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Latest entries from the Weather Journal blog
About Kevin
Kevin Myatt grew up in Arkansas to the tune of tornado sirens and the rhythm of hailstones, aspiring to be a meteorologist before his studies and career were turned to journalism instead. Though he often chases storms, he prefers living in the cooler, more tranquil weather of the Blue Ridge. He moved to Roanoke in 1999 to take a job on the copy desk of The Roanoke Times; writing headlines and editing copy is his principal work for the newspaper today.
Each May, Kevin assists Pulaski County High School / Virginia Tech meteorology instructor Dave Carroll in leading college and high school students to the Plains to observe severe weather firsthand. The accounts of many of his storm chases can be found here on the storm chasing page of his weather blog on roanoke.com.
Kevin was an editor for "Hurricanes and the Middle Atlantic States," a book written by D.C.-area weather enthusiast Rick Schwartz and published by Blue Diamond Books that documents hurricanes striking the mid-Atlantic states since colonial times.
The Weather Journal column began in 2003 and appears on Friday's Virginia section front in The Roanoke Times. The Weather Journal blog began in 2006 and follows weather day-by-day between the larger columns.
Timing puts icing on forecast
By Kevin Myatt
The Roanoke Times
We had been through the same song and dance many times before.
Winter storm watch goes up for threat of ice. Ice storm warning goes up with those scary words "ice accretion" and warnings about the mayhem it will cause.
Roanoke's overnight temperature hovers several degrees above freezing. The rain arrives. Seemingly everyone else around gets at least some ice, but Roanoke's temperature halts its downward slide at 33 degrees.
There's a little ice on the trees up by the Mill Mountain Star, but it's just a cold rain in the valley.
But on Friday, it went differently.
This time, we did get the ice in the Roanoke Valley, and in an unusual twist, the ice still was collecting on the trees late Friday morning while most of the usually more winter weather-prone New River Valley had already warmed above freezing.
The official temperature at Roanoke Regional Airport fell from 39 to 30 in four hours early Friday morning. It did not get above the freezing mark, 32 degrees, until noon -- exactly when the National Weather Service's ice storm warning expired.
It was not quite a major ice storm, but certainly a significant one, enough to break some trees and knock power out for a few thousand people in the area.
So what happened differently this time? Why did the Roanoke Valley get iced Friday when it did not on Dec. 16 and Feb. 13 of last year in seemingly similar circumstances?
The critical factor this time was the depth of cold, dry air in place as the precipitation arrived.
Dew points on Thursday were running in the single digits even as temperatures climbed to the upper 30s and low 40s. That is extremely dry air.
The warmth and moisture moving in on top of that cold, dry air also was impressive, with temperatures a few thousand feet in the atmosphere topping 50 degrees. But the moisture being brought by those warm winds had to fall through the cold, dry air to reach the surface.
Rain fell. It evaporated. Each evaporating drop of rain took a little heat out of the atmosphere. The air cooled. Eventually, the rain reached the surface, and so did the evaporation and its cooling effect. That's how we were able to chop off 9 degrees so quickly.
In both the Feb. 13 and Dec. 16 ice events of last year, the air was simply not as dry near the surface. Temperatures only begrudgingly moved downward.
The early-morning timing also likely aided in getting the Roanoke Valley below the freezing mark. The precipitation moved in at the time of day when heating from the sun is at its least, and also the furthest away from when any daytime sun had baked asphalt and concrete in the city.
In the other two cases, precipitation moved in during the day, and temperatures slowly fell through the day into the early evening.
The ice storm would have been much worse, of course, with colder temperatures or more precipitation. Looking at the bright side of a wintry weather type that displeases snow lovers and warmth lovers alike, any form of precipitation is still needed to ease our long-term drought problems.
But Friday proved that the Roanoke Valley really can have an ice storm in a borderline case. Roanokers will have to be just a little less skeptical the next time an ice storm warning is issued.
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