December 19-22 High-Impact Blizzard Event

**This post is dedicated to Rachel Davino, age 29, a victim of the Connecticut shootings.**

I am holding firm with yesterday's call as far as the track goes, but PLEASE DISREGARD THE SNOWFALL FORECAST. I have a new snowfall forecast below. I still expect the system to move from the Plains through the Midwest, most likely through north Indiana and southern Michigan. These areas will have a tougher time getting any precipitation, as dry slotting issues may occur. As the storm strengthens, it will wrap in air through its southern flank in response to very humid air (the precipitation) wrapping around its northern side. Wherever the low pressure system travels, dry slotting could cut down precipitation of any kind.

I'm still holding with my idea of a rain-to-snow situation in much of north Illinois, southern Michigan, Missouri and Kansas. The main snows for these areas will depend on the strength of the backside snow. Models were earlier indicating a heavy band of backside snow coming through the Midwest, and if such a solution happened, a few inches could fall.

The model consensus has aligned itself overnight with my track, leaving me with the logical option to hold this forecast in place.

Snowfall is expected to be heavy, and, combined with winds, will make travel dangerous (see Impact Scale below). I am anticipating amounts of 1 to 3 inches in the light blue colors. This is the tricky part, because this involves the areas right along the rain-snow line, something that troubles may forecasters and such rain-snow line forecasts are prone to 'busting', or failing. I am confident in a good 3-6 inch accumulation in the darker blue, and a 6-12 inch plus snowfall over southern Wisconsin, much of Iowa, extreme northwest Missouri, extreme southeast Nebraska and northeast Kansas. Amounts will increase as you move northeast through this forecast in response to the storm strengthening. Again, such a strengthening storm and the tricky rain snow line makes forecasts difficult to confirm. Watch for amounts over a foot in Wisconsin.

Green: Low Impact
Yellow: Moderate Impact
Red: Heavy Impact
Pink: Major Impact
Blue: Extreme Impact

We here at The Weather Centre want to put out forecasts that best interest you and your safety. For that reason, earlier this year, we developed our Exclusive Impact Scale, where I can identify areas where travel may be hazardous, among other things, depending on the season. My forecast for this system involves a Low Impact forecast for much of the region that will see some precipitation that is not wintry from this system. Low accumulation spots on the order of 1-3 inches then includes the Moderate Impact spot, where some people could see slippery roads and slightly hazardous travel weather. Heavy Impact status is expected in much of the 3-6 inch accumulation stripe, where there will be fair travel delays. Flights will have issues, and driving will be a 'challenge'. Unnecessary travel is not advised. Finally, I hesitantly put out a pink stripe of Major Impact status for the 6 inch+ areas. The only reason I do this is for the wind- very high winds will make whiteout conditions common in rural areas, and long-lasting travel delays will stem from those areas.

And now, our final graphic is for the kids. This is another tool recently developed here at The Weather Centre. I have made a forecast chance for a snow day based off of my previous snow day experiences and putting myself in the situation of a bus driver, administrator and parent, the big question being "Can kids safely get to school?" Although there are 10 categories, DO NOT use them as a 1/10, or 2/10 chance- that is not the intent.

I marked down generally low probabilities for much of the impacted region simply because of the lack of significant snow. I did put a 'Not Very Good' chance for the 3-6 inch range (you may have to adjust it west a tad, or clip off the southern edge of the yellow zone). The Medium forecast is again based off of blizzard-like conditions (or just plain blizzard conditions). I then went ahead and went up to 'Good' for Wisconsin (you should consider it likely). I did not put likely in there without loss of visuals of the counties.

You can also use a formula I made a year or two ago for snow day potential by clicking here.

Hunker down, folks, this one looks to be a nice introduction to winter. I will have more updates on the Facebook page, which you can find on the right-hand sidebar. If you haven't given it a 'Like', go ahead and do it- you can find my latest thoughts not seen here on the blog.

Andrew