[Mortster]

Firstly, let’s look at the key indicators for winter forecasting.


Artic Oscillation

This has been in a negative shift for months now, past few weeks it has been very negative. At the moment, currently slightly negative and is predicted to remain on the negative side of neutral through the first week of December


PV ( Polar Vortex )

Like the AO, the PV is very weak and split, and not where it should be, with no signs of meaningful recovery is predicted. In fact, the models are predicting further weakening of the PV through the end of the month. The ongoing weak PV is likely to elevate the risk of wintry weather across the NH continents, especially Siberia but also including East Asia, Europe and the US during much of December.

Eurasian snow cover

Eurasian snow cover was above the normal level for the whole of October. It has stalled now, but is still well above where it should be for this time of year


Arctic sea ice

With a record low recorded this year (measured in sept) the Arctic ice levels are well below normal and show little signs of a fast recovery.

So, what does all this jargon mean exactly?


The PV is normally centred around or above the pole, this locks in the cold air to the high northern hemisphere reasons, its currently off centre, and unusually split. This allows the colder air to push much further south than it normally does. This allows cold air incursions into the habitable areas of the NH. We saw this in motion a week ago, when it became much colder than average for November.


Eurasian snow cover helps to create what’s know as a Siberian High, again we saw first-hand what this does to our weather a week ago. The higher the snow cover, the colder the air above the region gets and stays. The Siberian High then blocks the weather coming across the Atlantic. This sits over to the east of us, sometimes referred to as the best from the east. Sometimes the block falls in our favour, and any rain heading our way is then more likely to fall as snow. When it doesn’t fall in our favour, if its set up just slightly further east, it blocks the weather from Europe, but we still get hit it (rain)


Last year the AO was positive pretty much all through the winter, and the PV was centred and strong. Most forecasters are saying a colder than average winter, with none wanting to commit to saying much colder winter (apart from the idiot from the express Nathan Rao who says it every year regardless)



The longer the AO stays negative, and the longer the PV remains weak and split, the higher and increasing chances are of the winter being colder than the past few years. Also the El Nino event of last year has now switched to a la Nina, which means there won’t be as many storms rolling in from the Atlantic.