After the sizzling summer of 2015, you may be wondering if this summer will be just as hot.
The highlight of my summer outlook is the strong confidence of seeing less than 20 days at 90 degrees or hotter, meaning we'll see much cooler weather than one year ago.
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 five of the six 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.
- TEMPERATURE: Above normal, with 16 90-degree days expected. (The number would be roughly half of the record summer of 2015.)
- RAINFALL: Near normal. (June could be near 2 inches, but July and August will likely see an inch or less.)
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 La Nina 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-degree 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.
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 percent. My projection of last winter seeing a good snowpack on Mt. Hood and a good water year for Portland was correct.