Round 3 of overrunning moisture/cold air wedge commences late Monday night/early Tuesday. A strong low pressure system (again) tracks well northwest of us, spreading a blizzard (again) in the central/southern Plains, while pulling Gulf of Mexico moisture (again) northeastward over colder air at the surface (again) pushed southward by high pressure (again) against the Appalachians (again). The major difference in this system and those of last Tuesday and Friday is that there will be a lot more moisture thrown over us – total rainfall may be near an inch by late Tuesday. How much of that is freezing or frozen precipitation at the front end is the sticking point in forecasts, and one that will (again) vary greatly by location and elevation in Southwest Virginia. Working against widespread frozen precipitation will be that we will likely be coming off highs that could top 50 on Monday, and that the level of warm air being pulled northward aloft with the moisture is much stronger than in two previous episodes, largely because the low will be tracking just a little closer to us. Working for frozen precipitation is that the wedge of below-freezing air has been modeled consistently poking down the Interstate 81 corridor for a few hours late Monday and early Tuesday (behind the blue line on the 0Z NAM model at left). Best idea now is a quick transition from sleet and/or snow (mostly less than 1 inch accumulation) to rain/freezing rain, with higher elevations along the Blue Ridge south of Roanoke and locations north and west of Roanoke generally having a better chance of staying below freezing longer. Winter weather advisories will probably be issued Monday for some or all of our regiond (UPDATE 8:30 AM: They have been, with more expected). Most locations should be above freezing by late morning on Tuesday, but there could be some pockets that linger below freezing longer, raising the specter of some locations getting heavy ice, with rain amounts expected to be much higher than the two systems last week.
This system does look to be the end of the train on this particular storm track and overrunning/wedge setup. An unseasonably cold pattern is due to take hold for much of the southern and eastern U.S. by late week, with some periodic chances of light snow, and frequent upslope snow showers and squalls as northwest winds blow over the mountains. The cold air pattern will likely last a week or more, so that still being more than 10 days out from now, whether there will be a larger winter storm before it breaks is too far out to be very clear.
(Chance of 1 inch of snow this week, rated from 0 to 10)
Roanoke – 4 snowflakes ****
Blacksburg — 6 snowflakes ******
Outlook: The third in a series of similar systems pushes in late Monday and early Tuesday, as some moisture will likely catch up to cold air being pushed down the east side of the mountains by high pressure. A mix of snow, sleet and freezing rain is possible, changing to all rain by midday Tuesday or so across the region. Late in the week, a windy, unseasonably cold air mass will welcome us to March, the start of meteorological spring. There may be a couple of weak disturbances squirting through that could produce light snow, and also the persistent northwest winds squeezing out typical snow showers and squalls as they blow up and over the mountains. I’m not sure Blacksburg will get an inch of snow on any individual day this week, but adding up minor amounts from Tuesday morning and later in the week may add to an inch, so I’m giving six snowflakes. Unless it all happens Tuesday morning, Roanoke probably won’t compile an inch in all that, so I’m going with only four for the Star City.
Looking back: Blacksburg did it again, barely squeaking out an inch (1.4 total, including 1.1 on Friday) to tag me with a sixth straight loss on the snow meter, as I picked only four flakes out of 10. However, Roanoke only got 0.1 inch, so my less than five flakes pick (four) was good for a win there, with far less than an inch of snowfall. I’ve clinched a winning record for the season at Roanoke with three weeks left. I’ll have to win them all to do the same at Blacksburg.
Current records: 8-4 for Roanoke; 5-7 for Blacksburg.