Tuesday, August 19, 2014

Perfect-Scoring Winter Analog Paints Ominous Picture for Upcoming Season

For the first time, an analog year has matched all five of my parameters for the upcoming winter season, and is now indicating that the upcoming winter could be another rough one.

The analog year that matched all five parameters was the winter of 1958-1959.  The image above shows 500mb height anomalies during the December-January-February period of that winter season. In this graphic, blues and purples depict stormy and cold weather, while yellows and reds indicate warm and quiet weather. The winter of 1958-1959 saw strong ridging/high pressure positioned over the north-central and northwest Pacific regions, with some stormier weather observed near the Gulf of Alaska. This Pacific ridging extended well into the Arctic, helping to dismantle the mid-level polar vortex, sending it to lower latitudes like we saw last winter.
In North America, we observed what appears to be the polar vortex centered in the Canadian Maritimes, spreading its influence across Canada and into the North US. Some slight ridging was recorded in the West US, especially into the Southwest, as well as the Southeast.

Let's push on to the temperature composite for the winter of 1958-1959.

During the winter of 1958-1959, much of the nation was locked into a rather brutal winter, with temperature anomalies in the North US dropping below -6.0 degrees Fahrenheit, anomalies not too far off from what we saw this past winter, in 2013-2014. The core of the cold was placed from the Upper Midwest into the Great Lakes, but below-normal temperatures snaked their way through the entirety of the Central and East US, save for Florida, which saw weak ridging. The West US saw a very warm winter in December-January-February of 1958-1959, again a similar story to what was seen in 2013-2014.

Lastly, let's go ahead and check out precipitation anomalies from this analog.

During the winter of 1958-1959, very dry conditions plagued the Southern Plains, Gulf Coast, and southern Ohio Valley all the way into the Northeast and Mid-Atlantic regions. Precipitation anomalies below -5.0 inches were recorded in Mississippi, Alabama, Louisiana and Oklahoma, just to name a few. The dry conditions extended north into the Midwest and Upper Midwest, but wetter than average conditions prevailed in the upper Ohio Valley, along the eastern Great Lakes. This was also the scene in Florida, and coastal Texas. The Pacific Northwest experienced a rather wet winter in 1958-1959, while some parts of the Southwest dealt with dry conditions.

Let's break this all down.

The winter of 1958-1959 matched five out of five parameters I set forth that indicate what this winter will look like. For instance, it is expected that the winter of 2014-2015 will see a positive PDO, and the winter of 1958-1959 had that as well. Such a comparison happened, successfully, four other times. It's quite rare to find an analog as similar to projected conditions as this one, and we can only hope that the similarities stick as we head into fall.

Analog forecasting gives us a general idea of what the upcoming winter may be like. It's not a set-in-stone picture of what we will experience. While I cannot confirm that we will see a very dry or cold winter, the chances of both are considered to be elevated, if this analog year is to be believed.


Monday, August 18, 2014

Modoki El Nino Gaining Control; Winter Outlook Grows Colder

It appears that a Central-Based, or Modoki El Nino is now gaining control, resulting in the outlook for this winter growing colder.

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The image above, provided by the JAMSTEC agency, shows typical sea surface temperature anomalies during a Modoki El Nino. The presence of this Modoki Nino is clearly shown by the positive anomalies in the central portion of the Pacific, hence the interchangeability between Modoki and Central-Based El Nino. During the Modoki Nino, cooler than normal SST anomalies tend to appear offshore Ecuador, something we'll discuss a little later in this post. Looking towards the north Pacific, predominantly warm SST anomalies are observed, from the Sea of Japan, to the Bering Sea, to the Gulf of Alaska. Warm water anomalies are also recorded near Baja California.
Out in the Atlantic, warmer than normal waters surround Greenland and are placed into western Europe, with cool water providing a separation between that mass of warmth, and the second body of warm water juxtaposed near the Canadian Maritimes. The Indian Ocean also exhibits a slightly negative Indian Ocean Dipole signal (identified by cold water near Somalia and warm water near India) during Modoki El Ninos.

Let's now compare this typical  Modoki set-up with today's SST anomalies.

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Taking a look around the globe, we can identify several points of interest and discussion when comparing the Modoki composite image, and the daily SST anomalies from August 17th. Beginning in the Pacific, we see warm water anomalies off the coast of Ecuador, and cool anomalies in the central Pacific, basically opposite of a Modoki set-up. We'll dive deeper into that a little later in this post. Moving up to the North Pacific, we observe a swath of warmer than normal water temperatures in the Northeast Pacific/Gulf of Alaska, nearly identical to the anomalies seen during a Modoki Nino. The comparison is once again similar when we confirm warmer than normal waters stationed off Baja California, as also seen in the composite image. The Sea of Japan was well above normal earlier this week, as it is during typical Modoki El Nino events, but has since cooled due to the passage of Typhoon Halong over that area.
Transitioning to the Atlantic, additional similarities are found. We can see the warmer than normal waters near Greenland, pushing east into western Europe, as was also found in the Modoki composite image. There isn't much of a cold pool of water just south of Greenland, but warmth is observed near the Canadian Maritimes. The Indian Ocean is also displaying the same negative IOD pattern observed in a typical Modoki El Nino event.

Now, all of these similarities are impressive, but what about the El Nino itself in the Pacific? It looks nonexistent- actually opposite, of what the Modoki composite image shows us.

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The animation above shows us water temperature anomalies, the same variable examined earlier in this post, but now analyzed on a depth chart. The legend on the left displays depth in meters along the Equator, while the bottom legend indicates longitude lines. Looking over the animation, we can see that opposite pattern of cool waters in the central Pacific (top-middle of animation) and warm waters in the eastern Pacific (top-right of animation), but what is stirring below is even more interesting. We find a body of cold water pushing to the surface in the eastern Pacific, as well as a swath of positive water temperature anomalies manifesting itself below the surface in the central Pacific. Put two and two together, and the Modoki signal in the Central Pacific is definitely present, just not at the surface yet.

Now that we have shown how the Modoki El Nino is nearly completely present in water temperature anomalies around the globe, let's talk about the effects it may have on the upcoming winter.

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The graphic above displays worldwide temperature anomalies during a Modoki El Nino. As we can see, cold weather is typically observed in much of the Central US during a Modoki El Nino, while warmth prevails in the Western US. Slightly warmer than normal anomalies are also visible along the Eastern Seaboard.
What this tells us is that, at least for now, the risk of another cold winter in the Central US is rising, while a warm winter along the West and into Alaska is also becoming a real possibility. Those in the East may need to watch for a slightly warmer than normal winter.


Sunday, August 17, 2014

Probability of Negative NAO During Upcoming Winter Increasing

The likelihood that we will see high pressure over Greenland this winter, a sign of the negative North Atlantic Oscillation, is on the rise.

The image above shows sea surface temperature anomalies for the day of August 16, 2014. In this image, we can see quite a few areas of interest that we are monitoring for the upcoming winter, but today we'll focus in on Greenland and around the Canadian Maritimes. Looking towards that part of the world, we see a swath of well above normal SST anomalies stretching from the waters south of Greenland towards the Arctic circle. The warm waters also extend to the east, immediately offshore of Greenland.

It is well known that sea surface temperature anomalies can exert a significant influence on the presence of high or low pressure in a given area. For example, areas with warmer than normal waters tend to observe high pressure more often that low pressure, while colder than normal SST anomalies usually result in stormy conditions prevailing over quiet conditions. This was observed well last winter, when the body of positive SST anomalies in the northeast Pacific brought about strong high pressure along the western coast of North America, which permitted the cold weather to penetrate deep into the US.

In Greenland, with the presence of a rather large swath of warmer than normal waters, I wouldn't be surprised to see persistent ridging over this part of the world this winter. If such a scenario does play out, we would enter the negative phase of the North Atlantic Oscillation (NAO), which would allow cold and stormy conditions to prevail over the Central and East US, the latter of which may experience episodes of intense snowstorms, as can happen in negative NAO events.

In the graphic above, we see SST anomalies over four different parts of the Pacific Ocean, centered along the Equator. Nino region 4 is located near the Oceania region, while Nino region 1+2 is centered just offshore Ecuador. By looking at these panels, we can identify a body of warm water on the surface in the west-central Pacific in Nino region 4, as well as the far east Equatorial Pacific in Nino regions 1+2 and region 3.

It is expected that all of these regions may experience additional warming as we progress into Fall, which is when we anticipate the emergence of a Weak El Nino (SST anomalies +0.5 to 1.0 degrees above normal).

Weak El Nino's affect the United States in many ways, but the primary effect is through manipulation of the jet stream. When this happens, the jet stream is forced south along the Eastern Seaboard, allowing cold air to flow deep into the Central and East US. Storm systems are then pushed south as well, and end up following the jet stream along the South US before shooting north as the jet stream is pulled up towards Greenland, where a ridge (Negative NAO) resides. Consequentially, snowstorms pose threats to the Northeast and East Coast, in addition to the cold weather.

The negative NAO and weak El Nino generally tie into each other, as they seem to work in a tandem. If current projections verify for this winter, and the SST anomalies near Greenland persist, the likelihood of a negative NAO throughout the winter significantly rises.


Friday, August 15, 2014

New Climate Model Outlooks Fix Errors; Cool, Snowy Winter Possible

Long range climate model projections of the upcoming winter season, the same ones we discussed a little while back, have been updated. The latest models still retain errors, but two models have come in with drastic improvements.
Bear in mind the typical caveats with long range forecasts still apply.

The image above shows a compilation of multiple long range outlooks, projecting the El Nino-Southern Oscillation phenomenon from the present to next spring. In this chart, we can see the majority of models favoring an immediate commencement to the El Nino expected to form later this year. The issue here, which we elaborated on in the link above, is that these models want to make the El Nino start immediately, something unlikely to happen. Complicating the situation further is the fact that these models want to bring the El Nino to Moderate (+1º to +1.5º above normal) or even Strong (over +1.5º above normal) levels by this winter. Again, this is unlikely to happen. Consequentially, we have been forced to discard these forecasts, as the incorrect SST projections then ruin the remainder of the forecasts.
The new update to these models came in to me today, and I was surprised to find two models that have changed their tune. In the chart above, instead of all models going up and up with the El Nino, the GFDL (turquoise colored line) and GFDL_FLOR (beige line) prefer either an ENSO-Neutral situation, where the El Nino is unable to form, or a weak El Nino, which is what my preference is for this winter. It finally seems as if we have two models that may stand a chance at verifying this winter.

Without further ado, let's review the forecasts from these two models for this winter.

 The first model we will review for the temperature outlook is the GFDL_FLOR. The image above shows projected temperatures across the United States for December-January-February 2014-2015. In this graphic, we see that the model keeps the majority of Alaska and western Canada warm, which can be indicative of persistent ridging over the area. Whether that is the case, we don't know, but such a feature would help chances for a cold Central/East US winter. Now looking at the United States, we find the majority of the nation experiencing average temperatures for the winter, with the Plains experiencing slightly below normal anomalies.
This is a rather substantial shift from earlier forecasts of a blowtorch (excessively warm) winter for the nation, which was due to the incorrect SST forecasts. It can be expected that models may project normal anomalies, because these forecasts are being made for months out. However, with this being the first forecast that is not retaining major SST flaws, things are looking up for those wishing for a cold winter.


Turning our attention to the GFDL model, we find a slightly different temperature forecast in store. Much of the Central and Western US is experiencing average to slightly below average temperatures, while the Great Lakes, Southeast and East US in general experiences a warm winter. We see this warmth extend into northeast Canada and towards Greenland, which makes me think that we may need to watch for ridging building off the East Coast if this forecast is correct (which, as we know by now, is not a given).

We now turn our focus on the precipitation outlooks from the two models. The GFDL model, pictured above, shows a wide swath of above-normal precipitation extending from Texas to south-central Canada, bringing the heaviest anomalies to the southern Midwest and western Ohio Valley regions. Wetter than normal conditions are also observed across the Eastern Seaboard, while dry weather prevails into the West Coast.
I'm not willing to say much on this outlook just yet, but since this is the first forecast that doesn't have that dreadful SST flaw, this sort of precipitation pattern may bear watching for this winter. If it did verify, it could spell disaster for California and other drought-affected regions.

Taking a look at the GFDL_FLOR model, we see a somewhat similar outlook as the one portrayed by the GFDL system. In this outlook, the December-January-February period features a very dry West US, remarkably drier than the GFDL model outlook. Slightly above normal precipitation anomalies extend from the Southern Plains and Gulf Coast into the Midwest and Great Lakes. The Central Plains is also included in this wet trend.
Again, though there's not much else to say here, it could bear watching.

Lastly, we'll take a look at the model-projected upper air pattern for the coming winter. The image above shows the Z200 outlook over December-January-February from the GFDL model. We want to maintain focus more on the contour lines than the color shades for this post. Taking a look around North America, we find a ridging signal over the West Coast and into Alaska. As we've discussed extensively, persistent above-normal water temperature anomalies in the Gulf of Alaska may support such a scenario, which could then lead to another chilly winter. Looking downstream, we do see a slight suppression in the contour lines, potentially indicative of some stormy weather. We saw a similar outlook in the months leading up to last winter.
Something else to note is the suppressed contour lines over Japan. This could indicate stormy weather there, and if we apply the Typhoon Rule, it could then affect us here in a substantial way.

Finally, shifting to the Z200 outlook from the GFDL_FLOR guidance system, we still see a cold signal across North America. Eerily similar to outlooks from last year anticipating the winter of 2013-2014, we see strong ridging over the West Coast and into Alaska. This ridge looks to be of similar strength to the one observed last winter, which was the mechanism responsible for the polar vortex scraping the northern US. Once again, we see suppressed contour lines in Japan, again indicative of stormy weather. The most interesting feature, by far, is the depression of contour lines over eastern Canada and into the United States. This is definitely a cold weather signal, dare I say the same signal that eventually brought the polar vortex south. I'm not saying that whole episode will happen again, but if this model is right, cold weather becomes a significant possibility.

All of this looks pretty supportive of a cold and snowy winter, but when it comes down to it, remember that this all rests in the realm of possibility, not certainty. Things do look good from these error-corrected models, but we will have to wait and see if these solutions stick with the updated model forecasts next month.


Thursday, August 14, 2014

Sea of Japan Rapidly Cooling; Winter Implications Possible

The Sea of Japan has experienced rapid cooling in recent days, something that could come into play later on this winter.

The image above, recorded on August 4th, 2014, shows sea surface temperature anomalies across the Pacific Ocean basin, extending from eastern Asia to the west coast of North America, and down to Australia. Though there are many things to be analyzed in this image, we want to focus in on the Sea of Japan, in the top left corner of this image. The Sea of Japan is located between mainland Asia and the island nation of Japan. On August 4th, SST anomalies read well above normal in this area. This was a concerning feature, as above normal water temperatures can induce persistent high pressure to form over the area, an ability well documented this past winter with positive SST anomalies in the northeast Pacific, and consequential high pressure in that same area, which enabled the polar vortex to grace the northern US.
The feature was primarily of concern for winter weather fans, as the persistent high pressure forming over Japan due to the warmer than normal Sea of Japan could continue into the fall and winter, which would then allow for increased risks of warmth in the United States during the coming winter season. The mechanism which may allow for this warm winter would be the highly-touted Typhoon Rule.

In just 10 days, however, the scenario for the coming winter changed drastically.

The image above shows sea surface temperature anomalies, still projected over the same part of the world, but now valid on August 14th, 2014. Gazing around the chart, we find a stunning reversal in water temperatures in the Sea of Japan. Instead of +3.00º to +4.00º-plus anomalies in the Sea of Japan, we now see widespread negative or neutral water temperature anomalies. This rapid cooling also appears to have affected the waters immediately south of the Sea of Japan.
It's quite possible, even likely, that the destruction of these warm water anomalies is due to a strong low pressure system traversing the Sea of Japan. It is quite common for strong cyclones to "mix" the water it passes over, reducing warm water temperature anomalies in the process. It looks like this same process has happened in the Sea of Japan.
If, and I say 'if' because things can very much change in the next several months, these cool water temperatures are to sustain themselves in the Sea of Japan, and warm waters do not return to the area, the chances of a warm winter would likely be reduced. However, we'll need time to monitor this development for another handful of weeks to see exactly what will end up happening.