at 12:12 PM by Pierce Larkin

Significant Snow Event Affects Iowa and Illinois

Yesterday, one of the first winter storms of the season impacted much of central/northern Illinois and eastern Iowa.

h/t NWS Chicago
h/t NWS Chicago
h/t NWS Quad Cities
h/t NWS Quad Cities

An amplified and fairly strong shortwave trough propagated eastward across the central Midwestern states yesterday, setting the region to see a fairly significant snowfall. Much of the day, strong divergence was present within the mid and upper levels of the atmosphere, and this promoted the sustainment of intense precipitation as it propagated into the region.

The divergence in the upper levels of the atmosphere was strong, and helped foster heavy precipitation. h/t SPC
The divergence in the upper levels of the atmosphere was strong, and helped foster heavy precipitation. h/t SPC
Much like with the upper levels of the atmosphere, there was fairly strong divergence in the mid levels of the atmosphere. h/t SPC
Much like with the upper levels of the atmosphere, there was fairly strong divergence in the mid levels of the atmosphere. h/t SPC

Additionally, there was strong forcing present to help intensify precipitation. A strong vorticity maximum was moving eastward into the region, and this combined with warm air advection in the lower levels of the atmosphere to create a very good source of forcing for intense precipitation. There was also a fairly strong temperature gradient in some of the lower levels of the atmosphere, which aided in lifting and the creation of strong precip.

The strong vorticity maximum that moved into the Illinois/Iowa region yesterday produced heavy snowfall. h/t SPC
The strong vorticity maximum that moved into the Illinois/Iowa region yesterday produced heavy snowfall. h/t SPC
Warm air advection, while not strong, was present and helped to enhance precipitation. h/t SPC
Warm air advection, while not strong, was present and helped to enhance precipitation. h/t SPC

All of this combined for a pretty significant December event. What was weirder about this event was that it sort of came out of nowhere. Hindsight is 20/20, and the brief description of the meteorological background above shows why this event was of high magnitude. Some records were broken:

  • Moline, IL -> 7.8″; second heaviest first snowfall on record
  • Rockford, IL -> 5.3″; second highest total for Dec. 4 on record
  • Chicago, IL -> 6.4″; highest total for the Dec. 4 on record
  • Davenport, IA -> 10.2″

The general idea of this storm ahead of time was that 3-5″ would be the max, but it didn’t end up being that. Once the event was actually occurring, the atmospheric dynamics that drove the higher totals were resolved, and it was easier to see that this would be a bit bigger than was initially estimated. Additionally, the temps across the region were mostly near or slightly above freezing for a lot of the event. This created heavy, wet snow, which created some beautiful pictures.

(h/t @TheBestDroneVid)

(h/t @skydrama)

Another winter storm is anticipated across the far northern Plains this afternoon and evening, so there may be an update on that one once it is over with!