Tuesday, November 27, 2012

Late November 2012-2013 Winter Thoughts

This is a post concerning my winter thoughts as of Late November. We'll get things going right away.

ENSO Region SST Anomalies

Latest Weekly SST Anomaly Over the ENSO Regions
The El Nino-Southern Oscillation, or ENSO phenomenon involves the warm or cool anomaly of sea surface temperatures (SST's) over the Equatorial Pacific waters. The top image shows the ENSO anomalies per region, with Nino 1+2 being the furthest east near the coast of South America, and Nino 4 being west of the 180th Meridian. As you can see, Nino regions 4 and 3.4 are pretty warm, actually achieving El Nino state. An El Nino is when these waters are at or above 0.5 degrees above normal. A La Nina has water temperatures at or below -0.5 degrees below normal. Both temperatures are in Celsius. If you now look at the bottom pair of images, you will see the observed SST's and SST anomalies. The warmest waters are centered from 140W to 160E, which does include the Nino 3.4 and Nino 4 regions.

Despite this warming and hinting of an El Nino, I support a Neutral ENSO winter, which is neither an El Nino or La Nina. The neutral ENSO phase can be thought of as if you're taking a shower and the water is room temperature- neither hot nor cold.

This image above is an observed image of the Quasi-Biennial Oscillation, or QBO. The QBO involves wind directions in the upper levels of the troposphere and stratosphere. When the QBO is negative, winds are westerly, or eastward. A positive QBO involves easterly, or westward winds. The Lower 48 is most commonly given colder weather in a negative QBO, as a negative phase of the QBO is able to influence the North Atlantic Oscillation (NAO) into going negative, which only continues to enhance cold potential, especially for the East US.

In the image above, negative anomalies (Negative QBO) is shown in white, while positive QBO values are shown in grays. As you can see, there has been a positive QBO movement from the upper stratosphere recently. When the positive QBO movement progresses down into the troposphere, this occurs at a rate of about 0.6 miles per month. However, the movement has been slowed recently at the 20mb mark. If we look on the right, it shows kilometers. If the QBO descends at 1 km per month, it would take the entire winter to get down towards the 30mb mark.

AMO Values for 2012. These are organized in months, with
January the first value after '2012', to October, the most recently calculated month.
The line of values above is of the Atlantic Multi-Decadal Oscillation, or AMO. In a positive phase of the AMO, the water temperatures in the far north Atlantic are above normal. This, in turn, enhances the potential for ridges of high pressures to form and sustain themselves over Greenland. This phenomenon is commonly called the negative NAO. In a negative AMO, cold water temperatures are observed, leading to a stormier trend over Greenland, bringing about an increased likelihood for a positive NAO.

This is a comparison of October 17th water anomalies and November 14th water anomalies. You can see a diminishing of warm waters over northern Canadian waters and west Greenland waters, signifying a dying positive AMO. However, the New England waters are well above normal, supporting at least part of the positive AMO. The positive AMO has been dying off slowly as shown in the values listed above, and this has been happening by about 0.100 per month. If we apply that to this situation, we could see the positive AMO gone by January or February. However, the strong warming trend over east Canada tells me that the positive AMO should stick around through the winter months.

This is a graph showing Northern Hemisphere snow anomalies from October through November of this year. Typically, when October snowfall is above normal, the Arctic Oscillation goes negative the following winter. Likewise, when the snowfall anomalies are below normal, the AO tends to stay above normal in the following winter, meaning warmer than normal temperatures. An analysis of this past October shows a negative anomaly for the first half of October, which means December could be lost to warmth. Considering we already have the Bering Sea under a massive Omega block, such a solution is not out of the question. I expect January into February to favor cold temperatures, with the latter month bringing down the hammer as far as cold weather goes.

All in all, I'm expecting a gradual turn-around from these warm temperatures to cold weather, especially in the latter half of the season. A negative NAO / Negative AO combination will support cold weather and storm action for the Northeast, some of which will be diverted west thanks to an intermittent positive PNA. Winter will hit the best in the Northeast, with the runner-up being the Midwest, Plains and Ohio Valley.


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