Potential Impacts Midwest Snowstorm: 20-21 December 2012

For the last couple days, model output and the Analog Guidance has been advertising a high-impact event across the Midwest on December 20th and 21st. Although the track of the model output has varied (see graphic below from the Milwaukee, WI NWS Forecast Office issued this morning), what has been consistent is that a strong area of low pressure will develop over the Southern Plains and track north-northeastward into the Great Lakes.
This consistency in strength gives an opportunity to extract some potential impacts from one of the most similar analogs to the upcoming forecast: 27 January 1996.

Image courtesy of the Milwaukee, WI NWS Forecast Office

The 96-h GFS forecast (20121217/0000 initialization) has a 984-mb surface low is centered over the northern part of Lower Michigan, strong 850-mb circulation, negatively tilted and closed midlevel trough, and excellent upper-level jet support (top image below). Remarkably similar, and the most statistically similar historical event to this forecast during the last 30 years, is the 27 January 1996 event. Using the synoptic-scale 4-panel images below to compare the forecast to the analog, it is easy to see the similarity (strength and position) of the atmospheric features between the two cases. In addition, the track is extremely similar to this forecast as well (use analog event gui here). Although still cold enough for snow, the low-level temperatures in the January 1996 event were around 4-8C colder on average...which will most likely impact total snowfall amounts.

Regardless, the similarity between the forecast and historical event allows meteorologists to pull the potential impacts from this historical case. The 72-h snowfall from this event had a large area of >8" from the Missouri/Iowa border northeastward to Lake Superior with an organized area of >12". Embedded within that area were also numerous locations receiving over 15". Giving even more support for a similar scenario is this morning's 20121217/1200 NAM 24-h snowfall forecast for the event which has the snow swath in almost the same location as the January 1996 analog (third image below).

One of the concerns with these strong Midwest systems is the potential for blizzard conditions to the northwest of the surface low track as strong areas of high pressure build into the area. The 6-h maximum wind gusts ending 27 January 1996 at 0600 UTC show the strong winds with this event as there was a large area of wind gusts from southern Missouri to the Great Lakes greater than 30 kts (35 mph) and numerous locations across Iowa and Illinois with wind gusts exceeding than 40 kts (46 mph).

Some of the NCDC Storm Impacts written by the meteorologists working the January 1996 event are as follows.

From East Central and Southeast Iowa:

"A winter storm system moving northeast over the Mississippi river brought nearly 10 inches of snow to portions of east central Iowa, with snowfall diminishing to 3-6 inches near the Mississippi river. Schools were cancelled due to extreme blowing and drifting of snow. During the afternoon and evening winds of 20 to 30 mph became even stronger and the Winter Storm Warning was upgraded to a Blizzard Warning for many Iowa counties. Numerous motorists were stranded on highways and interstates and a State of Emergency was declared, by the Governor. The State of Emergency mobilized National Guard units to assist local Law Enforcement in the rescue of stranded motorists."

From Central Iowa:

"Blizzard conditions developed by the mid day hour. North winds of 30 to 40 MPH were reported statewide, with occasional gusts to between 50 and 55 MPH. Whiteouts were reported everywhere with visibility no greater than 1/8 mile anywhere in the state. All school districts were closed, most businesses closed early, and travel became impossible. Thousands of cars and trucks were in the ditches with many thousands of people stranded or in shelters. By evening, most highways were impassible and road crews were called off the roads. Interstate 35 was closed from Ames north to the Minnesota border. Interstate 80 was closed east of Grinnell. The Governor declared a state of emergency at 1745 CST. Snow drifts of 6 to 8 feet were common, with several reports of drifts 10 to 15 feet high. By the evening of the 26th, nearly all activity in the southeast half of the state had ceased. The storm claimed two lives near Grinnell. Two males became stranded in deep snow out on the highway. Attempting to keep out of the elements and avoid freezing to death, they succumbed to carbon monoxide poisoning. The engine of the car subsequently started on fire and they burned to death."

From Southeast Wisconsin:

"The snow became convective as lightning and thunder put on a show in the afternoon hours. Snowfall rates peaked at 3 to 4 inches per hour, with Madison gathering 8 inches in only 2 hours! Coupled with northeast to northwest winds gusting to 40 mph this snowfall rate lowered visibilities to near zero at times. Snowplow crews were pulled off the roads in many areas by 1900CST. There were at least 800 vehicle accidents (indirectly related to the storm), and 6 people were briefly hospitalized. Airplane flights were delayed several hours. Interstate 90/94 was closed in stretches around Madison. Scattered power outages resulted in about 500 customers loosing electricity in the Sheboygan to Milwaukee area. Many schools canceled classes, or dismissed students early; and many evening high school basketball games were canceled."

From Southwest Wisconsin:

"A strong winter storm moved up from Iowa and blanketed much of the region with 10 to 18 inches of snow. The heaviest snow occurred along an axis from La Crosse northeast toward Fort McCoy and into northeast Wisconsin. An isolated report of 18 inches was received 6 miles east of La Crosse while most areas average 10 to 13 inches. Blizzard conditions existed during the height of the storm during the afternoon and evening leaving drifts of 4 to 8 feet. Travel was nearly impossible."

It is very clear that this was a life-threatening high-impact event across the region with blizzard conditions, power outages, stranded motorists, and even a state of emergency declaration. Model output and National Weather Service Forecasts will continue to be refined as the storm approaches over the next few days. However, these are the types of impacts that can be expected with a storm this strong with heavy snowfall across the Midwest.

The analog run that this blog post was written from is available here.


Update 18 December 2012 at 0027 UTC:

Winter Storm (dark blue counties) and Blizzard Watches (neon green counties) have been issued for portions of the Plains and Upper-Mississippi Valley.