Today and Saturday will continue to be below normal in temperature, but highs in the 40s today and maybe even some low-mid 50s on Saturday will feel a little milder after Thursday’s almost ridiculous early spring cold afternoon. There will be some more clouds on Saturday … and perhaps a small chance of some rain/snow showers, especially south of Roanoke, though most of it will stay south of us.
Looking ahead to the Palm Sunday storm, forecasters and forecast models are differing somewhat on whether the front side of Sunday’s storm — during the day — is where we might see significant snowfall, or whether it will wrap around the back side on Sunday night. Count me now as standing heavily on the front-side side of this discussion. In my opinion, the best chance at seeing a few inches of snow from the Roanoke and New River valleys south and west will lie with precipitation bands moving into the banked cold air along and east of the Appalachians on the front side of low pressure Sunday morning into the afternoon (the 12Z NAM depiction of precipitation as it would appear on radar early Sunday afternoon is at left). This is where it appears there will be the most moisture, which, falling through colder, drier aloft, will enhance evaporational cooling. Also, it could provide snowfall rates sufficient to pile up on a ground that, despite recent cold weather, will still be holding some warmth from the higher sun angle and longer hours of sun of early spring. The thing about the front side, though, is that is possible warmer air aloft could be pulled in, changing precipitation to sleet and rain and shutting off the snow rather suddenly. Depending on how this battle between warm-air advection and cold-air wedging transpires, a sharp rain/snow line may develop somewhere across or near our region, where locations to the north or northeast stay in snow hours longer than those to the south. Wherever snow falls, higher elevations are likely to see it earlier, and also likely to collect deeper accumulations than lower ones.
I’m not too confident the coastal low will develop early enough or strongly enough to be a major factor for us, and don’t expect more than patchy light precipitation wrapping around on Sunday night and early Monday. But be aware that some models have shown the coastal low, teamed with an upper-level impulse, adding another round of snow late Sunday and early Monday .
This is another in a long series of murky winter weather situations. I think most of us see some period of wet snowflakes, but this could easily slide toward mostly rain/sleet mix or toward a heavier snow with only subtle atmospheric differences.
Here are my probabilities of specific snow accumulation levels at Roanoke and Blacksburg:
At least 1 inch: 60 percent; 4 inches, 40 percent; 6 inches, 20 percent; 8 inches, 10 percent.
Chances are less to the south and greater to the north. Maybe add 10 percent for each 20 miles north, subtract for each 20 miles south — excluding 2,500+ Blue Ridge elevations south of Roanoke that , as typical, will have better chances of accumulating snow.