June 2014 was the first drier-than-normal month at Reagan National Airport, Washington, D.C.’s official observing station, since January. The airport reported 3.31″ vs. a normal of 3.78″ (both Dulles and BWI saw above normal rain levels though).
The just-completed June marks the third month in a row with above normal temperatures in D.C., but it is still not enough to offset the chilly first quarter of the year. 2014 overall is still running slightly cooler than normal (see more on this below). The preliminary average June temperature of 77.2F is two degrees warmer than the 30-year mean of 75.2F.
For both precipitation and temperature, we really did not see anything too major as they are both sufficiently close to “normal” or climatology. Putting this data in the context of the 2000s shows the following charts, which again highlight’s 2014’s status inside the range of variability seen so far this century. The temperature contributes to the slight upward trend, while precipitation seems more difficult to discern, but may have a slight downward trend.
Temperatures in detail
In terms of daily temperature anomalies, we saw over twice as many warm vs. cool days overall. Our hottest day of 97F came at mid-month, but then our coolest day (75F) came not too far beyond that. While we came very close several times, June 2014 only saw temperatures in the 90s on four of the 30 days (13%) and two of those days were only at 90F, although the heat indices were sometimes quite uncomfortable.
Precipitation in detail
In terms of daily precipitation totals, National was the dry spot in June with the other nearby stations doing better against their climatology. For the most part, rains under-performed expectations more often than not. We never saw a day with over 1 inch of rain at National, but we did have wet periods along with several days of very light “trace” precipitation reports at National. But drought-worriers should definitely not fret over June’s outcome, because for the year we are still running nearly 6″ wetter-than-normal there. Here is how the daily results stacked up at National and overall monthly comparisons to the other airports.
We had a few records this past month- here’s the listing:
June 17: Record high temperature of 97F beating 1991’s 95F
June 18: Record warm minimum of 77F matched 1957’s 77F
June 8: 1.71″ of rain broke old record of 0.96″ from 1978
June 18: Record warm minimum of 71F beat 2004’s 70F reading
June 19: Record warm minimum of 71F best 2011’s 70F reading
June 19: Rainfall record of 1.50″, getting ahead of 1996’s 1.38″
The weather pattern
Some serious weather pattern challenges affected us over this past month. While warmer weather dominated, we did have some cooler interludes with very nice low humidity air (like this past weekend!).
We did not have a strong stable heat ridge pattern that tends to characterize our hottest summers, while we also did not have a prevailing cool trough that leads to the unsettled or coolest summer weather. Instead, we had a hodge-podge of pattern signatures that netted out to the slightly warmer side over the Eastern U.S. as shown in the upper level height anomaly map below.
A key issue in June is that while an El Niño continued to slowly develop in the Tropical Pacific, there was not yet much of an atmospheric response to it yet. Therefore, the typically cooler/wetter summer impacts from most developing El Niño summers had not taken hold. It is definitely not unusual to see a lag between the ocean warming and atmospheric response. The big question now is how long before we start seeing that atmospheric domino fall? We’ll discuss that a bit more down below in the July initial thinking discussion.
June’s warmer and drier trends work against the prevailing 2014 story that has been cooler and wetter than normal instead. Now with the inclusion of June, we have the 4th coolest first six months of the 2000s and still the 3rd wettest. With El Niño developing in the Pacific, there tend to be correlations toward cooler weather over the Eastern U.S. along with above normal precipitation, so there is a chance that this status could be reinforced later this summer into the meteorological autumn (Sep-Nov).
July 2014 outlook: Some trickiness
The first half of July is poised to see considerable back-and-forth weather with a hot start over the first few days, a cooler (maybe wetter) holiday weekend, another burst of warmth next week, and then yet another transient cool push behind it. Like June, the warm periods seem to outweigh the cool periods. We still don’t see a significant atmospheric response to the emerging El Niño yet, so there is a chance we could continue this slower/warmer summer situation like 2002 and 2006 vs. the faster-responding cool 2004 and 2009 cases. My feeling is that the answer may be in the middle, and we’ll need to watch closely for a possible bigger pattern flip in the next few weeks as we get deeper into July.
The National Weather Service (NWS) final July outlook shifts a slight increase in zone covered by warmer-than-normal temperature probabilities to just about D.C., but focused toward the Southeast into the lower Mid-Atlantic vs. Northeast. It has precipitation in the EC category again. EC means Equal Chances of above, below, and normal precipitation. You can look at the NWS final July 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: