Is It Going to Be A Hot Summer?

May 20, 2014

Most years I don’t get many questions/emails along the lines of “what will the summer will be like?”.  For sure each summer’s approaching weather doesn’t generate the interest I see as we approach each winter.  But this year I’ve had a few people ask, so I took a look.  Even I was a bit surprised by the result.

Let’s jump into the details…it appears that for the first time in 5 years an El Nino is developing in the equatorial Pacific Ocean.  In fact NOAA is pegging that chance at 70-75% by late summer or early fall


I think we all know that IN GENERAL when we have that warming of the tropical waters we tend to see the jet stream develop much farther south in the wintertime.  California tends to have stormy/wet winters and we tend to be a bit milder and definitely drier than normal in those winters.  But what about summer?

I went back and looked up the last 10 episodes in which an El Nino was developing over the summer and compared it with our summer weather that year.  The years are 1977, 1982, 1986, 1991, 1994, 1997, 2002, 2004, 2006, 2009.  Some of those were weak El Ninos, two were strong, and a few were moderate.  Then I ran those years through a nifty tool on the NCDC website.  You can plot temperature/precipitation anomalies for any year or group of years.

First, all 10 years showing the summer season temperature departure, that’s June, July, August:


Just July-August, the real summer season here:


And just June:


They are all basically the same.

Summers with a developing El Nino have a strong tendency to be warmer than average in the Western USA, including our area

How about 90 degree and 80 degree days?  Both are tallied below.  Blue is below average and Red is above  In this case Portland’s 90 degree average is 10-13 (we average more now than we used to) .

1977  14  43
1982  14  50
1986  17  58
1991  16  67
1994  13  75
1997   9  57
2002  12  55
2004  12  64
2006  21  65
2009  24  64

Same thing with some real hot summers in there.  But notice a significant minority did not see extreme heat.  So an El Nino summer does not guarantee an unusually high number of hot days.

Most interesting to me is that none of the last 10 El Nino summers have been cooler than average; none were “chilly”.

The September maps were a bit different…notice just about average, the real warm signature disappears after Labor Day:


And the rain anomaly shows a bit wetter than average once we get into September:


There are other things we can look at, not just El Nino stats from the past.  For example, here is the Climate Forecast Model (CFS) temperature anomaly forecast for June-August.  It has been very consistent for more than a month showing above average temps this summer in the western USA:


Again, this is no indication of a scorching hot summer.  That will depend on whether we get several episodes of strong upper level ridging sitting directly overhead which kills the mild onshore flow.

Sea surface temperatures are running well above average in the northeast Pacific off our coastline too, note the warm anomalies on the bottom of the graphics below


the warm pool has been there since at least early winter, probably leading to several episodes of ridging to our west.  This isn’t likely to change through the summer.

To sum it up…

I’d say the odds are tilted away from a cooler than average summer west of the Cascades.  More likely we’ll see a normal to above average summer; good news if you have trouble growing tomatoes or cantaloupes.  Bad news if you don’t have air conditioning; hopefully when it does get hot it’ll be a dry heat.

Chief Meteorologist Mark Nelsen