After temperatures in the 60s on Sunday and 70s on Monday, the other shoe will be dropping this week…slowly and in stages. 3 cold fronts will cross our region this week. The first, shortly before sunrise on Tuesday, will deliver modest cooling. Chillier air will set in on Wednesday, relax a bit on Thursday, and then the storm system and its cold front-which-means-business arrives during Friday. Behind the third cold front, temperatures at around 5000 feet will cool to -5 to -7 or -8 degrees C during Saturday. With the lakes still relatively warm, the difference in temperature between the lake’s surface and the atmosphere close to a mile–the “lapse” rate of the temperature dropoff with altitude–will be sufficient to develop lake effect showers. And the near surface temperature will become cold enough to support some wet snow or graupel pellets mixing in with the lake effect showers during Saturday into Sunday morning. There may even be a few wet snowflakes in the mix at lower elevations later Saturday night into early Sunday. In fact, I can’t rule out a thin coating of slushy snow at the highest elevations in that time frame. The airmass on Sunday will be a little drier, making lake effect showers thin out to some extent.
During this coldest period, the flow in the lower part of the atmosphere (meteorologists call this lowest part the “boundary layer”) will originate mainly from the WNW and NW. In general, a NW flow means the wind has a much shorter stretch of water it can pass over, and that limits how much moisture that wind can pick up from the lake. Such a flow tends to favor the hilly terrain to the south with more numerous lake showers and snow showers. As of this posting, there are no indicators this setup will deliver any truly significant snowfall to even the hills, but the Meteorologists of 4Warn Weather will be tracking this situation all week. In any case, lake rain and snow showers in mid-October at not at all unusual at higher elevations. And, this visit from “Almost Winter” will be a short visit. The winds will become SW by Monday, and readings will begin recovering to seasonable levels, with further moderation likely later next week.