Good evening and welcome to my first winter post of 2014! In today’s post I will be talking about Eurasian Snow Cover/Advance in October (SAI) and how this correlates to winter, the OPI Index, solar sunspots and some early stratosphere warming!
So, first up I will go to a subject that has been floating around social media and the media in general: The OPI. You may be thinking: what is the OPI? The OPI is short for the October Pattern Index, it is a numerical summary for the northern hemispheric conditions during October! A lot of research has gone into this tool and a really good correlation (when looking back at previous data) has been found! When the OPI is really negative overall, there is a much stronger likelihood that winter will be colder and harsher; this is due to the increased likelihood of a negative AO (probability that cold air will be displaced from the pole).
If we go ahead and take a look at how the current OPI is shaping up, we can clearly see how negative it is. No bar on that graph has appeared positive during October. That would suggest that a cold winter may be ahead, but nothing is ever certain!
Just to put that into proof, here is some data for you to see the correlation:
Take a look at some examples and research it, the winters that were cold/very cold had OPI’s of -1.5 or lower! For example, October 2009 had an OPI of -3.15 and that winter was exceptionally cold! Whereas October 2013 had an OPI of 1.6 and that winter was exceptionally mild! So, now, if I was to tell you that we were homing in on the second lowest OPI since the data started, what does that say? A cold winter may be ahead of us…
Next up is a minor part of the post, solar sunspots. Despite having quite a large sunspot recently the number is still low compared to other years and it looks to be on the decrease! Take a look at the graph below, you will see that the cycle has increased lower than the previous peak and will soon be on the decline by the looks! Could this play a key part in keeping things cold this winter? It isn’t extremely low but it may just be enough!
Finally, we have the Eurasian Snow Cover Extent during October. This one is a cracker this year! I will show you a picture of what snow cover was like on the 1st Oct 2014, this year:
Then finally, take a look at this cracker! The snowfall extent is hugely different to the beginning of the month!
Also, it’s larger than last year by a long shot! It’s said that there is a good correlation between big Eurasian snow cover extent and a cold winter for Western Europe, this is mainly due to the fact that firstly it causes surface cooling. This therefore strengthens the Siberian high in time, which increases the poleward heat exchange which can in turn cause an SSW. The SSW breaks down the stratospheric vortex and then we get a –AO which results in a cold winter. Also, take a look at the dramatic rise in snow cover this year, it truly is incredible, the largest extent since 1976! And this has a correlation to a cold winter!
Also, we can actually see that this strengthening snow cover may be affecting the stratosphere already. Look at the warming on the graphs, located above where we would find this extent of snow and ice. Could this be the first early weakening? The path to a cold winter?
Lots of key signs and statistics are coming together as we approach the winter period, however this still needs monitoring! Dare I say that it is looking good? Soon we shall see, but my inkling at this stage for this winter is a –AO/-NAO and colder than average!
Thank you so much for reading, feedback and questions welcome!