10/22/2014

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Was this the best summer in recent Seattle memory?

Was this the best summer in recent Seattle memory?
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Those who enjoy sunny days that are warm, but not too hot, with occasional days of thunderstorms sprinkled in were sure all smiles this summer, especially on the heels of the last few years which didn't exactly get glowing reviews.

But now that it's October and summer is really, truly over, I wanted to know: Just how did this summer stack up against others? Let's check the data, using some traditional methods, and some not-so-traditional methods.

Yes, it was warmer than usual

Probably the most notable aspect of the heart of the summer were the number of days around Seattle it was in the 80s, but only two days that reached 90 (none in July or August -- it was June 30 and Sept. 11). Seattle had 40 days at 80 or above this year, tied for fourth-most ever (record was 47) and way above our average of 25.

Of those 40 days, 15 reached 85 degrees or warmer - although many of those days it was Sea-Tac alone who was up in the upper 80s; much of the rest of the Puget Sound region was about 2-4 degrees cooler. And those along the coast and North Sound had it even cooler with many of those days in the 70s. So it was a very warm summer but not exceedingly hot.

Officially, Seattle was +3.4 degrees above normal for June, +2.3 for July, +3.3 for August and +2.2 for September. It was so warm that for much of July, we were even out-summering Los Angeles for a while.

And even when the West Coast baked in late June with a historical heat wave that tied the all-time record high of 117 in Las Vegas and set a national June heat record for with 129 degrees in Death Valley on the 29th, Seattle was somewhat protected as the ridge sat a bit further inland and "only" got to 93 -- even though the air mass was likely hot enough to go over 100 had the ridge been closer and we had an east wind.

Yes, there was more sunshine than usual

Going hand-and-hand with the warmer temperatures was the abundance of sunshine. While hot days in the 90s were rare, cool, overcast days in the 60s were few and far between as well. There were only 3 days in the 60s in July and August.

Counting up the 122 days from June 1 through Sept. 30, Seattle saw sunshine on 99 of them. That means only 23 overcast days -- ahead of the past few years that saw 27 overcast days in 2012, 29 in 2011 and 31 in 2010.

That sunshine tally includes a remarkable July that saw 30 of 31 days with sunshine and 13 days totally sunny.

Don't forget our big dry streak

In addition to the sunshine and warmth, the summer was relatively dry, especially in July. Those 30 days of sunshine translated to no measurable rain during the month -- part of a 35-day dry streak that leaked over a bit into June and August. It was a bit wetter in August, which ended up about half an inch above normal, but it was a bit more East Coast like in that the rain came in clumps on thunderstorm days than spread out through drips and drabs.

We did have to pay the piper in September, which ended up the wettest on record thanks to a few more thunderstorm days early in the month and a very abrupt and early start to the autumn stormy season in the second half.

Summer weather was duffers' 'fore'te

So you might expect with some of those gaudy sunshine and warm temperature numbers that it would be tough to keep people cooped up inside. How to quantify this? How about asking those who depend on nice summer weather: golfers.

Paul Wilkinson, the Director of Golf Services for the City of Seattle, was kind enough to research the number of rounds of golf that have been played on Seattle courses over the past five summers:



This summer (at least through August), Seattle city golf courses have seen more activity since the very hot summer of 2009. Note that this past July crossed 40,000 rounds -- remember it was home of the 30 of 31 days of sunshine and no rain. Wilkinson says it was the first time a month had over 40,000 rounds since July of 2008 -- although he says economy can also affect golf numbers.

(And then, you can easily tell that our record-rainy September wasn't very conducive to hitting the links!)

Over 5,000 minutes of summer

Another way to check how nice the summer was? How about counting the minutes it was over 80 degrees? The daily tally I keep @SummerMinutes showed a final score this summer of 5,443 minutes at or above 80 at the University of Washington. Again, that was the warmest since 2009's big heat wave.

Here is how 2013 compared to past to past summers, back to 2000:

Seattle Summer Minutes at or above 80° as measured from UW Atmospheric Sciences Bldg.
  May June July August September Total
2000 0 1613 662 584 229 3088
2001 365 0 138 1117 0 1620
2002 41 1709 1569 1623 0 4942
2003 0 2320 3663 516 1423 7922
2004 0 2229 3703 2375 0 8307
2005 1156 0 1843 2424 0 5423
2006 293 2601 5436 2975 1927 13232
2007 973 659 2528 1508 745 6413
2008 780 1712 1861 3688 452 8493
2009 40 1657 6429 2295 1102 11523
2010 0 0 2802 3468 47 6317
2011 0 0 351 1352 1703 3323
2012 0 0 58 3592 738 4388
2013 449 1270 1932 1299 493 5443
Average: 293 1126 2355 2058 633 6360

Why was it so nice?

The summer will also be known for it's frequent thunderstorms, high humidity and warm nights -- especially in August. Actually, all three go hand in hand in a way.

The weather pattern throughout the summer was quite unusual for us. Typical summers have the weather vary as the marine breezes strengthen and weaken in response to thermal troughs and shifting ridges of high pressure or passing troughs to our north. This year, we had a big ridge of high pressure that was parked off to our northwest for much of the year but was positioned in such a way that we had very weak marine flow for several days. That would keep the coast a little cooler (70s) but allow Seattle to warm into the mid 80s, yet not allow the hot, east wind to form that would boost us into the 90s.

The lack of hot, east wind days also prevented stronger marine pushes from energizing, keeping our cloudy, 60s days at minimum too.

But the absence of marine wind nor east wind allowed our humidity levels to creep up. In addition, what wayward storms we had were courtesy of upper level lows that approached from our southwest -- in the exact perfect spot to wrap around flow to where it's coming from our south/southeast.

Southerly flow taps into warmer air from the south -- sometimes tropical air from warmer sections of the Pacific Ocean; sometimes monsoonal air from the Desert Southwest. That's been bringing the mugginess here, but also gives more moisture to fuel thunderstorms.

The muggy nights kept our nighttime lows warmer to where August obliterated its record for number of nights at 60 degrees or warmer at 16, beating the old record of 11. For the month, August's average low was 59.9 degrees narrowly missing the first 60 degree average monthly low on record and breaking the all time record of 58.4.

For the year, Seattle has had 34 nights at 60 or warmer, nearly doubling the all-time record of 18. Wow.

As for the number of thunderstorm days, Seattle has had only 8 officially (7 is the average) but I say we've had way more days of hours-long thunderstorms (about 5) than usual -- again due to that setup of lack of marine air, extra mugginess, and storms approaching from the south/southeast.

But I'll bet the thunderstorms and muggy days were a small price to pay for sun fans who have been waiting for a summer like this for a long time.

How would you rate it?

In the middle of the summer, I posted a poll asking you to grade the summer and a whopping 87% of you gave it at least a 'B' (60% said 'A'!). What would you grade it now that it's done? Still an 'A'? Does September's storms downgrade it at all? Cast your vote in the poll on the weather blog page and let us know!

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