UPDATE: Here is the latest on what we are expecting Sunday at this point.
This storm is going to end up being more of a "now-casting" event simply because there are so many variables, and a degree or two is going to make a big difference.
This will start Sunday morning from south to north, so Rockbridge, Augusta, and Highland county will likely see snow first.
Then it will move northward. At this point we are looking for the changeover to sleet/freezing rain sometime after lunchtime.
There is still the question of how long it will sleet/freezing rain before the changeover to a cold rain.
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It's hard to believe we are eyeing a winter storm when it's almost 70 degrees outside, as of Thursday.
But that is just the roller coaster Mother Nature has planned for us.
Look at this temperature swing across the county. These are Thursday afternoon temperatures.
Notice between Dallas and Brownsville Texas, a difference of almost 50 degrees!
Between Nashville and Bristol Tennessee, there is a difference of 30 degrees.
That is quite the cold front, and the cold air mass that is heading our way.
The cooler air will move in by Saturday, although Saturday is generally looking to be a dry day.
As an area of high pressure moves overhead Saturday and Saturday night, that will shift our winds to the northeast. As this cold, Canadian high pumps in the cold air, that cold air becomes wedged between the mountains to the east and west. This is what we call a cold-air damming setup.
That cold air is heavier then warm wair (warm air rises) so the cold air gets wedged in the Valley.
This setup can typically produce a day or two of unusually cooler temperatures and clouds.
But in the winter, we have to closely watch this setup because when moisture moves up from the south, it runs into the cold air and then we have a wintry mix (or mess).
There are still many details that need to be hammered out.
But it looks like cold air is going to be in place not just at the ground, but thousands of feet up into the atmosphere creating a cold colum of air.
That means that our precipitation early Sunday morning will likely start as snow.
The change to ice comes when warm air, rises over the cold air at the ground. So you have a layer of warm air aloft, creating a melting of the snow, or plain rain.
That leads to sleet, and freezing rain once that precipitation hits the cold layer towards the ground.
We know that warm air, and above freezing temperatures, will move in but the question is, how quickly?
Generally with cold-air damming events, the cold air is in place a little longer then anticipated. So it will become an even bigger problem if the warmer air doesn't erode the cold until let's say 6pm Sunday night. That would lead to many hours of a wintry mess.
However if it warms just enough by 2pm, then the cold rain will melt away the snow and ice. It's still going to be a mess, but a cold rain is better than hours of snow, sleet, and freezing rain.
As the details are still being worked out, now is the time to just get ready. If you don't use your supplies this weekend, then you'll already be ahead for the next storm. We still have all winter.
Arthur Miller, Deputy Fire Marshall with the Harrisonburg Fire Depatrment said it very well. "We don't have to think back too far to remember a serious power outage with the storm that came through and knocked out power for a signifigant amount of time. If we remember those items that we needed then, that's a good place to start your list now for what you missed then, make sure you have it for this event."
He was referring to the Derecho of 2011 but that's a good place to start.
I would prepare to at least not be on the roads Sunday, power companies are closely monitoring the weather in the event of potential power outages. And V-DOT is very proactive about road preparations and having crews on standby before a storm hits. Just be prepared.