Colder air invades...potential Winter Storm next week

After a below normal October and above normal November, temps have, once again, dropped below normal numbers for our first week of December, and it doesn't appear the cold air is going anywhere anytime soon. In fact, long range models showing an even colder air mass heading our way for the end of next week. That cold air will help to stir up what appears to be the first significant snowfall of the season. Exactly where the snow will fall, and how much will fall is still way up in the air, but both the GFS and European models show this potent low, with the Euro being the stronger of the two. European models have great track records during winter months, and the GFS is coming into alignment with it. Some things in our favor...the cold air is here, and this system looks plenty cold. Surface temps will have a good week to cool off, so the snow shouldn't have a problem sticking. The models have also trended a bit north from where they were yesterday, bringing the low up close to Chicago, rather than across southern IL. If this system can nudge a bit further north and west, and track over Madison, then we would be in business. However, even now, accumulating snow looks possible. I think the kicker with this storm will be the timing of the very cold air mass behind it, with the low riding up the leading front. If the front moves slower, it should push the track further west. Faster movement means it would just shove the whole thing too far east, so there's still much to watch. Some other interesting facts about these systems...they are good wind makers, so even a little bit of snow, along with the wind can create very hazardous travel. Add a chill in the air, and you've got winter in Wisconsin. Second, snow ratios increase as the system progresses. The colder the temps are, the higher the ratio..so it could very easily start out around 13:1 snow:rain, and end up at 20-25:1 ratio. Higher snow ratios means it would take less liquid to accumulate snow, and the more powdery the snow is. (Example: .25 inches of liquid, 10:1 ratio would be 2.5 inches of snow...15:1 would be 3.75...25:1 would be 6.25 inches of snow...and so on.) Not great for snowman making, but simple to clear off a sidewalk or car. There are some downsides too, for those who like snow. Stronger systems can draw drier air into them, pretty much killing off any precip more quickly than expected. Also, if there's any strong/severe weather between here and the Gulf, then the potential is there for those storms to rob the moisture trying to make it up here. The good thing is that it looks like it will start far enough south that it will be able to draw the moisture down there and carry it north. Either way, this system will be closely watched, as many model runs are between now and Tuesday. In the shorter term, some accumulating snow is possible for southwest WI for the end of this weekend, mostly south of the I-90 corridor. COME ON SNOW!!