Weather! Weekend snow update

Here’s an update regarding my thoughts for this weekend. If you’re a fan of snow, the forecast is in your favor!

February 17, 2012; 7:19 PM • by Weather Dan

While I’m generally a severe weather fan more than I am a winter weather fun, there’s something that I enjoy about a good snow. I’m not sure why, but I enjoy snow once it’s on the ground. As for forecasting snow, that’s another story entirely.

I know this is easier said than done, but try to set aside whatever preconceptions you might have about the science of meteorology and weather forecasting for a moment.

Snow forecasts are hard, y’all. Harder than your typical forecast – there’s a lot of extra variables that one doesn’t normally have to take into account.

That said, here’s what I’m thinking with regards to this weekend’s event.

Rain will begin to ramp up Sunday morning around sunrise, heavy at times. The upper atmosphere begins to cool enough to support a changeover to snow in the afternoon, and it all wraps up in the wee hours of Monday morning. Total accumulations in the Richmond metro area will run somewhere around two inches, up to a maximum of four.

We’ve got quite a few things working against any higher snowfall totals. First off, we stay above freezing until after the rain starts Sunday morning. We’re going to be relying on the precipitation to be doing the bulk of the cooling at the beginning of the event, simply because there’s just not a lot of cold air in place already. The ground will take some time to cool below freezing as well, so unless we get a relatively intense band of snow at the outset, some snow is going to be lost to melting as it hits the surface as well.

As far as uncertainty goes, there are two big factors that could cut into – or improve – snowfall totals. The northern edge of this storm is going to have a very sharp snowfall gradient. Compared to the areas that see the most snow, locations only 50 miles north may see just half of that, or less. Thus, a jump southward by 75-100 miles will make a big difference in terms of snow, and we won’t know a lot about that until later Saturday. The other factor is moisture. The trend lately, and not just with this storm, is that models have generally been overdoing the precipitation amounts, and I’ve found it’s rare that we ever actually get what a model forecasts in terms of snow accumulation. Taking those snowfall data verbatim is just asking for a forecast to bust.

That said, there’s still quite a bit of bust potential in this forecast in both directions. If we don’t get enough cold air for the rain to switch to snow in the afternoon – especially if we don’t get a good heavy snow band to mix in, then that changeover becomes delayed and we lose some of the snowfall to rain. If the storm tracks too far to the south, or we don’t even get enough precipitation to match my estimates, then the snowfall totals will go down further, too.

The opposite could happen as well – if we get heavier bands of snow and we change from rain to snow earlier in the day, then naturally accumulations will go up; same with the other factors I’ve talked about. They all depend on processes that take place over smaller areas than can really be well-handled by many of the models, so there’s still some speculation in all of this. However, of the three scenarios (my forecast, lower amounts, or higher amounts), this last one is the least likely.

If you’ve got travel concerns this weekend, areas north and west of Richmond, especially along the eastern Blue Ridge from Charlottesville westward into the Shenandoah Valley, are going to be looking at quite a bit more snow. I’d recommend keeping an eye on the weather and road conditions in that area before deciding to venture in that direction on Sunday.

I’ll put together another update later Saturday evening looking at the latest situation, and let you know of any significant changes.

February 17, 2012 7:19 PM 2