There is a lot of buzz about snow potential in our area this weekend, but it would be smart at this point to temper your expectations. The slideshow below shows you where 3 forecast models are showing accumulating snow. Check the banner in the top right corner to see which model is which. One model shows virtually nothing for our area while another shows the heaviest snow in our southern communities again. None of these is necessarily right, but it's important to note how different they are.
When you see this much discrepancy between models a few days before a potential winter event, it's important to look deeper at what is causing them to show such different outcomes. That's what we will do today then look closer at the most likely scenario(s). This sequence of images pairs the GFS and Euro model output. The GFS is the American long-range model, and the Euro is the European forecast model.
The low pressure center that swings this moisture through the Ohio and Tennessee Valleys comes to us off the Rockies. It will then swing south of us before connecting with a coastal low in the Carolinas/north Georgia and swinging back into the Northeast. That's the very general pattern this system will take; the specific track is much more difficult and means the difference between snow and no snow for us. The Euro is taking the low farther south Saturday afternoon which positions it southwest of us. How far south is the key to how much snow our area gets Saturday. The farther south, the less snow for us.
By Sunday afternoon the positions are closer for the hand-off to the coastal low, but the temperatures tell the story. The Euro is slightly warmer so it presents a mixed precip solution while the GFS is a bit cooler and brings more snow. We will look more at this below, but this is where the threat of sleet comes into play for our southern communities. By Sunday evening the GFS is more progressive with the low already up in Virginia bringing us snow for a shorter amount of time. The Euro still has the low in North Carolina through the same time frame leaving snow in our area longer.
The forecast for the Ohio Valley depends completely on where the turn happens. Spots that are on the down-swing west of here or the up-swing east of here have a little bit of a more stable forecast because it's definitely diving south then definitely rising back north. If the system turns in Arkansas instead of Mississippi or in Alabama instead of South Carolina, our forecast changes significantly.
Like all good snow forecasters, though, you know our potential for snow is not solely determined by what happens down here near the ground. We need to look up through the full column of air to see what the atmosphere brings us. The slideshow of images above is from 2 AM Saturday to 6 PM Sunday. The circles will draw your attention to the things we discuss below:
2 AM Saturday (image 1): There is enough moisture in the middle levels to build snow flakes, shown in the top circle. In the lower/middle levels, though, there's a significant layer of dry air. The second circle shows an area roughly 150 mb deep with dry air. It would be tough to get snow in this scenario.
9 AM Saturday (image 2): The sounding is more saturated and temperatures are below freezing. This is the type of setup that could bring us some light snow.
11 PM Saturday (image 3): The sounding has dried out again. We are now dry enough in the middle levels to not really be growing snow, but any snow that does grow evaporates in the larger layer of dry air below before it reaches the ground.
6 PM Sunday (image 4): Drier air at the surface and in the region where we grow snowflakes will make it tough to see snow here.
While there are a few times that snow would be possible Saturday and Sunday, this doesn't look like a huge snowstorm with this much dry air still in place above our heads at different times through the weekend. Keep in mind these soundings (vertical profiles) are only generated for Louisville. This doesn't show you the different levels at play over Campbellsville or Seymour, but it does help paint the picture of this complicated forecast. Tune in to WDRB News tonight as we learn more about this system. It just moved onshore in the Pacific Northwest, so now our weather modeling and observation system can get a better look at it. Marc Weinberg and Rick Deluca will share the new data with you all night.