June ENSO Update: El Nino Increasingly In Danger for Fall and Winter

It seems to me that the El Nino is in increasing danger for its survivability during the fall and winter months, with a variety of recent observations suggesting the El Nino has weakened and that near- to medium-term prospects are similarly downbeat. Click on any image to enlarge it.

We first begin with a look at the latest sea surface temperature (SST) raw values and anomalies.

Observed sea surface temperatures (top panel) and SST anomalies (bottom panel) for the seven-day period centered on June 12th.
Source: CPC

The actual observed temperatures, as shown in the top panel, are arguably more pessimistic with regard to the current state of the El Nino than temperature anomalies reflect. Indeed, where the top panel seems to suggest a total erosion of warmer waters and a filling-in of cooler waters (which appears symptomatic of a La Nina), the anomalies in the bottom panel are more sanguine, reflecting aggregate-neutral anomalies from the western coast of Ecuador to about 130 degrees West longitude. To the west of that, a swath of above-normal SSTs reflect the presence of El Nino conditions in at least some part of the Equatorial Pacific. 

In other words, while sea surface temperature anomalies (SSTAs) are rather mixed in the eastern Equatorial Pacific, it certainly looks more like an El Nino than a La Nina, a relief for fans of winter weather in the eastern United States. Of course, it’s never as simple as merely viewing one or two pieces of data. This situation gets far more intricate. In fact, there’s four different regions of the Equatorial Pacific that each make the situation rather intricate.

The four regions used for monitoring the ENSO phenomenon.
Source: CPC

There are four different parts of the Equatorial Pacific that meteorologists monitor to determine the state of the El Nino-Southern Oscillation (ENSO), the phenomenon that defines an El Nino or La Nina. When these sea surface temperatures are above normal, we call it an 'El Nino' event. When these anomalies are below-normal, we call it a 'La Nina' event. While we monitor the entire Equatorial Pacific to analyze the ENSO phenomenon, these four primary "zones" are:

Nino 1+2. This is a small slice of the Pacific located between the Equator and the 10º South latitude line, extending from the far western tip of Peru to the 90º West longitude line.

Nino 3. This is a larger slice of the Equatorial Pacific which spans from 5º North to 5º South latitude lines, and from 90º West to 150º West longitude lines.

Nino 4. This is also a larger slice, and also extends between 5ºN and 5ºS on the latitude markers. For Nino 4, however, the space is spread by longitude from 150º West to about 160º East, crossing the dateline in the process.

Nino 3.4. This is the critical area to watch, and is typically viewed as the primary space with which to assess the state of the ENSO phenomenon. Spatially, it extends from 5ºN-5ºS latitudinally, and 120º West to 165º West longitudinally.

Why do we break this space up into four different pieces rather than just average out the sea surface temperature anomalies and call it a day? A number of scientists with far more knowledge and research than I have come to determine that there can be more than one type of El Nino - where typically El Nino's bring warmer than normal waters to the eastern Pacific, an "El Nino Modoki" event brings warm waters to the western Pacific, and cooler waters to the eastern Pacific. This is not a trivial difference, but for our purposes here, we won't dive into that topic. For now, the key is understanding there are four different regions in which we monitor the ENSO phenomenon, with the Nino 3.4 region broadly being of most importance.

Now that we have an understanding of the parts of the Equatorial Pacific that are most important when analyzing the state of the ENSO phenomenon, we can proceed on to other observational data as of late.

SST Anomalies over the last year for the four ENSO monitoring regions.
Source: CPC

When breaking down observed SST anomalies over the four ENSO regions for the past year, as in the image above, it’s clear that this El Nino event is not clean-cut across the board. In Nino region 4, anomalies were recently seen about 1 degree C, a level that has been breached a number of times over the last year and a pretty strong signal of an El Nino event being in place – at least for that region. In Nino region 3.4, while positive SSTAs have been consistently seen over the past year, they aren’t at the same magnitude as in region 4, with a recent peak at the end of May only barely reaching 1.0 degree C above normal. Still, with this region consistently exhibiting anomalies above +0.5 degrees C, this region is also indicative of an El Nino, even if the signal is not as strong as in region 4.

Continuing eastward, region 3 is where this analysis begins to run into some troubles. While the recent history of region 3 anomalies has been positive and mostly above +0.5 degrees C, this same region saw anomalies turn negative as recently as early September 2018, with most-recent readings looking to dip below +0.5 degrees C to possibly a four-month low. Again, anomalies in this region have been pretty consistent in remaining above the +0.5 degree C level, which tells us an El Nino seems to be present. But the last year has shown anomalies that aren’t as stable as those seen in the last few months, which (at the very least) informs us that the current El Nino seems less established in eastern Eqautorial Pacific waters as compared to waters further west. Indeed, moving to Nino 1+2, this concept is confirmed. Anomalies are only now beginning to exit marginally-negative levels in this region, anomalies on a magnitude that set a ~10 month low earlier this month. Nino 1+2 seems to be more reflective of an ENSO-neutral set-up as opposed to the El Nino environment portrayed by the other three ENSO monitoring regions.

So far, we’ve established that there is indeed an El Nino present as per sea surface temperature anomalies. This is nothing new; the Climate Prediction Center has maintained an El Nino Advisory for some time now to reflect this. Let’s now turn to convective anomalies along the Equatorial Pacific and discuss something called the Walker Circulation.

If you’ve learned about the weather to some degree, you’ll know that a critical component to meteorology in the aggregate is the concept of heat transport. Whether it’s certain large-scale circulations like the Walker Circulation or Hadley Cell, or smaller-scale but still significant features like Rossby Waves or Kelvin Waves, the atmosphere has a plethora of ways by which it moves heat around the planet. Here, we’ll discuss the Walker Circulation.

Typical Walker Circulation pattern in a La Nina.
Source: Wikipedia

The Walker Circulation, in a nutshell, is an atmospheric circulation along the Equatorial Pacific that is closely intertwined with the ENSO phenomenon. Indeed, the ENSO phenomenon itself is a consequence (and, to a degree, an instigator) of heat transport in the atmosphere and in the ocean. The Walker Circulation changes with regard to longitudinal position of rising and sinking air depending on the state of the ENSO phenomenon, but the constant is that it involves an area of rising air, movement aloft of this air either to the west or to the east, and subsequent sinking air back to the surface before it moves either west or east (opposite the direction the air moved when it was aloft) back to the starting point to create that ‘circulation’ feature. 

The image above shows the Walker Circulation in a La Nina event as an example of how the circulation works. How can we tell this is a La Nina orientation of the Walker Circulation (aside from it being given by accessing the image)? Note the above-normal water temperatures in the far western Equatorial Pacific, just offshore Australia. This prompts convective activity, which sends warm air aloft. The air then travels to the east before cooling and then sinking over the waters just offshore of Peru. This sinking motion discourages thunderstorm development by suppressing air from rising. This air hits the surface of the water offshore Peru, and easterly surface winds transport that air back to where it started, just offshore of Australia. As a consequence of those easterly surface winds, water “piles up” offshore of Australia, a consequence of those surface winds pushing the water up against land. My favorite comparison to this phenomenon comes from the University of British Columbia where the author compares this “piling up” of water to someone in a bathtub blowing air towards the other end of the bathtub. In this scenario, the water is pushed to the other side of the bathtub and “piles up” there as well – albeit on a far smaller scale. To be sure, the actual piling up of water in the western Pacific from a La Nina Walker Circulation is also very small relative to the depth of the ocean, but it is still noticeable enough to address it. 

Let’s use observational data now to see if we can identify how the Walker Circulation is acting, to try and ascertain if the atmosphere is joining sea surface temperatures in signaling the presence of an El Nino.

OLR Anomalies over the Tropical Pacific from May 23rd through June 17th.
Source: CPC

The image above is titled with a strange acronym – “OLR”. OLR stands for Outgoing Longwave Radiation, and while much smarter people with much more research can provide a much better interpretation of it, for the purposes of this post we only need to understand how it relates to convection. Negative values of OLR correspond to increased convective activity, while positive values of OLR correspond to suppressed convective activity. Therefore, rising air / thunderstorms in the above image are shown by cooler colors, while sinking air / suppressed convective activity is shown by warmer colors.

Taking a gander at the above image, enhanced convection is seen across a good chunk of the Equatorial Pacific, namely between the longitude lines of about 150 degrees East to 150 degrees West. In contrast, broadly neutral to slightly positive OLR anomalies are seen east of the aforementioned area, extending all the way to the western coasts of Peru and Ecuador. With regard to the Walker Circulation, it seems as though the area of rising air is located east of Papua New Guinea, with that air then transported to the east and allowed to sink over the waters west of Ecuador. The surface winds would then appear to transport that wind to the west, completing the circulation. 

The only problem here is, this sort of circulation resembles the Walker Circulation in a La Nina, not an El Nino. In other words, if the Walker Circulation really is oriented like the paragraph above describes, water temperatures may support an El Nino but the atmosphere is more supportive of a La Nina.

Observed 200-millibar vector winds from May 23rd through June 17th.
Source: ESRL

Observed surface wind vectors from May 23rd through June 17th.
Source: ESRL

We can identify what the Walker Circulation is doing by checking out some composites of atmospheric variables as of late. For the benefit of comparison, I will view these variables using the same timeframe presented in the OLR graphic of May 23rd to June 17th. 

The top image above shows mean 200-millibar winds over the Tropical Pacific basin for this timeframe. In this graphic, we see the wind vector arrows looking like they’re ‘blossoming out’ away from a center point roughly located along the 180 degree line of longitude. This is called divergence, and represents air rising and then spreading out aloft. In severe weather, divergence aloft is crucial to sustaining thunderstorms, and the process is no different here. It is also no coincidence that the divergence aloft is juxtaposed with observed enhanced convection over roughly the same area – if there was convergence aloft and those arrows pointed in towards each other, convection would be suppressed. After the air rises east of Papua New Guinea, it has been transported to the east as shown in the graphic, before those vector arrows seem to converge at around the 120 or 130 degree West line of longitude along the Equator. This is that convergence phenomenon I just discussed, and represents air aloft that is coming together and now sinking.

After the air sinks back towards the surface, the second panel allows us to see how surface winds have been behaving over this ~month timeframe beginning in late May. After reaching the surface at around the 120 degree West line of longitude, surface winds have sent this air to the west and back to the starting point at about the 180 degree line of longitude, where the circulation starts over again.

In summary, over the last month the Walker Circulation has seen convection / rising air over about the 180 degree line of longitude, with the air then transported to the east aloft before converging and sinking at roughly the 120-130 West line of longitude. Once back at the surface, this air has been transported to the west back to its starting point, completing the circulation. Is this representative of an El Nino or La Nina? Let’s view the two Walker Circulation composites for each situation below.

Typical Walker Circulation cells in an El Nino state, with shading indicating SST anomalies.
Source: UBC

Typical Walker Circulation cells in a La Nina state, with shading indicating SST anomalies.
Source: UBC

When comparing the above two Walker Circulation composites for the two ENSO states to what was described / observed above, the circulation observed over the last month doesn’t line up exactly with either image. Looking solely at the recent flow aloft and comparing it to the above two images, the recent Walker Circulation has certainly been more akin to that seen in a La Nina. As both the La Nina image above and the recently observed flow show, upper-level winds are shown to be moving eastward after the 180 degree longitude line, and move westward over the waters offshore of Peru and Ecuador. This same pattern is shown in the La Nina image above, while the opposite is shown in the El Nino composite. At the surface, winds also reflect a La Nina pattern to some degree, with westward winds both observed and shown in the La Nina composite west of the 130 degree West longitude line, but observed winds are still easterly from the 130 degree West line of longitude to the coast of Ecuador, opposite of what a La Nina would see for that area. Also posing trouble in our interpretation of the state of the Walker Circulation is that observed areas of enhanced and suppressed convection don’t really line up with either composite graphic precisely, and again only seem to “lean” more towards a La Nina than an El Nino Walker Circulation. 

What do we then gather from all of this? Based on the behavior of the Walker Circulation, it seems that the atmosphere is more reflective of a La Nina than it is of an El Nino, in contrast to observed SST anomalies which promote a solid El Nino. This can be confirmed by viewing the Southern Oscillation Index (SOI), which has been seen at weakly-negative values (indicative of an El Nino) but also seen as “consistently near zero”, perhaps quantifying the somewhat-murky atmospheric features described above.

Recent history of the Southern Oscillation Index (SOI).
Source: BOM

So, we’ve got oceanic temperatures which are in favor of an El Nino, and atmospheric patterns which are broadly more akin to a La Nina than an El Nino. To try and remedy this discrepancy, we now look to the behavior of water temperatures in the Pacific basin below the surface.

Upper-ocean heat anomalies along the Equator.
Source: CPC

El Nino and La Nina events can be driven by Equatorial Kelvin Waves, and whether the wave moving eastward along the Equatorial Pacific is upwelling or downwelling. If that sentence made you raise an eyebrow, you're most likely not alone. I can assure you, though, it's actually pretty simple to understand. Let's break it down.

The phrase 'Equatorial Kelvin Wave' seems intimidating, so for our purposes here all we need to know is that, from time to time, these Equatorial Kelvin waves develop in the western part of the Equatorial Pacific and gradually move eastward along the Equator. When they move eastward along the Equator, they can be either 'downwelling' or 'upwelling' waves.

Consider the explanation of a 'downwelling' Equatorial Kelvin wave as described by the NOAA:

"Normally, winds blow from east to west across the tropical Pacific, which piles up warm water in the western Pacific. A weakening of these winds starts the surface layer of water cascading eastward..."

In other words, if this wind pattern that blows winds from east to west breaks down, that warmer than normal water begins pushing eastward along the Equatorial Pacific. This anomalously warm water works its way eastward gradually and tends to sustain itself in the process. As a consequence, downwelling Equatorial Kelvin waves tend to be associated with El Nino events. You can see my annotations of downwelling Kelvin waves as solid lines on the above image.

On the flip side, an 'upwelling' Equatorial Kelvin wave can be thought of as the ocean waters trying to get itself a little more in balance in the wake of this very warm downwelling wave. Thus, an upwelling wave again features a Kelvin wave slowly progressing eastward, but this time it cools down the upper-ocean waters to a degree that upwelling Kelvin waves are generally associated more with La Nina events. I’ve made an attempt to outline downwelling Kelvin Waves with gray lines, and upwelling Kelvin Waves with dark blue lines in the image above.

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Over the last year, we have seen several instances where warmer than normal waters traverse the Equatorial Pacific, as shown by the streaks of warmer colors. I’ve annotated these as downwelling Kelvin Waves. We have also seen a couple instances where either the warmer than normal anomalies subside in an eastward-moving fashion, or the anomalies outright flip to below-normal levels. I have highlighted these as upwelling Kelvin Waves in the above graphic. There are a couple items in particular I want to discuss with regards to the graphic.

First is how the recent downwelling waves seem to have been weaker with each iteration since a strong one traversed the basin beginning in late September 2018. With the exception of the wave which eventually strengthened significantly in March, recent downwelling waves have proved underwhelming. This poses a risk to the sustainability of the El Nino, as weaker downwelling waves make the El Nino more vulnerable to a deterioration to neutral-ENSO conditions, or even marginal La Nina conditions, especially if a strong upwelling wave propagates through with the atmosphere already unconvinced over the presence of an El Nino.

Second is how the far western Pacific has become increasingly cooler over the last several months. Indeed, anomalies on the order of between -1 and -1.5 degrees C have most recently been spotted right at the 150 degree East line of longitude, which marks the coldest anomalies over that part of the basin in at least a full calendar year. If this is the start of another upwelling Kelvin Wave and these deeper negative anomalies sustain themselves, there is a risk that the El Nino takes a severe hit in SSTAs, perhaps threatening its sustainability into the fall and winter months.

Model guidance for the Nino 3.4 region sea surface temperature anomalies.
Source: CPC

Seasonal model guidance is picking up on the increasingly-fragile El Nino. Where there is a good deal of spread between the individual model solutions in the above graphic, the general framework sees the Nino 3.4 region warming slightly this month into next before weakening through the fall, with a modest recovery back into weak-El Nino territory for the winter months. These models have a number of ensemble members of their own, which can all be tracked on a single image. As you might imagine, that image is very messy and does more harm than good in my opinion with regard to trying to explain what’s going on, hence why I’m not posting it here. However, I can tell you that the suite of ensembles and models show quite a spread in the forecast, implying substantial uncertainty over how the El Nino will evolve in the coming months. There is, of course, always uncertainty in these kinds of forecasts, but even for only a two-month forecast, the variation in ensemble forecasts for Nino 3.4 anomalies is from about -0.7 degrees C to about +1.75 degrees C. By December’s forecast, that variation blows out to a range of about -1.0 degrees C to more than +2.5 degrees C. The variation speaks to model uncertainty over how the El Nino will transpire over the next several months, including questions as to if it will be able to survive in what could be a hostile environment.

To Summarize:

- Current oceanic conditions indicate the presence of an El Nino, with warmer than normal SSTs present across most of the ENSO monitoring regions.

- Atmospheric conditions are more ambiguous, appearing more in line with vaguely-La Nina conditions as opposed to El Nino conditions.

- Further weakening of the El Nino appears likely moving into late summer and fall, which could bring the survival of the El Nino into question. 

- For the time being, it seems prudent to continue with the assumption of a weak El Nino moving into fall and early winter, but close monitoring is needed over the coming months as the El Nino is increasingly fragile.

Andrew

Spring, Summerlike Warmth Expected in Late April, May

I'm expecting the end of April and beginning of May to have seasonal to above-normal warmth across much of the country.

Tropical Tidbits

Shown above is the 500mb height anomaly pressure forecast over the West Pacific for April 26th. In this image, we see a strong ridge of high pressure stationed over Japan and East Asia, permitting the flow of above normal temperatures into the area. This event has significant implications on our weather here in the US. 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 use that rule, we can expect warmth over the United States around the May 1-5 period, if not for a longer time period than that.

The factors for warmth don't stop there- it goes far deeper, literally and metaphorically.

The image above may look complicated, but isn't that complex when explained thoroughly. Shown above is a graphical representation of a phenomenon called the Walker Circulation, also known as the Walker Cell. The Walker Circulation is most prominent in a La Nina situation, and forms when you have cool waters towards the Eastern Pacific, and warm waters near Oceania and Australia. The trade winds across the Pacific go from east to west in the Walker Circulation on the surface, due to the presence of high pressure in the East Pacific and low pressure in the West Pacific (think of it like a ball rolling downhill from the top of the hill (high pressure in the east Pacific) to the bottom of the hill (low pressure in the West Pacific), where the ball signifies the trade winds). When the trade winds reach the low pressure area in the western Pacific, the winds converge and begin pushing up into the atmosphere, creating thunderstorms. The air from the thunderstorms shoots up to roughly the 250mb to 200mb level before the winds spread out, as the air cannot rise further. From there, the air at 200mb flows from west-to-east, opposite the direction of the surface winds. Then, the high pressure and cool/dry atmosphere in the East Pacific pulls that air down back to the surface to start the whole process over again. As I said, this typically appears in La Nina situations, as cool waters in the East Pacific that are required for the Walker Circulation typically arise in conjunction with the La Nina.

The image above shows a view of surface pressure and surface wind vectors across the tropical regions of the world. We can use this image to identify the presence, or lack thereof, of the Walker Circulation. Taking a glance at surface pressures and winds from April 6th to April 10th, we do see surface winds flowing from east-to-west, a trait typically observed with the Walker Cell, and the low pressure center in Oceania also shows a characteristic of that circulation. This is rather odd, as we have been expecting an El Nino to arise, but the Walker Cell appearance here tells me that the El Nino has not hit the atmosphere yet, though it may start appearing in the surface temperatures. In recent days, the surface winds have been showing signs of weakening, indicating that the Walker Circulation may be weakening, which would herald the arrival of an El Nino if the winds reverse to a west-to-east stature.

For all intents and purposes, let's say that the Walker Cell's presence in the Pacific still indicates the presence of a La Nina (which is true in respect to the Walker Cell actually appearing, even though sea surface temperatures may argue otherwise). We can correlate sea surface temperatures in the Pacific to surface temperatures here in the United States. In the image above, the warm colors indicate a positive correlation of SSTs to surface temperatures (for example, warm Pacific SSTs would then correlate to warm temperatures in the US, or cool Pacific SSTs would lead to cool temperatures in the US). Blues in the above image then depict a negative correlation, where warm Pacific SSTs would lead to cool surface temperatures, and vice versa. In this case, with negative correlation signals across the US above, we can determine that below normal SSTs in the Pacific (La Nina) can then lead to above normal surface temperatures in the US, and vice versa. Thus, even though the SSTs in the Pacific indicate an El Nino, the atmospheric pattern is more supportive of a La Nina, which would then support warmer than normal conditions in the April-May-June timeframe. Despite this, since the Walker Circulation may be fading, this portion may just be a moot point in just a few weeks time.

This image here actually is pretty complicated, but I'll do my best to explain it. This graphic shows the layout of the Global Wind Oscillation (GWO), and what factors indicate the presence of the GWO in one of a possible eight phases. For example, if the GWO is to be in Phase 1, we would look out for negative mountain torque (MT) values, as well as enhanced tropical convection in the Indian Ocean. An additional description of the GWO comes from the ESRL, as shown in the screenshot below.

I outlined the Stage 1 description, as not only does it fit in with the current conditions that we're experiencing, but it is indicative of a La Nina, like we talked about earlier in this post. How do we know for sure that we're in the Phases 1-3 of the GWO (which are traditionally La Nina-esque phases)? Let's take a look at the indicators that depict Phases 1 through 3 of the GWO.

Observed Mountain Torque

Observed Relative AAM

If we look at the first GWO image we discussed, as well as the screenshot description of the GWO, we can see what defines these key phases. We see that negative mountain torque and convection in the Indian Ocean is a key definition of these first three GWO phases. Looking at that observed MT chart shown above, we see that the net MT is now below average, as the black solid line shows. While the convection in the Pacific is more displaced in Oceania instead of the Indian Ocean, the description highlights that the relative AAM is negative, and that relative AAM image above shows a negative anomaly. Overall, this does indicate the La Nina phases, also known as GWO phases 1-3, strengthening that correlation image, as well as the Walker Circulation discussion. Additionally, in the same sense that positive East Asian mountain torque can lead to cooler than normal temperatures in the US, the current negative East Asian mountain torque anomaly in the graphic above (red line two images above) indicates warm weather is more likely.

Importantly, in that screenshot description image, we see that the La Nina-like stages indicate a trough in the Western US. Typically, when we see a trough/stormy weather in the West US, we get a consequential ridge of high pressure in the East US, which is a textbook negative PNA pattern.

The image above shows observed sunspots in accordance with the 30-day sunspot cycle. As I've mentioned on this blog before, there is a known inverse correlation between the 30-day sunspot cycle and the Pacific-North American index (PNA). When the 30 day sunspot number is anomalously high, we tend to see the PNA in its negative phase. In the same sense, when the 30 day sunspot number is anomalously low, the PNA tends to reside more in its positive phase. Composite images of both the positive PNA and negative PNA are shown above, courtesy of NCSU.

500mb height anomalies of a negative PNA on the left (warm colors= high pressure, cool colors = low pressure)
Surface temperature anomalies of a negative PNA on the right

500mb height anomalies of a positive PNA on the left
Surface temperature anomalies of a positive PNA on the right

If we look back at the sunspot image, we see that the 30 day sunspot cycle is just off the charts, indicating a very high number of sunspots, or at the very least, elevated solar activity. If we use our solar correlation with the PNA, we may be expecting the emergence of a negative PNA regime in the near future. If we look at the composite image above for a negative PNA, we see that warm weather tends to prevail in that sort of situation. This fits in well with the GWO description we went over earlier, the presence of the La Nina Walker Circulation, and the East Asian correlation tool.

The last piece to the puzzle is the presence of enhanced tropical convection over Oceania.

The image above gives a global view of rising air in conjunction with enhanced tropical convection (blue shading), also known as negative Outgoing Longwave Radiation (OLR), as well as sinking air, exemplified by the beige shadings, which show suppressed tropical convection. The green contours highlight divergence, or air rising and spreading out due to thunderstorms, while red contours depict sinking of air. We see that there is an anomalous swath of tropical convection over Oceania, shown by the blues/tropical convection, and the wind vectors at 200mb going away from that convection. The placement of this tropical convection fits into a certain phase of the Madden-Julian Oscillation (MJO).

If we consider that the current center of the tropical convection is around the 165 East longitude line or 170 East line, we can see which MJO phase is best represented here. It looks like the MJO is currently in Phase 6 or 7, as the line on the 165 East shows splitting through the two panels on the right that are circled.

What does a Phase 6 MJO mean in the month of April?

The Phase 6 MJO looks like a typical negative PNA regime, with low pressure anomalies along the West Coast, and strong high pressure/warm weather in the Central and East US. This supports the overall warm weather idea, only adding to the rest of the factors supporting a warm weather regime in the late April and early May timeframes.

Let's summarize all of this.

• Based on a number of factors, warmer than normal weather is expected for the latter part of April, potentially well into the beginning of May.

Andrew