While a powerful east coast storm puts down plenty pre-holiday snow in the east, our chances of a White Christmas are in some trouble.  Wildly varying computer model and ensemble forecasts for Christmas Day have raised the possibility of more of a rain event than a snow event.  The potency of this storm, still out over the Pacific as of this posting, is in question–as well as its path. There is some chance of at least limited lake effect snow after Christmas, but it’s impossible right now to determine boundary layer wind vectors in a storm’s wake when we don’t even know a likely path for the low. Brace yourself for more flip-flopping over the next few days, since this storm is not going to be as much of a standout as last weeks 975mb low–which (in a sense) gave models and ensembles more to sink their teeth into in making forecasts.

With the nastiest wind and lake effect storm now ending, what’s next?  Some rain will arrive on a milder but breezy Sunday, though it could start as a mix.  But another arctic cold front will race across the region during Tuesday, and temperatures will start to tumble later Tuesday and make for a cold rest of the week.  Behind the front will be a blustery NW flow and daytime temperatures in the mid 20’s at best–though with a Nasty Wind Chill.  A NW flow generally creates multiple bands of lake effect snow off Lakes Huron and Ontario.  These bands tend to meander around, not staying over any one spot long enough to really build up big accumulations.  The fetch of the wind over Lk Ontario doesn’t compare with the amount of moisture a SW wind off Lk Erie can gather.  Further east, closer to Syracuse, the fetch is longer–but that’s their problem, right?

The truth will likely lie in between.  There is nearly no doubt that a developing storm will become a powerful winter storm for the central plains, parts of the midwest, and the Great Lakes.  But beyond the high synoptic probability are quite a number of both synoptic and mesoscale uncertainties.  Chief among them are the duration of snow versus a wintry mix overnight Tuesday, the strength of the winds near the sfc by Wed evening and Thur AM, and the strength and placement of lake effect snow. As mentioned in the previous thread, there are fortunately a few elements which may work against a classic destructive High Wind event (lower inversion lyr may limit mixing to sfc of max winds). However, I still feel we will endure a period of High Winds Wed night, with sustained winds of 30-40 and frequent gusts of over 50mph, and maybe some to 60. (The most classic events often include gusts of over 70). The very strong boundary lyr winds are bound to produce some speed shear which can disrupt lake bands and spray poorly organized lake snow well inland. There will be some synoptic snow as well, and the placement of what’s called a deformation zone is still somewhat uncertain. Nearly all models and ensemble members take the storm toward Lk Huron or nearby, and there will be SWly bndry lyr winds into early Thursday, before veering to Wly develops and takes the heaviest lk snow (well organized or not) into ski country during the day. So, if the bands survive the High Winds and strong winds to follow, the metro area will get a shot before the veering occurs.  In any case, there should be enough snow for Blowing Snow to produce some Whiteout conditions on Thursday.

As of this writing, poorly organized lake snow is located where high res models predicted (far nrn Erie, srn Niag, SW Orl & NW Gen Cos), but a lowering cap/inversion, some shear, and thin moisture have combined to keep the band from really getting its act together.  It may get a brief burst of life again early this evening in its current location, and then shift south, falling apart as it does so, late this evening.

The next system to watch will be around Wednesday, when major cyclogenesis is indicated in virtually all models.  While track is still uncertain, most models point to WNY getting into the warm side of the storm during the day, with a gusty southerly flow developing. But as the storm explosively deepens, there is some potential for a High Wind (or at least strong winds) setup by early Wed evening into Thursday. Strong cold advection will be likely, and lake effect snow (depending on how much shear occurs) will set up. The location of this LES is not really predictable at this range.

The long-advertised turn to a Colder pattern in December is still coming.  But the snow? That’s another matter. If we receive no measurable snow through December 3, that will set the all time Buffalo record for the latest first measurable snowfall. We’ve received only a trace in November. A cold front attached to a low pressure system will turn some rain to a little snow during Monday, but the chance for measurable snow with this is fairly low.  There is some limited lake effect potential Monday night into early Tuesday, but boundary layer winds may favor areas south of Buffalo, rather than the airport. Models are in disarray for Thursday, but cold air in the wake of a difficult-to-place low may produce some lake snow late next week. However, earliest signs point to a WNW bndry lyr flow.

A long-advertised cooling trend is still shaping up for the middle and latter part of Thanksgiving week.  While there are no signs of true arctic air reaching us, temperatures will drop below normal as we get into Wednesday night and Thanksgiving Day.  Some Shwrs may mix with wet snow Wednesday night, and indications point to a Raw Thanksgiving holiday with some Rain & Snow Shwrs that could even turn to all snow before the day is out.  Temperatures look marginal for any significant lake effect snow at this point, but a slight shift in the orientation of the polar branch of the jetstream could makes things interesting.

El Nino has continued to strengthen over the last 4 weeks, and already attained Moderate intensity. Most computer models project additional strengthening and persistence through the coming winter. Moderate el ninos do correlate with higher probabilities of warmer than average temperatures much of the time during the cold weather season.  The correlation with snowfall amounts is weaker, and still leaves quite a bit of uncertainty. However, should el nino attain Strong intensity, the probabilities for warmer temperatures in our region become high confidence, and a tendency for lower snowfall amounts becomes more likely.  BOTTOM LINE: I am projecting a Warmer than Average Winter Season for our region, though this does not mean the pattern won’t break down and become wintry from time to time.  As for snowfall, the correlation between a Moderate el nino and reduced snowfall is weak, so snowfall potential remains very uncertain.  Further explanation follows below.

No extreme chill during the week, but chilly enough–especially by Thursday. A short wave and a cold front will set us up for a cold NW flow. As the cold advection continues Thursday night, current indications point to enough lift being generated synoptically by the wave to allow some limited accumulation on the hills to the south.  A pattern change will begin to evolve on Friday, but especially over the wknd into early next week, as a ridge builds in the east and a warming SW flow develops.  An el nino analysis follows below.

Mild Pacific air will continue to dominate into Saturday, although a bit of cooling can be expected Thur night and Friday. An area of low pressure will edge some showers into WNY by late Friday, increasing overnight and into Saturday, probably diminishing later Saturday.  Sunday will be Chilly & Breezy with only a Few Shwrs.  Signs continue to point to a Chillier finish to the month, into the beginning of November.

After a pretty nice Columbus Day, some showers will likely move in later in the evening and continue into at least a portion of Tuesday, with chillier temps moving in and staying for awhile.  Any lake shwrs Tue night will be lighter, on a NWly flow, but a few flakes could mix in over the hills.  850mb temps will be cold enough for flakes or a mix midweek, but no significant disturbance will be around to tap the cold air.  By Friday, a deepening low in the southern plains may move toward the Appalachians.  Earliest indications point to a cold rain developing for Friday, but there might be a mix in spots at the outset.