Tuesday, November 17, 2015

Snow, Cold, Winter, Oh My

A pattern change is ongoing across the entire United States this week. A trough in the west will push east in the coming days and cold air funneling in from the north will bring the contrast in temperatures needed for atmospheric lift and precipitation. A wave of low pressure will develop along this boundary and move through the southern Great Lakes by the early weekend. On the cold side of the system a band accumulating snow will set up on the backside of the track of low pressure. We have plotted where "plowable snow" will set up according to three major numerical weather models, or 3"+ of snow. Some models takes the system up through lower Michigan and deepen the surface pressure. This could drop heavy snow over Lower Michigan and ramp up lake effect snows on the back side of the cyclone as it pulls away Saturday and Sunday. The potential exists for nearly a half foot of snow in areas such as Chicago through Grand Rapids, Michigan, with 2-5" as our best estimate over Iowa. With it being 4-5 days out there are a few discrepancies and issues in the forecast:

*The timing...warm ground and pavement temperatures would limit accumulations if the snow comes during the day, accumulates more efficiently at night
*The track...where the low pressure goes will determine the general area of snow
*Phasing...if this storm cuts north as it passes east of the Mississippi River heavier snow could fall

Either way, the storm will bring in northwest winds by Saturday and Sunday which will usher in much colder temperatures across the Midwest by the weekend and beyond. Low temperatures for Sunday morning are plotted below, off the ECMWF model. Notice the lows will be ~10 degrees cooler in areas with fresh snowfall, due to radiational cooling. Keep it here to Midwest Weather for updates throughout the week.