Storm of April 1978 brought mix of weather miseries
Tuesday, April 30, 2013
Asked about the most memorable extreme weather events of the past half-century, the 1985 floods and the 1993 blizzard are often at the top of the list for many Roanokers and Southwest Virginians.
But a storm in late April 1978 combined some of the worst elements of both of those events.
The April 26-27, 1978, storm remains an extraordinary event 35 years later, one with no real historic parallel in our region for its combination of flooding rain and heavy snow.
Flooding forced 1,000 people out of their homes in the Roanoke Valley while residents in higher elevations were buried under a foot or more of wet snow more than a month after the calendar had flipped to spring.
The Roanoke River crested at 18.95 feet (flood stage is 10 feet). At the time, it was the river’s second highest crest on record, trailing only the 19.61-foot crest of six years earlier. Seven years later, the river’s mighty 1985 flood would reach 23.35 feet.
Had it been a month earlier, the late April storm of 1978 would have probably been a huge snowstorm for all of Southwest Virginia, even the lower elevations.
The setup was classic for a large winter snowstorm, as a strong upper-level low was forced southeastward from near Chicago to Charlotte, its more seasonable east or northeast track re routed by another strong low off the coast of Newfoundland. This “50-50 low” — so named because it’s near 50 degrees latitude and 50 degrees longitude — is an atmospheric feature present for many of the large winter storms that hit Southwest Virginia and much of the Eastern U.S. the hardest.
The strong low aloft helped spin up a similarly intense surface low that tracked slowly across Tennessee and near the North Carolina/South Carolina border before moving offshore. This track allowed the storm to sweep in abundant moisture off both the Gulf of Mexico and Atlantic Ocean, initially arriving on southeast winds that helped lift it against the Blue Ridge, squeezing out even more heavy rain.
The upper-level low trailing the surface low brought an extremely cold pocket of air overhead, and brisk northeast winds circulating counterclockwise around the surface low as it neared the Atlantic coast brought in much colder than normal temperatures at ground level. Dynamic cooling, or the lowering of the freezing level occurring as barometric pressure drops, brought subfreezing temperatures far enough downward to allow snow to reach the ground at elevations above about 2,000 feet for at least part of the event.
A Roanoke Times article from April 28, 1978, reported that the state highway officials had measured 24 inches of snow in Floyd County between Willis and the Blue Ridge Parkway, with up to 18 inches on Bent Mountain in Roanoke County. The heavy, wet snow on top of already blooming and green trees sagging onto power lines resulted in about 10,000 customers losing power.
Snow fell for a shorter time in slightly milder temperatures in much of the New River Valley, but still accumulated 6 inches at Blacksburg. That remains the latest measurable snowfall on record there as well as the second largest April snowfall, trailing only the 10-inch snow of April 7, 1971. Its ranking was challenged, but not quite superseded, by the 5.4 inches measured on April 4 this year.
For the Roanoke Valley, the late April storm was memorable as one of a trilogy of extreme flooding events in the 1970s and 1980s, the others occurring in June 1972 and November 1985.
Damage estimates in 1978 topped $10 million — which would be close to $55 million today, adjusted for inflation.
The flooding of 1972 was caused by the inland remnants of Hurricane Agnes, while that in 1985 was caused by the inland remnants of Hurricane Juan.
The 1978 flood, however, did not have its genesis in a tropical storm. Atlantic tropical season runs June 1 to Nov. 30, and the infrequent systems that form in other months almost never get close to Virginia.
It doesn’t take a hurricane to wreak a good deal of misery on Southwest Virginia.
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THE ROANOKE TIMES
