No time for great detail on this busy Wednesday evening, but a widespread Winter Storm still appears likely to deliver its heaviest snow to the Niagara Frontier, with somewhat lesser amounts to the south. There is still the question of how much–if any–of an icy mix may develop to the south of the metro area Friday, which would hold down accumulations but make travel more treacherous. There is also the question of a cutoff time to the heavier snow as of this posting, with the NAM and our Vividcast quite a bit faster than the GFS. Most models now are not showing full tilt snowfall rates until we’re into the Friday AM commute, rather than in the predawn hours. If that trend holds true, it’s going to make school delays and cancellations a more difficult call. The wind will be sufficient to cause some Blowing Snow, but currently appears below the threshold for full whiteouts, unless the snow is truly coming down VERY hard. (It will be a different story in NYC-Boston, where the coastal storm will develop powerful gusts by later Friday into Saturday AM, resulting in a Blizzard Watch for Boston to Providence.) If the operational GFS were looking to be a best bet, then I’d have to raise my earlier preliminary estimate for the Lk Ontario counties above the 8-12″ in my early evening forecast. Still working on that, and have to see the next set of SREF output.

Another coastal development may bring more snow to our region and parts of the NE around Thursday next week.

As we told you last week, the next batch of cold weather will bring us back to below average temperatures, with the coldest day looking to be Friday this week. But it simply will not be as cold as the previous batch. As of this posting there are continuing mixed signals on the strength of prefrontal warm winds Tuesday night and Wednesday AM. The NAM numerical output is quite strong, which is climatologically unusual when the boundary lyr winds are more southerly than SWly. Usually strong to high winds are better indicated in the majority of models–this one’s a tougher call. There may be a convective line with the passage of Wednesday PM’s cold front if the strength of depicted dynamics in some models is realized.

Most of the LES on Thur-Fri should again be occurring over Ski Country and the s tier based on current output. A clipper (strongest in the 00z Euro) will bring a little synoptic snow, shear, and shifting wind directions on Saturday, and another one may approach by Monday. There are signs of some moderation in the ensembles around Feb 6-9th, but not a fundamental pattern shift.

Extended range computer guidance–especially ensemble means for 850 mb temps and 500 mb heights–have been very consistent about the very cold air which is headed our way by Sunday evening into next week. This will certainly be the coldest pattern of the season. The question will be how much moisture can be wrung out from what is essentially a dry pattern. One element working in favor of some snow, of course, is our proximity to the Lakes. The other will be the occasional passage of short waves which will provide some lift to produce limited snowfall. This will not be a snowless pattern, but there are no signs of a prolonged SWly or WSW flow when the arctic air is in place to impact WNY with any huge LES storms. The coldest of this pattern  in today’s (Tuesday) runs will have passed by the end of the week, but moderation after that should be slow. The 00z Euro ensemble has more significant moderation occurring by the following week than had previous Euro runs, so that will have to be watched. Even in the Euro, however, there is a hint of new cold advection over the northern plains in the last time period, so that tendency toward a zonal flow in the new Euro is still uncertain.

By recent years’ standards (not those of 76-78), this will be a somewhat harsh pattern for people and pets, but it will afford ski resorts with snowmaking capabilities a chance to rebuild bases. As for “loose talk” of a more favorable storm track at the end of the month or early February, I don’t see such a track in the 16 day time frame. Beyond that is–for me–nothing more than idle speculation not really supportable  in the data.

You often hear meteorologists talk about computer models, blog newcomers. But over the last decade a new set of important tools are being used by professionals who have been keeping up with this aspect of the science. A few words about “Ensembles”: because we cannot know the precise state of the atmosphere at any given moment (far too many variables, far too much unavailable or missing information) supercomputers with enormous crunch power run models with 20 or more different-but-reasonable-variations on initial conditions at the start of model runs. That is, an NWS model may have  over 20 different runs, each a member of an ensemble. When these 20 ensemble members show only relatively small differences between one another, confidence in the use of that model and its ensembles increases. But if the spread between those ensemble members is large, and the ensemble shows a huge range of outcomes, then confidence shrinks. The NWS global model, called the GFS (Global Forecast System) has a counterpart from Environment Canada, and from the European Centre for Medium Range Weather Forecasting, in England. The latter, the European model and ensembles, is generally thought of as the most reliable global model. But NO model or ensemble can be counted on to automatically be the best on a daily basis (some models run 4x per 24 hours), so we need to look at all of them. One might assume that the Mean of the many ensemble members is most likely to be the most accurate, but it doesn’t always work out that way. Sometimes members close to being “outliers” turn out to do best, but it’s very difficult to know when that’s going to be the case. The best we can do is to combine basic meteorology (looking at surface and upper air observations, satellite imagery, buoy data, doppler radar products, etc) and combine that current reality with the performance of models and ensembles in the near term. If a model is already way off the mark early in its forecast, the odds favor it being even more way off further out in time. Ensemble forecasting is the wave of the present and the future. Meteorologists who fail to jump in to this new and complex statistical set of tools do so at their own peril. The NWS and academia have led the way in putting these tools into everyday use, and those of us in the private sector have caught on as well. Ensembles, particularly those from the European model, are what made the forecasting of Superstorm Sandy so incredibly accurate before the disaster unfolded.

As for what those ensembles are showing now…our snowpack will take a significant hit during the week of January 7th, with airmasses of Pacific origin replacing the arctic air. Temperatures will likely move well above average by midweek and late week, and to make matters worse for ski resorts and snow mobile trails, some rain is likely to hasten the thaw around Thursday and possibly again by Saturday (European ensemble). However, it had been looking until yesterday (the 3rd) as if that mild trend would persist most of the time over the next 16 days. Today’s ensembles are now showing seasonably cold air (not brutally cold) which had been slated to stay over the northern plains and Canadian prairies will be able to make it back to the eastern Great Lakes by around the 17th-19th…possibly a bit sooner, future runs will determine that. Right now there are no signs of truly harsh, bitter cold getting to us, but the temperature scheme I’m seeing in these ensembles will be returning closer to average or a bit below average and, in any case, it will be chilly enough for rain events to be replaced by snow events.

Colder than average temperatures will be with us for the next week, but the next big storm will largely miss us. That system on Saturday may send some very limited snowfall our way, but will be too far to the east to have a direct impact. After that, a series of short waves/lows, each with a cold front, will send reinforcing shots of cold air into the northeast, cutting off any real advancement of milder Pacific air for a while. That means the slopes will be keeping their snows, and good snow making conditions will help the resorts add to their bases most nights. After late next week, the oscillating indices which affect the overall patterns across the eastern US will change to their warmer phases (the AO, NAO, and PNA), allowing that Pacific air to advance farther east for a while. That does not preclude some short waves bringing more active and colder weather for short periods during this pattern shift, but the Mean will be milder.

Speaking of milder, no matter how cold it is between now and New Years Eve, this will be the warmest year on record for Buffalo, going back to 1871.

What started as a twinkle in the European model’s eye midweek last week looks very likely to bear some serious snow to our region, starting Wednesday afternoon and intensifying Wednesday night. While I’ve had some concerns about warmer air mixing in, Monday morning guidance is highly favorable for mostly snow or all snow. I can’t rule out some sleet mixing in for a short time early Wednesday night, but that prospect is looking fairly unlikely. The intensity and favored track for this double barreled storm should provide enough vertical velocity/lift/cooling of the column to create a deep dendritic growth region. Strengthening E to NE winds Wednesday night will make for blowing snow and hazardous travel a real problem, with snow winding down to snow showers on Thursday morning. There is good model and ensemble agreement now, but amounts are still uncertain as to whether we’re talking about 6-12″ or even greater amounts if everything comes together just right (or wrong, depending on personal preference). This same large storm system will probably bring a significant or even major severe weather outbreak to parts of the Gulf states into the SE and maybe even lower middle Atlantic states starting later tonight in SE TX into Wednesday. Significant tornado outbreaks on Christmas Day are rare, but tomorrow may be an exception.

Tonight’s Christmas Eve snow will be ‘small potatoes’ but should provide a White Christmas for most folks who don’t have anything to show for last Friday night’s storm (not a problem for Ski Country, I know). Roads will probably become slick, and may still be slick on Christmas morning on untreated surfaces…a little freezing drizzle may be falling in spots. The midweek storm will be much more important, and will be disruptive for post-Christmas travel from Oklahoma City to the interior of New England.

Another system will bring some limited snowfall into our region by Saturday afternoon, if the European model is correct. In that model, this system will deepen explosively as it nears the northern New England and Maritimes coast, bringing cold & windy conditions  with sct lake snow showers into the eastern Great Lakes. Its circulation could also make for quite a nasty wind chill on New Years Eve.

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.

Examining computer output here on the evening of December 5th, there are still no signs of a protracted truly cold pattern in the Great Lakes or the east. That is not to say the weather will remain as snowless as it has been. Of course, climatology tells you that much. But actual current data tells more.  In the near term, both the 18z GFS and the latest Canadian GEM (far from my favorite model, the GEM) are showing rapid deepening of a low pressure system by Monday, with more snow potential than is seen in the Euro–which also has not been consistent in the east in recent days. The GFS would bring the potential for a cold deformation zone reaching WNY by late Monday/Monday evening, which would allow accumulating snow with strong winds. This would be followed by weaker lake snow on Tuesday, with much less  potential. What’s most supportive of this operational run is the 18z GFS 500mb Ensemble Mean, which shows a sharp height fall coinciding with this rapid near-bombogenesis, and stronger cold advection to go with it. The operational GEM also has tremendous deepening of this low at about the same time. FAR from a high confidence forecast, but definitely worth watching.

Other items: Lake Erie is 2 degrees above average today, at 44 degrees. And, the GFS Ensemble Mean is showing stronger Greenland blocking developing in the next week than we’ve seen. Before winter fans get too excited, the Pacific ridge–despite the Greenland block–stays too far west (with no +PNA) for consistently lowering heights in the Great Lakes. But the blocking may allow the NAO to take more frequent dives. Pardon the cliche: Stay tuned.

Thanks to Tom Niziol, who forwarded to me an interview with winter outlook researcher and forecaster, Judah Cohen. The interview was conducted by a private sector meteorologist, who works for a group called The Capital Weather Gang, in Washington. They are regular contributors to the Washington Post. Surprisingly, Dr. Cohen has partially “spilled the beans” in a public way early in the season. While part of the interview’s focus centers on D.C., much of what he discusses is relevant to the NE as well.

A couple of important notes before you hop on the link, please. Cohen and his group have developed a new index on how to look at October Siberian snowfall; the Snowfall Advance Index, or SAI. He now correlates a faster rate of snow accumulation  with a -AO more than with just a monthly anomaly. It is clear that this professional (me) and some of you weather hobbyists have not been interpreting the Rutgers Global Snow Lab data (which he mentions) the way Cohen does. As for this year, despite what we saw on the Rutgers site, the SAI is favorable for a colder than average winter in the east and NE, and a more -AO/NAO. I think many of my fellow fans of wintry weather will be greatly encouraged by much of what he says here.

Another note: Cohen does not generally go into detailed precipitation outlooks. I would remind you all again that the “Snowmaggedon” winter of 2009-2010 left Buffalo with only 74 inches of snow. That record negative AO brought us cold, but not that much snow. So in MY opinion, we still can’t extrapolate much on snowfall from this hopeful outlook, except to say that both statistical odds and expected pattern dominance would favor more snow than last winter. The statistical side of that is an easy call. The pattern dominance is a predictive call.

And 2 puzzles: Cohen and a few others seem to enjoy treating the NAO and AO as if they were virtually identical, and virtually a single index. I can’t say I agree with that. There are parallels, but I have seen periods in which one was highly negative and the other wasn’t. Clearly, the majority of forecasters still go with 2 indices. Cohen may be favoring his approach to simplify matters for clients and the public…I don’t know.

The other puzzle is why he never mentions the MJO, nor does The Capital Weather Gang. The MJO is recognized by CPC as playing a role in temperature anomalies during the winter season. There is a highly suggestive body of evidence that its anomalous behavior last year was a very significant forcing mechanism in “defeating” la nina climatology over much of the northern latitudes of the U.S. And, when I asked Dr. Kerry Emanuel of MIT about this in August (one of the most accomplished meteorological scholars we have), he agreed it was a good hypothesis.

Now that I’ve said my piece, here’s the interview: http://wapo.st/WxMLXq

Please use the link in my first comment for ease.

The Climate Prediction Ctr has updated its Winter Outlook and its Monthly (December) Outlook today. If you were looking to the CPC–or me–or anyone else to reduce the uncertainty about a winter outlook, you’ll be disappointed. CPC is maintaining its EC/Equal Chances status for much of the east. They’re reasoning is partially tied to the lack of predictability of the phase of the AO/Arctic Oscillation or the NAO/North Atlantic Oscillation beyond a couple of weeks. The MJO/Madden-Julian Oscillation is briefly mentioned but, not much was said about its current active phase due to that lack of predictability. On the matter of time scales CPC put a little more emphasis on the role of the PDO/Pacific Decadal Oscillation, which is in a Cool/Negative phase. Before anyone gets excited about what that might mean, PDO phases tend to run on the order of 20-40 years, as opposed to the typical 30-60 days for the MJO. They seemed to imply that the negative PDO, which weakened in October but is expected to strengthen again by summer next year, may have been enough to kill off what would have only been a weak el nino and keep ENSO neutral.

I might have expected them to give more weight to the current active phase of the MJO, which favors above average temperatures in the central and eastern U.S. Since this active phase has run only 2-4 weeks, that would still leave it with at least several weeks more time in this phase, which could weight the start of winter with above average temps in the central & ern U.S. In my mind, that might have tilted the odds toward a positive temperature anomaly for December, with the emphasis on the first couple of weeks.

Now that I’ve said all that, I do not have the tools and experience of the long range specialists of CPC, and I have very little experience balancing the PDO with shorter term oscillations. That is not false humility. That is a statement of fact. If the MJO returns to the normal longevity for its phases, we could well see a notable flip in the overall pattern  later next month. The length of active phase time the MJO took on last winter was highly anomalous, and didn’t follow the rules. Could that happen again? No one knows. If it does not happen again, we may see a return to more variability in 4-6 weeks.