It rained and rained in Washington this summer, and it was unusually hot, too.

The rain was exceptional from mid-July through August, and the heat — while not as extreme — proved persistent.

In all, 20.13 inches of rain fell between June and August, the sixth-most on record and the most since 1942. And thanks to warm nights and a steady supply of 90-degree days, the summer also ranked as the ninth-hottest on record.

August, in keeping with the summer’s warm and wet theme, was 2.9 degrees warmer than normal, while rainfall was 2.29 inches above the norm.

August’s average temperature of 81.0 degrees outdid July by 0.3 degrees, even though July is usually the hottest month of the summer. This August tied with 2012 and 1983 as the sixth-hottest on record.

The 17 days of at least 90 degrees during the month tied for 10th most in August and about a week more than typical. We started the month with a streak of eight days in a row with 90+, the longest streak of summer and longer than any streak last summer.

The city’s August rain total of 5.19 inches, while not exceptionally rainy, helped 2018 stay on track among the wettest years since 2000 (see more below on that).

August weather extremes and records

While August’s average temperature ranked among the top 10 hottest, it is notable that it never got above 94 degrees. The lows were frequently very warm, partly thanks to all the rain and humidity.  While it was not as wet as July, we experienced frequent days with rain.

All of the daily records that happened in our region in August were either from rain or warm low temperatures:

Washington:

  • Aug. 21: Record rainfall of 2.46 inches tops 2.12 inches, from 1906
  • Aug. 30: Record warm low temperature of 78 degrees beats 76 degrees, most recently set in 1991

Dulles:

  • Aug. 1: Record rainfall of 1.09 inches tops 0.91 inches, from 1969
  • Aug. 21: Record rainfall of 2.72 inches tops 1.43 inches, from 2014
  • Aug. 30: Record warm low temperature of 72 degrees, ties 2005

Baltimore: 

No records set

August weather pattern

The upper-level weather  pattern in August was similar to July. Dominant high-pressure ridges or heat domes on both coasts helped most of the United States (especially the eastern and western thirds) run hotter than normal:

High-altitude winds continued to be weaker than normal, which favored the development of these heat domes throughout the Northern Hemisphere mid-latitudes.

The summer’s weather in perspective

This summer’s rainfall stood out as exceptional, especially in relation to recent decades. Notice that in the top 10 wettest summers on record, 2018 is the only year falling after the 1970s:

But the heat was not exceptional compared to recent years, considering almost all of the hottest summers have occurred since 2000:

Since 2010, the upward tendency in summer temperatures may have slowed somewhat but continues to show a rising trend:

January-through-August temperature and precipitation rankings

Washington’s fifth wetter-than-normal month in a row and fourth in a row with at least five inches means 2018 remains among the top two wettest years in Washington since 2000.  We are likely to stay behind 2003 in September, as Hurricane Isabel occurred that year, but notice how wet we are compared with the other years of this century so far.

The hotter-than-normal August was not enough to shift 2018 from ranking eighth among hottest years since 2000.

August forecast evaluation

A month ago, just ahead of August’s start, we made the following predictions:

Temperatures: Near to slightly above normal, averaging between 78 and 80 degrees, slightly hotter than last year’s 77.4-degree average. The average temperature is around 78 degrees.
Rainfall: About three to five inches, which is slightly above the average of 2.93 inches. Last year, we received 4.58 inches.

Here is what happened:

Temperature:  81.0 degrees — it was slightly hotter than we predicted.
Rain:  5.19 inches.  Just like the temperature, we got the sign right (wetter than normal), but missed the intensity since the total exceed five inches.

Given the correct forecast for a warmer and wetter-than-normal August, but the slight miss on intensity, we’ll give ourselves a grade of  “B” for the August outlook.

Ian Livingston contributed to this post.