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Another round of snow?

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Posted at 10:09 AM, Jan 18, 2016
and last updated 2016-01-18 13:42:44-05

After a little taste of snow on Sunday, we could be looking at a round two this week. This week’s snow chance has the potential to be bigger… The key word there is “potential” (not a guarantee).

A note before I get started… Today is Monday, we are expecting this event Friday/Saturday. Obviously, that is several days away. As we get new forecast information, expect the forecast to be fine tuned and changed as need be over the next several days.

The Set UpFronts_FriFronts_ThuFronts_Sat

An area of low pressure will move into the Mid-West by Thursday and begin to move east into the Southeast. In the first image you can see it on the Texas/Oklahoma border. By Friday this low will make a slight NE turn and head into the Mid-Atlantic. On image two you can see it moving into Georgia. By Saturday the low is off of the VA/NC coast and moving up toward the New England states. The counter clockwise flow around the area of low pressure will bring moisture up from the Gulf and eventually the Atlantic. At the same time another push of cold air will slide SE from the Great Lakes. You know the equation… Moisture + Cold = Snow. The biggest question for us will be, how far south and east will that cold air extend. (Surface maps from NOAA)

The Timing

As of now, it looks like the low will start to bring precipitation into Eastern NC and VA late Thursday night (after midnight) and early Friday morning. Precipitation will stay with us Friday, Friday night, Saturday, and taper off Saturday night.

Rain vs SnowSnow_SatSnow_FriSnow_Sun

As we typically see in this region, a few degrees can make a HUGE difference. The rain/snow line will be the key to this forecast. If the line shifts west/north, we see more rain. If the line shifts east/south, we see more snow. As of now, the rain/snow line (while moving) spends most of the Friday/Saturday time frame between Hampton Roads and Central VA. You can see the “bulls eye” of snow expected to our west and north, over northern VA and MD. Note: A shift in the rain/snow line could dramatically change the look of those maps. (Maps from NWS/NOAA)

How much?

It’s always the first question people ask when I mention the “S word”. But… It’s often the most difficult thing to predict.

A little learning footnote first… When it comes to rain and snow totals, they typically have a 10 to 1 ratio. Yes, that ratio varies, sometimes in a very wide range, but usually 10:1 is a pretty good ballpark. So 1″ of rain would fall as about 10″ of snow.QPF7day

This map is what we call a QPF (Quantitative Precipitation Forecast). It gives us an idea of how much rainfall we can expect in a particular time frame. This is what it looks like for the next 7 days. Notice that most of eastern VA and NC is in the 1.5″ to 2.5″ range. (Map from NOAA)

So when asked, “How much snow will we get?” I can’t give you a reliable answer this far out. Here’s why…

If (and IF is the key word) that rain/snow line stays to our NW, we see two days with all rain. So “How much snow will we get?” Zero

If (and IF is the key word) the rain/snow line slides all the way to to our SE, we see two days with all snow. So “How much snow will we get?” Based on the QPF and our broad brush 10:1 ratio… 15″ to 25″!!!

Do I think we will see all rain, No. Do I think we will see all snow, No. But you can see the wide range of possibility.

Bottom Line

This system is still several days away. (That low is literally along the West Coast right now, so it has an entire continent to cross.) If the current forecast holds we will likely see major snow accumulations (double digits) in parts of Virginia. As of now, it looks like those big totals would stay to our NW. A change in just a few degrees could bring that “bulls eye” closer to home for us.

Questions…?

If you have made it this far then I should have answered most questions, at least the ones that can be answered at this time. If you think of something that I have missed, feel free to post or send me a message on  Facebook.