brooklynwx99

overall, this event is certainly a "thread the needle" type storm, but things still look interesting given today's trend of a stronger, slower SS vort with less NS interaction. a GFS-like solution cannot be discarded at this juncture it looks like the American models are doing a decent job with this, as the ECMWF and RGEM took some steps towards the GFS/NAM. the 18z ECMWF made a nice shift towards a more favorable solution: of course, this remains rather unlikely, but I think it's worth looking to see if the 00z runs continue this trend

yeah... this system is pretty intriguing if that southern stream energy can separate enough. if so, it would be able to amplify and become something like the 00z GFS, which is a gorgeous solution at 500mb. cold air would not be a problem given a good source region in Canada and a rapidly developing SLP the ECMWF made a step towards holding the SS energy back, which is the main thing to look for here imo the GEFS is also more in favor of greater stream separation as well as a more amplified southern stream... these both bode well for this event more amplified ridging out west as well, this likely helps the SS gain amplitude

My original disagreement with those posts was that, at the time of my post, the -PNA was not nearly at the strength that it was. Therefore, I was claiming that the 3 SD ridge over Greenland would overpower the -PNA, which happens an overwhelming majority of the time. However, we ended up getting 510dam heights over Seattle, which is something that nobody could predict more than a few days in advance, let alone more than 10 days. I did anticipate the -PNA, but there was no way that anybody could see its record breaking nature at that lead time, which is what fully overwhelmed the pattern. Look, LR forecasting is hard, and I did not want to derail my intuition based on the slight possibility that an unprecedented event would occur. It would be just as bad if I said there would be a blizzard over the metro if there was a mean trough over the E US at 180 hours. Everyone makes mistakes though, the weather humbles everyone.

Unfortunately, although the anomalous -NAO/-EPO couplet did develop, it is impossible to overcome a record breaking -PNA. If the PNA was negative but not completely unprecedented (which is what I wrongly predicted), then this month would’ve turned out much differently. Nobody could’ve have seen the PNA being that overpowering, as it was literally a historical event, and there was no indication that an event of such magnitude would unfold. A “normal” -PNA would have been easily overcome by the -NAO, not a -3 sigma trough. So yes, there was a complete pattern change, but we got very unlucky and I’d be lying if I said I wasn’t a bit frustrated about it.

The GEFS and EPS have a gorgeous pattern evolution towards the end of their runs... this is thanks to the extension of the Pacific jet in the medium-long range: This jet extension is thanks in part to the +EAMT that is forecasted to develop in the short range: So, overall, it looks like there is some forcing that may be able to shake up this pattern. The jet extension will allow for the anomalous Aleutian ridge to build poleward and kick the mean trough out of the Pac NW and into the N Plains. This, in turn will allow for cold air to bleed into the E US: It's nice to see the changes to the Pacific jet, as those kinds of shifts on modeling are usually representative of a large shift in the pattern and not a temporary blip. It's great to see the blocking signal still holding strong as well, as the 50/50 ULL and -NAO remain prominent features throughout the runs. As long as the mean position of the trough changes to anywhere east of where it is now, that would be a massive improvement. The patterns on the end of the runs would be quite cold and stormy with the Pacific becoming much more favorable with the cold dumping into the midsection of the country. Now, of course, this could be a head fake, but I really don't believe so. The MJO is taking its time propagating through the Pacific, and Phase 7 forcing is more favorable in January anyway, so I don't see it as an issue. The +EAMT is also forecast to begin very soon, and the changes to the jet over the Pacific aren't very far out either. The forcing mechanisms that might help shake things up are in a tangible range. Overall, I would like to see these changes continue into the weekend. The Jan 2 period is intriguing, as there could be some TPV influence in Canada and some SS wave trying to cut underneath. That's really all you can say at this range. However, it's nice that we're getting some chances, and we have that possible threat as well as the small WAA push in a couple days that's worth keeping an eye on for some light snow.

The GEFS and EPS have a gorgeous pattern evolution towards the end of their runs... this is thanks to the extension of the Pacific jet in the medium-long range: This jet extension is thanks in part to the +EAMT that is forecasted to develop in the short range: So, overall, it looks like there is some forcing that may be able to shake up this pattern. The jet extension will allow for the anomalous Aleutian ridge to build poleward and kick the mean trough out of the Pac NW and into the N Plains. This, in turn will allow for cold air to bleed into the E US. It's nice to see the changes to the Pacific jet, as those kinds of shifts on modeling are usually representative of a large shift in the pattern and not a temporary blip. It's great to see the blocking signal still holding strong as well, as the 50/50 ULL and -NAO remain prominent features throughout the runs. As long as the mean position of the trough changes to anywhere east of where it is now, that would be a massive improvement. The patterns on the end of the runs would be quite cold and stormy with the Pacific becoming much more favorable with the cold dumping into the midsection of the country. Now, of course, this could be a head fake, but I really don't believe so. The MJO is taking its time propagating through the Pacific, and Phase 7 forcing is more favorable in January anyway, so I don't see it as an issue. The +EAMT is also forecast to begin very soon, and the changes to the jet over the Pacific aren't very far out either. The forcing mechanisms that might help shake things up are in a tangible range. Overall, I would like to see these changes continue into the weekend. The Jan 2 period is intriguing, as there could be some TPV influence in Canada and some SS wave trying to cut underneath. That's really all you can say at this range. However, it's nice that we're getting some chances.

The GEFS and EPS have a gorgeous pattern evolution towards the end of their runs... this is thanks to the extension of the Pacific jet in the medium-long range: This jet extension is thanks in part to the +EAMT that is forecasted to develop in the short range: So, overall, it looks like there is some forcing that may be able to shake up this pattern. The jet extension will allow for the anomalous Aleutian ridge to build poleward and kick the mean trough out of the Pac NW and into the N Plains. This, in turn will allow for cold air to bleed into the E US: It's nice to see the changes to the Pacific jet, as those kinds of shifts on modeling are usually representative of a large shift in the pattern and not a temporary blip. It's great to see the blocking signal still holding strong as well, as the 50/50 ULL and -NAO remain prominent features throughout the runs. As long as the mean position of the trough changes to anywhere east of where it is now, that would be a massive improvement. The patterns on the end of the runs would be quite cold and stormy with the Pacific becoming much more favorable with the cold dumping into the midsection of the country. Now, of course, this could be a head fake, but I really don't believe so. The MJO is taking its time propagating through the Pacific, and Phase 7 forcing is more favorable in January anyway, so I don't see it as an issue. The +EAMT is also forecast to begin very soon, and the changes to the jet over the Pacific aren't very far out either. The forcing mechanisms that might help shake things up are in a tangible range. Overall, I would like to see these changes continue into the weekend. The Jan 2 period is intriguing, as there could be some TPV influence in Canada and some SS wave trying to cut underneath. That's really all you can say at this range. However, it's nice that we're getting some chances, and we have that possible threat as well as the small WAA push in a couple days that's worth keeping an eye on for some light snow.

thanks! I usually post in the NYC subregion but I figured that most of the time my thoughts are just as applicable down here I really am quite optimistic about this pattern to close out the month. it's not perfect by any means, but it will provide chances and that's really all you can ask for in late December. early January could be nuts though if the WC only gets a touch better with that -NAO. it wouldn't have to be a big shift at all

That much of an anomalous west-based -NAO on a 10-15 day mean is just insane. We should start to see some chances around Christmas into the New Year with shortwaves rolling underneath the block (like the 12z GFS). It might warm up for a bit as the SE ridge pumps for a day or two in that timeframe, but that will be transient if it happens. Models often take a while to see the full effect of the block on the longwave pattern, and the EPS has generally done a horrible job from the start determining the strength of the block to begin with, so I'm not so sure I trust its depiction of the pattern over the CONUS as much as the other ensembles. The progression of tropical forcing will allow for the PNA region to become much more favorable for larger snowfall chances heading into early January. The GEFS and GEPS show this well as the trough focuses more towards the Rockies and cold air begins to spill into the E/C US as ridging begins to move towards the WC: That would be all this pattern needs to go from a bit better than average to something with huge potential, and it looks to be progressing that way as of now. Also, I've been hearing a lot of complaints about temperatures not being cold enough yet (not here, just generally), and I don't think that's as big of an issue as many make it out to be. Usually, when we see these big -NAO patterns, we're late in the season and climo is much more unfavorable temps-wise. However, we're in peak climo, and above normal 850mb temperatures are still cold enough to snow. We don't need big negative departures: Most of the NE/MA is either at normal or very slightly below average at 850mb, but temperatures are more than cold enough for any system going south of the region. With a pattern that'll allow for that, this is all that's needed to see snowfall events.

That much of an anomalous west-based -NAO on a 10-15 day mean is just insane. We should start to see some chances around Christmas into the New Year with shortwaves rolling underneath the block (like the 12z GFS). It might warm up for a bit as the SE ridge pumps for a day or two in that timeframe, but that will be transient if it happens. Models often take a while to see the full effect of the block on the longwave pattern, and the EPS has generally done a horrible job from the start determining the strength of the block to begin with, so I'm not so sure I trust its depiction of the pattern over the CONUS as much as the other ensembles. The progression of tropical forcing will allow for the PNA region to become much more favorable for larger snowfall chances heading into early January. The GEFS and GEPS show this well as the trough focuses more towards the Rockies and cold air begins to spill into the E/C US as ridging begins to move towards the WC: That would be all this pattern needs to go from a bit better than average to something with huge potential, and it looks to be progressing that way as of now. Also, I've been hearing a lot of complaints about temperatures not being cold enough yet (not here, just generally), and I don't think that's as big of an issue as many make it out to be. Usually, when we see these big -NAO patterns, we're late in the season and climo is much more unfavorable temps-wise. However, we're in peak climo, and above normal 850mb temperatures are still cold enough to snow. We don't need big negative departures: Most of the NE is either at normal or very slightly below average at 850mb, but temperatures are more than cold enough for any system going south of the region. With a pattern that'll allow for that, this is all that's needed to see snowfall events.

I can also take OP runs from 192 hours at face value

with a block that anomalous forcing confluence in SE Canada, a shortwave crashing in from the WC would be able to amplify given sufficient blocking of the flow it doesn't need to be super cold either since we're in peak climo, and average 850mb temps are -2 to -5 C March 2018 also had a significant WC trough, and it actually has a lot of similaities to the upcoming pattern w/ the Aleutian ridging and stout -NAO

if this pattern is a big problem then I have no idea what to say at this point

textbook retrograding -NAO on the 12z GEFS. gorgeous evolution here all around

I continue to remain confident on a wholesale change to the 500mb pattern over the next 10 days... this is mainly due to the strong MJO wave propagating towards the dateline, which will provide the impetus for -EPO ridging, as well as the anomalous Scandinavian trough which will retrograde into the NAO domain. The MJO is currently in Phase 7, and looks to make a break for Phase 8 as well within the next 10 - 14 days, which is favorable for high-latitude blocking and cold air intrusions into the E/C US. Although there have been some murmurs about the -ENSO interfering with the propagation of the wave, having it die before reaching Phase 8 with high amplitude, the -QBO state often allows for stronger, slower waves. This should allow for the MJO to continue its propagation through favorable phases. The Scandinavian ridge that's been talked about since the beginning of the month is now starting to form in the short range, and will reach +2.5 sigma: This cutoff ridge will retrograde towards Greenland, providing stout -NAO blocking that will, in turn, lead to significant confluent flow over Nova Scotia. This should keep the SE ridge at bay even with the -PNA. There will also be a great cold feed into the US from the -EPO forced by the MJO, which is a complete 180 from what we've been seeing recently. Both of these drivers should lead to a coast-to-coast trough, which becomes more apparent towards each of these runs: I've heard a lot of concerns about the -PNA, and I don't believe that they're totally founded. We will probably have to deal with the SE ridge before the blocking is fully established, but once the -NAO begins to retrograde, the compression of heights in SE Canada will ensue. This almost always crushes the SE ridge and allows for redevelopment of any systems that would try to cut. So it might be a problem towards the 20th, but the maturation of the blocking should allow for confluence to take over. Anomalous -NAO blocks like this have the potential to completely overwhelm patterns, and this one looks to become more and more west-based over time, which is optimal. If anything, a +PNA here would likely lead to supression until the block eventually decays. The negative anomalies throughout the Atlantic also lead me to believe that this is a legitimate -NAO, as the flow in that region is completely backed up. The high-latitude blocking will also lead to dramatic heat fluxes into the stratosphere, which look to constantly disrupt the SPV. I don't believe that the SPV will be able to consistently strengthen, and a weakening of the SPV may allow for prolonged blocking. A SSW isn't on the way as of now, but that would significantly disrupt -ENSO climo if it were to occur, and this would certainly be a step in the right direction. This December will almost certainly finish with a -NAO/-PNA combo. The Januaries that historically followed Decembers with a -NAO/-PNA featured favorable patterns for the E US with a significant west-based -NAO: Overall, I am quite excited for the end of the month, as things get very interesting any time we see blocking of this magnitude. I expect the SE ridge to continue to correct weaker as the -NAO trends stronger with time (as hemispherically forced -NAOs usually do), allowing for a coast-to-coast trough look. This would be the "just cold enough" type pattern where waves roll under the block with good climo. Hopefully we continue to see these corrections as we endure a dismal pattern through the 20th.

There has been research on the MJO-QBO relationship, and it has been found that easterly QBOs often lead to slower, higher amplitude waves of convection, so I am not overly concerned with the MJO dying out in Phase 8: "In summary, it has been found that the composite OLR anomaly shows a larger negative value and a slower eastward propagation with a prolonged period of active convection in the QBO easterly (QBOE) phase than in the QBO westerly (QBOW) phase." https://journals.ametsoc.org/view/journals/clim/32/21/jcli-d-19-0013.1.xm

really great look for us here with the huge -NAO developing. yes, there is a -PNA, but the persistent deep trough over Nova Scotia will likely provide significant confluence, making it difficult for storms to cut W of us a +PNA with that kind of block would likely lead to suppression (good for the MA/SE) until it decays later on

This is not a cutter pattern. Even the EPS with the most aggressive look with SE ridging, there is significant confluent flow in SE Canada modeled thanks to the anomalous -NAO blocking Not saying that this is a conducive pattern for large storms whatsoever, but the loading patterns for major snowstorms actually features significant western troughing that was overcome by the -NAO, so a -PNA isn’t a death sentence by any means

I’m not saying that everyone here is trashing the pattern here. All I was saying is that I think that the general tone of discussion is overly negative for what will be at least a serviceable pattern showing up around Christmas, that’s all

not sure why there’s so much doom and gloom with this kind of blocking showing up but I suppose you’ll always be disappointed if you want a perfect pattern also some of the goalposts have been shifted in here a bit. first, it’s “there’s gonna be a +AO/+NAO/-PNA” now it’s “the -PNA is solely going to ruin the pattern” when blocking like that does have the ability to overwhelm otherwise unfavorable pattern

Overall, I remain very optimistic about the end of this month, even if the next week or so will be an unabated blowtorch. There are a couple of pattern drivers that lead me to believe that a pattern change is on the way, both of which have been discussed in this thread already! 1) The tropical forcing. We are currently in phase 6, and there is considerable agreement that we will enter phase 7 (and perhaps 8!) at high amplitude. This is shown by the RMM plots as well as standard OLR anomalies: Phase 7 in December and January in -ENSO are correlated with very cold patterns for the E US as a whole: Therefore, I do believe that the MJO will have a positive effect on the pattern. There is a chance that the La Nina could destructively interfere with the propagation of the MJO, but the overall weak status of the ENSO state as well as the very high confidence of propagation overall lead me to believe that this is unlikely. 2) The Scandinavian ridging that is going to develop in the medium range with very high confidence. Both major ensembles are in great agreement that a highly anomalous Scandinavian ridge is going to form. A 2 sigma ridge will certainly have an impact on our pattern. These cutoff ridges are known to retrograde towards the NAO domain and provide intense blocking (March 2018) as well as provide heat fluxes to disrupt the SPV, which is also being shown on modeling as well. This is also coupled with a strong MJO pulse into 6/7, which has been known to help disrupt the SPV as well. Both of these may work in tandem to significantly perturb the SPV and promote prolonged blocking (this has been shown in some extended model runs). Based on the two significant pattern drivers noted here, I do expect a pretty quick change into a favorable (perhaps highly favorable) pattern for winter weather around Christmas week. There will likely be a period of time where the cold air dumps into the W US, but it should leak over as it usually does. The one wild card is if the MJO wave is interfered with. If this is the case, there could be some prolonged ridging over the E US as the western trough remains in place. However, I really don't buy it here. Generally, based on the composites shown, the MJO will have more of a positive impact on the EPO domain (and some Greenland blocking influence), and the Scandinavian ridge will have much more of an impact on the NAO domain. It's certainly nice to see all of these pattern drivers move forward and become stronger in time, and it shows that the pieces will likely be in place to shake things up. Therefore, I do expect some insanely warm weather over the next week, but I have the impression that it'll snap the other way to close out the month.