After the rain, the power outages from the ice storm, and the still-in-progress Tonawanda Creek flooding (at the time of this posting), the return to wintry weather will prove to be relatively benign…at least at the outset. Some limited lake snow will develop toward Tuesday morning and into Tuesday across Chautauqua County and western Cattaraugus County, with moderate to marginally heavy amounts on some hills. Thanks to a synoptic trough, snow showers will flare up over much of WNY on Tuesday, giving many parts of WNY a shot at a White Christmas, albeit a thin coating.
What is the bigger story is the return of our oft-discussed “indices” to having a role in our longer term pattern. That’s opposed to the cold weather which has resulted from a ridge over the north Pacific and an eastern trough which encouraged a polar flow from NW Canada (not Siberia). For the first time this cold weather season, the PNA will be slightly positive/cold phrase, the NAO will trend to slightly negative/cold phase, and the AO looks to trend sharply negative, as it had been earlier in the autumn. The 500mb ensemble means in the ECMWF, GFS, and Canadian GEM all support a ridge closer to the US west coast and an eastern trough–with no signs of a return to any lasting period of mild weather. We’ve already had those symptoms, but our indices were out of phase–which is quite unusual. There will be some quick ups, but undoubtedly the downs will outweigh and outnumber the ups over the next couple of weeks, minimally.
Lake Erie has bounced back to 36. That won’t last long. There are no signs of any major synoptic snowstorm in the next 6-7 days, but ski resorts will be able to make new snow and get some occasional help from nature.
Even as I type this post on Monday, lingering though weakening lake effect snow continues well south, and a little well north of the metro area. After this dissipates, the weak clipper we talked about last week will still bring us a minor snowfall later Monday night into Tuesday AM which will prove barely noticeable in places socked by Sunday evening’s LES blast. In the wake of this system, more significant LES will return later Tuesday night into Wed AM. Most models favor enough of a westerly flow to keep the bulk of this LES below the Buffalo Stowns, a trailing short wave might still be able to produce enough backing of the boundary lyr winds to get this stuff close to the Buffalo Stowns…this will bear careful watching, as accumulations in this band will likely be fairly heavy. And after this dies out Wed night, that’s the last we’ll see of LES for at least 5 days, if not longer.
The long advertised temporary moderating trend will set up on Thursday, with rainshowers moving in on Friday. Temps will drop back a bit on Saturday, but all 3 deterministic models show a well organized low coming up the Ohio Valley on Sunday, bringing widespread rain on the currently projected path. After that storm goes by, a colder pattern (not quite as cold as what we’ve been experiencing the last few days) will return for most of Christmas week. It’s a bit out in time, but the GFS and ECWMF both show a weak clipper approaching toward Christmas Eve, and another possibly better organized one behind it by the 26th. So, we may get a thin fresh coating of new snow to cover up the crustier older snow left after the rain.
Buffalo has a 30 year 57% probability of having 1″ of snow on the ground. I’d say our odds this year in the metro area are a little higher than climatology. However, the probability of 5″ or more is 23%, and I’m not prepared to make a call on that one. Some of it will be contingent on how much old snow survives the moderation and rain.
And this week will be no exception. As of this posting (midday Monday), it appears lake effect snow will begin fitfully with some minor amounts this evening, possibly near the metro area for a time, before settling to south of the metro area. On Tuesday, what’s called an anticyclonic curvature will be found in lower level winds, which makes for more drying and sinking motion in the boundary layer at least into early afternoon. When winds back to SW later in the day, ahead of a trough/short wave, lake snow will begin to become better organized…but there still may be some disruptive shear for a short time due to the trough. After a relatively brief visit to the metro area, with some limited accumulation, the axis of the trough will pass and winds will quickly veer to the Westerly flow which sends the LES into Ski Country. Between Tuesday and Thursday, several short waves will traverse the northern Great Lakes, each producing some backing and veering. The amount of backing (which would impact the metro area & possibly NE ‘burbs) is low confidence. The MEAN dominance of the westerly flow is somewhat higher confidence but, as some of you know, that doesn’t tell the whole story. There also will be variations in moisture availability and periods of shear. That means this isn’t going to be a “steady state” singular snow band all the way from Tuesday evening through Thursday. There will be ebbs and pulses, making for extraordinarily difficult accumulation forecasts.
In the extended range, the zonal-ish flow at the 500mb level toward mid-December no longer looks so zonal. The 3 main ensemble means show a rebuilding of the ridge in the eastern Pacific, and some troughing crossing the N Central states and the Great Lakes. The ECMWF and Canadian GEM are strongest with that ridge as we get closer to Christmas. The GFS ensemble is strong with it initially next week, but weakens iT during the 21st-24th. But even the GFS shows heights which would be cold enough to support snow in advance of the holiday. Before we get to that, though, there is good agreement in the medium range of an area of low pressure bringing us some synoptic snow during this next weekend. It may be on the slushy side, and it doesn’t currently look like a blockbuster snow storm, but it doesn’t look like a 90 pound weakling, either.
The work week will see readings moderate on Wednesday into Thursday, ahead of a slow moving cold front later in the week. An area of low pressure passing across the northern Great Lakes should bring a downslope flow on Wednesday, allowing readings to rise into the low–possibly mid 50s. Rainfall in scattered showers arriving late Wednesday and Wednesday night looks minor. A cold front oozing across the region by Friday may provide a pathway for some mixed precipitation, but most guidance takes the front far enough south and east so that WNY would miss the bulk of the moisture headed up to the middle Atlantic and NE states. Friday will be Cooler, and the weekend will be Colder, but nothing extreme. Some model ensemble members bring an area of low pressure close to us by Sunday night or Monday, but the majority of guidance shows nothing all that impressive. The European deterministic/operational model at 00z Monday was showing next week to be colder in general, but the ensemble mean doesn’t look as cold as the operational model.
Not my most exciting blog entry to be sure. But on the other hand, December is not shaping up to be milder than average in its first 2 weeks.
By Tuesday evening, WNY & northern PA may be under the gun…a snow gun…of highly uncertain caliber. As I’m posting this late on a Sunday (due to expected workload on Monday), there continue to be increasing signs of measurable snow heading into our viewing area Tuesday night from a deepening storm system which has a most favored track taking it into southern VA, then southern NJ. As per usual, track uncertainty on a tighter but critical scale remains high, even if the overall broader track has come together better today. A small shift to the west in the track would bring heavy snow into parts or all of our region, and a slightly greater shift to the west would cause the snow to become a mixture. A shift to the east could leave us with minor snow or snow showers. The speed of the storm suggests the steadiest and heaviest precipitation would occur Tuesday overnight, with somewhat lighter snow showers lingering on Wednesday. On this most favored track, major east coast cities and their airports would be impacted by heavy rain and gusty winds, causing air traffic delays (though not nearly as bad as heavy snow would produce) Tuesday night and Wednesday. In the storm system’s wake, Thanksgiving Day will be Cold with the chance of limited multiple bands of lake snow again on a NNW flow. It will be a cold and breezy Turkey Trot, with a significant wind chill. The afternoon high is likely to be in the mid to upper 20s, with some sunny breaks as well to help with the chill. Some moderation in temperatures will occur next Friday into the weekend, getting back toward the upper 30s by next Sunday.
Here’s the portion for more familiar weather enthusiasts: The 12z GFS and its ensemble mean have come into better agreement with the Canadian GEM and the ECMWF. All 3 operational models keep the heaviest snow just east of the 8 western counties, as do the ensemble means. However, when you examine the individual ensemble members, there is still enough spread so that mixed precip can’t be ruled out, as well as heavy snow–nor can lighter snow be ruled out with some of the eastern members. All in all, however, the probabilities for significant snow have increased, if not exactly heavy, and the probabilities of a “miss” have decreased. Our 15z RPM shows all snow, with moderate to heavy amounts, the heaviest E & S of Buffalo. Just E/SE of Allegany & McKean Co, a mixture shows up. Greater precision is just not possible right now.
Here is the just released Winter Outlook from the National Weather Service’s Climate Prediction Center. It is NOT a high confidence outlook, to be sure. But I agree with the uncertainties the Center has detailed:
This is a time of year in which normal climatology brings us lots of ups and downs in weather. We’ve recently had a few Novembers in which temperatures averaged a fair amount above average. This November often been Windier and occasionally Stormier than in those recent years.
This week of November 18th starts out seasonably cold and shifts over to seasonably mild temperatures before another transition to wintry temperatures occurs this weekend. This weekend: “Aye, there’s the rub.” Lots of uncertainty abounds, with large difference between the models, and their ensemble means. Sunday night, there were signs in the European model of a storm system which would have headed toward eastern New England and which might have given us a chance at some widespread snow. The Euro’s subsequent run took that storm farther north and east, with something of a cold blast moving in by Saturday night and Sunday. The GFS never showed that first Euro storm being close enough to us to give us widespread snow, nor did the Canadian. However, there is good agreement the coldest airmass of the season will be on its way this weekend with gusty winds and snow showers, along with some lake effect snow potential on a NW flow, which would focus the heavier LES on the hills again, well south. The GFS is considerably faster, bringing that arctic airmass in Saturday afternoon. I won’t dismiss that speed, since last week’s late week GFS wasn’t bad on the speed of Sunday night’s cold front. As of this Monday evening (bottom line) there are no good signs of a widespread heavier synoptic snowfall in WNY this weekend–though I’m not ruling out such signs recurring in future runs. But there’ll be no questioning the wintry atmosphere, with temps probably staying in the mid-upper 20s on a cold, windy Sunday, with a little moderation early next week. The GFS is chillier for Thanksgiving Day than the Euro, which has kept us consistently seasonable for that day. I won’t touch precipitation this far out.
For the bigger picture, the Climate Prediction Ctr (for newcomers…we just call it CPC) expresses high confidence for below average temperatures in the 6-10 day outlook, and average confidence for the 8-14 day outlook. That major 6-10 day cold anomaly may imply much below average temperatures for that whole stretch. However, I’m still expecting some ups within those downs. Here’s why. The indices don’t match up with a western ridge/eastern trough all that well. While I would expect the 2nd half, or even the last 2/3 of the weekend to be much colder than average, the pattern remains too progressive for a stable wrn ridge/ern trough to take up residence for too long a time. Plus, the positive heights which are showing up so frequently over the far SE also may be related to the lack of a persistently -NAO/-AO, and help to flatten the trough in the Grt Lks and NE. There continue to be no signs of a fundamental change in the PNA to cold/+ phase, so a western ridge which could force a cross polar flow simply won’t be there in the next 2 weeks. This doesn’t mean I’m expecting big Ups with any major above average temp periods…just not steady arctic air.
The MJO remains “incoherent”, weakly active, and is not expected to have a measurable impact on global weather in the next 2 weeks, at least not at our latitude. The ENSO forecast remains unchanged…neutral through next spring.
Temperatures will be heading back to near normal, then well above normal as we get into the weekend and next Monday. The initial warming will be tempered by gusty winds, adding a wind chill to the air. These winds will relax on Friday, and Saturday a more southerly flow will boost readings into the 50s. We’ll be even warmer on Sunday, with a gusty SSW wind. However, a deepening area of low pressure to our west will inject moisture into our region. The storm system will bring a strong, moist southerly flow to WNY on Monday. Both the ECMWF and GFS deterministic/operational models are in good agreement now this storm system will be deep as it passes to our north. It will bring more widespread showers into our region on a warm & windy Monday, and I’m seeing signs we may also experience some Sct Tshowers or even TStorms as a strong cold front approaches Monday night.
With this new agreement between the models, it now appears temperatures will drop rather sharply by Tuesday into Wednesday, ahead of some moderation later next week. Post frontal winds may be an issue, possibly reach Advisory criteria (or even stronger–too early to tell).
The ensemble means suggest some weak troughing either over the north central states or the Great Lakes right around Thanksgiving. As per usual, at that time range short waves and their respective amplitudes can’t be seen. The mean may end up being the smoothed mean of a higher amplitude flow. The Canadian mean has that hinted-at troughing moving back toward N & S Dakota, while the ECMWF has the trough axis at the Great Lakes. If the timing doesn’t change (and the odds on it not changing are fairly slim), Thanksgiving Day would be more likely to be cool than warm.
As I type this post, a Freeze Warning will be in effect late tonight for much of WNY. But the overall trending favors a gradual transition to above average temperatures occurring more often than not over the next few weeks. The western ridge will be “beaten down” by Pacific troughs/storm systems, allowing a mainly zonal flow to dominate by the end of the 1st week of November and into the 2nd. This continues to be a fairly high confidence extended forecast…more on that in a moment.
Within this milder than average mean trend, there will–of course–be ups and downs. Short waves will still buckle the flow, starting with a strong storm system late this week (that will produce winds approaching Advisory criteria by Friday). In its wake will be progressively chillier weather over the weekend, though nothing extreme. Some lake effect may develop in a WNW flow on Saturday, as rain showers. Some moderation will return by Monday, with signs of another short wave toward midweek, next week. Beyond that, short waves cannot be seen in the ensembles.
As for the zonal flow, the PNA ensemble has that index going negative/warm; the AO positive/warm; and the NAO positive/warm. None of this can be tied to the MJO which is weak, expected to remain weak for the next 2 weeks, and which is not propagating to the east.
But for snow/winter fans, I call your attention to the 3 words in my headline: “for a While”. This is not necessarily a sign of how trends are going to go later in the cold weather season…due to the usual variables which are not predictable beyond a couple of weeks.
Last week’s headline was telling, concerning “Hints of a Pattern Change.”
The signs are now clear we will be heading into a chillier pattern, in stages. What remains unclear is HOW chilly. And will snowflakes accompany the chilly pattern at any point?
In the broadest sense, the 500mb ensemble means offer good support for below average temperatures most days starting late this week, and amplifying by mid/late week next week. The more erratic deterministic/operational GFS & ECMWF runs at least have decent agreement between themselves on 850 temps dropping to -4 to -5, then -6 by late next week (0 or -1 or-2 generally won’t cut it at this time of the year unless there is unusual upward vertical velocity). In the GFS, the coldest part of the pattern seems to hold off until next Thursday-Friday.
If those temps were to verify, and if we had a cyclonic curvature to the flow, that would favor some snow at high elevations at times, with some possibility of a mix even at lower elevations. While these global models tend to show a predominantly NW flow during that period, they lack the resolution so far out to pick out lesser troughs/short waves which can cause alternate backing and veering of the boundary layer winds. The global models favor some periods of LES or LES/R during this cold period, but amplitudes can lessen between now and then. There may also be a trough in the SW undercutting the amplitude of the western ridge to some extent. So, while there may be some hints of excitement here for snow lovers, the cliche applies; “I wouldn’t get too worked up about it.” Not yet, anyway.
The MJO remains active, but it is weaker and will stay weak to moderate over the next 2 weeks (still considered active) with some possible eastward propagation. That weaker active status is reducing its impact at tropical latitudes to a limited extent. The indices are a mixed bag over the 2 week period. The AO is out of phrase with the NAO, tending to be closer to neutral. The NAO is sharply negative for a while, with a weakening amplitude later in the month, heading upward to neutral or even a little positive by Nov 1. The PNA is positive initially, but there is major spread in its ensemble members in week 2. The ensemble means have a flatter flow close to the end of their runs, which may be reflective of the less favorable NAO & PNA. But I wouldn’t say the mean goes completely zonal…just low amplitude.
Finally, there is continued high confidence for neutral ENSO conditions to continue well into Spring 2014.