When will it snow again?

Posted at 7:55 AM, Jan 22, 2013
and last updated 2013-01-22 09:09:53-05

RICHMOND, Va. (WTVR) – After our first snowfall of the season in Richmond (and for all of central Virginia) last Thursday, January 17, many of you are asking when we’ll see snow again. The Southeast snowstorm stretched from the Mississippi River to Delmarva Thursday, which you can see in this snowfall map below showing snow precipitation Thursday into early Friday morning:


With the coldest air-mass settling into the Mid-Atlantic in two years, we certainly have the cold weather set-up that hands down supports snowfall as the precipitation type reaching the ground…if it falls in the first place.

So what would it take to get snowfall this week? In this upper-level pattern, clipper systems (fast-moving upper-level disturbances riding along the jet stream that produce typically quick and relatively light snowfalls) are the first suspect. And we’ll have one of those upper-level disturbances swinging southeast over Virginia late Wednesday. Here’s what that disturbance looks like in the forecast data (I put a yellow X over us):


This disturbance will provide the energy necessary for snowfall, and the air-mass from the cloud-base to the ground will support only snow as the precipitation type.

However, dry air settling into our region today and tomorrow may hinder that precipitation surviving to the ground as it tries to fall through very dry air. With that factored in, any snowfall looks relatively light right now in central Virginia for overnight Wednesday into early Thursday morning. We’ll be tracking that developing and approaching system for its snow potential!

Let’s look ahead to the next system that may bring us winter weather Friday. A forecasting tool called “critical thicknesses” can serve as a quick guide to the type of air precipitation will be falling through. Anything north of these squiggly lines will be all snow as the entire column of air is below freezing from the cloud to the ground. However, it gets messy when you start taking slices of the atmosphere to search for warmer-than-freezing layers. Check out the critical thickness forecast from the GFS model for Friday mid-day:


The purple roughly indicates energy that can produce precipitation. And you can see, that is over us mid-day Friday as precipitation approaches from the west. By the time precipitation is overspreading all of Virginia Friday afternoon and evening, all of those critical thickness lines are in North Carolina. That means snow.

Let’s look at a forecast taking a vertical slice of the atmosphere, called a “forecast sounding.” This shows mid-day Friday, with all levels of the atmosphere to the ground to the left of the 0 Celsius blue slanted line (meaning, sub-freezing).

GFS forecast sounding

GFS forecast sounding

If this verifies, then we’d see accumulating snowfall Friday in Richmond and other parts of central Virginia. As the precipitation begins early Friday, there could be a winter mix (remember the critical thickness lines spread across Virginia?) as precipitation falls through alternating sub and above freezing layers of air (you can see a “warmer nose” indicated in the forecast sounding above, even though it remains to the left of the freezing line). Certainly by Friday evening as deeper, sub-freezing air invades all of Virginia, any continuing precipitation will be all snow, and end before sunrise Saturday, based on current forecast information.

But this atmospheric investigation we just went though is purely theoretical right now. It’s a computer forecast, trying to solve a puzzle days in advance, based on input data it registers now. This forecast will likely change in the coming days, but I’ve seen the “signal” for winter weather Friday for several days now. Any shift in the track of this system, or the profile of the air-mass over us, or on the moisture availability will impact the forecast.

We will provide updates on both of these opportunities for Winter weather online and on the CBS 6 News. My advice for right now is to keep this “heads up” tucked in the back of your mind for your end-of-week planning purposes. Just to be safe, I’m changing my hair-cut appointment for Friday to another day. Just in case, right?

Stay with CBS 6, we’ll keep you ahead of the storm.

Meteorologist Carrie Rose
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