A Hatful of more Wintry Maybes by Late in the WeekDecember 16th, 2012 at 9:22 pm by Don Paul under 4 Warn Weather
I’ll have to keep this post suitably vague due to the lengthy lead time involved. As I began talking about on air Friday evening, I still have rather high confidence that we’ll feel some impact in our region from a deep and vigorous area of low pressure beginning on Thursday, taking us into wintrier weather overnight Thursday and into next weekend. That’s the big picture. The relatively high confidence fades quite a bit when digging for details due to model differences and ensemble differences–which are to be expected. One of the main questions concerns the path of this future cyclone. The European and many of its ensemble members takes the low nearly over us, which lessens the pressure gradient but still could get us into some wraparound snow followed by lake effect snow on a primarily NW flow. The GFS and many of its members take the low on a more common/climatologically favored path which would get us into strong to high winds by Friday, possibly with some initial dry slotting ahead of lake enhancement, then lake effect. Winds would veer to the W, then the NW, with lapse rates increasing as the WNW/NW flow takes hold. What cannot possibly be seen this far out is embedded short waves in the mid-level flow which could cause some occasional backing and veering.
I have a number of concerns, one being the GFS’ fairly big changes from the 12z run (not a true flip-flop, but still a marked lengthening of the period of time for cold advection, and a heightening of the strong to high wind potential by Friday AM). It is more important that the majority of the GFS MREF (ensemble) members show decent agreement than just the operational GFS run. On the other hand, the GEM is now closer to the Euro in operational runs, and the Euro is–as we know–often the better of these models. I can’t call it a “toss up” right now, because there are more than 2 outcomes possible. But we’ve now had approximate agreement on the bigger, fuzzier part of the picture for 3 days running. In other words, this system may prove to be more exciting and potent, or somewhat disappointing. But it’s not going to just disappear.
The trite phrase applies: The Devil is in the Details.