December 8-9, 2009 Major Winter Storm
A major winter storm impacted Southern Wisconsin Tuesday evening, December 8th, through Wednesday morning December 9th. Heavy snow fell over a large portion of the area (many areas reported thundersnow), with numerous locations reporting over a foot. The hardest hit area was across central Dane county, where 15" to 18" of snow fell. The 14.1" reported at Dane County Regional Airport was the 6th highest 2-day (calendar day for December 8 and 9) total reported since records began there in 1948.
Here's a list of the Top Ten 2-day totals for Madison (calendar day):
1. 17.3 12/2-3/1990 2. 16.1 12/10-11/1970 3. 15.4 2/22-23/1994 4. 14.5 3/18-19/1971 5. 14.2 1/25-26/1996 6. 14.1 12/8-9/2009 7. 14.0 4/8-9/1973 8. 13.7 12/19-20/2008 9. 13.7 4/9-10/1973 10. 13.4 1/26-27/1996 10. 13.4 2/5-6/2008
Far southeast Wisconsin received much less snow due to the effect of warmer air close to the center of the low pressure system, as well as from the flow off milder Lake Michigan waters (water temperatures at the time were around 43 degrees). Snow amounts on the Lake Michigan shore were less than an inch while just a mile or two inland, those amounts climbed to 4 to 5 inches. This was the case from Sheboygan south to the state line.
Here is a text listing of all the reports received from around southern Wisconsin.
Below are contoured maps of the snowfall for southern Wisconsin and the entire state. There is some estimation and smoothing used on these maps. The two statewide maps depict the 2-day snowfall (these numbers are taken from local weather observers who submit their reports around 7 AM each morning.) The state map on the right is hand drawn with considerable smoothing.
This storm became a blizzard in many areas and left over a foot of snow from the Central Plains into the Great Lakes. This can be easily seen from space using MODIS imagery. The left image below is a two frame loop showing conditions prior to and after the storm. You can see there was very little snow cover at the end of November and things were relatively quiet across the central U.S. until this winter storm. The image on the right is a zoomed up image over southern Wisconsin. Note the lack of snow cover right along Lake Michigan...especially Wind Point. Madison and Milwaukee are circled in red.
These MODIS images are courtesy of UW Madison/SSEC/CIMSS. Here is the direct link to MODIS Today from CIMSS
The low pressure system that generated this winter storm not only produced heavy snowfall and strong winds across parts of Wisconsin, but produced very low barometric pressure readings as well.
The track of the low pressure center passed right over the Milwaukee area around 8 am the morning of the 9th while it was steadily deepening. This resulted in Milwaukee having the lowest pressure of all the cities in southeast Wisconsin that morning. Readings across the remainder of Wisconsin were also very low, but not as low as they were in the Milwaukee area.
|The image to the left is a graph of the Air Pressure, Wind Speed and Gusts at the Kenosha C-Man observation site. This is a marine observation platform located at the Kenosha harbor. Note the minimum pressure was around 8 AM on the 9th.|
Milwaukee began observing a decrease in pressure the evening of the 7th, with the pressure dropping from 30.28 inches (1026.4mb) to 28.84 inches (976.8mb) by 8 am the morning of the 9th. The all-time lowest barometric pressure experienced in Milwaukee was 28.71 inches back on April 3, 1982. The lowest barometric pressure ever observed in the month of December in Milwaukee was 28.83 inches on December 4, 1973.
Madison began seeing a decrease the evening of the 7th as well, dropping from 30.27 inches (1026.5mb) to 28.91 inches (979.8mb) by 7 am the morning of the 9th. The all-time lowest barometric pressure experienced in Madison was 28.62 inches (969 mb) back on April 3, 1982
For comparative purposes, the February 5 - 6, 2008 winter storm/blizzard generated a minimum barometric pressure of 29.69 inches (1005.4mb) in Milwaukee and 29.76 inches (1007.8mb) in Madison.
Because the low pressure center moved right over southern Wisconsin, there was actually a lull in the winds Wednesday morning. The winds were strong out ahead of the low where the isobars (lines of constant pressure) were tightly packed. As the low moved over southeast Wisconsin, the winds became very light or calm in many locations. After the low moved by, the tightly packed isobars returned and the winds picked up again out of the northwest. This is quite similar to what happens in a hurricane, known as the "eye" of the storm. See the animation on the right.
Below are maps showing the track of the December 8-9, 2009 low pressure system.
The image to the left is a water vapor satellite loop from 715 PM, December 8 through 915 AM, December 9. This loop was compiled by NWS Green Bay.
Here are a few neat photos showing the snowfall.
These photos are part of the public domain and can be freely used. Although not required, please credit the NWS and the photographer.
If you have some photos you'd like to share with us (and have us post them on our web page where they become part of the public domain), please send them to:
The National Weather Service Offices below have great post storm write-ups as well.