upper level flow will change from a northwesterly to more of a zonal. A baroclinic zone will be setting up to our south. This will allow some warm air advection to filter in with periodic chances of snow from Thursday through Saturday. This shortwave has a critical track which will be very important in regards to the winter precipitation type that we receive here in LAF. While models are showing the 540 line north of the area, what is important to note is the amount of precip that will be falling. Some models are hinting that the vertical profile temps will be near or at freezing. This would occur if the precipitation band associated with this shortwave ends up being moderate to possibly heavy at times. Current Thinking is that Snow may begin with this system but as it moves closer to our area, with warmer air moving in, we will see some sleet possibly mixing in or changing completely over. As mentioned earlier, what will be crucial will be how heavy the precipitation will be which will allow some evaportative cooling to take place and cool off the layer to the point that all snow could fall for most of the event. This would significantly increase snowfall accumulation in excess of 4 inches. If the precipitation isn't as heavy when it moves in, expect snow changing to sleet and even some freezing rain or drizzle at the end before a high pressure moves in and drops temperatures off into the upper teens to low 20's for highs Sunday.
The second and more potent storm has to be monitored very closely as well for late Tuesday and most of Wednesday. Cyclogenesis will be taking place in Eastern Texas and then moving to the northeast. A surface high pressure will be located in the northern plains and its position will be very important as well as how fast this cyclone deepens. If the high pressure is closer to us or if the storm doesn't deepen as fast, the storm will end up moving just to the south of us with southern indiana getting in on all the action while we may be scraped or spared from the storm and allow all the snow removal crews to sleep in for the first time in quite a while.
Here is the 0z run which shows that the secondary systems snowfall is mostly over texas through the Tennessee river valley. The surface low doesn't deepen as fast and the high pressure is situated closer to the Great Lakes.
the 12z however brings us a much better chance for some good old fun heavy snow. the surface low deepens quicker and the high pressure is situated further west allowing the precip to move closer towards our area. Keep in mind though that we are still seven days out from this event and models will tend to fluctuate from a little bit to quite a lot.