This Year's Big Storm
This one has been in the works according to some weather models for about a week now, especially the European. The European seems to have been doing well this year tracking low pressure centers (not perfect) from early out. It was also one of the first to bring Hurricane Sandy onshore near New Jersey.
Now that we are closer, every model agrees that we will see some wintry weather... how much is more of a question.
This is where we sit now at the surface:
Our low pressure center is working it's way through Kentucky and Tennessee. However, more importantly the upper level support behind it is following right in line to intensify the storm. This picture shows the 500 mb vorticity.
A simple way to think of vorticity is energy aloft, or energy higher up in the atmosphere. This is a perfect set up of “positive vorticity advection” to help the storm. Simply put, that means energy at higher levels of the atmosphere is moving toward an area of surface low pressure, and because of this, the low will deepen (get stronger).
As these two get stacked up, the storm will strengthen then ultimately transfer it's energy over to the coast and continue to strengthen with some warm Gulf Stream waters.
This low pressure system is tracking and intensifying in a sort of sweet spot for the Valley. With the coastal low intensifying between the Outer Banks and Virginia Beach, we often get high amounts of snow. The other time we often see our highest snow totals is when that low starts more to our south and tracks north (think Winter '09 - '10).
This sets us up for a lot of upward motion in the atmosphere. Upward vertical motion is key to see heavy rain or snow. In this case, we will likely see both. It will also pull continued moisture into the Commonwealth from the Atlantic Ocean.
Other than some very isolated activity through the day, we can expect the heavier precipitation to start late this afternoon and this evening as a rain and rain/snow mix, especially likely after dinnertime. As the precipitation itself cools the atmosphere and colder northerly air is pulled in around the low, we will watch this change over to all snow.
I think the majority of the area can expect to change over to all snow around midnight. It will be heavy at times and visibility will be reduced. This will be a heavy wet snow making it tough also for trees limbs and power lines.
Here is the latest Snowfall Forecast Map:
Assuming you will see anywhere from 8"-14" across our area is likely a safe bet. There will also likely be a bulls eye with this system. Where that bulls eye will land is still somewhat up in the air. I'm pin pointing the Northern Valley to get the brunt of this at this point. Also, as usual, expect higher ridge tops to collect more snow, because accumulation will start earlier. At lower elevations, snow will continue to melt early on.
Wednesday will be much windier meaning power outages are more likely, and driving in the snow will be even more dangerous. It is recommended that you stay off the roads if possible starting late tonight through Wednesday. If you MUST travel be sure to give yourself plenty of time, have an emergency kit in your car, and let others know where you are going and when you should arrive.
Stay safe and have fun in our biggest snow in two years!