A summer morning on the National Mall. (David Nagy via Flickr )

We might not be setting any big heat records this summer, but it’s been far from a pleasantly cool season. In fact, you might say that it’s been a record-breaking simmer for much of the Mid-Atlantic and Northeast, with no escape from the enduring heat.

Washington, D.C., along with several other cities in the Northeast, are seeing one of their longest, most sustained periods of warm weather on record, measured by number of 80-degree days and very warm nights.

80-degree days

Around Washington, D.C., the broader Mid-Atlantic and the Northeast, summer heat tends to be measured by the number of days at or above 90 degrees. However, in a similar way, the 80-degree day count can be used as a longevity and persistence measure for the warm season. Across the region, this covers the six months from April through September.


80-degree days through September 3 across the D.C./Baltimore area. (Ian Livingston, NOAA data)

As CWG’s Matt Rogers pointed out recently, meteorological summer (Jun-Aug) ended up fifth warmest on record for Washington. During that period, 84 of 92 days were 80 degrees or higher in D.C., or 10th highest on the list for meteorological summer. That came after a May which had 22, the most on record.

So far, 2015 is in second place in terms of 80-degree days, behind 2011. We’ve seen 112 days days at or above 80 degrees this year, compared to 113 through Sept. 3, in 2011. Of course, 2011 was in the midst of our hellish three-year run from 2010-2012 which featured scores of other records, including the hottest summer (2010) and hottest year (2012) on record in D.C.

While D.C. has decent odds to add at least another 10 or so days to this count, it remains to be seen whether the city stays in the running for a record year. It’ll need to top 129 80-degree days to crack the top five, and 136 to tie or best the all-time high in 2007.

At Baltimore-Washington International, 2015 is presently running in the number five spot with 106 days 80-degrees or higher. Dulles has seen 101 such days, which puts it in a tie for 11th most at this point in the year.

70-degree lows

It’s not just the high temperatures that can make summer feel oppressive. The very warm overnight lows can set a steamy mood, and don’t allow for any cooling off while boosting averages in the process.


Days with 70 degree or higher lows through September 3 across the D.C./Baltimore area. (Ian Livingston, NOAA data)

Looking at lows at or above 70 degrees, 2015 has been an impressively warm year in Washington, D.C. There were 76 such days through Sept. 3, which brings the year-to-date just short of 2010, which saw 77 days thus far with temps that didn’t drop below 70 degrees.

It’s getting near the end of 70-degree low season by the start of September, and the city has already locked up the number two spot for a whole year as well. 2010 added a few more from here through the end of the month and finished with 82 such days for the record.

Excessive 70-degree lows are often a strong reflection of the urban heat island in this region. As such, the numbers for BWI and Dulles are considerably lower because neither sits near the heart of an urban center. Both spots are a ways off from knocking on a record for this count.

When it comes to Baltimore and any comparison to D.C. here (especially in light of thermometergate), we do have to keep in mind that their recording station moved from being within the city to its current and comparatively rural location at Baltimore-Washington International. Even 2010 only ranks number 11 there, with almost all the records occurring when the station was in the city.

Other spots

National’s thermometer is the 800-pound gorilla in any temperature discussion most years, and particularly of late, with a propensity to run very warm compared to the surrounding region. But National’s tally of 80-degree days falls very close to the other locations, so it seems likely that this measurement is a good representation of the summer’s heat.


Monthly temperatures compared to normal for the 80-degree season through August. While much of the core of summer was either near or even below normal in a good chunk of the northeast, even cool is warm from June through August. May was a big month everywhere across the region. (PRISM Climate Group/Oregon State, modified by CWG)

Even so, I wanted to look a bit further since there are always so many questions about stations being representative of their broader regions. I pulled up numbers for a few other big cities across the northeast U.S. — places you would expect somewhat similar urban conditions to D.C., if slightly modulated by latitude.

The small sample below is all long-period stations, with records of at least 100 years if not back into the 1800s. All comparisons are year-to-date through Sept. 3 unless otherwise noted.

South of D.C., Richmond, Va., (KRIC) has seen 116 80-degree days, which ties for sixth most. The 47 days with lows at or above 70 ranks number 12 there.

To the north in always sunny Philadelphia, Pa., (KPHL), there have been 105 days 80 degrees or higher. This ranks number two behind 109 in 2010. 51 days have had lows of 70 or above, which ranks fifth to date.

New York City (KNYC) is arguably facing the brunt of this slow boil. New York has seen 98 days with highs at 80 degrees or higher, putting 2015 in first place, year-to-date. The annual record of 107 in 1944 is also potentially in-reach, and top 10 is assured. It’s now been 56 days in a row with highs 80 or above in N.Y.C., destroying the old record stretch of 41 in 2011. On the 70-degree low end, the city is running at 4th most with 50 days. That already ranks number eight annually, and will continue to climb.

Despite a very cold start to the year in Boston, Ma. (KBOS) the city is running tied for 11th when it comes to 80-degree days at 62 thus far. For 70-degree lows, it’s been pretty run of the mill at 12, likely partly thanks to cold ocean waters much of the season.

It does seem that while the warm season has been something of an ink blotch for extreme heat, much of the urban northeast megalopolis has seen a notably long and consistent run of warm days and night.

The best news may be that we’re quickly running out of time to add many more digits to any of the counts above.