL
(June could be near 2.00", but July likely an inch or less and August, likely an inch or less)
The headline of my Summer Outlook is the strong confidence of seeing less than 20, 90-degree days, meaning much cooler weather than one year ago! While my research found signs supporting a cool-wet summer, the evidence of past years highly supports a sunny Northwest summer without the intense heat of one year ago.
The National Weather Service currently projects dry and warm weather through the month of June. I feel Portland has a 50-50% chance of seeing near normal rainfall during May and June. Remember, my projection for a dry April, ending the soaking El Nino rains seems to be correct so far! My seasonal forecast accuracy going back to 2001 is 65%. My projection of last winter seeing a good snowpack on Mt. Hood and a good water year for Portland was correct.
Rod Hill
