June 2015 was a historical month for many cities across the Northeast and Mid-Atlantic. Usually in June we’re talking about record high temperatures, but this year we dealt with record amounts of rainfall. Major cities like Washington, Baltimore, and Philadelphia received anywhere from 9.00 to 13.00 inches of rainfall for the month, which is 2.5 to 4 times greater than normal. In May, these major Northeast cities only received 1.00 to 2.00 inches for the month, which was well below normal, so it was a tale of two extremes in the final two months of spring.
The pattern that set up over the last couple of weeks was quite similar to that of this past winter, featuring a ridge of high pressure over the West and a trough of low pressure over the East. This trough helped steer storm systems, such as Tropical Storm Bill, into the Northeastern and Mid-Atlantic states. Besides Bill, various areas of low pressure (the June 27th storm seemed like a throwback to winter) and their associated warm and cold fronts rode along the trough, bringing numerous rounds of scattered showers and thunderstorms. While Bill brought a substantial amount of rain to the Mid-Atlantic, the majority of June’s rainfall came from thunderstorms, in which the heaviest ones dumped as much as 2 to 3 inches of rain in an hour or less, leading to flash flooding.
As for totals, Washington’s 11.94 inches of rain in June 2015 ranked as the 4th all-time wettest month in history, while Baltimore’s 13.09 inches was the 3rd all-time. Philadelphia’s 8.88 inches of rain was still impressive, ranking as the 2nd wettest month of June in history. For reference, the normal June rainfall for these cities is on the order of 3.50 to 4.00 inches. June 2015 is definitely one for the record books, and I’m sure many folks are happy that it is over.
