After a rather warm May across the area, we've had a downright hot June, though for the most part it has come in the form of persistent temperatures well above normal, but with relatively few individual daily records being tied or broken., including the 101 degrees that we finished the weekend with. That high was still shy of the previous record of 104 for the date, but continued to push our average temperature for the month farther above the long-term average.
In April and May, average monthly temperatures at RDU ended up 3.9 and 4.9 degrees F above normal, respectively, each of which was the 5th warmest on record for the site in 67 years of observations. Including data up through the 27th of June, we are averaging 81.5 degrees, or 7.1 degrees above normal for that period. The old record for hottest June was set just two years ago in 2008, with 80.7 degrees. If our forecast temperatures for today, Tuesday and Wednesday are reasonably in the ballpark, there is a good chance that the final average temperature for the month will only change by a tenth or two either way, and will surpass 2008 to set a new record.
That will also likely leave us with the hottest 3-month period ending with June, due to the combined warmth of April, May and this month. For a sense of how any recent stretch of unusual temperatures or precipitation compares to history, there is a cool "Climate Perspectives" tool at the Southeast Regional Climate Center (SERCC). It shows today, for example, that the past week, two weeks, month, and three months, have the highest average temperatures for those periods recorded at RDU.
Why it's been so toasty relates back to a persistent upper level ridge of high pressure that has developed and re-developed across the central and eastern U.S. during the warm stretch, leaving us with warm subsiding air, a fair amount of sunshine on frequent occasion and a west to southwest flow in the lower atmosphere. It is always difficult in the short-term to go back and pin the reason for that persistent ridge to some larger underlying factor. We have had a rapidly dissipating El Nino pattern in the Pacific, and given the correlation between El Nino and colder than normal winters here, the rapid breakdown of El Nino might have some influence on the swing from a below-normal winter to a en especially warm late Spring and early Summer, but that is pretty speculative at this point.
In any event, it appears we'll see a northeast wind set in around the middle of this week to bring temperatures down some, and with any luck it'll be a nice break that holds at least into most of the holiday weekend!