19 November 2014
You could hardly put together a better synoptic weather set-up for a HUGE lake effect snow event than what happened today in Buffalo. A mid-January type outbreak of Polar air rushing across the Great Lakes (that are still “November warm”), and the result is nearly 4-5 feet of snow in Western New York.Travel is totally stopped to the South (and southeast) of Buffalo this evening, and heavy lake effect is falling in other spots around the Great lakes as well.
Lake effect snow is a tough forecast for meteorologists, and my fellow Broadcast Meteorologists all know that Don Paul is the person to talk to when you have a question about lake effect. Don has been forecasting it for years, and he called this one on the money. It’s not everyday that you forecasts snowfall in feet or meters, and you can check out Don’s Facebook page for some incredible pics from his viewers.
There are several factors that are critical to forecasting lake effect events, and the two most important are the temperature difference between the surface of the water, and the air at about 5,000 feet above the surface. Meteorologists look at the 850 millibar pressure level which is about 5,000 feet, and when the temp. at 850 mb is lower than the lake surface by about 13-15C, then the air over the lake will be very unstable and convective showers will form.
Another critical factor is the wind direction, because the greatest snow events happen when there is a long fetch of wind down the lake, rather than across it. The longer the wind travels over the warm water, the more moisture will evaporate. Wind shear is also an important factor, and in general you want the winds to be generally in the same direction in the bottom 2 km of the atmosphere All of this was in play today in Buffalo, and if you look closely at the NASA satellite image from today, you can see the snow bands blowing nearly parallel to Lake Erie. Notice the bands across Lake Michigan are crossing a shorter body of water, and they dumped only about a foot of snow in Western Michigan. The much longer fetch of air across Lake Erie is dumping over 50 inches of snow south of Buffalo! (UPDATE Wed. Nov 19: The heavy snow line was very sharply defined with the Buffalo Airport getting 4 inches, while Lancaster 12 km away had 60 inches!)
Just a wind change by as much as 10 degrees can greatly affect the areas and the amounts in a lake effect snow event, so it is indeed a tough forecast to make. Smart forecasters tend to become experts on the high impact weather events that they most often see in their area, and folks like Don Paul (and the local NWS forecasters) in the lake effect areas are just that. Here in Maryland, I worry about nor’easters and East Coast hurricanes!
One last thing to mention, and that has to do with how a warming planet will impact lake effect events. When the lakes freeze the snow machine stops, so if we see less lake ice during the winters in the future, then we may see more lake effect snow than we do now. It’s a tough call though, because we may see less cold air as well. There does seem to be a trend upward in snowfall however, as the graphic produced by the folks at Climate Central below shows. Great lakes ice is highly variable from year to year, so a trend is more difficult to see, but there does seem to be a trend down in maximum ice cover over the Great Lakes as a whole.
I leave you with this meme that is floating around the internet tonight.