Strong El Niño May Be Materializing Faster Than Predicted

The strong El Nino that was discussed in a recent post, where we analyzed the possibility of an El Nino that may rival the 'Super El Nino' event(s) of the past, may be forming now- far sooner than originally thought. Note: This post is an update to my previous post on the impending El Nino, which can be accessed by clicking here.

Let's refresh our memories about the El Nino-Southern Oscillation phenomenon.

The image above shows sea level anomalies associated with the El Nino phase of the El Nino-Southern Oscillation (ENSO) phenomenon, as well as the La Nina phase. As is shown, an El Nino sees substantially higher than normal sea levels in the eastern Equatorial Pacific, while a La Nina sees below normal sea level anomalies. In the same sense, an El Nino observes warmer than normal waters over those same areas, and a La Nina depicts colder than normal waters in the same blue and purple areas shown.

The image above shows observed values of the Southern Oscillation Index, also known as the SOI. The SOI is calculated by observing pressure differences between Darwin and Tahiti near the Equator. Negative values of the SOI, namely below -8, indicate the dominance of El Nino-like conditions, while positive values above +8 show the presence of La Nina conditions. This graph goes back to January 2012, when we began to see a consistent negative SOI values. However, we then returned to typical fluctuations of the SOI in 2013. It is only now, in March 2014, that we have observed an absolute crash of the SOI in recent days, well into definitive El Nino territory. This collapse of the SOI well into negative values tells me the atmosphere is priming itself for the onset of the El Nino that we discussed a few days back. We've known for a while that the El Nino is on the way, but the SOI crash indicating an El Nino arising is happening far faster than originally predicted. But how can we know this is an actual El Nino emerging, and not just your normal fluctuation of the SOI?

The graphic here shows water temperature anomalies by depth over the eastern Equatorial Pacific, more specifically from the 140E longitude line to the coast of Ecuador, right along the Equator. Let's take a look at the top panel of this graphic, which shows the anomalies by depth (the bottom panel shows temperatures by depth, not anomalies). What we see is quite startling- there is a body of extremely warm water just under the surface of the Equator, controlling the waters 100 meters to 200 meters below the surface.  This swath of warm water tells us that there is a Kelvin Wave afoot.

This graphic, drawn up by Mike Ventrice, shows the sort of situation we're experiencing with the Kelvin Wave. As the Kelvin Wave pushes east, we see sea level anomalies rise in conjunction with the anomalous warmth. Ahead of the Kelvin Wave, we then see downwelling, which lowers sea levels and cools sea surface temperatures, leading to a 'false Nina', where the SSTAs might tell us there's a La Nina, but it's actually just a byproduct of the Kelvin Wave beginning to push east. 

This Kelvin Wave has been sitting in the waters below the Equator for some time now, but it is only recently that we're seeing the Kelvin Wave actually start to impact the surface waters. We can see how this is happening, as the temperature anomaly by depth image above shows two arms of warmer than normal waters stretching from the Kelvin Wave up to the top of the image. It's no surprise that the Kelvin Wave is impacting the surface. What is surprising, though, is how fast this is happening- the formation of an El Nino was expected to be around a 2-4 month timeframe, but now we could be looking at formation in just a matter of weeks.

We're also seeing skyrocketing upper ocean heat anomalies, confirming the idea that this is a true El Nino, and not just some random SOI fluctuation or the odd, small body of warm water pushing to the surface.

A more startling feature of this phenomenon is, even though we're seeing the warm water push to the surface, the Kelvin Wave is getting stronger rather than weaker.

This image shows three panels of observed sea surface temperatures on March 20th. We see climatology of sea surface temperatures (SSTs) on the top panel, actual observed SSTs in the middle panel, and anomalies of the observed SSTs on the bottom panel. We're going to be focusing on the bottom panel, where we can see the full strength of the Kelvin Wave. If you go back to the Super El Nino post, we saw the last observation of the Kelvin Wave at abut +5.35º C above normal. However, this image shows how the Kelvin Wave has strengthened to +5.64º C above normal- a +0.29º C increase in just a week! When you take into account that the Kelvin Wave that produced the 1997 Super El Nino was only +4.3º C above normal at the same time as this image (in March of 1997), it looks like we might be looking at the strongest Kelvin Wave observed to date. This would help the idea that we're looking at a Strong El Nino to evolve in the next few months (or weeks depending on how fast the Kelvin Wave propagates to the surface).

All of this tells me we are looking at the El Nino arriving much sooner than first predicted. Rather than the original 2-4 month timeframe I had been planning, it's possible we see an El Nino in just 4 to 8 weeks. I wouldn't be surprised if we saw the emergence of a moderate El Nino in about 6-12 weeks from today, with a strong El Nino arising in as soon as 12-16 weeks. This may seem like a long time, but when you consider my original projection for a potential strong El Nino was after August 2014, this is certainly a much sooner projection, reflective of what the Kelvin Wave has been doing in the last week or so.

Impacts on the United States include a potentially more active severe weather season, which I will address in my 2014 Severe Weather Season Outlook, to be issued tomorrow (Sunday). We may also see a more suppressed hurricane season, and this will be addressed in my 2014 Atlantic Hurricane Season Outlook, which will come out later on in April.

Andrew

Seasonal to Above-Normal Temperatures Just Days Away

Though one of the harshest winters to hit this nation in recent memory is still leaving its mark to this day, with below normal temperatures continuing to persist across the country, I'm finding new, concrete data indicating that warmer weather is as little as 10 days away - and it could be here to stay.

Tropical Tidbits

There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. In this sense, we can use the long-term weather pattern over Japan to predict when some seasonal, warmer weather will arrive in the US. Take a look at the graphic above. We see 500mb height anomalies from the GFS Ensembles over the Western Pacific. I use the ensembles rather than the GFS model itself, as I find the ensembles to be more useful in determining the synoptic (large-scale) pattern than the one model (remember the GFS Ensembles have multiple 'members' that add credibility and accuracy to its forecast). The image here shows 500mb height anomalies valid for March 24th, and looking towards Japan, we see oranges over Japan, indicating the presence of high pressure and warmer weather. Using the 6-10 day correlation, we can thus expect warmer, quieter weather in as soon as March 30th. We're about 9 days away from that today, and it might seem like one of those passing warm shots that then leads to another cold blast. The truth of the matter is, this warm-up looks to be sustained.

Tropical Tidbits

Fast-forward to the GFS Ensemble forecast on March 27th. Once again, we're looking at 500mb height anomalies over the Western Pacific. Looking at Japan, we see sustained high pressure and warmer than normal weather still over the area. At this point, if we go out to the end range of our 6-10 day gap from March 27, we might expect this warm-up to go as far out as April 6th. Bear in mind that this would be a relatively uninterrupted warm-up, as ridging would stick over Japan during this entire timeframe. No big storm systems, only quiet, warm weather. So, using this tool, we've established a warm-up timeframe of March 30th to April 6th. That's a full week of potentially non-stop seasonal to above-average temperatures!

But the warmth just keeps coming.

Tropical Tidbits

The image above shows 500mb geopotential height anomalies over the Western Pacific, now valid on April 1st. We are still seeing strong ridging over Japan, meaning our warm-up here in the United States could extend as far out as April 11th, the end range of our 6-10 day correlation tool. Beyond this timeframe, the ensembles get too spread out and we begin to see less and less confident forecasts in terms of projecting 500mb height anomalies in above or below normal categories. This is natural, as the ensemble members typically diverge in more noticeable features as the forecast period goes on. Despite that, the agreement of ensembles on continuous ridging over Japan is remarkable, and would give us at least 2 weeks of sustained warmth.

That's not the only item arguing for a end to winter in the next several days- the stratosphere is also doing its part.

The image above shows two panels of observed temperatures over the North Pole. The left image gives you observed temperatures at the 10 millibar level of the stratosphere, with the average temperature line in gray. The right panel depicts observed temperatures at the 30 millibar level of the stratosphere, with the average temperatures for that level shown in gray. The 10mb and 30mb levels are pretty high up in the atmosphere, when you consider that we live at the surface level of 1000 millibars. They seem even higher up when you consider most airplanes only fly up to the 250 millibar level or so, which is around that 35,000 foot mark. You can see on both panels how temperatures have been really bouncing around in recent months, until the last several days, when temperatures have skyrocketed to well above normal levels. After a relatively calm November through January in the stratosphere, what's going on up there?

The polar vortex is collapsing.

In my post the other day, I discussed how we were seeing a reversal of zonal winds in the upper levels of the stratosphere, indicating the collapse of the upper stratospheric polar vortex, and the significant weakening of the overall polar vortex. I talked about how this phenomenon was likely the result of the Final Warming, which is a massive stratospheric warming event in the end of winter that dethrones low pressure and instates high pressure in the stratosphere, a natural occurrence that happens each year. These Final Warmings usually signal the end of the winter in the stratosphere, and typically result in the end of winter 2-4 weeks later here at the surface.

The image above shows a six-panel graphic, each marking a day's observation of zonal wind anomalies by latitude, as the legend on the bottom shows, and by height in millibars, as the legend on the left shows. Going from the top row of panels to the bottom row, from least to most recent, we see a notable and rather sudden drop in positive zonal wind anomalies in the upper right-hand corner. Looking closer, we find this drop in anomalies over the 1 to 10 millibar level, in the highest reaches of the stratosphere (remember that we are based at roughly the 1000 millibar level, so 1 millibar is far higher than even what planes cruise at). Now, this transition from orange colors to blue colors in the top right hand corner of the most recent observation, marked under March 19 2014, means that the winds have reversed. In the Northern Hemisphere, positive zonal winds are also known as 'westerlies', as they move to the east in a counterclockwise formation. That is why we look for areas of positive zonal winds to identify the polar vortex in the stratosphere, because the polar vortex is essentially just one big low pressure system. In the same sense, negative zonal wind anomalies define 'easterly' winds, as they blow towards the west. Recall that high pressure winds spin to the west in a clockwise motion, providing the reason why we look for negative zonal winds to tell if the polar vortex has weakened. In this case, rather than the positive zonal winds just weakening a bit, it looks like they completely reversed in the far upper stratosphere, marking a collapse of the polar vortex at that level. We saw that reversal of winds in the upper stratosphere a few days ago, but it's only now that we see a rapid decline in oranges and reds across the middle and lower stratosphere, as well as the staying power of the negative zonal winds in the upper stratosphere. This all tells me that we are indeed in the process of the Stratospheric Final Warming, and we should see the end of wintry weather in the next 2-4 weeks, when the effects of occurrences in the stratosphere usually impact the surface. There may be a chill in that timeframe, as this is still, to some degree, a stratospheric warming event, which can result in chillier than normal weather. However, this would likely be short-lived, as our East Asian tool tells us warmer than normal weather is the new norm in coming days and weeks.

To summarize:
• There are increasing amounts of data that suggests we will see sustained warmth to start off April.
• The stratosphere indicates we'll be seeing an end to wintry weather in just 2-4 weeks.
• Other indications suggest sustained warmth may be just 10 days or so away.

Andrew

March 25-27 Potentially Significant Blizzard

I'm watching the potential for a potentially significant snowstorm that model guidance believes will become a blizzard.

The image above shows 500mb geopotential height anomalies from the latest run of the GFS model over the Western Pacific, valid for March 20th. As this image shows, we see strong negative height anomalies present over Japan on March 20th, indicative of a rather strong storm over the area. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. So, if we take this March 20th storm and move it ahead 6-10 days, we find a potential storm system around the March 26th through 30th period.

Let's take a look over current model guidance. Shown above is the latest forecast from the Canadian GGEM model, valid on March 26th. We see an extremely strong storm system positioned just offshore of the Northeast, dumping heavy precipitation on the order of over 12" on inland areas, with multiple FEET of snow falling on coastal locations. The GGEM model has already been shown to be suffering from convective feedback issues on this run, meaning precipitation amounts are grossly exaggerated and incorrectly altered due to this specific bias. Thus, this forecast run is overdoing precipitation amounts and is not correct in its forecast at this time. What I do agree with, however, is placement of the storm. We look to be in a northwest flow regime, a pattern notorious for providing a very favorable environment for East Coast snow events, and we'll discuss this a bit later.

We now move on to the ECMWF model, which also shows a very strong storm system displaced just east of the Northeast coastline. This is of similar strength to the GGEM model and would likely be putting down some pretty darn heavy snow amounts, but because we lost access to the main provider of our weather maps, we can't give an indication as to just how severe this storm looks to be on the ECMWF. However, once again, we're seeing this strong storm in the midst of a northwest flow pattern, as we see the dashed lines dropping down to the southeast from Canada. This is crucial to the forecasts of a strong East Coast storm.

The American GFS model is far less enthusiastic about this storm, only putting down modest precipitation along the coastline and sparing inland regions from any accumulating precipitation, snow or otherwise. This is considered the outlier forecast when taking into account how the GGEM, ECMWF and ECMWF Ensembles believe we'll see a strong East Coast-hugging storm, but in the grand scheme of things, there is high model agreement on a storm at least threatening the East Coast in this timeframe, and that's what we're looking at here.

Take a look at this graphic above. This image shows a few things important. The main item we see first are the negative 500mb and positive 500mb anomalies, marked by contour lines in blue and red, respectively. Just glancing over the image, we find a sustained northwest flow scenario unfolding, with deep negative height anomalies pressing into the East US, with high pressure surging northward in the West US. The second item we need to discuss are the dates on the bottom right hand corner. They are analog dates, listed from top to bottom, and the date at the top means its pattern is most similar to the pattern forecasted in the graphic itself, which is valid around the March 26-30 period, right on top of the timeframe outlined for this potentially significant storm. Look closely at the dates- are you picking up on one particular date in that list? If not, check out the second date from the top. That pattern was deemed to be the second most similar to the pattern expected to unfold as this storm system impacts the East US. And that date - March 16, 1993 - spawned the 'Storm of the Century'.

Now, there are some who are anticipating another Storm of the Century because its date has shown up on these analog images, and they might tell you to prepare for feet of snow. All that we know now is that model guidance is hinting rather consistently at the potential for an all-out blizzard in the East US, specifically the Northeast. As of right now, there is disagreement on who could get hit by the storm, and there's even disagreement on if there'll be a storm at all. As of now, the potential for a significant storm is rather high due to the East Asian correlation, but it remains to be seen if this could be a blizzard for the East Coast, hence all the caveats throughout the post.

Andrew

Stratospheric Polar Vortex Collapsing; Final Warming Occurring?

We're going through a collapse of the upper stratospheric polar vortex at this moment, and it's now possible that we are seeing the Final Warming event occurring.

The image above shows a six-panel graphic, each marking a day's observation of zonal wind anomalies by latitude, as the legend on the bottom shows, and by height in millibars, as the legend on the left shows. Going from the top row of panels to the bottom row, from least to most recent, we see a notable and rather sudden drop in positive zonal wind anomalies in the upper right-hand corner. Looking closer, we find this drop in anomalies over the 1 to 10 millibar level, in the highest reaches of the stratosphere (remember that we are based at roughly the 1000 millibar level, so 1 millibar is far higher than even what planes cruise at). Now, this transition from orange colors to blue colors in the top right hand corner of the most recent observation, marked under March 15 2014 means that the winds have reversed. In the Northern Hemisphere, positive zonal winds are also known as 'westerlies', as they move to the east in a counterclockwise formation. That is why we look for areas of positive zonal winds to identify the polar vortex in the stratosphere, because the polar vortex is essentially just one big low pressure system. In the same sense, negative zonal wind anomalies define 'easterly' winds, as they blow towards the west. Recall that high pressure winds spin to the west in a clockwise motion, providing the reason why we look for negative zonal winds to tell if the polar vortex has weakened. In this case, rather than the positive zonal winds just weakening a bit, it looks like they completely reversed in the far upper stratosphere, marking a collapse of the polar vortex at that level. Also note the lack of strong zonal winds in the mid and lower stratosphere, also indicative of a very fragile polar vortex.

An analysis of the 1 millibar level's temperature and height contours tells the story. In this view, covering the Northern Hemisphere (if you look closely you can see the continent outlines in white), we see high pressure duking it out with low pressure-- and winning. The high pressure has taken over the Arctic Circle, pushing the upper stratospheric polar vortex to the south. The swath of warmer than normal temperatures is also helping to weaken the polar vortex to the point that those zonal winds have reversed, meaning the polar vortex has fallen.

Let's take a look at another multi-panel graphic to get an even better handle on this situation. On the top panel, we see something we're already familiar with- the turquoise line denotes zonal wind values at the 1 millibar level, and the prominent dashed line indicates the separation line between positive zonal winds (upwards from the dashed line), and negative zonal winds (downwards from the dashed line). This graph tells us that as of late, zonal winds at the 1 millibar level have been sustained at negative levels, confirming this idea that the winds have reversed in the upper stratosphere, leading to a failure of the polar vortex. The panel just below that one shows us zonal winds for the 10 millibar level (blue) and the 30 millibar level (red). While these two levels are not seeing negative zonal winds, they're awfully close to zero on that graph, and that tells me something else is going on here. I'm led to believe that we are now under a final warming warning, if you will.

In the winter, there are sudden stratospheric warming (SSW) events that see massive quantities of warm air shoved up into the stratosphere, disrupting the polar vortex and sending frigid air down to lower latitudes, such as Eurasia and North America. However, in late winter or early spring, we see a massive warming event that reverses zonal winds to negative values for the summer. This means that we see the polar vortex disintegrate for the summer, replaced by dominant high pressure. This process is natural and happens every year. Now that we're in March, and we're seeing a stratospheric warming event that looks like it's dragging down positive zonal winds across the stratosphere to zero or negative values, it looks to me that this could very well be the Final Warming for the winter, heralding the end to the winter of 2013-2014 (at least in the stratosphere).

The 10 day ECMWF zonal wind forecast, the same format as we saw in the six-panel image at the top of this post (except valid 10 days from today), gives a prognosis that the Final Warming is either occurring or will occur soon. Even 10 days from now, we see slightly negative zonal winds now extending from the top of the stratosphere down to the 20 millibar level. Yes, we see a spot of positive zonal winds centered around the 30 millibar level on the right side of the graphic, but no big rebound to a strong polar vortex in 10 days' time tells me the stratosphere is shutting down for the summer.

This means, in layman terms, that winter could be over in just 2-4 weeks. It might seem like a long time, but it's better than not knowing if it will end at all, right?

Andrew

March 26-30 Potentially Significant Storm System

The potential for a potentially significant storm system over the March 26-30 period remains alive.

Tropical Tidbits

The image above shows 500mb geopotential height anomalies from the latest run of the GFS model over the Western Pacific, valid for March 20th. As this image shows, we see strong negative height anomalies present over Japan on March 20th, indicative of a rather strong storm over the area. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. So, if we take this March 20th storm and move it ahead 6-10 days, we find a potential storm system around the March 26th through 30th period.

In an earlier post, I had addressed the idea of two strong storms in this timeframe. Model guidance has dropped the idea of two storms on March 20th in Japan, and appears to be going with one storm instead.

Tropical Tidbits

If we look at the long range GFS jet stream forecast for March 26th, the beginning of this four day timeframe where a storm is expected, we see a few things. The primary thing we want to discuss is the active subtropical jet stream. If you recall, there are two jet streams which have the most effect on our weather (there are three jet streams in total): the Pacific jet stream, which comes from the Pacific and is a primary driver of weather pattern, and the subtropical jet stream, usually located in the South US, with less influence but high-impact effects at times. In this case, I'm concerned because an active subtropical jet stream combined with this potentially strong storm system may create a severe weather situation. There are a lot of variables that need to come together for this to happen, but we've at least established the idea of a strong storm system hitting the US in this timeframe. This is indeed something to watch out for.

Andrew