ABOUT POSSIBLE MINOR SNOW EVENT VA MD DEL southern WV JAN 31-FEB 3
There is no doubt that this winter has been an extreme disappointment for those who like cold and snow across much of the eastern CONUS but especially in the Middle Atlantic and the Tennessee Valley regions. As a general rule, La Nina Winters are not big snow winters in southern New England, the Middle Atlantic, or the Upper South. But even in the domain of La Nina winters, the winter of 2022–23 appears to be at the extreme end of all La Nina Winters for these regions. Perhaps nothing epitomizes the lack of snow and the frustration regarding the overall pattern than with this upcoming event from January 31 through February 3rd.
As we have mentioned many times, the overall La Nina jet stream pattern for the winter season is one that features a consistent bias that is hostile to the development of the big East Coast snowstorms and Nor’easters. That being said, there IS a way that moderate snowfall can occur in the Middle Atlantic, southern New England and the Tennessee Valley regions during La Nina winters. It has to do with the process known as “overrunning”. In this kind of precipitation event, a cold front drive southward then stalls across Tennessee and North Carolina while cold air builds down from the Great Lakes, northern New England, into the Middle Atlantic and Tennessee Valley. This is often followed by a development of a weak area of LOW pressure on the front which helps drive moisture into the cold air north of the stalled front and this can produce several inches of snow in these regions.
At first glance, the mid-week winter weather threat for the Middle Atlantic and the Tennessee Valley regions would seem to be a classic winter season overrunning event. A strong cold front is going to move through the eastern CONUS on January 30–31 with rain and showers.
This front is going to stall in a more or less west — east direction across the Gulf coast states as the cold air comes southward from the Great Lakes and northern New England. This would seem to set up a classic winter overrunning event which produces ice and snow north of the cold front mainly in Virginia, northern Tennessee, the southern portions of West Virginia. southern Maryland and the Delmarva. But in order for this kind of overrunning event (snow/ ice) to develop, it requires that the cold air stay in place north of the cold front when the precipitation comes north.
However, this upcoming potential winter weather event for the Middle Atlantic and the Tennessee Valley regions appears to be out of phase.
By that we mean to say that when the cold air is in place, the precipitation is staying to the south. So no precipitation actually falls north of the cold front (now snow and ice). Later on in the week, when the precipitation in the Gulf Coast and the Southeast regions decides to come north into the cold air, the cold air retreats so the precipitation type stays as rain.
This image shows the cold front coming in as it crosses the Ohio Valley and moves into the Delta regions. By Monday night /early Tuesday morning the cold front is pushing its way through New England into Virginia and into Tennessee. There are a few areas of light to moderate rain developing in Arkansas and Mississippi, with sleet and light snow in northeast Arkansas into northwest Tennessee and southwest Kentucky.
By late on January 31 (see below) the rain snow line which is depicted here by the thick black line can be seen situated across central Virginia in a more or less west — east direction. But even here, temperatures at the surface are still too warm with readings on Tuesday afternoon around 40° in Richmond, 44° in Roanoke and Lynchburg, and in the mid and upper 30s from Fredericksburg northward into Maryland and across the Delmarva.
However, the cold air continues to sink Southward during the night of January 31 into the morning of February 1. We can see this by looking at the thick black line which is now reached the North Carolina Virginia border by the morning of February 1 Temperatures have dropped several degrees and could support wet snow but at this point all the precipitation is south of the North Carolina Virginia border. When the precipitation begins to move north into the cold air on the evening of February 1 there could be a period of light snow across the southern half of Virginia, but surface temperatures are marginal at best. All of the significant cold air is still north of Washington DC.
February 2nd looks fairly quiet but there is a lot of rain developing in the Deep South. A new LOW pressure area forms in Georgia and begins to move /drive the moisture northward but as it does so it pushes the rain snow line back into Washington DC and the northern Shenandoah valley. Thus, any precipitation that comes up from the Carolinas into Virginia is rain. And where the air is cold enough to support snow, the precipitation doesn’t reach and it stays dry across the Delmarva, central and northern, Virginia, West Virginia, northern Tennessee, or southeast Kentucky.
Of course, we can look at some of the other models but they are looking even less optimistic for any kind of snowfall in any portion of Virginia or the Carolinas, Maryland, or Delaware. The European model has the cold air coming in so strongly on February 2–3 that the southern LOW is driven well to the South so that the rain doesn’t even make it as far north as Charlotte, Raleigh, or Elizabeth City, NC In other words when the really cold air finally arrives, all the precipitation is suppressed well to the South.
Based upon the most optimistic forecast and data that I can find it looks like there may be a period of wet snow late on January 31 covering northern Virginia and the central Delmarva. Essentially from Interstate 66 in Washington DC over to Dover southward with the southern snow line running from Charlottesville to Fredericksburg to St Mary’s to Salisbury Maryland. There may be a rain snow mix and even if it is all snow, it won’t be heavy snow and it might not stick to anything except for the normally colder surfaces for a few hours.
There may be a second period of wet snow or snow or rain mixed across the southern third of Virginia from Roanoke and Lynchburg to Richmond and Williamsburg as far south as the Virginia North Carolina border On the afternoon and evening hours of February 1st Again this may be a rain snow mix that might not even stick to anything or if it accumulates or sticks at all to any surfaces it would be your normally colder services such as trees bushes porches car tops that sort of thing
One final note it is quite ***possible** we COULD go through the entire month of February without accumulating snow in the Middle Atlantic region. Once this cold shot moves through next weekend there is little hint of any cold air returning for the rest of February into the Mid Atlantic or the entire Eastern US.