The summer of 2015 is likely to go down as the warmest such on record for much of the Pacific Northwest, especially for the states of Washington and Oregon. It was also anomalously warm in other parts of the country. Here are some of the details.
In a blog I posted on August 1st I summarized the many sites in the Pacific Northwest that were on track for their warmest summer on record as a result of record heat in June and July. Although August was not as anomalously warm as those months, it was warm enough to allow for the warmest climatological summer on record to occur for most sites in Washington and Oregon (as well as western Idaho). It was also the warmest summer on record (actually a tie) in Phoenix, Arizona. Hawaii also saw record summer heat.
Here is a list of some of the significant sites (with long periods of record) that measured their warmest climatological summer (June-August) on record:
Table of sites in the U.S. (top) that broke or tied the record for their warmest climatological summer on record. The map (bottom) illustrates the location of these sites among the 300 sites for which I have data for hottest summers/coldest winters. Hawaii is not included on the map.
In another blog I posted last May: Hottest Summers vs. Coldest Winters I tracked the climate history for 300 sites in the contiguous U.S. in an attempt to determine the annual and decadal occurrences of hottest summers vs. coldest winters. The blog explains the methodology used in the choice of these sites. Of the 300 sites I followed, 16 of them observed their warmest summer on record this past summer (Hawaii and Alaska were excluded). The summer of 2015 ranked as the 4th hottest summer so far as the most number of sites observing a record for such.
In the above mentioned blog I reproduced graphs illustrating the number of occurrences of ‘hottest summers’ versus ‘coldest winters’ by year and decade for 300 sites with long periods of record in the contiguous U.S. Below is how these graphs now appear following this past summer:
Although, the summer of 2015 ranks in 4th place for having the most number of sites experiencing their hottest summer (among the 300 sites I follow) this, of course, does not indicate that it was the 4th warmest summer on record for the contiguous U.S. In fact probably far from such. Much of the central portion of the country was normal or even cooler than normal. The final ranking for this past summer will appear in data scheduled for release by NOAA on September 9th. You can find this by accessing this NOAA web site. I will be out of the country by then, and hence this ‘before all the facts are in’ blog post, apologies for this!
Despite the warmth of the summer in the Pacific Northwest no all-time absolute maximum temperatures were set at any of the 300 sites I follow, although several sites did experience their hottest single month (any month) on record. These included:
Yuma, AZ 97.8° in August (old record 97.5° in July 2009
Seattle, WA 71.2° in July (old record 71.1° in August 1967)
Salem, OR 73.1 in July (old record 72.5° in August and July 2014)
Roseburg, OR 76.1° in July (old record 74.8° in August 2014)
Not included in my 300-site selection are Hilo and Kahului, Hawaii that also endured their warmest month on record as well in August and also their warmest summers ever observed. For a summary of all the remarkable heat records set in Hawaii during the summer of 2015 see my previous blog entry about such.
Another facet of the record warm summer in the Pacific Northwest was the number and duration of several notable heat waves. Seattle measured more 90°+ days (12 of them) then any other year on record (previous was 9 in 1958). Portland, Oregon also set its record for such with 27 90°+ days (previous record was 24 during the year of 2009).
Arizona and California: Some Notable Heat Records this summer
Outside of the Pacific Northwest some record-breaking heat occurred in California and Arizona as well. Phoenix reached 117° on August 14th, its hottest August day on record (amidst its warmest summer on record) and saw three consecutive days with minimums of 93° (August 14-16), also a record for such.
Speaking of record high minimums, San Francisco (downtown site) saw 15 daily record high minimums during this past August (but just one daily record high). This was the greatest total of any variable of daily temperature records ever measured during any single month in city records (temperature records began in 1875).
August 2015 saw 15 daily record high minimum temperatures, the most daily record temperatures of any kind for any month in the city’s weather history (since 1875). Table from NOW data NWS-Monterey.
The 66.0° average temperature (in August) was just 0.1° shy of the all-time warmest climatological summer month on record for the city: 66.1° set in August 1993 (but note that September is normally the warmest month of the year here). The cause of these warm minimum temperatures in San Francisco is that the Pacific Ocean sea surface temperatures off central California have been the warmest on record for August, averaging between 61°-67°, about 7° above normal. These warm SST’s are not necessarily related to the developing El Nino but rather to a persistent region of extremely anomalous SST temperatures that have been in place in the northeast Pacific for a couple of years now, known as ‘The Blob’ by some meteorologists. By the way, San Francisco (downtown) has seen only 3.21” of precipitation since January 1st (normal 14.60”), its driest calendar year on record (precipitation POR since 1849) as of September 7th. This is less rainfall (since January 1st) than Phoenix or Las Vegas has seen so far this year. Among the major cities in the U.S. only Yuma has been drier. In 2013 San Francisco measured a TOTAL calendar year rainfall of just 5.59”, its driest calendar year on record.
Elsewhere in the U.S.
It was warm in portions of the Northeast U.S. as well. Caribou, Maine experienced its warmest August on record with a 68.2° average temperature (old record 68.0° in August 2012). This is especially ironic given how cold this past winter was at the site. February 2015 was its coldest such on record with a 2.8° average temperature (the summer of 2015 was, overall, close to average). It is also interesting to note how BOTH Caribou and Yuma endured their warmest Augusts on record: diametrically opposite sides of the country, one of them one of the coolest locations in the country and the other one of the warmest on an annualized basis.
JFK Airport in New York City also observed its warmest August on record with a 78.5° average, although records go back to only 1948 at the site. New York City’s official weather site in Central Park has now logged 60 consecutive days with maximum temperatures attaining 80°+ (since July 11th) and still counting as of September 7th. This streak has smashed the previous record for such of 41 days observed in 2011. This record streak looks likely to extend until mid-September given current forecasts.
Christopher C. Burt
Weather Historian
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