Small Scale Heavy Snow Event
December 16, 2005
A small upper disturbance, rotating around the west side of a larger upper level low pressure system to the east, helped trigger this mesoscale event. The large upper low and it's associated surface low over the eastern Upper Peninsula of Michigan was the remains of a big storm that had just occurred on the 14th and 15th.
Narrow bands of moderate to heavy snow began moving into Duluth from the northeast shortly before daybreak and continued through the morning. One burst of snow produced 1 inch in 30 minutes. Snow accumulated generally 6 to 8 inches. The National Weather Service received 6.6 inches. An unofficial observer, that would be me, measured 7.5 inches.
As the small upper low pressure circulation approached Duluth, the hint of a weak surface low pressure circulation formed over the head of the lake. Lift and instability due to the upper disturbance, convergence associated with the surface low, and moisture off the lake all appeared to contribute to the snow. Onshore winds to the north and east of the surface low pressure system may have produced some weak terrain enhancement. Further study of the event is needed to test the validity or extent to which each factors contributed to snowfall production.