Sunday, August 14, 2011

2011-2012 Winter Forecast: 2nd Version

Hello everyone, this is the 2nd version of the 2011-2012 winter forecast for the US.
The Weather Centre has determined that a weak La Nina is likely going into this winter. The CPC has issued a La Nina watch, indicating a La Nina is possible but not certain. Let's start off by taking a look at current Surface Sea Temperature (SST) charts.
On the top we see current SST charts. Notice the cooling in the eastern regions of the ENSO regions. Last year, we had a strong 'east-based La Nina'. What this means is that the coolest SST anomalies were centered in the eastern regions of the ENSO area. For ENSO region locations, see the image below.

To the image at the top, we see SST anomalies aren't displaying any significant signs of a La Nina. However, with the SST's falling rapidly, it can be expected that a La Nina will occur. And while many other factors go into these forecasts, this remains our preliminary forecast, and we will base it as such.

Something else we can forecast for is the NAO, or North Atlantic Oscillation index.
The NAO is basically associated with a permanent low pressure system over Iceland (Icelandic Low) and permanent high pressure system over the Azores (Azores High). These two vary in daily and monthly etc. strengths, and that variation is called the NAO. Below you can see an example of the variations in pressure.

 When the pressure difference (because high pressure has higher pressure and low pressure has lower pressure) is strong, that is a +NAO index. When that difference is lower, that period is called a -NAO index. Below is a graph depicting past NAO index readings.
You can see how the NAO went negative during practically the whole 2010-2011 winter. Recently, the NAO has also been down. When the NAO is negative, it leads to heat waves across the US. you can see how the heat relates to the negative NAO by taking a more short-range past look at the NAO below.
You can compare the recent massive heat waves with the NAO index.

All that information considered, we have constructed the 2nd version of the 2011-2012 winter forecast. See the charts below.
The Weather Centre anticipates much of the North US to be cold and possibly frigid. And while that may be too far south, it is expected that at least some of the southern US will be warm. This comes as solar activity begins to decrease to a very large degree. This will actually cool the whole world down, but since we will be entering at least a slight La Nina, the southern US will be at least a bit warm.
Precipitation will probably take another slight form of last year, but at this point, i'm not really sure. The reason is that there are tons more parameters that we are not able to correctly forecast at this time. That said, we are making an educated guess on this precipitation forecast.
It will be more snowy in the Northeast as more monster storms will bear down on the area. Additionally, there will probably be more snowfall in the Great Lakes into the Upper Midwest, with the best likelihood in the lake effect snow areas and Upper Midwest. But we will see.

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