UPDATE 3 PM: Snow — mixed with sleet and rain in spots — has been rapidly spreading up the Blue Ridge through the New River and Roanoke valleys this afternoon at the leading edge of a large area of precipitation. Slushy accumulations are already occurring in many spots. Warmer air aloft may eventually change snow over to rain/sleet from the south … we’ll just have to see if, and when, that happens. Paved roads will not be fast to collect snow, but watch out for slushy spots, especially if this continues into evening. END UPDATE
UPDATE 8 AM: Some overnight forecast models suggest a burst of sleet and/or snow to be a little more likely later today or early tonight, especially along the higher elevations of the Blue Ridge south of Roanoke, and into some of the New River Valley. Do not be surprised anywhere in Southwest Virginia today to see wet snow or sleet for a period of time near or shortly after the onset of precipitation. END UPDATE
Wednesday’s Weather Journal column in The Roanoke Times looked back at the wild contrast in March weather Southwest Virginia had between the sometimes-summerlike warmth of 2012 and the late-hanging-on winter of 2013. Included is a graphic comparing some numbers between the two Marches (a technical problem has blitzed some numbers on the “March Days in Roanoke” part of the graphic — lines should say “at or above” 80, 70 and 60, from top to bottom, then “at or below 32″). It was the widest disparity between March average temperatures in consecutive years — or any month, year to year — since 1960 and 1961, when Blacksburg went from 27.7 degrees to 47.7 degrees and Roanoke went from 34.0 to 51.1. Another unusual feature about March 2013 that I didn’t mention in this column is Roanoke getting nearly 40 percent more measurable snowfall than Blacksburg in a calendar month. Nothing like that has ever happened before in my 14 years here, I am sure. Spotty snowfall records at both sites would probably preclude tracking how rare that is, historically.
I am declaring Thursday night’s cold rain in Southwest Virginia as winter’s belated last gasp. There may be enough evaporational cooling — precipitation falling into dry air aloft, taking heat from the atmosphere as the moisture evaporates — for there to be some sleet or maybe even wet snowflakes on Thursday afternoon and evening, especially at 3,000-foot-plus elevations. Don’t be stunned, even in the Roanoke Valley, if you see some bouncy icy bits or even an oddly-plopping slushy rain drop. While the storm track along the Gulf and up the East Coast would be almost textbook for a significant to major winter storm in a colder time of year (or even a more strongly blocked pattern like 2 weeks ago), the placement of high pressure (due east, offshore) is not the most conducive for holding cold air in place, even if it were mid-winter. Most likely, all precipitation goes to rain after a couple of hours — but we’ll keep half an eye out for any pockets that can stay frozen longer, especially at higher elevations. Also, later forecast model runs have tended to show the storm a bit weaker and farther east than we were expecting a couple of days ago, so it’s looking like a little bit less of a soaker than we were thinking. Probably more like 1/2 to 3/4 an inch of rain rather than an inch-plus in most places. Temperatures may not make 50 on Thursday and then will likely fall into the mid and upper 30s as it is raining, so this will be every bit a cold rain situation more akin to something that would frustrate snow lovers in January rather than April. Most of the rain should be done by midday Friday, with just a few lingering showers into the afternoon and early evening.
After this storm system goes by, the full-scale pattern change will be under way. We zoom into the 60s/some low 70s areawide by Sunday (weather looks great for racing at Martinsville Speedway), and likely more widespread 70s into early to mid next week. Southwesterly flow will bring occasional bouts of showers in the new pattern — I think a lot of the heavier rain and storms will be focused in the Mississippi and Ohio river valleys to our west, but perhaps some occasional April showers (and a few storms) to bring May flowers the next few weeks. The first shot at this may occur Tuesday and Wednesday.