THE LATEST THOUGHTS ON SNOW...
The weather system that is expected to bring rain changing to snow to much of my local area remains on track for the period Friday into Saturday morning. Here are the latest odds on receiving an inch of snow.
There have been some changes in the snow totals due to slightly warmer thermal profiles. That means rain which initially develops Friday will be slower to transition to snow and thus reduces the potential for accumulations. Additionally, Thursday's exceptionally warm temperatures which soared in the 60s in spots has allowed warm ground and road temperatures that will melt some of the snow on impact. Look at these readings Thursday afternoon. That looks like April as opposed to mid December.
That said, winter weather advisories are in effect for 1-4" of snow in parts of central and SW IOWA. With time these will likely be extended into EC Iowa, NW Illinois, and the SE third of Wisconsin.
You can see the system is coming together on Thursday nights water vapor loop with moisture returning to the Midwest after a 12 day dry stretch.
As I mentioned above, initially there is plenty of mild air that will have to be scoured out to get the rain to go over to a sloppy wet snow. In my southeast counties, especially southeast of the Quad Cities that may not happen until Saturday morning towards the tail end of the storm. This part of my area will see a healthy rain event with little if any snow. Here's what models are indicating for total precipitation.
The 3k NAM
As far as snow is concerned, the heaviest band should run from Des Moines to near Cedar Rapids, on to Dubuque, and to near Madison. There is nothing harder than calling a storm where you need to figure the rain snow line as well as a transition from rain to snow. A few hours sooner or later can waste or add several inches of snow so this forecast as I indicated yesterday is low confidence and will need to be monitored right up to the end. I will show you the latest models but as I've been continually saying, these are not specific forecasts, just model guidance that shows trends that will eventually be used to formulate a forecast. I like the general positioning of the snow band indicating the primary swath NW of a line from Ottumwa to near or north of the Quad Cities northeast to De Kalb and the north side of Chicago, but I'm not at all confident in the amounts.
The 3k NAM
The 12k NAM
The GEM (Canadian)
A tough forecast to be sure. We're down to the nut now so Friday's data will be the calling card for what ultimately happens with this storm and its snow. Stand by for more and roll weather...TS