While we don’t expect a repeat of the brutal summers of 2010 and 2011 — the two hottest on record — we do anticipate a classic hot and humid D.C. summer, similar to last year’s.
We predict all three months to be warmer than normal, with plenty of 90-degree days and warm, stuffy nights.
If you’re looking for solace, it may come in June, which we favor to be the coolest month compared with what’s normal. So the persistently nasty heat may be staved off until July and August.
Caveats: When putting together a summer outlook, we’re less likely to see the signals for extreme warmth or cold (relative to average) that we sometimes see in advance of winter. As such, our outlook is of low-medium confidence. This kind of seasonal forecasting is experimental, and errors are possible.
Summer outlook by the numbers
Temperatures: Somewhat above normal, two degrees above average
- June: One degree above average
- July: One to two degrees above average
- August: Three degrees above average
Number of 90-degree days for June, July and August: 40 to 45, compared with a normal of 31
Longest streak of 90-degree days: 10
Number of 100-degree days: One or two
Precipitation: Slightly below normal rainfall
The following factors are among those considered in preparing the outlook. It should be noted that any one factor does not necessarily correlate with a particular kind of summer (e.g., warm, cool, dry or wet).
We are currently experiencing the end of a rapidly weakening strong El Niño event.
We expect weak El Niño conditions to quickly weaken to neutral conditions as we start the summer and eventually to weak La Niña conditions. Summers preceded by El Niño events lean warmer than normal on average for the Mid-Atlantic.
Pacific decadal oscillation
The PDO (Pacific decadal oscillation) has been in a positive stretch for 27 consecutive months, and there is no reason to believe it won’t average positive through the summer, perhaps strongly so. A strongly positive PDO has some correlation with warmer-than-normal summers in the Mid-Atlantic (although, note that the PDO was negative during our hottest summers on record from 2010 to 2012).
With respect to normal, our spring has gotten cooler and wetter. March was very warm and dry, April a mixed bag, and May so far has been quite cool and wet.
Ten out of the past 11 summers have been above normal. It is hard to bet against a warmer-than-average summer, especially with Washington’s urban heat-island effect consistently elevating overnight lows, even in air masses that are yielding average afternoon highs.
The analog years, or the years when some of the above factors were present to some extent, are 1973 and 1995. The weather during these summers was given some loose consideration in formulating our outlook.