Weather Blog

So, is there any hope for a sunny summer?

So, is there any hope for a sunny summer?

There are about 10 e-mails sitting in my inbox asking if this spring gloom means we're on our way to a hopeless summer for any kind of extended sunshine or warmth. As much of a rain fan I am (and I have to admit, I've enjoyed the cool period) I think there is still some hope for sun fans.

Now, giving you any kind of exact forecast for this summer is difficult -- a fair number of you already wonder why we try and forecast the weekend, much less what it'll be during SeaFair -- but here is at least some anecdotal evidence that I've collected.

Let's Try Official Forecasts

First up, the official forecast from the climatologists at NOAA. These are the 30- and 90-day forecasts they issue each month, and they go out for over a year. But these forecasts only give odds for whether a given period will be warmer/colder and wetter/drier than normal. For a long time, the Pacific Northwest has been painted with greater than an equal chance of warmer and drier than normal conditions. And as you can see out your window, sometimes these forecasts don't exactly pan out.

What has changed recently is now for the summer outlook, the Northwest has been pulled back out of the "higher than equal chance" for a warmer than normal summer, and now we're in the generic "equal chances" which is climate-speak for: "We have no overall climatological signal to determine whether we think it'll be a warm or cold summer, and it's 50/50 either way." Although the Northwest is still painted with a roughly 65-70% chance of a drier than normal summer. (For those who are statistics majors or really like complex math, NOAA has an explanation of how those blobs translate into actual probabilities.)

El Nino Offering Any Help?

OK, so the official long term forecasts aren't too much help. What about El Nino?

We are just coming out of an El Nino winter and newest forecasts from the National Climate Prediction Center say we are now at neutral conditions and rapidly running toward the opposite La Nina conditions, and a growing number of long range computer models think we could be there by August, while others maintain we'll be neutral through spring 2011. (More on what that means for fall/winter later, since we're concerned about summer right now.)

That said, El Nino/La Nina primarily affects Northwest weather in the fall and winter, and typically does not have much effect on summer. But for kicks, people have been asking me to compare past summers that have had similar spring El Nino circumstances to where we are right now.

I used this chart that tracks Oceanic Nino Index (ONI). The numbers in temperature departure from normal, in Celsius. Red numbers are El Nino (anything +0.5 or greater) and blue are La Nina (-0.5 or less). Black numbers are neutral periods.

The spring of 1958 is almost dead on exact in matching our current ONI of the past few months. So how did it rate? Well, May of 1958 was the second warmest on record, and June was quite a bit warmer than normal too. So much for that. Another year that was close in our ONI was 1992. That's the year that happened to have the warmest May on record. Those years were also quite dry in May. On the other hand, 1965, which was reasonably close on the ONI Index, had a very cold and wet May -- similar to where we were.

So El Nino isn't helping get any kind of signal, but if you want to try and pin something on 1965, they had a hot July and average August and reasonably average rain.

Let's Try Something To Make Sun Fans Smile

We've been talking ad nauseam about this year being the latest ever to see a 75 degree day. But other years that have had similar late starts to warmer weather have made up for it in a hurry.

The record year we just broke was June 9, 1991. But 1991 had a July, August and September that were all quite warmer than normal, marked by a 99 degree day on July 23rd which at the time was tied for the hottest day on record (since broken with 100 in 1994 and 103 in 2009) is now tied for third-hottest day on record.

Second place was 1955, and that streak broke with a mid 80s day, followed by a 95 degree day (100 at downtown Federal Building). However, the rest of that summer was relatively cool.

Also high on the list was 1981, but ironically, August 1981 was the king of the hottest stretch of weather in Seattle history until last summer knocked it off its perch. 1981 also featured a 99 degree day and was bookmarked by a brutal stretch of several days over 90 degrees.

And don't forget that even last May was quite cool and wet for the first two weeks, and you know how that summer ended up.

So there is some evidence that a late warm up doesn't mean no warm up.

Even "Worst Summer Ever" Had *Some* Sun

I've been working in weather for nearly 20 years here, and probably the "gray" standard for recent summers is 1993, when June was cool and cloudy, and then every day in July was cooler than normal, helped by a stubborn jet stream that flooded the region with marine air each day. There was even a day it only got to 59 in mid-July.

But even that summer, August featured a few stretches of really nice days, including a 95 degree day, and 3-4 multiple day sunshine stretches of 80+. It wasn't the warmest August ever, but it did afford plenty of chances to get some sun before fall arrived.

That said, there have been some summers that have truly been MIA. According to stat guru Jason Phelps, in 1921 it hit 80 degrees exactly once at the Seattle City Office, on August 12th. In 1980, it took until July 21 for the first 80 degree day (that was the year Mt. St. Helens erupted. Yes, a volcano erupting nearby can have localized cooling effects as sulfates in the eruption cloud make a haze that reflect sunlight back to space). In 1996, it took until July 7th, and in 1954 the one and only 80 degree day was on July 6.

Speaking of volcanoes, can we blame the Icelandic One?

In a word, no. That eruption wasn't as high as others that have affected global climate, and it's at the wrong latitude to really get swirled around the globe. And as the UW's Cliff Mass wrote in his blog, "There is NO reason to suspect our cold weather is due to... the oil spill in the Gulf, or El Nino/La Nina. It does not have any connection with global warming or sunspots."

The conclusion?

I think despite our cool start, there will still be some stretches of sunny and warm weather this summer, so don't go listing the swim trunks and beach towers on Craigslist just yet. But we do have to wait a while, as I think June is destined to also remain cooler than normal.

Our actual day-of forecast models go out to 16 days, and while forecasts beyond a week are dubious, they have been consistent in the pattern of moderate to strong onshore flow for a while -- probably not unlike July 1993 was. So I'd expect plenty of days with morning clouds and then afternoon sunshine with pleasant temperatures in the mid 60s to low 70s. I think a big majority of locals would take that, even if it's not really all that warm.

Going on my own gut feeling for July and August, I think July will probably end around normal for temps but drier than average, and then a few hot stretches in late July and mid August, followed by an warm start to early September, but getting back into our fall weather pretty quickly, especially if we are heading into La Nina. But then again, my gut is probably about on par with using that little rock that says if it's wet, it's raining, and if it's moving, it's windy, etc. :)

Still, to answer my headline question: Yes, I think there is hope for a sunny summer.

What about winter?

And for those already looking past summer, those long range 90-day forecasts do paint a higher than average chance of below normal temperatures and above normal precipitation for the upcoming winter. This is likely due to bets that we'll be in a La Nina pattern, which typically feature cool, wet winters and a better chance of getting occasional snow (well, anything's better than the "trace" of snow Seattle got last winter).

For the record, the winter of 2008-09 was La Nina :)