The month of May at Washington Reagan National Airport (KDCA) was just under one degree warmer (+0.7F) than normal (based on 1981-2010 benchmark) and 1.17 inches drier than normal.
Both Dulles (KIAD) and Baltimore (KBWI) also were slightly warmer than normal (less than one degree) with varying degrees of a precipitation deficit (from -0.56 inches at BWI to -1.35 inches at Dulles).
The temperature range at National was an impressive 49 degrees ranging from last Friday’s 91F peak to May 14th’s low of 42F. The month’s only records locally were established at BWI (34F, tying 1996) and IAD (32F, tying 1996) on that chilly May 14 morning.
In the context of the 2000s, May was sort of in the middle for temperatures and on the drier side of the range for precipitation. You can see how 2013 shapes up in the comparison table and line charts below. The dashed line is the 30-year normal comparison:
Looking at the daily May data at National Airport reveals the sparse nature of our rain events with the biggest one being just last week with 1.34 inches falling. While May came in short of normal and last year, the year-to-date is running 1.88 inches wetter than last year, and it seems like this summer should continue running to the wetter side vs. 2012 too.
For daily temperatures, the red days (above normal temperatures) slightly outnumbered our blue (below normal) days overall, but it was really a near even match with the monthly 31-day average being just a few tenths warmer than normal at all three airports. You can see the ups and downs of May in the bar chart below:
The end of May also marks the end of 2013’s meteorological spring (Mar-May), so we can look at how well this year performed in the context of last year, the 2000s, and climatology (long-term averages) too. Here are the temperature and precipitation rankings along with how the meteorological springtime periods have changed over the course of the 2000s:
Our 2013 temperatures were very close to normal and cooler than last year, while precipitation was more than last year, but in the driest third of 2000s cases (fourth driest). The warmer/drier trend you see over the last 3-4 years matches well with the stronger negative Pacific Decadal Oscillation (PDO) we have seen over the same period. That tends to translate to a drier/warmer signal for our region. It has weakened this spring, which is allowing for us at least to trend cooler/wetter than last year, and it may offer a summer that is cooler/wetter than the last three as well.
Now that we’re walking into the early days of the meteorological summer, should we expect any major pattern changes? The strong heat at the end of May into the first weekend of June was the biggest one so far this year, but the trends over the next few weeks are back to the cooler direction such that June may follow May’s lead in averaging fairly close to normal for temperatures. A bigger difference could be precipitation as we’re getting a wetter start to the month. However, June is the second wettest month of the year normally (after May), so we run that risk of coming up short again even though we are not experiencing any drought concerns.
The National Weather Service is not offering us much of any significant guidance by favoring equal chances of wetter/drier/normal precipitation and warm/cool/normal temperatures as can be seen here.
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: