It is now a foregone conclusion that a substantial storm will affect most of Virginia between March 5-7, with the greatest impacts on March 6. As the old expression goes, “the devil is in the details.”
The storm will produce lots of precipitation, and it still appears mostly in the form of snow and rain (ice… not really much of an issue here).
Much of the numerical guidance (GFS, CMC, ECMWF) is in good agreement on the track and fundamentals of the storm. But the thermal fields still have a lot to be desired. In other words, who gets dumped on with snow?
One feature is the wind speed and direction about 10,000 feet up (700mb). When there is a broad and fast flow from the east or southeast through that part of the atmosphere, it tends to enhance precipitation (for my weather friends, I’m talking about a cut-off low at 700mb passing across North Carolina). All the guidance suggests that will be the case during the peak of this storm. But how strong will that feature be?
As much as I respect the ECMWF solution, there is something to be said about the 18z GFS snow depth forecast.
Admittedly, I am not a fan of simulations initiated without a full complement of upper-air data (i.e. 06z and 18z), but the pattern of snow depth here is telling, following a more classical climatological distribution of snow depth.
Taken at face value, it suggests only an inch or so across Southside Virginia, a few inches in Greater Lynchburg, but a rapid jump to a foot north and west toward Charlottesville and Roanoke. Again, it is not the specific numbers involved here, it is the pattern: rapid changes in snow depth from northwest to southeast across our part of Virginia.
The snow depth forecast for the same period for the ECMWF simulation (not shown for legal reasons), is much more coarse in its spatial pattern. However, it has been the most consistent of the simulations with the structure of this storm through this entire event.
The storm is coming onshore in the Pacific Northwest tonight. The data gathered over the next 24 hours (00z and 12z runs) should help the computer guidance better simulate the thermal structure of the storm. Better data should help provide a better forecast on those thremal fields… which are critical to how much snow actually ends up on the ground.
So while I am increasingly concerned about a 6″+ snow in Central Virginia, I’m not convinced yet that we end up with a foot of snow on the ground… yet. But the risk is certainly there. Lots of time still ahead of us.
I was at a wedding today, and an attendee asked me, “Are we really gonna get that storm this week?”
“I’m worried about it,” I told her.
“Well… I’ll believe it when I see it,” she quipped back.
I told her, “I understand. But if it means anything to you, I’m hitting the grocery store either tomorrow or Monday.”
Her face dropped.
At this time… these are my best guesses:
Greater Lynchburg: 3-6″
Southside Virginia: 2-4″
Roanoke and New River Valleys: 4-8″
To reiterate… these numbers will be adjusted in the coming 1-2 days. This thing will not start until Tuesday evening… and probably as some light rain before the cold air races in as the storm intensifies to our southeast.