September is the Driest Month, or the Wettest.
By Heidi Sonen & Roscoe Shaw
Virginia is blessed with ample and consistent rains all year. An average of 45 inches falls annually and the totals are quite consistent. 95% of the time, we finish the year with somewhere between 30 and 60 inches. A standard month is about four inches, which is what August brought us.
July is the wettest month on average with 4.84” and January is the driest with 3.06”. That is mostly because warm, humid, summer air can produce quick downpours that pad the totals. Rain actually falls more often in January.
But September is the most peculiar month for rain. Most of the time, September is dry and pleasant, free from the summer muggies or the winter cold. September is often the driest month of the year. Most recently, in 2014, we had only half an inch the entire month. Summer thunderstorms drop off noticeably and the fast moving storms and fronts of winter have not yet arrived.
Hurricanes are the wild card, though. Only rarely are hurricanes a serious wind issue for central Virginia but they bring most of the heavy rains during the month in the form of “leftovers”. Big hurricanes develop in the tropics and then die, but the moisture gets swept from the Atlantic or Gulf and can dump enormous rain totals over the state. Camille in 1969 was the most notorious, but during most years, we get at least one batch of leftovers. The result is generally beneficial, recharging the water table and fueling the fall growing season.
So while September gets “average” rainfall overall, the records show that it often ranks near the driest or the wettest. It is a month of rainfall extremes. The wettest month ever was 1987 when 17.87” was measured. 1944 dumped over 16 inches and 1999 had almost 14 inches. Feast or famine is the theme.