Stratospheric Trifecta Signals Brutally Cold February Ahead

It now appears that the stratosphere will kick off a number of indices that deem February to be the coldest prolonged period of winter thus far. In today's post, I will address multiple indices that favor a significantly colder than normal February.

Part I: The Stratosphere

•First Warming

In the opening days of January, we saw a stratospheric warming event occur. This event was minor, as the chart above (depicting temperature anomalies in the upper latitudes) shows. Nevertheless, this first warming event, coupled with the ongoing warming event is helping to destabilize the polar vortex in the stratosphere. So far this winter, the stratospheric polar vortex has been resistant to any and all attempts to be put down. We can attribute this to the positive phase of the Quasi-Biennial Oscillation (QBO), which is unfavorable for a weak polar vortex. These two first warmings are just tastes of what is to come. While the first warming was minor, it seems to have shaken up the vortex at least a bit, and this ongoing warming event right now is most likely helping with some slight (at the very least) destabilization of the polar vortex.

•Second Warming

There looks to be a second stratospheric warming event in the making about 5 days away from today. The GFS model indicates we will see a spike in stratospheric temperature values on January 17th, centered in northern Russia. If we take a look at how this warming is angling itself at the polar vortex, so to say, it is clear that this is going to be a Wave 1 event. There are two major types of wave activity- Wave 1 and Wave 2. In Wave 1 activity scenarios, the stratosphere undergoes distress as a major ridge attempts to displace the polar vortex from the Arctic, while keeping it fully intact. With Wave 2 activity, the polar vortex is experiencing ridging across the upper latitudes, making the vortex want to split into two vortices. These vortices can then shift to lower latitudes and bring extreme cold weather to the regions affected. The Wave-1 activity is usually seen as the strongest stratospheric intrusion out of the two, as a significant push of ridging/warm air is made to displace the vortex. With a Wave 2 pattern, you have two areas of high pressure, making it relatively easier to break up the vortex. Considering we see the polar vortex (depicted here as the very cold air mass) being pushed off to one side, with a swath of warm temperatures to the west, it does appear that this would be a Wave-1 stratospheric intrusion. Interestingly enough, this warming is one of the trifecta of warmings that could ultimately significantly damage the polar vortex...

The ECMWF model system is in agreement on this Wave 1 activity, and we can see how it projects temperature and geopotential height values to spike in Wave 1 denotations, as seen in the dark blue lines on the first two panels from the top, and the dark red lines on the third and fourth panels from the top. The top image shows Wave 1 and Wave 2 forecasts for temperatures at the 10 millibar level, and the spike in the dark blue line there confirms what the GFS is already telling us about the chances of a Wave 1 intrusion. The same is true for the second panel, where we see geopotential height forecasts for Wave 1 and Wave 2 activity at the 10 millibar level. Again, the anomalously high Wave 1 values confirm the idea that this second stratospheric warming event would come as a result of strong Wave 1 activity. The same ideas are portrayed in 30 millibar projections of temperatures (third panel from top) and geopotential height values (fourth panel from top)- the consensus is that this would be a Wave 1 intrusion.

•Third Warming

On January 23rd, the GFS starts another stratospheric warming event in roughly the same location as the warming event we just analyzed above. The difference from the second warming event and this third event is that the polar vortex is now well displaced from its usual domain in the Arctic Circle. The polar vortex is now elongated and is being pushed down towards Eurasia as the stratospheric warming events are now having significant impacts on the vortex. The ECMWF does not forecast past 240 hours, and since this forecast is valid at hour 276, we'll have to rely on the GFS. The effects these significant Wave 1 events can have are quickly shown by these two projected stratospheric warming events, and if they're true, we could be dealing with a pretty weakened polar vortex by the time we get around to February.

•Fourth Warming?

The long range GFS indicates that we will see a fourth, even stronger warming event in the closing days of January. We see the polar vortex has now reconsolidated itself from an elongated vortex to a more compact version. Despite this effort to regather itself, the polar vortex remains significantly displaced from its usual spot in the Arctic Circle. Based on temperature anomalies, it looks like this stratospheric warming event would be the strongest one so far in this series of warmings, though because this is just before the end of the GFS forecast time (forecast valid for roughly 16 days away), we can't really guarantee that this event will happen. However, if it did, there is a strong likelihood that it would be another crushing blow to an already-distressed stratospheric polar vortex.

Part II: The Bering Sea

This is the GFS Ensemble 500mb height anomaly forecast for January 18th over the Northern Hemisphere. We can see the highly meridional (wavy) jet stream, as is shown by the significant ridging and troughing over North America. The big story we will focus on here is the Bering Sea. If we look over towards the Bering Sea, we see a plethora of deep negative height anomalies, with the spaghetti charts on the right highlighting that body of water as being the epicenter of at least a decent-sized portion of the polar vortex. According to this forecast image, the Bering Sea would be encountering the polar vortex on January 18th. The reason I'm showing this is because of the Bering Sea Rule.The Bering Sea Rule states that by watching storm systems make their way across the Bering Sea, one can identify where and when a storm system will show up in the United States. The general timeframe is 17-21 days after a storm appears in the Bering Sea, a storm will appear in the United States. In this case, it looks like instead of watching for a storm, we might just have to watch for the polar vortex to enter the United States. If we extrapolate January 18th out 17-21 days, we arrive at a February 4-8 time frame. But that isn't all. The Bering Sea looks to be stormy from January 14th and onwards, meaning we could kick off February with some very cold weather- and stay that way. Time will tell, but this Bering Sea Rule signal is looking mighty cold for the US.

Part III: The Teleconnections

Long range Madden-Julian Oscillation forecasts from the University of Albany's Kyle MacRitchie call for the MJO to enter Phase 7 to kick off February. A common bit of knowledge for those familiar with the MJO is that the latter and early phases of this phase space (particularly phases 7, 8, 1 and 2) tend to favor more wintry weather over the central and eastern United States, whereas the middle phases aren't as supportive of snow and cold in those areas. This CFS Ensemble forecast image takes the MJO into Phase 7 for the first week or two of February, before it starts to swivel down into Phase 8. If the MJO can enter Phase 8 and stay there for the remainder of February, I can easily see the chances of significant cold weather in the US rising.

Temperature composites centered on February for each phase of the Madden-Julian Oscillation show how the big cool-downs start in Phase 8, and continue through Phase 3. While Phase 7 may look warm, I'm not that confident in the idea that the MJO would be able to overpower the other indices (i.e. PNA, NAO, etc) and create a warm environment. Regardless of just how the MJO plays out, it is apparent that we will see a shift towards those latter, wintry phases of the MJO. That should be enough to continue the early February cold through the month. The intensity may vary, but the idea of a cold February will most likely remain intact, especially after accounting for the stratosphere and the Bering Sea.

The second teleconnection to discuss is the atmospheric angular momentum index, or the AAM.

This AAM forecast, from Nicholas Schiraldi, shows the GFS projection of AAM anomalies on a time/latitude graph on the top panel, as well as an overall AAM anomaly forecast on the bottom panel. In the short and medium range we see a relatively neutral AAM, but towards the longer range, the GFS has been consistent in its idea that the AAM will be tanking well into negative territory as we approach February. If you were to take a look at the AAM phase space, the AAM is projected to hit Phase 1 before beginning to cycle through the low AAM phases, as you can see below.

If the AAM does cycle through these early, low AAM phases, one could expect an anomalously cold February. The reason? I took the time to look up February mid-level geopotential height anomalies when accounting for the January AAM values. The result is below.

This map shows correlation values over the Northern Hemisphere. Basically, this chart was constructed by taking January AAM values and looking at the next month's (February) 500mb height anomalies. If the AAM in January was positive, one could expect high pressure in Canada and the Northern US because there are positive correlation values shown. In the same sense, if the AAM were positive in January, February 500mb anomalies would ne negative, due to the negative correlation shown in the Southern US. In our case, we look to average out in slightly negative AAM values for the month of January. If we look at the chart above, we could anticipate seeing unusually cold and stormy weather in the North US, because the positive correlation means a negative AAM produces negative height anomalies. It's even possible that the polar vortex would come down to Canada again, but it's way too far out to speculate about that. As far as the South, it's possible we see some high pressure due to the negative AAM showing a negative correlation there (that equals positive height anomalies: high pressure). I don't think we would see that significant of ridging in the South, mainly because the other parts of the pattern support much of the East being chilly, not just the Northeast. Regardless, this does bode well for cold weather prospects for February in the US.

Part IV: The Forecast

I believe we will see February start out with brutally cold temperatures, as the Bering Sea argues. I have relatively high confidence in this cold really hitting the US hard to open February. Beyond the opening week of February, I anticipate we will see a continued cold pattern, but it will likely fluctuate. As any stratospheric influences begin to affect the US, we may or may not see enhanced cold weather- it will depend on the synoptic pattern around North America that will dictate where the core of the cold will go. Beyond mid-February, we should see the MJO enter Phase 8, which, if the forecast is correct, will allow for continued cold weather, specifically focused on the East US. Naturally, as time goes on my forecast confidence lowers, but the point is, there is definitely potential there for a very cold February.

Andrew

Atmospheric Pattern Discussion: Short Range, Long Range, Storm Systems

This is a pattern discussion which will highlight my thoughts for the short range period, the medium/long range period, and the long-long range time period into February.

Satellite imagery last night showed the development of a Kona Low just north and east of Hawaii, as the swath of enhanced water vapor shows in the bottom center part of the satellite image here. Satellite animation shows that this Kona Low is already flexing its muscles, inserting its moisture into the subtropical jet stream. The Kona Low typically not only enhances the subtropical jet stream, but also strengthens the chances of a negative Pacific North American (PNA) pattern, which involves stormy conditions in the West US and high pressure in the Central and Eastern US. This development of the Kona Low jives well with the predicted weather pattern in the next week or so, which should involve that stormy weather in the West US and quiet, warmer weather in the nation's heartland and along the East Coast.

This warmer weather will be weaving in an out of occasional storms and cool shots, as the Pacific jet is starting to rev up near the Gulf of Alaska. As the jet stream starts to head towards the nation, water vapor imagery tells us we can expect some storm systems to hit the west coast of North America in the next few days, and medium range ensembles agree, bringing a storm into the Central US in the next 3 to 4 days, and also bringing a second storm system ashore in southwestern British Columbia. It is this second system where we will find ourselves reverting back to the pattern that just brought us record-breaking cold as the polar vortex swiped us to the north.

The GFS Ensemble guidance believes we will see a piece of the prevalent polar vortex (shown above as being located in northwest Canada on January 12th) break off and begin to push southeastward into the United States. This piece of the vortex will force weak ridging located in the Central US out of the way, which will allow that polar vortex to push east. At the same time, as the piece of the vortex pushes east, we will see that suppressed ridging in the northeast Pacific (which looks to be putting up a very impressive Pacific jet stream) shift eastward, and actually form another situation where high pressure intensifies along the West Coast. This ridge intensification then permits the piece of the polar vortex to deepen and slow down, as the West Coast ridging tries to create a blocking situation.

By January 15th, we can clearly see the situation I described above, with the ridging intensifying along the West Coast and allowing the piece of the vortex to deepen and press further south. However, this event will be different than the one we went through earlier this workweek. When this next cold outbreak comes along, high pressure will be more suppressed and placed more to the east than before. This looks to be a consequence of that intense Pacific jet stream, which will allow high pressure to extend east and actually prohibit certain parts of the Rockies and Plains from getting in on this second wave of cold weather. Because of that eastward propagation of the ridge, I think we will see the Central Great Lakes into the Northeast really get in on this cold outbreak, with the western Plains and parts of the southern Plains getting snubbed by high pressure.

The next item to discuss is that January 17-21 potential Colorado Low / Panhandle Hook storm. If you recall, I have been touting this idea of a storm system for a while now in recent posts.

The pattern in the couple days prior to this time period looks a lot like what you see above, but another piece of the vortex looks to break off and deepen again in the Central and Eastern US to provide another cold weather opportunity. This storm will really depend on where high pressure will be located in the Western US, and how it will affect potential high pressure development off the East Coast. If we see the ridging centered more west, I can see better potential for this Colorado Low / Panhandle Hook storm verifying. However, if it is centered more to the east, the storm might not be able to pull off its act, as ridging may overpower it. Model guidance is pretty cloudy on just how this event will evolve, so right now I'll leave it as the storm being possible. I had previously had higher confidence, and still do in the sense that there will be some wintry weather in this timeframe, but location issues of this possible storm mean that this high confidence is somewhat reduced.

Confidence is reduced because of the projected East Asian weather for January 12th. Knowing that a storm in East Asia results in a storm in the US 6-10 days later, we can use that January 12th Japan storm that is shown above to project a storm in the timeframe of January 18-22. That falls right in the other timeframe for this storm. The reason my confidence is reduced in addition to the potential ridging issues is because that Japan storm is pretty far north in the country, almost to the north of the country itself. This may indicate that our storm system between January 17-22 may actually be more to the north than we thought. I'm not going to jump to conclusions, just something to ponder.

ECMWF Ensemble 500mb height anomaly guidance for January 24th shows us that the nation would be in for a cold but progressive weather pattern. This is exhibited well by the intense ridging along the western Coast of North America into the Gulf of Alaska. That intense ridging is the same high pressure pattern that made the environment conducive for a brush with the polar vortex earlier this workweek. However, we see some stormy weather just to the east of Greenland, and that tells me that the chances of seeing prolonged cold outbreaks and persistent west coast ridging are low. When you have stormy weather near Greenland, it results in a positive North Atlantic Oscillation (NAO), which means the pattern wants to keep everything moving west-to-east, not letting any high or low pressure system staying in one place for a long period of time. Thus, I expect we will see a cool end to the month, gradually easing up as the upper stratosphere has been cooling recently.

I have also been talking about a January 24-28 winter storm that may be either an Apps Runner or Nor'easter per my latest post. Now, we can add onto that with new data.

This image shows observed weather on November 27th. We can use data from the past to predict the future by utilizing the Lezak Recurring Cycle (LRC). The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a regular 40-60 day interval for the next ~10 months before it dissipates over the following summer. Considering this LRC season cycle length is 57 days, give or take a day or two, we can extrapolate November 27th out 57 days to get the reoccurrence of this coastal storm system. When we go ahead 57 days from November 27th, we arrive at January 23rd. And if you look closely, you'll find that it matches right up (off by a day, but who's counting?) with the January 24-28 timeframe for a coastal storm. Considering we have support from multiple indices at this point, confidence continues to grow for a late January coastal storm. Unlike some uncertainties with the Panhandle Hook storm, this East US storm looks more promising with this new data.

As we head into February, I'm thinking we will continue on the road of gradually easing out of the cold weather pattern we will have been in for much of January. Despite this, long range indices tell me we could see some continued stormy weather, and I'll be monitoring that potential in coming days and weeks.

An early Super Bowl forecast: Be on the lookout for a storm system on the East Coast in the couple days after the big game. Depending on the Pacific pattern, some cold air may be available to sweep east into the Northeast if an early February coastal storm does come to fruition.

Andrew

January 24-28 Potential Apps Runner / Nor'easter Winter Storm

There is the potential for an "Apps Runner" or Nor'easter winter storm around January 24-28, as a storm begins to traverse the Bering Sea in a favorable position.

This is the ECMWF 500 millibar anomaly forecast for the afternoon of January 5th, the day this post was published. You can see the deep negative geopotential height anomalies over the southwestern portion of the Bering Sea, and I drew a line outlining a rough track of where this storm system is projected to go in the next few days. Around January 6, the storm begins to cut north across the central/eastern Aleutian Islands, and then turns a little northwest to swirl in the Bering Sea. This is a telltale sign that we may be in for an Apps Runner or Nor'easter winter storm, as Joe Renken's Bering Sea Rule describes.

The Bering Sea Rule states that by watching storm systems make their way across the Bering Sea, one can identify where and when a storm system will show up in the United States. The general timeframe is 17-21 days after a storm appears in the Bering Sea, a storm will appear in the United States. This rule is already in use with the January 17-21 potential Colorado Low, and now it looks like the Eastern US might encounter some stormy weather if the Bering Sea Rule verifies correctly (which it has, when used previously).

The storm in the Bering Sea skirts in the southern portion of the waters across the January 5-6 time period, before cutting north on the January 6-7 time period. If we extrapolate that time frame 17-21 days out to use the Bering Sea Rule, we end up with roughly a January 24-28 period that we should watch for a potential winter storm. The reason I am labeling it as a possible Apps Runner or Nor'easter is because of how far east it cuts north. Joe Renken indicates that the further west storms cut north in the Bering Sea, the further west they end up 17-21 days later in the United States. In this case, our storm system here cuts far enough east that an Apps Runner or Nor'easter scenario does seem viable. The Bering Sea system is also displaying traditional characteristics of a Nor'easter scenario, where the storm moves in the southern waters of the Sea before cutting north quickly. A Nor'easter forms in a similar fashion, where the energy traverses the Southern US before shooting north along the East Coast.

To sum up:
There is potential for a winter storm over the January 24-28 time period, and indications are it could affect the Ohio Valley via an Apps Runner, or the Eastern Seaboard by way of a Nor'easter storm system.

Andrew

January 17-21 Colorado Low / Panhandle Hook Winter Storm

This is an update to the previous January 17-21 Potential Colorado Low/Panhandle Low Winter Storm post. Everything remains intact with this storm, and now the GFS is biting.

The following is copied from my December 27 post on this storm.

This image above from the Weather Prediction Center (WPC) shows the mid-level pattern over Alaska on January 1st. There are two systems marked on here; one storm system is over Alaska, as the dip in the height contours shows, and another storm is marked by the red 'L' just offshore of far eastern Russia. We're going to be watching the red 'L' for this storm system. Model guidance sees this storm cutting north over the western Bering Sea, and this is where we employ Joe Renken's Bering Sea Rule. The Bering Sea Rule states that when a storm moves through the Bering Sea, a storm system then moves through a portion of the United States 17 to 21 days later. If we see this system cutting north in the western Bering Sea around the December 31 - January 1 timeframe, we can then predict a storm system to cut north in the US as well 17-21 days later, which brings us to the January 16-22 time period. Because the storm is projected to cut north in the western Bering Sea, Joe Renken does believe that this signals a Great Lakes Cutter system around the 20th of January. Other subjects I will discuss below lend additional credibility to this timeframe laid out, as well as the predicted track of the storm.

The following MJO OLR portion is copied from my previous December 23 post on this storm, because the information remains valid.

The Bering Sea Rule isn't the only long range piece of guidance we can use to detect a potential storm. Here, in a CFS four-member ensemble forecasts developed by Kyle MacRitchie, we see the long range projection of the Madden-Julian Oscillation, in its eight-phase phase space diagram. Using this graph, we see that the MJO is projected to enter Phase 5 around December 27th, which all ensemble members agree on. Now, we'll take a look at the Outgoing Longwave Radiation (OLR) composites in the mid-latitudes for a Phase 5 MJO.

This MJO composite, developed by Nicholas Schiraldi, shows OLR anomalies in the 30 day period before and the 30 day period after the MJO hits Phase 5. In this case, negative lag days on the left side of the image show the number of days before the MJO gets to Phase 5 territory, while positive lag days on the left legend depict the number of days after the MJO hits Phase 5. We can substitute the lag day of 0 for December 27th, as that is when the CFS forecast above predicts we will get into that Phase 5 MJO. Looking ahead, we will ignore the red circled portion (that is for an upcoming post) and will instead take a look at the black circled part of the graph, where you can see blues shaded in. A look at the longitudes at the bottom of the image tells us the strongest negative OLR anomalies will be centered between the 85 West and 100 West longitude lines. If we put that together with the indication that this OLR anomaly chart is valid for latitudes between 55N and 40N, we find that the latitude lines cover the entire United States from Canada to Mexico, while the 85W and 100W longitude lines cover the US from roughly the Central Plains to the Great Lakes. If we clarify that negative OLR anomalies mean stormy weather, and observe that the circled blues are moving north and east, we can deduce that a Phase 5 MJO results in a storm system crossing the US across the Plains, Midwest and Great Lakes in roughly a northeast (or even east-northeast) direction. If we glance at the lag days on the left for when this storm would occur, we find that the circled blues encompass lag days of +17 to +25, meaning the storm would hit anywhere in a 17 to 25 day timeframe after the MJO hits Phase 5. 17 to 25 days after the projected December 27th arrival of the MJO at Phase 5 puts this potential storm system in the January 15-23 period. Now, in order to cut down on the large timeframe, I decided to shorten the positive lag days to cover the strongest negative anomalies only, which gave me a projected storm timeframe of January 18-21.

So we now have two timeframes for a potential storm system. The Bering Sea Rule gives us a timeframe of January 16-20, while the MJO OLR Composites give us a broad timeframe of January 15-23, which I shortened to January 18-21. If we put those two dates together, we end up with a broad-brush timeframe of January 15-21, which covers all dates outlined by either one or both indices. If we shorten that January 15-21 period to only include dates that both indices highlight, we end up with a January 18-20 timeframe for this potential Plains/Midwest/Great Lakes storm system.

How do we know the track of this storm?

Well, we've already deduced from the OLR charts that the longitude and latitude markings would strongly suggest a Plains/Midwest/Great Lakes storm system, moving northeast as it crosses those regions. With that in mind, I took a look at a device created by Larry Cosgrove and found two plausible storm tracks.

Image created by Larry Cosgrove.

The first track possible is a Panhandle Hook (A) system. We can see that this system fits the bill that was outlined by the OLR charts. It originates in the Plains and move northeast through the Midwest and Great Lakes. These systems tend to bring heavy wintry precipitation to the Midwest, Great Lakes and upper Plains, and, if all goes right, these systems can attain massive amounts of moisture from the Gulf of Mexico to enhance these wintry precipitation prospects.

Image created by Larry Cosgrove.

The second track that also fits the bill is a Colorado Low (A). The system originates in the Plains and then moves northeast across the Midwest and Great Lakes before progressing into Canada. The MJO OLR charts confirm that this storm is also a possibility, and the last time I used the MJO OLR charts to make a long term prediction, the results were spectacular. Because this potential event is still about a month away, we don't know how the teleconnections will react to possibly force this storm in a different direction than what the MJO OLR composites predict will happen. (End copied portion from Dec 27 post)

The latest 18z GFS has actually caught onto a storm in this timeframe, with the above image showing a storm valid on January 18th. I can guarantee you that this forecast will change, but it is interesting that we have seen the GFS bite on this idea of a storm system.

I expect we will see additional solutions with a storm around the 20th come about, just because of all of the factors supporting a storm in this timeframe. There are model solutions about a storm system just a few days before this projected storm system, and while they would technically fit into the MJO OLR Composite idea of stormy weather in and around the January 17-21 time period, I still believe the timeframe currently set forth will come to fruition.

Andrew

Long Range Outlook: January 1, 2014

ECMWF (left), GFS (center) and CMC Long Range 500mb anomaly forecast

Long Range Discussion
January 1 2014

Multi-model guidance above for the 8-10 day period shown is in average agreement, with highest disagreement area over northern Canada into Greenland, leading to additional disagreement over the Northeast United States. Model confusion revolves around whether to allow development of strong low pressure over Greenland, which would then help chances for ridging out towards the Northeast and East Coast. ECMWF and GFS are in the "best" agreement of the three model suite, with the ECMWF centering the anomalous low pressure west of Greenland and the GFS strengthening said low pressure system and placing it south and east of Greenland. The difference in location will affect the large-scale weather pattern, with a more compact solution with that upper-latitude low pressure system as exhibited by the ECMWF leading to stronger ridging along the East Coast. On the other hand, if the system is to be placed east of Greenland, the low pressure would be elongated from the Bering Sea out to the waters east of that land mass, and that would temper ridging prospects in the East US.

Model guidance is in good agreement on ridging keeping a chokehold on the Arctic Circle, which will prohibit reformation of the polar vortex across that area, and thus will keep the risk for cold weather across lower latitudes rather high. All modeling systems are also in agreement on ridging appearing over the southern Gulf of Alaska and into the north central Pacific, and we also find a consensus among the guidance with deep low pressure over the Bering Sea into Alaska. Now, for the long range that we are watching over for this time period (8-10 days out), this means we will be seeing a pattern that will most likely keep out extreme cold weather like we will see to kick off the upcoming workweek. In the long-long range, this somewhat-anti-cold pattern will flip over.

This map from Michael Ventrice shows 200 hPa velocity potential anomalies over a time-longitude graph. Blues and dashed ovals indicate the presence of enhanced convection (and thus a Madden-Julian Oscillation / MJO wave), while solid ovals and warmer colors signify a suppressed MJO wave. Taking a look at past, present and future conditions, we see how the MJO wave has been progressing across the Indian Ocean and towards the central Pacific for some time, oscillating through the various phases of the MJO. Some dynamical models were giving off a false "dead MJO" signal, where the guidance indicated the MJO was too weak to track. In reality, this was another body of enhanced convection firing over South America. This dual-placement of tropical convection is referred to as a "Wave 2" pattern, due to the two waves of active convection. In reality, the MJO signal was always oscillating around the phase space, as the progression of the MJO wave in the graph above shows. Now, as we look ahead, the GFS projects the MJO wave to continue pushing east, to be centered at the ~170E longitude mark around January 10th. This is a classic forecast of the MJO pushing through Phase 6 (centered around 160E), and Phase 7 (centered around 180). Model guidance should see an intensification of either the zonal flow across the US or ridging on the East Coast, as ridging in the US is common in a January Phase 6 event. A January Phase 7 event results in significant ridging in the West that will then transition us into the mid/late January cold blast that I began discussing earlier today.

Teleconnection forecasts from the ESRL agency appear to be handling the upcoming pattern decently well, with a few spots that may be refined in future forecasts. The Pacific North American (PNA) index is projected to be deeply negative in the short term, meaning deep troughing across the West US. I expect we see this deep negative forecast moderate to more neutral territory, as the MJO does not really support such a huge -PNA event. I find it more likely that this strong troughing will be more displaced to the east, as ensemble guidance supports. From then on, we see another negative PNA spell before spiking positive. I have good confidence in that +PNA spike in the long range, with some decent confidence in relatively neutral PNA values in the medium/long range. For the North Atlantic Oscillation (NAO), the index is projected to remain positive throughout the forecast period. I figure we will see a slight negative trend in the long range +NAO values, as an MJO Phase 7 supports more negative NAO values. However, other than that, I feel confident in the prolonged +NAO forecast. The West Pacific Oscillation should stay positive for much of the forecast period before a reduction to neutral or negative territory comes about in the long range in response to the transitioning MJO. I disagree with this WPO forecast. The East Pacific Oscillation (EPO) looks to me like it will be more negative than positive. The medium and long range EPO is projected to be positive, but ensemble guidance disagrees and places the EPO at a more neutral or slightly negative stance. I expect we will see some correction in that direction for future teleconnection forecasts.

To summarize, I anticipate some warmer weather arriving in the wake of brutal cold for the second week of January, before we see a trend towards colder conditions in time for the end of that second week and into the third week of January.

Andrew