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A "snow hole" formed along the eastern Blue Ridge (WDBJ7 -First Alert Weather / January 18, 2013) |
Thursday's winter storm went from rain to sleet then huge wet flakes, and even thundersnow. It was a storm that left in a hurry, but left a lasting impact on the minds of meteorologists.
As the snow amounts came in, 3 inches. 8 inches, even a foot, a photo appeared in the email inbox the looked suspicious.
How could one area see a foot of snow, while a neighboring hometown, get absolutely nothing?
This "snow hole" if you want to call it, went along the eastern sides of the Blue Ridge Mountains and included parts of Bedford County, Smith Mountain Lake and even northeastern Roanoke County.
Viewer photos show zero accumulation, just a wet ground in parts of those areas.
WDBJ7 First Alert Meteorologist and winter weather specialist Leo Hirsbrunner explains, "we barely had enough cold air to produce the snow. Without the cold air aloft from the cloud to the ground to keep the snowflake from melting, we just have rain."
What areas in the snow hole were lacking was some of that cold air that stopped along the Blue Ridge Mountains.
As cold air from the northwest seeped into the Highlands, the New River Valley and the Roanoke Valley it changed from rain to snow and it quickly added up.
However, as the moisture came over the mountains, there was very little cold air on the eastern side of the Blue Ridge to change the rain to snow fast enough to produce the "sticking" snow.
"Since this 'snow hole' covers more than Bedford County, we think the minimum was the result to two different processes," explains Phil Hysell, Warning Coordination Meteorologist at the National Weather Service office in Blacksburg."As the surface low started to gain strength, a second swath of heavy, convective snow (similar to a summer storm, even with lightning) occurred across the eastern portion of our forecast area. So, while precipitation did fall in this snow minimum, the dynamic cooling wasn't there."
Bottom line, until the storm created its own cold air, through convection, it couldn't produce the same snow rates as it did in the New River Valley, Roanoke Valley and Highlands.
Once the storm was strong enough to produce snow, it had already passed over the same area now known as the "snow hole."
That left some areas with nothing but snowflakes, and big puddles of water and slush.
