Changeover to Snow Starting in Great Lakes- 12/27

Precipitation is occurring in big green blob over Great Lakes.
Theoretically, everything inside the black and red lines is snow.

We are beginning to see a changeover to snow in the Great Lakes this morning as a storm system moves eastward across the southern half of the country. There is an outline of a red line. Inside that red outlined area is the boundary layer at 0 degrees celsius. That same red outline also contains a black outline. That black outline symbolizes that everything inside that area is surface temperatures at the freezing level. We expect this area of freezing temperatures to expand as a cold front works its way from Canada down south. It appears that states such as Ohio, Pennsylvania, and western New York could get in on the heavier snows.

850mb temperature advection

We can see that the cold front is present by taking a look at 850mb Temperature Advections. There is a region of substantially lowered temperatures over the last several hours in the North Great Lakes as that cold front progresses southeast-ward. We need to keep an eye on the cold front, as the amount of interaction, area of initial 'impact', and temperature difference all depend on snow totals. If there is a greater amount of interaction than forecasted, i.e. the cold front dips farther south than anticipated, snow totals may increase further south. If there is less interaction, snow totals may be lower than forecasted. The area of initial impact is where we expect the first cold wave from the cold front to hit. If it hits somewhere other than forecasted, that 'somewhere' may end up with more snow due to a quicker changeover. Finally, temperature difference depends on the snowfall. Like a cold front in spring that ignites storms, this cold front may ignite areas of heavy snowfall. Depending on how much difference there is in temperature, we may be seeing heavier snow if there is more difference, or less snow if there is a lesser difference in temperatures.

HRRR Total Snowfall Accumulation