Washington, D.C.'s Hot Days Appear to be Growing Hotter

[donsutherland1]

Today saw the mercury eclipse 100° for the 4th consecutive day in Washington, D.C. The Capitol Weather Gang has done an exceptional job in covering the extreme heat wave. Must reads include "The Longest, Strongest Heat Wave," "Washington, D.C. Breaks Record High for July 7," "Washington, D.C. Hits 101."

Through today, Washington, D.C. has registered 21 days on which the temperature reached at least 90°, 14 days on which it reached at least 95°, and 5 days on which it reached at least 100°. In other words, 66.7% of 90° days saw the mercury reach or exceed 95°, and 23.8% of 90° days saw the temperature reach at least 100°. Both percentages are far above the highs since 1950. They are also somewhat ahead of the benchmark hot year, 1930. At that time, the downtown location at which the City's temperatures were recorded, saw 52 90° days, 26 (50%) 95° days, and 11 (21.1%) 100° days.

For the 1950-2011 period, the highest percentage of 90° days on which the mercury reached or exceeded was 52.1% in 1999 (25 of 48 90° days). The highest percentage of such days on which the mercury reached or exceeded 100° was 12.5% in 1954 (4 of 32 90° days). The only other years in which the mercury reached or exceeded 100° on at least 10% of the 90° days occurred in 1997 (11.9% days), 1988 (11.9% days), and 2011 (10.0% days).

When one takes the 30-year moving average to obtain a climatic snapshot of Washington's evolving climate, one finds a slight uptick in average annual 90° days and a more dramatic uptick in both 95° days. The trend for 100° days is also more robust than the trend for 90° days.

In terms of the share of 90° days reaching or exceeding 95°, the following are the 30-year moving averages for the 1950-1979 through 1982-2011 periods:

1950-1979: 16.1%

1960-1989: 20.1%

1970-1999: 27.0%

1980-2009: 30.4%

1982-2011: 31.4%

The share of 90° days reaching or exceeding 100°, the following are the 30-year moving averages for the 1950-1979 through 1982-2011 periods:

1950-1979: 1.6%

1960-1989: 2.0%

1970-1999: 3.1%

1980-2009: 3.4%

1982-2011: 3.6%

In sum, the 30-year trends provide a glimpse that Washington, D.C.'s hot days (90° or above) appear to be growing hotter, with those days more frequently reaching or exceeding 95° and even 100°.

[TalcottWx]

Thank you. Very cool facts!

[yoda]

Thanks for the post Don. Always full of information

[astarck]

Great analysis. We'll probably have to revisit this in a few years for 105 degree readings.