CUTTING IT THIN ON A MAJOR SNOWSTORM...
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CUTTING IT THIN TO WIN ON SNOWFALL AMOUNTS....
It may not look like much on the satellite imagery but a winter storm is going to cause a whole lot of problems from the Plains to the northeast over the next 48 hours. Technically, it's not what I would call a true storm in the sense that is does not have the classic wrapped up surface low winter storms are known for. This system is is basically driven by a nearly stationary boundary separating Arctic air to the northwest from warm moist tropical air to the southeast. Near and north of that line, intense frontogenesis creates a broad area of over-running precipitation that falls for an extended period of time. The end result is heavy snow, sleet, and freezing rain for much of the mid-Mississippi and Ohio Valleys.
Below you can see the sharp baroclinic boundary (temperature differential) driving the system late Tuesday. Sub-zero temperatures in North Dakota and readings near 60 along the slow moving front as far north as St. Louis.
Below you can also see the high levels of water vapor (precipitable water) the system has to work with coming out of the Gulf of Mexico. Of particular note for my area is the dry air sinking southward into Iowa and the upper Midwest. For the NW half of the region that is the death knell for snow forcing it further south into a more moist and conducive environment.
While there are two parts to this system it appears that only the first one will impact my area. Snow that starts Tuesday night will exit my southeastern counties early Wednesday afternoon. A quick hard hitting band of frontogenic driven snow.
For days now, the challenge for forecasters has been determining the depth of the dry air and the northern extent of the snow shield. My belief since last Friday is that the greatest impacts for my area would occur in my counties southeast of a line from Burlington to Kewanee to the NW of Princeton where the 2-6" accumulation line lays out. (Southeast of that, WC Illinois could see amounts greater than 8" which is discussed below). The greatest challenge is pegging the northern edge of the snow band which has a very hard edge. For example, amounts in Knox County, Illinois on the 3k NAM go from 1" in the NW tip to 10" in the SE corner (roughly 30 miles). Models such as the EURO and GFS are still showing as much as 1-3 inch totals on a line from Washington, Iowa to the Quad Cities and off to Sterling/Rock Falls. Take a look.
The high resolution CAM's such as the 3K and 12K NAM are substantially further south and barely have any accumulating snow north of a Burlington to Kewanee line (certainly nothing in Washington, the Quad Cities, or Sterling). The hi-res CAM's are designed to perform better in this short time frame window but seem to be doing poorly. Which model do you believe? This is a really tough call as to whether or not we can get enough saturation to push that 1 inch+ snow line past the Quad Cities. It will be close but the GFS and EURO seem to be handling the situation better. Here's the 3K and 12K NAM snowfall output.
The 3k NAM
The 12K NAM
SO WHAT TO DO
The best of the hi-res solutions belongs to the HRRR but it may be a bit low on the NW edge of the snow band. The HRRR lays down 1/2 to 1 inch of snow in the Quad Cities. I am leaning towards a middle ground compromise between it , the GFS and EURO. Splitting the difference, I like 1" totals in the QCA. This is still a low confidence call even as snow begins to enter the region. The 3" to 5" line runs from Burlington to Kewanee and west of Mendota. On the high end parts of Hancock, McDonough, Fulton, Knox, and Stark counties could see some 6-10" amounts. Central Illinois really gets clocked. Places like Bloomington and Champaign could rack up 15" totals before it ends. Even parts of Chicago could see 12"+. NW of the Quad Cities this is a nothing burger. Watch and wave as it safely passes by.
This is the official NWS snowfall forecast.
That NW edge of the snow is a real challenge to call. Look how fast amounts go up to the southeast of it.
EXTREME HIGH IMPACT STORM FOR SOME...
Needless to say, for those who take the full brunt of this storm it produces major impacts and travel will be extremely difficult. Please keep that in mind if you will be traveling through Missouri, Illinois, and Indiana the next 24 hours. The Winter Storm Severity Index shows extreme to major impacts are expected from the storm. It's very, very painful for me to miss out in this by such a small margin. Snow like this doesn't come around very often. Ugh!
Below you can see the extensive amount of counties under winter storm warnings into Thursday.