Sunday PMJanuary 20th, 2013 at 4:12 pm by Bill Steffen under Bill's Blog, Weather
The first image on the left is the black and white visible satellite image from mid-afternoon (from ADDS). It’s sunny in Wisconsin. The clouds and snow flurries/showers we have are all generate by lake-effect…cold air coming across relatively warm water. Check out the current weather map. The temperature at each weather station on the map is the number in the upper left. There isn’t as much difference between eastern Wisconsin and West Michigan here in the late afternoon. The sun has warmed the air a little in Wisconsin during the day, so often the difference is a little less in the late afternoon in a situation like this than in the morning. The second image is Lake Michigan water temperature from GLERL. The actual temperatures are probably a few degrees cooler than what is indicated on the map. Lake Michigan goes through a process of overturning in early winter when the water temperature stays at around 39-40 degrees for a couple weeks and I suspect the water temperature is around 40. Note where the warmer water is located. You can see here that Lake Superior (farthest north) and Lake Erie (shallowest Great Lake) are the coldest lakes, and Lake Michigan and Lake Ontario are the warmest. When you try and forecast lake-effect snow, you have to look at many factors, including the water temperatures, the fetch – or how great the distance that the air will be coming over the water and the residence time (the time the air will spend over the water – if the wind is stronger, the air will spend less time over the water water). Here’s currents in the Great Lakes. This is dictated by the wind direction, speed and geography. Note that today, there is a uniform surface flow from north to south over Lake Superior, but a little more disrupted flow over Lake Michigan. BTW – I was at the station last night until 4:50 AM – around 1 PM, I updated radio forecasts from home and right now I’m checking weather and watching the Atlanta-49ers game. I’m on call if and when team coverage is needed. Kyle Underwood called early this afternoon and we went over the weather and how we plan coverage for all our media for the next 72 hours. There’s a lot going on behind the scenes. At this point I would lean on the slightly higher end of snowfall amounts – the most favorable lake-effect areas should see over a foot of snowfall this week. The latest NAM (Caribou) gives G.R. 7″ of snow this week and Holland 14.4″.
Also, the GRR NWS has wisely noted the possibility of ice jams on area rivers by the end of the week into early next week. Also (as is often the case) when we have a cold shot, the upper pattern aligns to bring cold air to Europe and Eastern Asia. Lots of winter going on in the U.K. and in Japan. London has had 10 days in a row with colder than average temperatures and during that time they’ve been 6 degrees cooler than average. Dublin, Ireland is in the mid 30s and snowing. The weather has moderated in northwest Mexico after some of the coldest temperatures in 42 years and heavy snow.