The middle of May is often one of the nicest times of the year in Washington. But last week, from May 12 to May 19, it rained for eight straight days. It was the wettest mid-May week on record.
The rain ruined outdoor plans and caused the Potomac River to swell to its highest level in four years. But, because the rain mostly fell at a slow and steady pace rather than all at once (Frederick, Md., was a notable exception), flash flooding was limited. All of the water also helped make up for drier-than-normal weather dating to last fall.
Washington, which posted 6.14 inches in all, logged at least 0.25 inches of rainfall on seven straight days, the longest streak with so much rain in recorded history. In fact, it received at least 0.4 inches on those days, a record-long stretch for that amount of daily rain as well.
Across the region, one to two month’s worth of rain fell in that eight-day period with widespread totals between four and eight inches. The heaviest rainfall, from six to 10 inches, fell in our far northwest areas from Winchester to Frederick and east and southeast of the Beltway toward Annapolis and Southern Maryland. Locations to southwest saw the lowest amounts, closer to four inches.
Here are some select totals:
- National Arboretum: 7.43 inches
- Dalecarlia Reservoir: 6.83 inches
- Middletown: 8.92 inches
- Leonardtown: 8.94 inches
- Crofton: 8.4 inches
- Bowie: 7.81 inches
- Annapolis: 7.12 inches
- Prince Frederick: 6.73 inches
- Hyattsville: 6.16 inches
- Takoma Park: 5.96 inches
- Laurel: 5.83 inches
- Baltimore-Washington International Marshall Airport: 5.73 inches
- Columbia: 5.45 inches
- Rockville: 5.34 inches
- Glenmont: 4.82 inches
- Damascus: 4.48 inches
- McLean: 7.75 inches
- Falls Church: 7.55 inches
- Vienna: 7.48 inches
- Fairfax: 7.38 inches
- Leesburg: 7.26 inches
- Arlington: 7.07 inches
- Oakton: 6.49 inches
- Annandale: 6.0 inches
- Burke: 5.66 inches
- Manassas: 5.46 inches
- Dulles International Airport: 5.43 inches
- Quantico: 5.05 inches
- Fredericksburg: 4.24 inches
- Warrenton: 3.91 inches
Washington’s 6.14 inches of rain so far this month is the most during May since 2009 and more than what fell in March and April combined.
With 11 days still to go, 2018 ranks as the 15th wettest May on record (back to 1872). The average rainfall for May, historically the wettest month of the year, is 3.99 inches.
As the National Weather Service predicts about an inch of rain in the week ahead, we should break into the top 10 wettest.
We’d need more than 4.5 inches of additional rainfall for this month to become the wettest May on record, which seems like a stretch. However, the period between Memorial Day and May 31 looks like a damp one, so it’s not entirely out of the question.