THU 9:30PM - There will be two main periods of snow accumulation. Long update.
- FRI 2am - FRI noon. Generally an inch or less with a couple spots over that in southern WI.
- A break with scattered to light showery activity. Effectively nothing with temperatures warming close to or above freezing south.
- FRI 6PM to SAT 6AMish - The better chance for accumulation. 1-3", perhaps more south. Lets talk about it.
The challenges starting now through the end of the event at SAT 6AM:
- Temperatures near or above freezing contributing to melt on contact or possible change over to mix.
- Gaps between accumulation events that allows for clean up, rising temps, compression, and reduction of overall impact. Same as the last two days.
- Spiraling, becoming stationary band of snow Friday night into Saturday over southern WI that could result in much higher snow totals in spots.
Here's what I see:
18Z GFS vs. 00 NSSL(NAM/EC similar) with bulk coming Friday night into Saturday AM
- Comparing model performance to today (Thursday). All models in general agreement. Were they disagreed was Illinois and GFS won. It handled that warmer environment the best while NAM was too much(w/ snow). NAM/GFS generally did good across Wisconsin and upper Michigan where temps were less of an issue.
- FOR FRI thru SAT however, VAST differences between GFS and NAM/EC across southern WI and Illinois. GFS is actually the lone outlier at this stage. Most met's will need to choose between GFS no snow and NAM/EC lots of snow. Conservatism, hot hand in the GFS, and natural disposition. Think GFS less snow gets the nod. Some just won't make a decision or water it down. I think this could be a totally different situation Friday night into Saturday and need to avoid getting suckered by the GFS. Day 1 = right . Day 2 = right. Day 3 = totally wrong. Nothing is impossible. Or maybe somewhere in between?
The NAM/EC have strong signals for snow and I'd be crazy to look away. I wouldn't call it heavy; but I will call it solid steady (typically helps if it's heavy snow for accumulation). Solid forcing up through the growth zone Fri night into Sat AM with below freezing profiles all but at the surface. Favorable timing for accumulation overnight even if temps are slightly above freezing. All signs point towards snow. I've seen similar situations with a storm parked over the same region where forecasts busts towards heavy snow. So that's what I'm preparing for.
I would regard the NAM/EC and basically all short range models as worst case scenario. In such situation I would add a 3-6" storm total zone where I have the target now. 2-5" Friday night into Saturday AM. This might be the grand finale of the 3 day snow event. (see map)
Ultimately I've decided to wait until Friday morning to make a call. It's late. If I went 3-6" now we would stick out too much - people not reading this probably won't understand - and I don't want to worry about that overnight. There is more value in waiting probably. If the NAM/EC are right that will become evident and it's more important to take action than be first to break the cold war like silence. This might put my forecast at a disadvantage since the NWS folks are early worms and may push out an advisory before I wake up. That's okay. At least you know what's going on. Full day to react tomorrow
Talk to you soon!