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Seasonal snowfall has moved back a little above average over the last few days. After the November lake effect storm(s), the airport (never hit full strength by those events) had gone to 29+ inches with an average to that date of 16+ inches. By midweek last week, the airport had slipped to several inches below average, following an unusually mild December (3.4 degrees above average) and well below average snowfall. We’ve gone back in the other direction this month up to this point. Temperatures have been significantly colder than average, and monthly snowfall has been above average.
Those trends will level off following the arctic shot for Tue-Wed, with temperatures slowly recovering to closer to average later this week (still on the cold side, but nothing like last week or Tue-Wed this week). Readings may head a little above average during the weekend. During the time period from around the 18th into the latter part of the month, there will be more occasion for more Pacific air to cut off the kinds of arctic blasts we’ve endured last week. However, the moderating trend will not be a totally smooth ride, and there will be some ups and downs, just fewer if any extremes. Ensemble means show a very broad ridge in the eastern Pacific at the end of the runs (26th-27th) and very broad troughing over the N Central and Great Lakes states. The amplitude is lower than it is now, to be sure. When ridges and troughs are so broad, it’s often a sign of large spread between the ensemble members which make up the ensemble mean. It doesn’t look as though there will be much phasing between the northern jet stream and the southern stream for awhile. However, large ensemble member spread can mask any individual features even more, so the more moderate pattern (not to be confused with truly mild, as would be the case with a well defined eastern ridge) is a very fuzzy one as depicted. In the next week (through the 20th or so) there are no current signs of any significant synoptic storms putting a hit on the eastern Great Lakes. And because there are no current signs of large lake effect potential, my “but Not for Long” headline is probably a safe bet over the next 7 or 8 days.
After some almost unseasonably mild weather before and during the Christmas holiday, the pattern will be shifting to a more wintry one for the last few days of December and the first few days of January. The northern branch of the jet stream is going to buckle again, but this time the trough will be “positive” tilt, with the axis running from Quebec to the Great Basin and SW. That will preclude any deep storm system in our region for at least a few days. A somewhat split, separate southerly branch of the jet may carry a vigorous system far to our south and toward the SE/middle Atlantic seaboard with no impact on us.
However, as the cold air deepens on New Years Eve, a brisk (and bitter-feeling) WSW flow will set up across the eastern Great Lakes. This means late night revelers should be dressed in their warmest, protective gear for any prolonged exposure, even though temperatures look “merely” cold that night. There will probably be some Lake Effect developing downwind of Lake Erie. Working against it will be early model and ensemble projections of this being a dry air mass. Working in favor of it will be some cyclonic curvature to the flow (the arctic anticyclonic ridge will be Well S & SW of us) and a pretty healthy delta T/low level lapse rate. Lake Erie is currently 3 degrees above average at 39. The lower res global models and ensembles are not very good at picking up all but extreme lake effect this far out in time, so they’re not showing much. I do expect some lake response by either late New Years Eve or New Years Day, slowly winding down by the weekend. The pattern will then begin to relax, and more seasonable temperatures (not mild, but seasonable) will return.
Judah Cohen is forecasting the AO to go predominantly negative for much of January, but also says there is uncertainty about the strength and impact of his predicted SSW during the month. Despite the AO showing a general trend toward the negative by the start of the year, the NAO goes positive for a while, so there are mixed signals on that front. But there IS good agreement on this cold period for New Years week, and the WSW flow setting up in the boundary layer, so things may get interesting for a few days.
Confidence is continuing to grow as of this Wednesday evening posting that a major storm system will be taking shape by Christmas Eve into Christmas. Confidence continues to be much lower by comparison as to that storm’s impact in WNY. As you should expect 8 days in advance, there is model disagreement on storm timing and placement, and there is some ensemble disagreement as well. However, there is unusually good agreement this far out between the operational GFS and ECMWF on the broader details. That is, there is good agreement an initial low pressure area and its trough will undergo a transformation as that trough begins to tilt from NW to SE, known as a negative tilt. That tilt encourages more rapid and deeper strengthening of a surface low with a broadening of the precipitation shield associated with the storm. The negative tilt will spawn a deepening frontal wave along the initial low’s cold front. This secondary low will undergo strong cyclogenesis, coming up from the S or the SSE. The new intense low will eventually merge with the original parent low to the N and become a rather powerful cyclone. Both the GFS and ECMWF deterministic runs take the central pressure of the merged low down to 964mb! The ensemble means of the 2 models drop the center to around 978-980mb. The GEM has some similarity, but its cyclogenesis is less impressive than in the GFS and ECMWF. The actual path taken by the new deep low in the GFS is faster and farther east than the ECMWF depiction, which would put us in the cold wraparound snow and strong winds more quickly than in the ECMWF.
Also strong to possibly High winds will be favored. On Wednesday, a strong SE flow will increase coverage and intensity of rainfall, and winds will strengthen, strongest near the Lake Erie shoreline south of Buffalo. As the main low shifts north with its near bombogenesis, the cold wraparound circulation should change the rain into an uncertain amount of snow overnight on Christmas Eve into Chrstmas morning. As of this Wednesday evening, both the ensembles and deterministic models favor strong to possibly High winds in the cold advection as well. It is too soon to speculate as to how much synoptic snow will fall vs lake effect behind the storm. Signs do point to potentially dificult travel by or before Christmas morning, and there will be the chance for damaging gusts and a seiche–depending on the orientation of the pressure field. There may also be especially strong gusts immediately following passage of the cold front, with an isallobaric coupling (pressure fall/rise couplet) possibly causing additional problems.
Much can and probably will change over the days to come, of course. We’ll keep you updated. If things get really hectic, watch on air and/or go to wivb.com for details.
As I type this post Monday evening, all of WNY is under a Winter Storm WATCH which begins late Tuesday night and continues into late Thursday night. For our 8 WNY counties, snow begins as a light mix Tuesday evening and turns to light snow later at night. Accumulations will slowly build from E to W on Wednesday and increase further later Wednesday night into Thursday. The wraparound “deformation zone” snow will pile up the most on hills from southern Erie & Wyoming counties into the Chautauqua Ridge and parts of interior Chautauqua & northern Cattaraugus Cos with much less accumulation closer to the PA line. The N to NW flow will also enhance the snowfall amounts N & NE of the City in locations such as Batavia, Medina, and parts of inland Niagara County. Amounts near the City will be somewhat reduced.
Beyond the storm, the warming for this weekend will be slowed a little by the slow departure of the vertically stacked, weakening storm system. Temperatures should edge up to a few degrees above average by Sunday and Monday, ahead of some cooling for a few days by midweek, next week. The overall pattern will return to warmer than average in the mean much of the time out to December 22 or so. CPC, in fact, shows not a hint of a pattern change nor do they discuss one in their 8-14 Day Prognostic Discussion. On the other hand, I am seeing signs of a change in the making. The GEM and GFS 500mb ensemble means seem to clearly show a western ridge rebuilding by the 23rd with somewhat increase troughing in the east. This may or may not be tied to a forecast weakening of the currently active MJO, which is still propagating to the east. Ensemble output favors the MJO weakening considerably by later in week 2, so that its propagation would not have much of an impact compared to what would have happened had it retained its strength. There is also the question about how much influence we can expect from a poorly mixed SSW.
In any case, I’m a little perplexed why CPC isn’t putting much effort into their prog discussions for the 6-10 & 8-14 day outlooks as of late. I would rather they also pointed to what I’m pointing to, but absent their agreement I’ll stand by what I’ve said. A pattern change to colder weather is coming by Christmas Eve and the rest of the month. How MUCH colder I can’t say yet…it may or may not be a big deal.
Now that nature is done doing its worst (let’s hope!) we’ll be catching a relative break on the majority of days over the next 2 weeks. Temperatures will run below average through Friday, with some weekend moderation. Readings will drop back early next week for a couple of days before rebounding midweek. Lake effect will be strictly limited in supply with no indications of moderate or heavy accumulations into next week. In general, the upper level flow will allow some ridging in the east–in the mean–though there will be ups and downs within this pattern. So, anyone looking at smoothed temperature anomalies on CPC maps as being the whole story will be disappointed from time to time. Near the end of the 2 week period, Arctic Oscillation ensemble members have a tendency toward becoming Negative/Cold, but there is still quite a bit of spread at the end of the run–as there usually is. And the PNA seems to be taking on a Positive phase late in the period as well. Model ensemble means hint at the rebuilding of western heights late in the run, with the GEM being the strongest on that ridging. However, it can’t be foreseen if this a temporary ridging in a progressive pattern of ups and downs, or if it is going to be the beginning of a new western ridge/eastern trough amplification. Having seen the 2 links on the previous thread (http://www.cpc.ncep.noaa.gov/products/intraseasonal/temp10anim.shtml) and (https://www.aer.com/science-research/climate-weather/arctic-oscillation) posted by Dave from Rochester and Ayuud, I’m inclined to think if the end of those runs isn’t yet indicative of a return to colder conditions, it might follow shortly beyond the 14-16 day range.
As for ENSO, we still can’t say an el nino event is now occurring because the standard calls for 3 consecutive months of el nino conditions to have occurred. However, warming has continued across most of the tropical Pacific east of the dateline, and key Nino region 3.4 is now at .9 degrees above climatology. So, it’s not an event, and CPC by definition says we still have a neutral ENSO in place for now. Nonetheless, we have el nino conditions in place. This warming was in place during the recent extreme pattern, so no one should jump to conclusions that this el nino condition is bound to be a match for the probable Sudden Stratospheric Warming which seems to have taken shape. We just have no evidence at this point such would be the case. Most ENSO models still indicate a weak el nino is taking shape, but there are now a couple more members (out of more than 20) which point to a short period of moderate el nino conditions than there were a few weeks ago. An interesting note: the CFS v.2 is an outlier for next year, showing a weak el nino weakening by spring and then redeveloping more strongly toward next summer. That time range is far beyond the window of known reliability for predicting ENSO phases in the first place, but it’s also the only model showing that redevelopment.
As of this posting (late Sunday afternoon), a Lake Effect Snow Watch has been elevated to a WARNING for Erie, Genesee, Wyoming, Chautauqua, and Cattaraugus Counties. This has the hallmarks of a true major winter event and will be highly disruptive due to rather strong winds creating near blizzard conditions within the movable feast of snow. (All this will be preceded by a few inches of water laden snow late Sunday into Monday afternoon, although there is still some chance of rain mixing in with that slushy snow at times).
BUFKIT and other models are showing Extreme instability from late Monday night into Tuesday, which virtually assures occasional thundersnow and locally very heavy snowfall rates. The lake snow will probably start over the hilly terrain Monday evening and shift northward through the Buffalo Stowns and into the rest of the metro area by Tuesday morning out to at least Batavia as the flow backs from W to SW. There are more indications as of this posting that enough backing of the boundary layer flow will occur for the LES to reach into the Ntown & NE ‘burbs, as well as the City (backing to 240 now indicated in the higher res NAM.). In a synoptic setup such as this (as noted by NWS AFDs), the climatological positioning of the 850mb low is favorable for such backing and for accelerated gusts. The passage of a short waves (I posted this in the previous thread) during Tuesday will allow some veering during Tuesday afternoon and evening back through the Stowns and into Ski Country. Winds are still likely to back to SW again by Wednesday AM, bringing LES back north. Rh values should diminish somewhat by Wednesday afternoon (along with some anticyclonic curvature around the ridge to our south), gradually lessening snowfall rates. Also as previously noted, another vigorous short wave will approach late Wednesday into Thursday, bringing more synoptic snow showers and some developing LES. The cold air trailing this low appears to be colder than in runs over the last few days, so some of that LES MAY be fairly impressive again if there isn’t too much directional shear–which can’t be determined this far out.
Bottom line: Confidence is High that this will be a major event. Confidence is growing that the metro area will suffer a big impact toward and through Tuesday morning, with veering returning a major impact through the Buffalo Stowns and then down into Ski Country by late Tuesday/Tuesday evening. Confidence is moderate and growing that the nearby northern and NE ‘burbs will also have a substantial impact. And, confidence is High that within this band Near Blizzard conditions will occur.
Our Buffalo Weather Blog regulars are already familiar with the probable relationship between rapid accumulation of snow in Siberia during October, and the pattern the polar jet stream takes on in the winter. There appears to be a fairly strong correlation between above average accumulating snow, particularly if the advance of snow cover is rapid in October, and how an oscillating feature to the far north (call the Arctic Oscillation; http://www.ncdc.noaa.gov/teleconnections/ao.php) takes on a colder phase. We call that phase a Negative Arctic Oscillation, or -AO for short). This correlation isn’t airtight, but during Octobers in which the advance of snow cover in Siberia is especially rapid, the correlation has been shown to be reasonably reliable. That kind of rapid advance occurred this past October at a much higher than average pace. Dr. Judah Cohen, who first discovered this correlation, has issued his winter forecast. He believes the -AO will be the dominant phase much of this winter (not all of it), with its greatest impact in the eastern US (including the SE), the midwest and over much of Europe. If that verifies, this will be the second colder than average winter in a row for the east. It cannot be known at this time whether it will be exceptionally cold as per last winter, or just somewhat below average. As of this posting, I am not seeing many signals from nature which would suggest a milder than average winter. That is, the majority of known indicators are pointing toward colder than average. I’ll post a link of a summary of Judah Cohen’s forecast below, along with a link which will give those who are drawn to more technical discussions, the actual forecast in detail. And, believe me, it IS technical, and part of it is beyond the scope I normally present on this blog. So, feel free to skip it if you’re not into semi-heavy lifting.
In the meantime, the coldest part of the air mass this week will focus more on the upper Great Lakes, northern plains, the northern Rockies and the central plains. It will turn notably colder in WNY too, but not so extreme as to our west. Lake effect snow will become more likely late this week. By then, a more persistent WNW flow will favor most of the lake snow to focus on the hilly terrain well south of the metro area, with only spotty lighter snow showers on the Niagara Frontier. It is possible that significant accumulations will develop on some of the hills. During the weekend, the flow may eventually become more WSW, then SW. That could bring a little more activity to the Niagara Frontier at times. More widespread snow showers may develop during Sunday into Monday in advance of colder temperatures which will spread throughout the Great Lakes early next week…colder than anything we’re going to experience this week. There will be additional lake effect potential next Monday-Wednesday, with gusty winds and the chance for some blowing snow. Of course, there is great uncertainty about any particulars involving lake snows so far in advance, including location and intensity. Temperatures will begin to moderate somewhat late next week.
It won’t be cold every single day, to be sure. And it’s too early to tell HOW cold it will be with any confidence beyond early next week. But after finishing a significantly 2.6 degrees milder than average October, we are likely to see more colder than average days from late this week through and past mid-November. A mild ridge of high pressure–something of a tall mountain in the atmosphere–will set up over western North America, forcing the northern/polar branch of the jet stream to go up and over the northern top of this ridge in western Canada. That’s where this jet will have a chance to pick up some modified arctic air and steer it toward the north central and Great Lakes states states. There will be some ups and downs within this overall pattern. Waves of low pressure will be preceded by short warmups and followed by renewed surges of colder air, after each low’s trailing cold front crosses our region. In pattern transitions such as these, precipitation tends to increase with each passage of a low pressure system and its fronts. It’s too early to determine whether the precipitation will be predominantly rain or snow. Typically when we’re early in November, there would be more rain than snow because we’re not talking about midwinter continental polar air just yet. Of course, there can be exceptions to this, so the meteorologists of 4Warn Weather will be monitoring these low pressure systems and the path of the polar jet stream very closely.
After unseasonable warmth on Tuesday, a cooler pattern will begin to take shape midweek. But the transition changes from cooler to Colder during Halloween into the weekend. A sharp disturbance will be able to tap in to the coldest air mass of the season. As this transition develops on Halloween into Halloween night, rain showers are likely to mix with snow and eventually turn to all snow by or during Friday evening, with some leftover snow showers around during Saturday. The chance for accumulating snow seems low near the Lakes, but a coating will be possible over higher terrain inland. One computer model has enough moisture for some modest accumulation over the interior, but another–the European–is less generous with the moisture accompanying the change to cold weather. This posting comes on a Monday night, so some change is still possible concerning snow chances. For historical perspective, it has snowed on 12 Halloweens in Buffalo, going back to 1871. The most recent significant snow was in 1993, when 2.8″ fell officially after rain during the day. While I’ve heard people’s selective memories picking out more frequent snowfalls on Halloween, actual data shows measurable snow is still a relatively rare event on October 31. Of those 12 Halloweens with observed snow for Buffalo, only 6 have been more than a trace (a trace means observed, but not enough to measure) and just 4 over 1″…and just 1 over 5″, in 1912 (6″).
As for this almost wintry hit Halloween night looks cold whether we have snow showers or mixed showers as a wind chill will increase; Saturday will be the coldest day of the season so far, with high temps only in the 30s, along with a nasty wind chill and some light snow or mixed showers. Sunday will be drier, and readings will edge back into the 40s. Temperatures are likely to go back above average much of next week, with some modest cooling possible late next week.