Forecasting months in advance is something that is incredibly difficult to do in particularly so for the UK’s weather because there are so many different variables that affect our weather, the fact that we’re sandwiched between a massive landmass and an ocean only adds to the complexity and chaoticness of our weather. Long Range forecasts should never be taken too seriously and should be used as more of a “guide” to most probable weather, rather than an actual forecast.
My regular readers will know that my forecast for last winter went spectacularly wrong, so much so in fact that the weather was the complete opposite to what I had forecasted, because of this I have decided to change the way in which long range forecasts are produced on this site. There will now be three issues of the winter outlook to take into account new data in the run up to winter, once the third and final forecast has been issued monthly forecasts which will be updated twice each month will take over in giving you forecasts based on the latest data to hand, the three seasonal forecasts will be issued on;
First Issue – 21st September
Second Issue – 31st October
Third Issue – 30th November
Please be aware that the first and second editions are NOT forecasts, they will be merely a run down of what current models are showing, what this means and what potential weather these could generate through the course of the winter months. A Winter Forecast will then be issued on the 30th November going into more of the specifics.
Winter Weather Outlook 2012/13 – Issue 1
Firstly, I’d like to take a look at the current Arctic Sea Ice Levels, this year we broke the 2007 record for ice minima and there has been some speculation that lower sea ice levels lead to colder European/UK winters, whilst this is pure speculation at this stage with little scientific backing or research, it does seem to tie in with our colder winters since the previous record breaking 2007 Ice Minima, bar 2011/12, whether this is simply a coincidence or not is something that’s yet to be seen, but I thought it might be worth mentioning.
Next I’d like to take a look at Solar Outputs, despite nearing a Solar Maximum sunspot activity is still very quiet compared to the more recent solar cycles, there’s gaining evidence and agreement within the scientific community to suggest lower solar activity lead to a more sluggish Jet Stream during the winter months, this in turn can leads to increased blocking in the higher latitudes which leads to cooler European/UK Winters.
Current Sunspot Activity – Considering we’re nearing a solar maximum it’s very, very quiet
Next we’re going to take a look at something slightly more technical, but I’ll try and keep things simple. The Quasi-biennial oscillation or QBO for short is the measurement of the equatorial zonal winds between Westerly and Easterly in the tropical Stratosphere, the alternating phases develop at the top of the Statosphere and propagate downwards over a period of months. Current forecasts suggests going into this winter we’ll be in an Easterly Phase and this basically speaking can lead to a higher risk of Sudden Stratospheric Warming which I’ll go into in just a moment.
QBO – Whilst it might look complicated, it’s fairly easy to read this chart. The darker colours indicate a Westerly Regime and the White indicates an Easterly Regime, if we look at this year we can see the white moving slowly down towards the bottom of the graph, this is the Easterly Winds progogating downwards and tells us we’re in an Easterly Phase
Above I mentioned Sudden Stratospheric Warming, a warmer stratosphere is usually indicative of High Pressure, the warmer air can disrupt the seasonal Polar Vortex allowing heights to build, Sudden Stratospheric Warmings are thought to bring colder weather to the UK a few weeks after occurring and at this time of year it’s hard to get an idea of what state the Polar Stratosphere will be in come winter. The Stratosphere temperatures are however incredibly important and can often over ride other global signals, SSW events often lead to a Negative Arctic Oscillation, the AO is the measurement of pressure over the Arctic.
Positive AO = Low Pressure, strong Polar Vortex
Negative AO = High Pressure, Weak Polar Vortex
Whilst all other factors could be pointing towards a bitterly cold winter, if the Stratosphere temperature is below average the risk of prolonged cold weather is significantly lower. Below is a chart showing how the temperatures at 30hPa look at the moment, the temperature in the Stratosphere is currently spot on average for the time of year.
Polar Stratosphere Temperature – Click to Enlarge
Now we’re going to take a look at the Sea Surface Temperatures, these can have quite a large impact on where pressure patterns develop and they can actually help us determine whether or not a negative or a positive North-Atlantic Oscillation is likely, the NAO is the measurement of pressure in the Atlantic.
The current Sea Surface Temperatures are fairly impressive, the excess and record breaking Arctic Ice Melt has lead to a very cold pool of water to the North of the UK and East of Iceland. Northerly Winds in this region have helped push the cold Arctic water down towards the Atlantic. Cold Sea Surface temperatures around this area often hinder Low Pressure development and favour High Pressure development, High Pressure in this area would bring colder weather to the UK, thats not to say High Pressure WILL develop here, but there is an increased risk if this cold anomaly continues into the winter.
We also need to take a look towards the Western Atlantic, off of the coast of New Foundland and to the South of Greenland we have these very warm Sea Surface Temperatures, this area here is what we call the Atlantic multidecadal oscillation or AMO and this is currently in its warm phase, we also have another area of warmer weather further South to the West of Africa and when we see Sea Temperature Anomalies placed in this particular way a negative NAO is favoured, as we talked about earlier a negative NAO can lead to cooler, snowier weather during the winter months.
The above SST chart as well as showing what I’ve just talked about above, also shows the state of the Pacific at the moment and whether we’re in a La Nina or El Nino, at the moment things are fairly uncertain whether El Nino is going to start to develop, the NOAA chart shows that if it does develop it’ll be a very weak affair so I think a Neutral ENSO/Weak El Nino is likely as we go into the winter months and whist this in itself is unlikely to have a major effect on our weather, it will allow other signals to effect our weather more strongly than they would if the ENSO signal was stronger.
Another thing we can gleam from the chart above which is interesting is the Pacific decadal oscillation or PDO for short, this is shown by the area of blue, colder weathers in the center of the Northern Pacific, this goes through varying 30 year phrases of warm and cold, it’s currently in it’s cold phase and because El Nino is a measurement of warmer waters across the Pacific, having a cold PDO does tend to hinder El Nino development.
ENSO Forecast showing a weak El Nino is forecasted based on the Mean
Now that we’ve spoken about a few of the more technical drivers to our weather, what they mean and what potential conditions they could bring, I’m going to talk about something slightly less technical and that’s the Long Range Model Forecasts. It’s important to remember that these models change fairly frequently and are subject to wild swings within their outputs, they are highly experimental and at this stage it’s really about spotting trends and consistency within the outputs rather than the what models themselves actually show, the drivers talked about above will probably offer more of an idea than the models below but I think it’s important to talk about what they show.
Firstly I’d like to talk about the JAMSTEC Model, to get a feel for this models consistency I’m going to post it’s July, August and September issue for the period December – February. All three are fairly consistent in what they show which is an average-slightly below average winter temperature wise
For the same December-February period I’m going to post the Precipitation predictions, what we see is fairly interesting. The model is forecasting average or below average rainfall across the UK with below average rainfall to the West of the United Kingdom so this is perhaps indicating High Pressure being out in the Atlantic more often than not during the winter months.
August Rainfall Issue
Whilst the model does change between the two issues slightly, the overall trend from the model is for average or below average rainfall, with average or slightly below average temperatures during the period December – February.
Next we’re going to take a look at the Met Office probability model, whilst this is fairly difficult to explain the chart itself I will lay out exactly what the model is showing to make it easier to anyone who’s only just getting into the realms of the weather models. Like above, we’re going to be looking at the period December – February.
Above Average: 0-20% so at this present time, there is around a 20% chance of an above average winter
Average: 20-40% so at this present time, there’s a slightly higher chance that we’ll see an average winter than we will an above average winter
Below Average: 60-80% which means, overall, the signal is for a below average winter, however we have to remember there is also a fairly good chance that winter will also be average, going by this chart alone.
Sticking with the Met Office charts, we’re going to take a look at Ensemble Predicted Pressure Patterns, the first graph below is for the period November through to January and as we can see the model predicts Higher Pressure to be located in the Atlantic stretching up to Southern Greenland with lower heights over Europe, this is generally indicative of a cold, North or North-Easterly flow.
This second graph is going to again look at pressure but instead will be for the period December through until February, again it is an Ensemble mean run as above – This chart shows a slightly similar pattern although with High Pressure in the Atlantic closer to the West of the UK and low heights across Europe not quite so pronounced, this generally indicates dry, settled and probably cold weather
I’m going to post the Met Office Precipitation charts now, although unfortunately they don’t really give us a clear signal at the moment, I often find the models aren’t very good at handing overall precipitation amounts. The chart below shows an equal statistical chance of Above Average, Average and Below average rainfall
I’m now going to take a look at and discuss the Beijing Climate Center long range computer model. The chart below covers the period December – February and shows us pressure anomalies at 500hPa, there’s quite an extensive high pressure system across Western Greenland and into Canada but lower pressure over the United Kingdom suggesting a very mixed weather pattern.
Beijing Climate Center
The temperature prediction from this website is going for warm being indicated by the oranges, this would generally make sense considering the 500hPa signal for low pressure.
Beijing Climate Center Temperature Prediction
The precipitation signal from this model, as you’d expect given the above to charts is going for quite a wet winter season
Beijing Climate Center Rainfall Prediction
Next we’re going to take a look at the CFS Model, again like the above models this model is also subject to wild swings within it’s output and at this stage shouldn’t be taken too seriously.
We’ll start with the Pressure Anomaly chart for the period December, January and February. The model is forecasting higher pressure down over the Mediterranean and lower pressure to the North of the UK, this indicates a mild and wet Westerly airflow.
Below is the temperature prediction for the months December, January and February, at this moment in time the model is predicting above average temperatures in the South and average in the North
CFS Temperature Anomaly
Below is the chart showing the precipitation signal, the model is forecasting above average rainfall for much of the country during the period December – January
CFS Precipitation Anomaly
Conclusion & Thoughts
If I were to base my thoughts on the atmospheric drivers talked about in the first section I’d be inclined to say that we’re heading for a below average winter with the potential for some cold, snowy outbreaks. The Weak ENSO, -NAO primed Sea Surface Temperatures combined with Low Solar Activity and a Easterly QBO really does point towards increased amounts of blocking across the Northern Hemisphere and a weaker Polar Vortex. However I also have to factor in the various Long Range Computer models.
At this current time I’m expecting winter temperatures to be slightly below average with more snowfall than we saw last winter. The models throwing up the milder patterns, despite being against current background signals do throw some caution into the mix which is why I’m holding back slightly on going for a significantly cold winter. I also have to think about the fact that we don’t really have an idea about how the Stratosphere will be this winter, as mentioned earlier the stratosphere can make or break a winter despite what seems like very good background signals.
My next update will be issued on October 31st, by then we’ll have a much clearer idea of the Stratosphere and I’ll hopefully be able to say with a lot more confidence, at least for the first part of winter, whether we can expect to see cold and snowy weather.
Never heard of this guy but I do what like he's saying. What do you guys think?
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