It’s that time of year! Memorial Day Weekend is just days away; the traditional “start of summer”. We’ve had a very warm spring (until the last few days) and endured 2 of the 3 hottest summers we’ve seen in Portland. 2015 was the warmest, followed by 2014 & 2009:
Remember last summer we had 27 days at/above 90 degrees, more than double the average number…it was a scorcher.
Will it happen for a 3rd consecutive summer? I think that’s unlikely…
SUMMER OUTLOOK HIGHLIGHTS
- Summer is June-August in weather circles…the 3 warmest months fo the year for most of the northern hemisphere
- It’s unlikely we have a scorching hot summer again, I don’t expect a repeat of last summer
- Of course we will have hot days (90+), but probably closer to the typical number, maybe 12-18 hot days.
- There is no evidence/modeling that implies we have a COOL summer on the way
- Most models & organizational forecasts are pointing to a warmer than normal summer
For the record…summers have been getting warmer since I was a kid (1970s). This chart includes all stations in NCDC’s climate zone #2 here in Oregon (Willamette Valley):
I’ve spent some time looking over LOTS of data related to ENSO (El Nino Southern Oscillation), PDO (Pacific Decadal Oscillation), and analogs (similar weather setups in the past). This is where we are right now:
May has been warm in the Pacific Northwest; what was looking like a record warm May has now been tempered by cooler weather that continues through the upcoming weekend:
Spring has been the warmest on record here in Portland. A few degrees warm in March, record warmest ever in April, and still running 4 degrees above normal in May.
Sea surface temperatures remain very warm along the Pacific Coast and hundreds of miles offshore. It shows no signs of cooling; a good chunk of this is due to El Nino effects lingering. This is not THE BLOB that we talked about during 2013-2015, but the effect is similar along the coast…warmer than normal water offshore means warmer than normal temps as the summertime northwest wind moves over the milder water. During the cold summers around 2010-2012 the waters were normal or cooler than normal.
El Nino is fading and models say we are headed towards at least a weak La Nina (or neutral on the cool side) Winter 2016-2017
The negative side represents La Nina.
The PDO is very much related to El Nino, but not always locked in together (warm PDO is not always right with an El Nino event). The theory is that PDO runs in twenty or so year cycles of cool & warm. The theory is also that we entered a cool period after 1998.
Talking to Cliff Mass about this last week at the AMS meeting, he suggested there is a line of thought (surprise!) that there is much more to the PDO than just a “15-30 year cycle”. Basically we have a relatively short period of record and it’s possible there is no such thing as a specific cycle. Look at what has happened right in the middle of the “cool phase”. We are now past the two-year mark of a very warm PDO. In fact the PDO number for April was the highest on record for that month!
We may have entered into a warm phase of the PDO, or it may be just a blip, a two-year warm period during a 30 year cool PDO. It has happened before…in the late 1950s:
although it didn’t go on for two years.
So we have an El Nino transitioning to La Nina, Warmer than normal SST offshore, and a positive PDO.
I looked back at the last 13 El Nino years, then a closer look at the 7-8 that transitioned to La Nina the following winter. A real mixed bag…4 of those 8 had normal or above normal number of 80 degree days (56) in Portland. But 4 did not…roll the dice. Not real helpful when using just that index. I even added in warm/cold PDO. Nothing significant sticks out. Could be that I’m using the 80 degree threshold.
Then the summers when we were going from El Nino into La Nina (like this year maybe)…an average summer in the Pacific Northwest but a hot one across the USA in general:
But if we take only warm PDO years with El Nino in effect or fading…
If we take out 2015, the hottest ever, and 1983, the “summer of green tomatoes”:
What I see here is that NOTHING INDICATES WE HAVE A COOL SUMMER ON THE WAY.
Here are 3 forecasts, none expect a cool summer…NOAA’s official outlook:
The Weather Company (formerly known as WSI):
I can’t show these images, but some model forecasts:
CANSIPS: Normal to above normal through August, SSTs remain above normal through December offshore
CFS: Well above normal June, above normal July-September, above normal SST through at least fall.
JAMSTEC: Above normal temps, above normal SST continues through winter offshore
One last thought…since all models appear to be headed to at least a weak La Nina this coming winter/spring, you can get used to this cool/wet spring weather. I have a feeling next February-April will be far different from what we have seen the past few years. Lower snow levels and cool/wet late winter and spring are likely…
Chief Meteorologist Mark Nelsen