Historically, Many Coastal Storms Have Surprised Us at the Last Minute
UPDATE: I now expect a solid 3-6" of snow for Franklin County and SML Friday night into Saturday morning, ending around noon Saturday. Roanoke will see 2-5", with Martinsville and Danville getting 4-10".
First things first: there is still plenty of time for whatever forecast you are hearing to change before Saturday. Even as late as Friday night, the forecast may change. So keep an eye on it. That said, right now, I'm not going to be forecasting a huge winter storm for southwest and west centeral Virginia this weekend. It just isn't in the cards. At least right now. However, many areas do have a good shot at accumulating snow starting on Thursday and lasting on and off into Saturday.
The first system Thursday into early Friday will likely give the NRV and Highlands a solid coating of snow. Some areas could see 1-2" from Thursday afternoon into Friday morning. The Roanoke Valley, Lynchburg and Southside will see streaks of snow, hit or miss. Where the bands of snow set up, a coating of snow could make roads slick by the end of the day Thursday and for the morning communte Friday.
Then on Friday night into Saturday, what looks to be a fairly disorganized storm system will be moving from the gulf to the east coast. Models show this system moving very fast and not making any progress up the Virginia coast, instead moving more east off the coast of North Carolina during the day. Right now it looks like mainly light snow developing Friday night across the NRV, developing east into Southside by Saturday morning. A general 1-4" is expected, mainly south of Roanoke. The northern edge of the snow may still give Roanoke and Lynchburg a solid coating, however. The Highlands will probably miss the second event. Areas from Danville to South Boston may see closer to 3-4".
Keep in mind, I'm not locking our these snow totals, however. Areas just to our south, from Charlotte to Raleigh, may see the most snow from the storm early Saturday. Raleigh may end up with 3-8". Keep in mind, a small tug to the NW, and our forecast will change quite a bit.
Just for kicks, let's travel back in time to Christmas Day, 2010. Similar to this week, a mix of excitement and dread had been building as meteorologists watched a possible winter weather event developing near the east coast. Like this week, various models had all kinds of back and forth solutions, going from the chance of a strong winter storm to no snow at all. A low developing off the Carolina coast was forecast to travel too far offshore.
Then, just when everyone had all but given up on any snow, the Christmas eve models started to show a westward trend with the moisture. Still, the snow was forecast to be east of our area, from Richmond to Virginia Beach.
Christmas Day, 2010, many woke up to a light, but steady snow. Accumulations ranged from 2-4" for many in our local area. Snow totals for the 2010 event are shown below.
A similar event surprised us in 2014 with surprise snow falling south of Lynchburg into Chatham, Southside, SW into the foothills of Franklin and Henry County.
Why do models sometimes miss these coastal storms?
One reason may be the natural temperature contrast that's created from land-sea interaction. While land cools quickly after a cold air outbreak, water takes much longer to cool. And don't forget, there's a warm gulf stream that sits right off the eastern seaboard. Storms like to form and then track where the temperatures contrast the most. Obviously not every storm rides the coast, but if the right conditions are nearby, the natural gradient can influence the path of the storm.
Models can also overlook something known as latent heat release over the ocean. As a storm system develops showers and even storms off the coast, the formation of clouds and rain (condensation) releases latent heat back into the atmosphere. The heat that's added to the environment off the coast further increases the temperature contrast near the coast, and can alter the path of the low.
Both of these factors CAN'T overcome the fact that the dynamics - the heart of the storm - will tend to keep both storms weaker and faster. But they can alter the storm's movement just a little. And in this case, a little movement will make all the difference in the world.
So while a general light snow event is what appears most likely Thursday-Saturday, remember how quickly things have changed for us in the past.
I'll be sure to update you if things change. Stay tuned!