Congratulations D.C.-area readers. You have just experienced — or tolerated, survived, and suffered — the hottest month in recorded history. We did it last July too, but this time we soared just over another degree on average to achieve an incredibly toasty 84.5F at Washington Reagan National Airport. That’s 4.7 degrees hotter than the new 1981-2010 normal or 5.3 degrees hotter than the old 1971-2000 climatological baseline. Also, it is slightly hotter than a normal July for Houston, TX and slightly cooler than a normal July for Dallas, TX. It’s like we were living in a whole different part of the country.
As you might expect for a month like this, precipitation ran below normal, but only .7” below the 1981-2010 normal of 3.70” at National Airport. This puts our running deficit over 4” since January 1st. It is dry, but it could be worse.
July 2011 daily low temperatures in D.C. compared to 2010
While we actually saw the same number of 100-degree days this July compared to last, and both were extraordinarily hot, this one took the cake on pretty much every high-temperature metric. Of those three 100-degree days, one was a record for the date 104F on the 29th. That was the hottest we’ve seen in D.C. since August 17, 1997 when it was 105, and it tied for the 5th hottest all-time. Previously, the second of back-to-back 102s on July 23 also set a new record for the date.
Other notable D.C. area 100-degree plus stats for the month include the all-time record high of 105F at Dulles Airport on July 22. Although the records there only go back to 1963, no other day had topped 104 with the last occurrence in 1988. On the same day, BWI hit 106F. That was the highest on record at the current location, and one shy of the all-time Baltimore record of 107.
A fourteen day streak of 90-degrees or higher, which now carries on into August, helped carve out a significant portion of the record 25 90+ during the month. July 2011 now stands alone in this field, besting two other months with 24 days – July 1993 and July 1987. Last year, we saw 21 days in July that were 90 degrees or higher. Stepping up to 95-degree plus days, July 2011 tied for the most on record with 1999 at 14. 1999 was also the previous high mark for an average daily high temperature, with a 92.8F. This year came in at an incredible 93.6F, which is 5.2 degrees above the new 1981-2010 average (88.4F) for the month
Like last summer, major contributors to this July’s phenomenally high temperature average (even if less focused on) were the low temperatures. An astounding eight record high minim.ums were tied or set this year in D.C. Compiling overnight records started early and went into high gear late. On July 12, a record of 77F was set. On the 19th, the low of 79F tied a record. From the 22nd through 24th temperatures barely dipped into and below the mid-80s with records on all three dates including all-time record warm minimum tying 84Fs on the 23rd and 24th. To close the month, an 80F on the 29th tied a record, while an 81F and 80F on the 30th and 31st put July 2011 in the books two more times.
The unheard of seven 80-degree or higher low temperatures not only blew the previous monthly king of three such days (in July 1876 and Julu 2010) out of the water, it also demolished the full-year record set just last year of four. Both the four-day streak and three-day streak now stand as one and two all-time, with two in a row being the most such days prior. Similar numbers continued down to 75-degree or higher lows, with this year tying 2010 for the most at 17 such days. Thanks to some oh-so-brief nicer weather after the Fourth of July, we only managed 26 days 70+ on lows, compared to the high of 29 in 1955. Yet, the big numbers more than made up for it.
The source article July 2011: The hottest month in Washington, D.C. history was published August 1st, 2011 by The Washington Post .