IT COMES DOWN TO A QUESTION OF LOVE...
When it comes to weather there has always been a love hate relationship between the northern and southern branches of the jet stream. Sometimes they mingle in a mellow way, other times they independently go their separate ways. And then, there are the times when they come together and love is in the air. That's when the sparks fly and its time to batten down the hatches and get out of the way.
A QUESTION OF LOVE
The issue that's comes to mind this weekend is the amount of love (interaction) that exists between these two branches of the jet...what we call phasing in the weather world. A few days ago models were all in for a healthy romance (an engagement of sorts) that would result in a fairly large wet storm for the upper Midwest with snow and rain all the way into Minnesota and Wisconsin. Now we've had a bit of a spat and at least for now the romance is off.
WHAT'S IT ALL MEAN
In a meteorological sense, this results in a weaker system with a more southerly track. My northern counties may see little if any precipitation at all as the rain/snow shield is suppressed southward. The other important change is that colder air is allowed to sink just far enough south to bring accumulating snow into play for the SE half of my area.
Before we get to the snow, here's what models are indicating for total precipitation with the sub-tropical (southern branch jet) being the dominant player. If there is one thing the southern branch is noted for, it's the ability to pull precipitation producing moisture northward when it's in play. You can also see the northern fringes if my area remain rain or snow free as high pressure sends dry air into that part of my region.
Precipitation in my area will likely start as rain Friday and then transition to snow Friday night before tapering off Saturday. The snow band is narrow but certainly could have some impacts if it develops as shown. Here's what the EURO is showing.
The GFS spares SE Iowa and WC Illinois with a warmer solution. That's possible but but this whole scenario looks shaky and low confidence to me. We should bet a much better handle on where this is headed in the next 24-36 HRS.