MAJOR WINTER STORM ON TRACK...

The major winter storm headed for the area late week was all the buzz Monday as people pondered the effects of the pre-Christmas storm. The combination of snow, wind, and bitter cold is expected to produce near white-out conditions at times, especially in the open country Thursday. Winter storm watches remain in effect for all of the central Midwest, that is if they haven't already been upgraded to warnings by the time you read this. Currently eight states are under watches.

The energy responsible for all the excitement is just now diving into the northern Rockies. Over the next 48 hours it digs southeast creating a closed 500mb low that brings the inclement conditions. You can watch the evolution of the trough and its energy on this 500mb animation generated on the GFS.

The system really gets cranked up Thursday when the energy sling-shots out of the trough. However, from the standpoint of snow a couple things will keep this from being a blockbuster snow producer in my area. First the system doesn't really get its act together until it is just SE of my area. That means moisture is initially lacking and slower intensification keeps the primary deformation band largely out of my area. The GFS is the only model currently showing somewhat stronger development sooner and further west. I think it may be an outlier, at least at this point.

Total liquid precipitation is generally now shown in the range of 2/10ths to 4/10ths of an inch (1/2 inch in spots on the GFS). In an average snow event with 10:1 ratios. that would yield 2 to 5 inch totals. In this case, snow ratios reach 20:1 in the later stages which should mean amounts end up more in that 4 to 7 inch range, maybe 8 in a few spots northwest. That's still a good snow but if we had opened up the gulf and wrapped up the low sooner this thing could have easily dropped well over a foot. In fact, 24 hours ago with 1 to 1.5 inches of QPF, the GFS actually showed this for snow totals. Good golly miss Molly, I knew that was too good to be true.

Now that models have obtained data from richer grids on the west coast, the noise in them has been reduced and snowfall forecasts have come back down to reality with less variance. Here's what guidance is now suggesting. Again, these are not true forecasts, just raw model output that is used to formulate forecasts.

The GFS

The Canadian GEM

The EURO

The National Model Blend.

In some cases snowfalls such as this is borderline winter weather advisory category, not warning. However, the cold and wind at the end of this snow will easily elevate it into the warning category.

The addition of the Arctic front to the system is when things get ugly Thursday afternoon and night. As it passes in the morning, rapidly rising pressures will allow winds to quickly increase out of the N/NW. Gusts will likely reach 40-45 mph by Thursday evening. This also coincides with a period of strong lift that causes most of the snow accumulations of significance to occur Thursday afternoon to about daybreak Friday. Temperatures during the day will crash roughly 30 degrees from 6:00am readings in the upper 20s to low 30s, to 6:00pm readings near zero. Conditions in this window go downhill rapidly. In minimal time near whiteout conditions could develop with the burst of heavy snow that's expected. Travel in the open country could be very dangerous with the wind howling all night long and lofting the powdery snow. Serious visibility restrictions and temperatures reaching 10 below are expected overnight. Dangerous wind chills of 25-35 below are likely.

The strong winds and bitter cold lasts Friday and Saturday (Christmas Eve). Falling snow is no longer an issue at this point but blowing snow and bitterly cold temperatures will still cause hazardous travel at times. Christmas day winds relax but temperatures remain cold in the single digits. I'll have more details in temperatures and wind chill as we work past the snow phase of the storm.

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