Published: 2007-12-09 11:55:16
Updated: 2007-12-09 11:55:16
Posted December 9, 2007 11:55 a.m. EST
MIKE MOSS SAYS: Bart, I remember that storm very well, as I was home on Spring break in Rocky Mount and we got about 19-20 inches in our front yard, by far the biggest snowfall I'd ever experienced until January 2000 around here. As for the dynamics involved, there is a fairly well-established set of conditions that are conducive to the really big snows in our area in a dynamic sense.
First, we tend to have a large upper level ridge over Alaska and western North America and a deepening trough aloft over the central and eastern U.S. that help in developing a surface low pressure area over the northern Gulf of Mexico. There tends to be a maximum (streak) in the polar branch jet stream just to our north or northeast and sometimes a maximum in the subtropical jet down toward the central ane eastern Gulf Coast. There is usually a strong, cold surface high over the upper midwest that either drifts east or extends east into the northeastern U.S. during the course of the event - this high is important as a source of low level cold air on the northern and northwestern side of the surface low that will eventually move this way from the south. That surface low will tend to advance along a frontal boundary across the northern Gulf of mexico and into the northern half of Florida before building northeastward around 100-200 miles off the southeastern coast, and is often crossing northern FL when precipitation begins here and is generally southeast of Wilmington or so when the snowfall rate is at its maximum, with the precip tapering off when the low reaches about the latitude of Cape Hatteras or a bit farther north.
That is a very brief overview but pretty well captured the type of evolution that occurred in the 1980 storm and a good number of others that have produced sizable snowfalls over central and eastern parts of our state. Of course, the devil is in the details, and while that scenario describes a lot of our big snows, it also decribes a lot of systems that mainly produced rain or a mix of precipitation types because somewhat warmer air was involved - the temperature structure of the lower and middle atmosphere is crucial. Also, the distance of the surface low track from the coast, and the speed at which it will advance toward the northeast are very important. The storms that produce the most snow over the coastal plain tend to be a little farther offshore than those that produce the most snow in the Triangle area and points west. Sometimes the upper level trough that helps support the surface low will close into a slow moving cutoff that causes the entire system to linger, making the onset and end of heavy precipitation a difficult call.
Finally, all of that is in reference to the large scale (synoptic) pattern involved. There are usually fine scale features within that pattern that will tend to concentrate the really heavy snows into relatively narrow bands, often oriented northeast to southwest, so that a shift of a few tens of miles one direction or the other can make a major difference. For an interesting paper that looks at some composite features and characteristics of southeastern U.S. snowstorms, see