This article has been updated to cover all 100F+ readings observed through August 1, 2011 when National Airport hit 100F and the other locations remained in the upper 90s.

While the Washington, D.C. to Baltimore, Md. area averages about one 100-degree day each year, it is not a super common occurrence, and stretches of years without them are — or, someday, where? — to be expected. Yearly numbers and a few other facts for both Washington and Baltimore follow, as does a quick look at the atmospheric setup for the area’s most extreme of extreme heat.

Washington, D.C. averages 1.2 days of 100F+ or above as of the 1981-2010 climate period. The long-term average is less than one day per year, with 109 days (including five so far in 2011) at D.C. that have hit or topped 100F. The highest temperature ever at D.C. was 106F, and it was reached on August 6, 1918 and July 20, 1930. A breakdown of all days 100F+ at D.C. is heavily skewed toward the lowest numbers. 44% hit 100 on the nose, 22% made it to 101, 17% to 102, 7% to 103, %6 to 104 and 2% each to 105F and 106F. The most recent “super heat” temperature came on July 29, 2011 when D.C. reached 104F, the highest temperature observed there in over a decade and tied for 5th hottest all time.

July 19-22, 1930 make up the longest string of days 100F+ in Washington at four, also featuring the hottest temperature on record. Washington has dealt with three other 100F+ streaks of three days, most recently in 1993. The most 100-degree days in any year was 11 in 1930, when two major streaks of 100F+ lasted for the record four days and three days (with a two day break in between) each. For 10 years in a row, in 1888 through 1897, no 100 degree or higher readings were recorded at Washington. The longest streak of sub-100F years in recent times was the seven years from 1970 through 1976.

Baltimore, Md. averages 1.1 days of 100F+ or above as of the 1981-2010 climate period. The long-term average is less than one day per year, with 108 days (including the five so far in 2011) at Baltimore that have hit or topped 100F since 1872. The maximum temperature at Baltimore is 107F on July 10, 1936. Right behind that, one day has hit 106F — July 22, 2011. Five days have seen temperatures of 105F, with one as recent as July 6, 2010. Like D.C., 100F+ occurrences are skewed to the low (but still way too hot) end. 46% of days got right to 100F, 22% climbed to 101F, 16% to 102F, 6% to 103F, 4% to 104F, 5% to 105F, and 1% to both 106F and 107F.

Also like D.C., the longest stretch of 100F+, at four days, occurred July 19-22, 1930. Baltimore has seen six additional 100-degree stretches of at least three days, most recently July 21-23, 2011. The most 100-degree days Baltimore has picked up in one year is seven in 1930, 1988 and 2010. Baltimore’s longest stretch with no 100F+ temperatures came over the 16 years from 1902 through 1917. More recently, 11 years from 1967 through 1977 featured no 100 degree readings.

Dulles, Va. averages 0.6 days of 100F+ or above as of the 1981-2010 climate period. The long-term average is the same, with 30 days (including three so far in 2011) at Dulles that have hit or topped 100F since 1963. Because 1963 was the first full year at this climate location, overall  data points are much less numerous than at Baltimore and Washington. The highest temperature recorded at Dulles is 105F on July 22, 2011. This bested 104F, recorded on two previous occasions: August 20, 1983 and July 16, 1988. Three other days have seen temperatures of 102F or higher at Dulles. 76.7% of 100F+ days at Dulles have been 101F or 100F.

Dulles’ longest stretch of 100F+ weather stands at two days, and it has happened on four separate occasions, most recently in July 2011 (and in the year prior). The hottest two-day stretch of highs happened on July 21-22, 2011 when a high of 100F was followed by the all-time record of 105F. The previous hottest two-day stretch happened on July 16-17, 1988 when highs reached 104F and 100F respectively. The most 100F+ days Dulles has recorded in one year is five in 1988. From 1998 through 2006, zero days of 100F+ were measured at Dulles, the longest such stretch without one there.

The images above represent composites of 9 times throughout history when Washington has recorded its most extreme (103F+) temperatures on a day in which at least one day surrounding it was also 100 degrees or higher. Interestingly enough, there is a large gap from the 1930s through 1980 without such high-heat scenarios. I have broken them out from left to right as 1980 and more recent (4 times), early period (1936 and prior, 5 times), and the entire sample of nine on right.

The composites are created off 18z (early afternoon) 500mb re-analysis on the day with the highest temperature of the grouping, and as noted are all 103F+ highs at D.C. Many if not all of D.C.’s most scorching days come from subtropical upper-level high pressure systems that build into the continental U.S. The 500mb maps represent that level and the highest numbered contours correspond with the highest upper-level pressure.

…Post edited most recently on August 4, 2011….

This post is part of a Washington, D.C. climatology series, both on and off site, that will be maintained at semi regular intervals.

7 Responses to 100 degree days at Washington, D.C., Baltimore, Md. and Dulles, Va.: Averages, extremes and what to look for

  1. Jerry says:

    Very helpful information. The IAD record of two consecutive 100-degree days could be in jeapordy. However, this is one record I’m not the least bit eager to see broken. Snow? yes!! Heat? Ugh.

  2. islivingston says:

    Hi Jerry. Yes, I think Dulles is probably most “at risk” with the coming heat. After last year was hoping for a break but does not seem like we got one this summer.

  3. islivingston says:

    Welp, there we go. All time record high at Dulles.

  4. thet says:

    where can i find a chart of the actual temperature for US/washington dc for the last 200 years or more ?

    • islivingston says:

      The National Climatic Data Center is probably your best bet for historical data, though I am not particularly familiar with the site as a majority of my data is in offline files. You won’t find anything that’s considered part of the record prior to the 1870s, but there is some record going back further into the 1800s from multiple sources in/around D.C. at least. Then more rudimentary stuff even earlier from journals etc.

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