Friday, October 17, 2014

Long Range Discussion, Concerns About Winter (Part 2)

Today, to wrap up this post, I'll discuss my concerns about the coming winter in conjunction with some of the long range paraphernalia we went over yesterday. You can click here for the Part 1 full post (I highly suggest reading through it).

The chart above shows observed temperatures in the Arctic, specifically north of the 80th latitude parallel. The red line shows observed temperatures, while the green line displays the average temperature at a given time in the Arctic, allowing us to determine temperature anomalies. The constant blue line depicts the temperature at which water freezes (as this is a Kelvin scale, you chemistry buffs may recognize that freezing number to be 273 degrees K). On this image, we see how during the summer months, temperatures in the high Arctic remained almost completely below normal, though the temperatures were still above 273K. The hope for many was that this below-normal trend would persist into the fall and winter, so cold air would be in abundance come December. However, there's been a change of plans. Arctic temperatures are currently above normal, and have been above normal for nearly the last 100 days straight. That's nothing to shake a stick at. This warmer than normal Arctic air, though it may still be below freezing temperatures, is playing into my worries that cold air might be more scarce than what it typically is in the winter season. This will be discussed more later on.

The graphic above shows geopotential height anomalies since the middle of this past June. The top panel gives an indication of these geopotential height anomalies on a time-by-height graph, where reds depict positive height anomalies (warm weather, high pressure) and blues indicate negative height anomalies (cold weather, low pressure). Check out that big swath of reds only a few days after the start of October. We saw significant ridging in the troposphere and even into the stratosphere, disrupting the jet stream and sending the Arctic Oscillation plummeting.

Typically, when the Arctic Oscillation is negative, the jet stream becomes very wavy and enables pockets of cold air to be flushed south to lower latitudes. It's not uncommon for North America to see cold weather when the AO becomes negative. In a similar fashion, the jet stream is stronger than normal, and thus not as wavy/broken up during the positive AO phase. This leads to warmer than normal weather.

I want to analyze those first days of October, when the AO went well below normal, as the blue bar graph shows, in conjunction with a storm system that hit during this same timeframe.

This image shows observed surface conditions on October 3rd, 2014. On this day, we saw a strong storm system pushing northeast into Canada, taking with it heavy rain that had plagued swaths of the Central US in previous days. Noting that the Arctic Oscillation was beginning its freefall into negative territory, and a substantial cold front was in tow of the storm, we were in line to receive our first big cold blast of the season. Right?


That thick blue dashed line, which shows the line between liquid precipitation temperature profiles and snow temperature profiles (fancy ways of saying the 32-degree temperature line) only made it as far south as extreme NW Iowa the next morning. For a pretty hefty storm system, a pretty decent cold front, and a pretty negative AO, that was pretty surprising. Cold air did come south, but not nearly as far south as it should have.

Let's use another example. This surface analysis chart is from October 14th, showing a strong upper level low beginning to push eastward out of the Midwest. Check out how far north that warm front is. We have to look to northern parts of Manitoba and Saskatchewan to find that thick dashed blue freezing line! Sure, this was a closed low in the upper levels, which typically don't support such sweeping cold blasts like the first example storm does, but still; we should see freezing temperatures at least near the US/Canada border at this point of the season.

The reason why I'm worried about what's happened the last few weeks for this winter, is because our winter pattern is setting up right before our eyes.

The Lezak Recurring Cycle appears to be setting up its new components for the 2014-2015 winter season. While many in the Midwest should be excited that October's been a very wet month (that is, if you are a snow fan), the cold air is what I want to discuss. The lack of cold air now could mean a lack of cold air this winter, especially given the warmer than normal Arctic temperatures.
"But wait! Last October, the temperatures in the East US were warmer than normal, while the West was cold, and the following winter turned out to be exactly the opposite!" That's correct. However, take a look at the SST anomalies from October, and you'll see where that set-up came from.

October 2013 SST anomalies
In the month of October 2013, we saw below normal sea surface temperature anomalies across the Gulf of Alaska, with the closest warmth displaced due south of the Aleutian Islands. These anomalies changed in time for winter, with well above normal SST anomalies evolving in the Gulf of Alaska. That's how we ended up with such a cold winter.
"The SST anomalies in the Gulf of Alaska are still well above normal, so we're in for another cold winter!" Not so fast.

This graphic shows weekly sea surface temperature anomalies from October 5th to the 11th, 2014. I used a world-wide view here to better show what's happening in the West Pacific this year. In the Gulf of Alaska, we do still see intense warmth with those positive SST anomalies. But take a look at the waters east of Japan. In a flip from last year at this time, rather than a tongue of warm water anomalies pushing east, we now see a tongue of cold water anomalies pushing east.

The daily SST anomalies from today (October 16th) are far more sobering.

Just like last year, but now flipped, we're seeing the SST anomalies from the West Pacific propagate into the East Pacific. Last fall, the warmer than normal anomalies transferred into the Gulf of Alaska to allow for a cold winter. This fall, colder than normal SST anomalies are transferring to the Gulf of Alaska. The consequences are yet to be seen, but I'm worried that cold winter prospects are on the fall.

Ridging over the Gulf of Alaska has been pretty consistent in the last 9-12 months or so. As a result, many believe this theme will persist, and will allow the warmer than normal Gulf of Alaska SST anomalies to stay put.

Unfortunately, that's not popular opinion anymore.

The chart above shows a mean 500mb height anomaly forecast from the GFS ensemble members, displayed by the big panel in the top-center. In this panel, warm colors translate to ridging/high pressure, resulting in warmer than normal conditions. Cool colors indicate troughing/low pressure, equalling stormy and cold weather. The small panels show individual 500mb contour forecasts for the given forecast time, in this case set at 12 hours out. In 12 hours (valid this evening), model guidance has a strong trough pressing into the Gulf of Alaska, something that's likely to happen quite a bit in the future (I'll discuss that later). You can bet that this stormy pattern in the near future won't help those warm water anomalies stay in the Gulf of Alaska. In fact, it would be logical to expect further cooling of the water temperatures in that region, as these storms move through.

But it doesn't stop there. The same forecast parameter from the GFS ensembles, now valid about 5 days from today, shows another strong trough placed squarely over the Gulf of Alaska. What do we see happening as a result in North America? A massive ridge of high pressure and warmth, except for the closed low in the Northeast. You get the picture by now- the medium range has a very stormy Gulf of Alaska, something that's likely to continue cooling the water temperatures there, further lowering the risk for a cold winter (talk about a change of thinking for the winter, huh?).

If this forecast comes true, as with the storm systems we discussed earlier, the very warm pattern outlooked due to the troughing in the Northeast Pacific may return in the LRC cycle this winter.

I briefly mentioned how this theme of a stormy Gulf of Alaska may continue into the future, so let's take time to examine that.

This graphic shows typical atmospheric responses to the El Nino phenomenon, when warmer than normal water temperature anomalies surface in the waters just west of Ecuador. Note how the typical El Nino sees a stronger than normal Pacific Jet Stream, bringing the storm track into the South US with highlighted 'wet' conditions. We then see the Polar Jet Stream pushing south into southeast Canada after having to push north in response to warm weather. In the middle of these two jet streams, what do we find? That's right, persistent low pressure in the Gulf of Alaska. As we head into an expected El Nino this winter, this sort of pattern may appear more frequently.

It's not all good news for warm winter fans, however.

The image above shows snow cover anomalies over the Northern Hemisphere as of October 16th. In this image, focusing on Eurasia, we see well above normal snow cover over Russia. Some of you weather enthusiasts may be familiar with the work of Judah Cohen, who came up with the concept of the Snow Advance Index, or SAI. In a nutshell, the SAI says that if snow cover advancement during the month of October in a specific portion of Siberia is above normal, the Arctic Oscillation is then expected to be below normal for the following winter, and vice versa.
So far this month, snow cover has been well above normal, more-so than in recent years, in fact. The big question is, will this snow cover advancement continue? If it stops its progress right now, and doesn't increase for the rest of October, the big snow growth in early October will be moot, and the cold winter idea will once again be in jeopardy, more than it may be now. For the time being, however, this is a good sign for a cold winter ahead.

The above image shows anomalies of the October Pattern Index over the last several days, since the start of October. The OPI, the concept of which was brought about by a group of Italian scientists, says that monitoring of the atmosphere during the month of October can yield great hints at what the coming winter will bring. October is a month well-known for big winter-predictors showing their cards for the coming cold season (i.e. the LRC, and Judah Cohen's Snow Advance Index (SAI)), but it may interest many to know what the OPI may be one the best, if not the best up-and-coming predictor of the upcoming winter season out of the three mentioned above.

We've seen the OPI sustained completely in below-normal territory for the month of October thus far. For winter weather fans, that's an incredibly encouraging sign; verification for the OPI ranges around 90%. When the OPI is negative, the following winter may be expected to be cold and stormy. The opposite result may be observed when the OPI averages positive. We have yet to see what the OPI will do for the remainder of October, but this is a healthy sign of a cold winter ahead.

Concerns About Winter Summary

- Arctic temperatures are warmer than normal, which may limit cold air availability this winter.
- Even though the Arctic Oscillation was strongly negative, cold air still was not observed in force in North America. This raises the concern of the winter not seeing persistent cold air.
- Water temperatures in the Gulf of Alaska are cooling, which, if continuing through the fall into winter, may allow for cold weather possibilities to diminish.
- Stormy conditions are expected in the near future in the Gulf of Alaska, likely further cooling those warm SSTs.
- Such a stormy pattern in the Gulf of Alaska may persist due to the El Nino set-up in the atmosphere.
- Despite these factors, there are still components in favor of a cold winter.

All in all: I'm worried that the risk for a cold winter is on the fall.