TO SNOW OR NOT TO SNOW...
That big temperature see saw we've been on the past couple of weeks has leveled off recently and the coming 7 days a fairly consistent brand of December readings are expected. The EURO indicated highs in the mid 30s to low 40s through the coming weekend. That's right where we should be in terms of norms.
One thing that hasn't changed is the dry pattern that's gripped much of the region the past 3 months. Here in Dubuque, if we don't have measurable precipitation Tuesday (which looks likely), that will extend our dry streak to 20 consecutive days. Since September 1st just 5.17 inches has fallen. The odd thing is that 3.42 inches of that occurred in an 8 day period November 4-11th. The other 89 days of the 97 day period totaled just 1.75 inches. In the graphic below you can see numerous streaks of 7-14 days with no rain. Pretty boring stuff for a meteorologist.
Here's the precip. departures since September 1st. Deficits of 2-5 inches are common north of I-80.
These are the actual totals since September 1st thanks to the Iowa Mesonet. NW Iowa has been exceptionally dry with totals there as low as 2.19 inches.
Some parts of NW Iowa are in extreme to exceptional drought. Abnormally dry conditions are present around much of the central Midwest.
There might be some light spotty light snow or rain showers around in my northern counties Tuesday afternoon, but saturation may be tough to achieve with dry low levels so I would not look for much if anything.
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RAIN OR SNOW LATE THURSDAY/THURSDAY NIGHT
Thursday is the day when we finally have a shot at some respectable precipitation totals. Low pressure will cut a path through Missouri and central Illinois, setting the stage for a nice over-running event. This is also a good track for snow but one factor is missing and it's a big one, cold air. The GFS in fact is mild enough that the only snow it scares up is north of HWY 20 in NE Iowa and southern Wisconsin.
The 12k NAM agrees but is heavier up that way than the GFS.
The EURO and Canadian GEM are a little colder and further south allowing some of the accumulating snow to get into my northern tier or two of counties. Here's what those two models are suggesting for amounts.
The national model blend.
It is plain to see that my southern counties are going to sit this one out with rain the dominate form of precipitation. That could even be the case in most of my northern counties if the U.S. based models rule the event. Even in the north, precipitation should start as rain Thursday afternoon but evaporative cooling should come into play turning rain over to snow at some point Thursday night. How soon that happens determines how much might accumulate. The track is another unknown that could alter amounts. A 50 mile shift north or south could make the difference between several inches of snow or primarily rain.
Lately trends have been for slightly warmer thermal profiles. If that continues in futures runs that is going to hurt chances up north. Runs the next 24 hours will likely tell the tale of where the snow band sets up. Clearly, the further north you go in my area, the better the chances for a wet accumulating snow, especially up near HWY 20.
At this point (and this is very much subject to change), the EURO shows about a 70-80 percent chance of an inch of snow in my far northern counties on up into NW Iowa and southern Wisconsin. We shall see.
As I mentioned, this system looks to be the biggest most widespread precipitation event in over 3 weeks. Here's what models are suggesting for total amounts Thursday-Friday.