May 2014 closed as a slightly warmer and wetter than normal month for Washington, D.C. It capped a three-month period (aka meteorological spring) that was much wetter but very slightly cooler than normal. The May mean temperature of 68.5F at National was 2.5F warmer than normal, while the total precipitation of 4.96″ was nearly an inch (+0.97″) above normal.
Spring 2014 (March to May)
The spring period at National Airport came in slightly cooler than normal (-0.3F) and considerably wetter than normal (+5.16″). Both outcomes went against general trends in recent years for spring: tending warmer and drier (compared to average). You can see those trends reverse a bit on the line charts down below. The trend line fit for temperatures shows an incline (warming) for the 2000s in spring, but the trend line for precipitation is essentially flat with lots of variability. This year and last year were the coolest springs since 2009.
May temperatures and precipitation
The May outcome at National Airport places this year as the 4th warmest and 4th wettest of the 2000s. The results were not exceptional in any category, and you can see how it all ranks in the chart below. There is a big jump from this year’s 4.96″ of rain to 2003’s 7.06″ and all the way up to 2008’s 10.66″ level. All three wetter May cases (2003, 2009, 2008) also saw generally cooler-leaning summers too. From a temperature perspective, 2014 was nestled right in between 2011 and 2010 (both hot summers) but below 2012 (hot summer) and 2004 (coolest summer of 2000s). As such, May is not a very good bellwether for the summer ahead.
In terms of daily temperature anomalies, we saw over twice as many warm vs. cool days overall. Our hottest day of 92F was just last week, while our coolest low of 49F at National was just the week before. Three warm and three cool periods occurred during the month with the warm stretches longer and stronger.
In terms of precipitation anomalies (differences from average), much of May’s outcome came from the mid-month flooding episode when National picked up a record-setting daily total of 2.25″ as shown below. Interestingly, Baltimore (BWI) did not do as well as National and Dulles this month and even finished the month with a minor deficit (-0.64″). As we move into the summer months, we tend to see bigger disparities between the local airports since precipitation is more associated with scattered thunderstorm activity rather than large-scale systems that affect all stations more evenly. Despite the differences, there are no drought concerns over the Mid-Atlantic currently.
Only one record was reached in each of three metro area airports this past month:
May 16, 2014: Record daily rainfall of 2.25″ besting 1983’s 1.91″ total
May 16, 2014: Record daily rainfall of 1.97″ besting 1983’s 1.62″ total
May 29, 2014: Record cool maximum temperature of 57F beating 58F set in 1996
The weather pattern
The upper level jet stream pattern for May oscillated thanks to typical springtime variability, but we did see more upper level warm ridging again at very high latitudes. That was a big issue this past winter with frequent ridges of high pressure around the Alaska area. If this trend continues into the summer, it would work against any major heat in the Eastern U.S. We had some marginal warm ridging on the mean pattern map over the Southeast into the lower Mid-Atlantic, which gave us the marginally warmer May outcome. But those bigger ridges farther north and west prevented any big hot weather surges for much of North America.
With May complete, the first five months of 2014 are now tracking as the third coolest and third wettest of the 2000s. We are running far wetter than last year at this time and almost 2 degrees cooler. The charts below show how both factors shake out for Washington Reagan National Airport:
June 2014 outlook: No severe heat seen
While we have some warm to moderately hot weather coming in the first week of the month, there are still no signs of any big sustained heat waves heading our way. Temperatures are expected to be more toward seasonal or even slightly cooler at times in the second and third weeks of June with the fourth week still uncertain yet, but the developing El Niño pattern in the Tropical Pacific keeps the odds higher for a cooler/wetter scenario more often than not.
The National Weather Service (NWS) final June outlook offers no guidance for our area with EC forecast for both precipitation and temperature. EC means Equal Chances of above, below, and normal temperatures. However, you can see that below normal temperatures and above normal precipitation are closer to our area than other options. You can look at the NWS final June forecast here.
For further information
The National Weather Service publishes nice monthly assessments about five days into the start of the next month:
You can click on your closest airport location here: