When Lake Effect Enters the Forecast, It’s Seldom Uncomplicated….December 9th, 2013 at 12:31 pm by Don Paul under 4 Warn Weather
And this week will be no exception. As of this posting (midday Monday), it appears lake effect snow will begin fitfully with some minor amounts this evening, possibly near the metro area for a time, before settling to south of the metro area. On Tuesday, what’s called an anticyclonic curvature will be found in lower level winds, which makes for more drying and sinking motion in the boundary layer at least into early afternoon. When winds back to SW later in the day, ahead of a trough/short wave, lake snow will begin to become better organized…but there still may be some disruptive shear for a short time due to the trough. After a relatively brief visit to the metro area, with some limited accumulation, the axis of the trough will pass and winds will quickly veer to the Westerly flow which sends the LES into Ski Country. Between Tuesday and Thursday, several short waves will traverse the northern Great Lakes, each producing some backing and veering. The amount of backing (which would impact the metro area & possibly NE ‘burbs) is low confidence. The MEAN dominance of the westerly flow is somewhat higher confidence but, as some of you know, that doesn’t tell the whole story. There also will be variations in moisture availability and periods of shear. That means this isn’t going to be a “steady state” singular snow band all the way from Tuesday evening through Thursday. There will be ebbs and pulses, making for extraordinarily difficult accumulation forecasts.
In the extended range, the zonal-ish flow at the 500mb level toward mid-December no longer looks so zonal. The 3 main ensemble means show a rebuilding of the ridge in the eastern Pacific, and some troughing crossing the N Central states and the Great Lakes. The ECMWF and Canadian GEM are strongest with that ridge as we get closer to Christmas. The GFS ensemble is strong with it initially next week, but weakens iT during the 21st-24th. But even the GFS shows heights which would be cold enough to support snow in advance of the holiday. Before we get to that, though, there is good agreement in the medium range of an area of low pressure bringing us some synoptic snow during this next weekend. It may be on the slushy side, and it doesn’t currently look like a blockbuster snow storm, but it doesn’t look like a 90 pound weakling, either.