Washington and Baltimore have not only witnessed a very wet July but also a very wet 2018. Both locations are nearing a year’s worth of rain, and yet five months remain in 2018.
Washington has picked up 34.88 inches of rain, about a foot more than average and just about five inches below its annual average of 39.74 inches. Baltimore has registered 41.36 inches, about 17 inches more than normal, and is just a brief downpour away from matching its average yearly total of 41.87 inches.
Year-to-date, these amounts rank high. Washington’s total is the eighth most on record through late July, while Baltimore trails only 1889.
Two periods in particular have catapulted this year’s rainfall tally into historic territory.
While the abnormally wet second half of July is probably freshest on your mind, also recall that this May was the sixth wettest May on record in Washington. A wet May — the wettest month on average in the District — certainly sets the stage for a wet year.
Then, following the driest first half of July on record, the heavens have unleashed just about all they can hold, resulting in the wettest second half of July on record and the most extreme dry-to-wet flip. At least 9.70 inches fell in Washington in July, and Baltimore has picked up an astonishing 16.62 inches.
It’s admittedly hard not to focus on Baltimore’s numbers. Eddie Lee, a Capital Weather Gang reader, has compiled a remarkable list of rainfall records set in Baltimore during this recent period. There are many.
Remarkably, Baltimore observed three days with three inches or more of rainfall over the span of eight days ending July 25. In no other year in the Baltimore record, dating back to the 1870s, have there been more than two.
The torrents in May and July have done a lot of the work in making this such a wet year, but certainly not all of it. In Washington, we’ve now seen 13 days with one inch or more of rainfall, including four in May and three in July. But we had also three such days in February and a smattering in the other months. The 13 days with at least an inch ranks third-most on record since 1871. In 1886, there were 18, and in 1891, there were 14 up to this point.
It’s a similar story in Baltimore, where there have been 12 days with at least an inch of rain. This is tied for second-most since records began in 1871.
What comes next
Does this super wet start to 2018 mean we’re going to set annual precipitation records? Yes and no.
The warm season months of April through October tend to bring the big rainfall totals. But we have already passed the months with the greatest rainfall potential. In Washington, our average rainfall peaks at 3.99 inches in May. June is in second place with 3.78 inches, and July third at 3.73 inches. Getting into August, the average dips strongly to 2.93 inches, making it our driest warm-season month on average.
However, September and October, to some degree, can produce big totals. These are months that are ripe for tropical storms and hurricanes. Occasionally, August can produce big numbers, as well, despite its lower average total. Baltimore’s wettest month on record, when 18.35 inches fell, occurred in August 1955. It is the only month in Baltimore’s observed history wetter than this July.
Given limits in long-term forecasting, it’s too soon to say much about where the annual precipitation totals will end up. And despite the soggy first seven months, we are a long way off from annual records.
Washington’s highest annual rainfall total on record is 61.33 inches, set way back in 1899. Since records began to be kept at Reagan National Airport in 1945, 60.83 inches in 2003 is the highest total. With 34.88 inches to date, we would need over two feet of rain to threaten those records. To crack the top 10 wettest years, we’d need about 17 more inches, a more manageable amount.
Baltimore faces similar albeit shorter hurdles, despite a higher rainfall to this point. The record of 62.66 inches annually from 2003 is 27.78 inches from where the city stands now.