What is a "Hot Summer," let's get scientific.

Example: How to measure the common perception that Summer 2009 was "A Long, Hot Summer?"

Period Rated was May 1-October 30, 2009

 Place  5 or more clear* days in a row  total number of cloudless-rated days May-October  most days in a row with maximums of 90 or more  the four hottest temps during period May-Oct  most days in a row with no measurable rainfall*
 Sea-Tac (Tacoma)  one time, and that was five days in a row  3  four  103, 97, 96, 94  one 15 day stretch and one 14 day stretch
 Olympia  unreliable data, but approx. the same as above  unreliable data  eight  104, 101, 97, 95  26 days
 Portland  three times, longest was nine days long  4, with several "1"s  ten  106, 106, 103, 97  28 days, and also a 20 day stretch with one day with a trace.
 Eugene  four times, longest was nine days, plus just missed a fifth 5-day stretch in October.  12, with several "1"s  five  106, 105, 102, 101  29 days, but with 3 days with traces; also 12 days, and 14 days, and also 18 days with one trace day.l
 Medford rating system was rendered meaningless because the vast majority of the days all summer long were CLEAR*

 87

(July had 30 days rated as clear, one rated as partly cloudy; all the "clears" were 0-2, with not even one 3).

 twenty-three  109, 108, 106, 105 (and even the first day of Fall sees 101)  17 days, then one "trace," then 22 more days = 40 days, with a trace on one of the days. Also a period of 28 days, with two days registering trace amounts.

* CLEAR. National Weather Service (NWS) official rating system of "clear" is a ten-point system, where 0-3 clouds get the "clear" designation. Note that during the very long daytimes of mid-summer, this means that several hours of a day can be worse than "clear," and the day still get a rating of "clear." This is one reason why I also am tracking the "cloudless" category (rated "0" on the NWS scale)......

"A Cloudless Summer Day" You get up in the morning to bright sunshine, have your morning coffee outside in the sun on the deck. When you go to lunch at noon it's a pleasant, sunny walk to your favorite eatery. When you drive home, it's a long evening of enjoying barbequeing and casual yardwork as the sun gradually sinks into the west. In the chart above, you will note that this is the type of day that Medford experienced for the great majority of Summer 2009.

Medford-- additional comment re: column one: even May and October had long periods rated as clear, whereas at Sea-Tac a single occasion in July was the only time when 5 or more consecutive clear days were recorded.

NOTE: Summer 2009's late July-early August HEAT WAVE was extremely abnormal, and especially so the farther north you went into the region extending from Medford to Seattle. In fact, Seattle broke its ALL-TIME RECORD H IGHEST temperature with a 105 degrees on July 29th (with a LOW of 71 degrees, which was also a big record-breaker)...... This heat wave moderated quickly around the Puget Sound, but persisted longer in the Portland/Salem/Eugene areas. In Southern Oregon, eg. Medford, the heat persisted MUCH longer, but Medford's all-time record of 115 degrees was not approached.

In reference to the criteria below, Summer 2009, at least around the Puget Sound, was marked by a confusing mix of factors. Two in particular probably contributed to public perception that it was an exceptionally long hot summer--- 1. There were extended periods without rainfall, 2. There was a truly record-setting heat wave in late July. Countering this perception were the realities revealed in the May-October data-- only one or two short heat waves, very few clear periods, virtually no cloudless days, etc.

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I offer my own version of criteria for what the public commonly might refer to as "A Long, Hot Summer."

1. Many clear periods, wherein five or more consecutive days meeting NWS criteria as "clear" days occur; public might call these "sunny" days (five or more in a row)

2. Heat waves, as measured by a number of consecutive days with daily maximums of 90 degrees or more (as in NWS data)

3. Prolonged dry spells, without rain, so that outdoor activities can be carried on without the hassles of covering things up, drying them off to prevent mildew and rust.

4. Days that are actually cloudless all day seem to rank especially high in a public perception of "Summertime." This may be especially true because summertime in the Northwest is when the largest numbers of "city" people are outdoors trying to enjoy camping, family reunions, weddings, and other such activities that expose them to "the weather" much more than at other seasons of the yearly cycle.

5. There are probably other criteria that affect public percetion; eg. extraordinary heat that leaves a memory far larger than its actual data. Also note that Public perception of "Summer" extends well beyond astronomical dates of June 21 to Sept. 21.
There are probably also other factors that can serve to lessen the impact of a single factor; eg. a summer that is very dry, but not very sunny, and not very hot overall, may come across in public perception as a wimpy summer.

Another "Hot Summer" analysis, Summer 2014

Reviewed July 2015