July 2013 is now history, and we move past the typically hottest month of year into the final month of meteorological summer.
On the whole, July was hotter-than-normal but we had all sorts of weather including unpleasantly high humidity and heat indices, very wet days, and also very comfortably cool days. Ultimately, the heat was not strong enough to rival the last three years, and we logged the second month in 2013 with above normal rain.
The big story of July 2013 was that we avoided 100-degree temperatures for the first time since July 2009 and its associated cooler summer. Mind you, we did manage some 100-degree heat indices during the early to middle part of the month, but the final week turned out to be a pleasant surprise (the coolest in the last 10 years).
Cooler-than-normal temperatures dominated the last seven days of July to bring down the monthly average to a minor 1.4F warmer than normal at 81.2F.
Overall, the month ranked as the 4th hottest of the 2000s (after the last three years) and tied with 1983 for the 13th hottest on record (dating back to 1872). You can see the rankings and how our Washington July periods have changed over the 2000s here:
We can definitely pick out a warming trend on July temperatures in this current century. The dashed black line is just the average (or mean) of the 2000s, which 2013 bended back toward.
We had twice as many warmer-than-normal (red) days as cooler-than-normal (blue) with four average days in July.
Low temperatures were disproportionately warm as we suffered through very high humidity at times in the first two-thirds of July which held nighttime temperatures up. We set two record high minimums at National (July 18 and 19) and three at Dulles (July 11, 19, 20). The 81F at National on Friday morning July 19th was the most painful, beating the prior record of 79F from just two years ago.
These warm low temperatures helped D.C. achieve an astonishing record long streak of 138 hours at or above 80 degrees.
Here is the daily play-by-play of temperatures compared to average:
For precipitation, we weren’t nearly as crazy-wet as June, but we did see some sizable rainfall totals at times. Dulles outperformed National this time scoring 7.27″ (3.6″ above normal) of rain vs. National’s monthly estimate of 4.43″ (0.7″ above normal). Dulles also had a rainfall record of 3.71″ back on Thursday July 11th, besting 1977’s 1.2″ for the date. For National, it was the wettest July since 2010’s 5.17″ result. For Dulles, it was the wettest since 2005’s 7.85″ soggy total.
Ranking-wise, 2013 was toward the middle of the list for the 2000s and ranked 58th wettest for the all-time history. You can see the list here along with the 2000s trend (mixed): We don’t see too much of a precipitation trend for July in the 2000s, but maybe a slight negative slope. Like temperature, the outlined mean is for just the 2000s.
The weather pattern
Our upper level jet stream pattern was characterized by two heat ridges over the U.S.- one in the West and the other in the western Atlantic. That western Atlantic (Bermuda) ridge would occasionally back up onto the East Coast early to mid-month delivering our very humid heat situation. It didn’t hurt that the super-saturated June pattern stocked our soil with lots of moisture ready to be evaporated during those heat events. By the end of the month, the Bermuda ridge was vanquished farther east over the open Atlantic allowing cooler Canadian air to penetrate southward.
Will the pleasant finale of July carry into August? It sure looks like it! The next two weeks are forecast to range from seasonal to mostly below normal temperatures with normal to above normal rainfall. That should keep us away from 100-degree temperatures, making it likely to be the first 100-degree free summer since the cooler 2009.
We may see some heat sneak back into the picture at times in the second half of August, but at that point our climatology is already cooling down toward the start of meteorological autumn, exactly one month from today (some of you will cheer that!).
The National Weather Service is again punting on our area forecast by showing equal chances of wetter/drier/normal precipitation and warm/cool/normal temperatures as can be seen here. But I will point out that the cooler and wetter anomalies are closer to our area than any other option, so at least they hint at it.
For further information
The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly):
You can click on your closest airport location here: