Hope you all enjoyed a fabulous mid-week of sunshine. Get the most of the burgeoning warmth too, because come Friday there's another set of big changes on the way.
HPC - Surface Map - Thursday Evening
On the surface, it looks like another set-up we had on November 1st and 17th (those two big wind-storms). It should be apparent however, that what we're dealing with in this case is a rather weak area of low pressure smushed between two strong areas of high pressure. The other two storms grew to around 980mb by the time it hit the UP of Michigan... This one isn't even lower than 1020mb (big difference).
Regardless, it's still a cold front, so we'll still experience a temperature crash when it comes through-- even if it's because of the strength of the high rather than what the low is going to pull down.
It's more of a gradual event, rather than a sharp contrast we had with those other two. Track the solid black line, representing the 0C like at the 850mb level (5,000ft up). From Friday morning to Saturday afternoon it traverses the Ohio Valley and cuts through the tri-state. This will bring us from about the 60-degree mark Thursday down to the 30s on Sunday (the temperatures will continue to fall from here). On this image Saturday afternoon, this is when rain will be finishing as snowflakes for the higher elevations that manage to hold onto the precipitation as those 850 numbers drop below -2C. But, this isn't the end of the opportunity for snow. Here's the scene by Sunday:
We've got a strong windflow between Lake Erie and Michigan. In addition (on the right-hand map) the GFS is showing temperatures at the 850mb level all the way down to about -15C. That's about the coldest we've seen this year. Keep in mind that the water temperature of Lake Erie is 46F (+7C). This makes a temperature difference of more than 20 degrees celsius (nearly 40F) across just 5,000 feet of vertical elevation above the lake surface. That, my friends, is some unstable air. The typical temperature threshold for lake-effect snow is a differential of about 13C, so we're beyond that. Even though the GFS is only showing sparse coverage of precipitation on Sunday morning, I'd probably pencil in more, even if it doesn't amount to much. I would expect accumulations where-ever the wind streamlines align from the Great Lakes themselves to the elevated locations (which can wring out more moisture just by terrain effects alone). Looks like the Canaan Valley and northern WV mountains are in line for some. And Sunday travelers would be wise to figure on some flying flakes along I-68.
...But even this is not the last of the snow opportunities this coming week...
Welcome to what looks to be our first southern-track storm system of the season! Just in time too (we've been talking about things like this on our winter weather preview) blog posts. The NAO is going down, but not quite negative by then, so we'll have to see just how much cold air we can wrap around the back of this system. Nevertheless, the 540thickness line (as indicated by the red dashed line on the Euro map) is waltzing back into the tri-state. It's a set-up that always bears watching, as there's a lot of moisture to work with in these storms (Gulf + Atlantic).
A White Thanksgiving perhaps? (Though I just said it first, you'd be silly to get your hopes up just yet). ;-)
Have a great day everyone!