Here it is Monday, and a storm system we’ve been advertising since midweek last week still has some uncertainty in its projected path.  It will pass south of us, but the question is how FAR south, and how quickly will it redevelop into a potent coastal storm.  The NWS has a Winter Storm WATCH up for the srn tier beginning Tue afternoon, continuing into Wed evening. I feel only light snow will reach Chau and Catt Cos tom’w afternoon, with the snow picking up in the evening and into Wed AM.  Morning model runs today favor the heaviest snow initially over SE Michigan, then Ohio into PA, and then the chance of greater snows and the likelihood of strong winds well east as the storm bombs off the coast. While all of WNY will pick up some accumulation, current operational models and ensemble members favor only a chance of marginally heavy snow in the s tier and nrn PA, with several inches possible on the Niag Frontier–no sign as of this posting that the storm will take a closer path to us and bring heavier amounts.

A quiet neither here-nor-there pattern will continue for some time to come. Only some weak troughiness will bring a bit of light snow developing Tuesday afternoon into Wednesday, with a hint of moderation. And most of that moderation will be found in the welcome lighter windspeeds, reducing the chill in the air still with us on Monday. The southern branch of the jet, fueled by a barely weakening el nino, will remain entirely out of phase with the northern branch, precluding any major storm at our latitude.  Only the operation Canadian GEM shows an inverted trough angling up our way at the end of the week (from the departing coastal low), and is clearly an outlier at this point.  Buffalo’s seasonal snowfall is nearly normal, but that deficit will be growing this week.  Next weekend will see a reinforcing short of arctic high pressure.

The wintrier pattern will be setting up fairly close to the projections we made last week. Marginal conditions for lake enhancement begin late Monday night into Tuesday on SWly to WSWly winds (by Tue afternoon). When the lapse rate does finally become sufficient for a better lake response on Wednesday, the moisture availability drops way off, so that potential looks quite limited. The coldest day of the week looks to be Friday, preceded by synoptic snow showers.  Conditions will be favorable for some blowing snow with gusty winds Tuesday, a little less so Wednesday, and again gustier ahead of the arctic front.  There may be a period of some limited moderation in temperatures by the end of the weekend, but the overall pattern still looks chilly for much of next week.

El nino’s current vigorous state is showing up rather clearly in a major pattern shift underway across the country.  While storminess will increase across the west, and typically cool and wet conditions will prevail in the south, the warm up in the eastern Great Lakes and NE will be tempered by a sometimes negative Arctic Oscillation,  and a slightly negative to neutral NAO.  A more zonal flow will dominate the lower 48, but occasional short waves in the northern branch of the jet will allow brief interruptions in the warmup in our vicinity, with shallow intrusions of arctic air.  There are signs of a brief shot of colder weather returning around Tue-Wed next week.  No major storms are showing up in models or ensemble members for our part of the country at this time.  This type of pattern evolution in which a trough develops near the west coast, particularly the Pacific NW, and ridging progresses toward the Great Lks is a classic signature of a moderate to strong el nino. Before winter lovers get too depressed, it’s unlikely this pattern will continue unabated for the rest of the winter.  I see it as more of an extended lull. On the other hand, there are no hints of a return to the very high amplitude negative AO, and climatology does favor much of the remaining winter to run milder than the last 2 or 3 weeks.

With the passage of a couple of short waves, lake effect snow and a bit of synoptic snow will flare up a little from time to time during Tue and Tue evening.  Slightly warmer and drier air will cut back on the snow showers for Wed into early Thursday, but another trough will set the region up for more widespread snow showers later in the week, accompanying a reinforcing shot of arctic air.  The NAO and AO will remain negative, though the AO may lessen in amplitude for a while.  The PNA will remain weakly positive. There are early hints that el nino may begin to reassert itself later in January–but only hints.

There also are signs of winds backing on Sunday to either Wly or SWly, tapping more into L Erie’s lake effect potential, ahead of warm advection by Monday.

After some fairly potent lake and synoptic snow in combination, multiple bands on a NW flow will make for very spotty accumulations overnight and into Tuesday, with blowing and drifting continuing.  Lake snow will begin to thin out further Tue PM.  Heaviest accumulations will be NE of Buffalo and in the hilly terrain to the south, where topography gives the Lks Huron-Erie moisture a boost.  Wednesday will be a quieter and milder day, but light snow will develop for Thursday, and we will have some mainly lt snow shwrs New Year’s Eve. That could create some black ice problems.  By New Year’s Day, a slow moving storm will begin to move toward either Long Island or SE New England, and eventually “stack up” vertically, nearly cutoff from the westerlies. This will keep the storm almost stationary over the weekend.  A trailing trough from this storm will be found close to the Grt Lks for several days.  Early indications point to the best lift in a deformation zone occurring by New Year’s Day afternoon, with some accum. likely, although the heaviest snow will be over the interior of New England and maybe the Adirondacks.  At least snow shwrs would appear likely thereafter into early next week.  Gusty winds will begin to increase later Friday into the weekend, making some blowing snow likely….an interesting period lies ahead.

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.