Winter 2009/10 early thoughts

Introduction
TheWeatherOutlook winter forecast will be issued in late November, and will take into account a range of factors. As we

are only half way through autumn it is too early to say what the forecast is likely to suggest, but at this juncture a few thoughts on the winter weather are possible. Before reading on, here are a couple of caveats. Firstly, as ever remember that all long range predictions for this part of the world tend to be inaccurate and secondly, this is not intended to be a forecast.

What data is available already?
UK Met Office (see here)
The data made publically available by the UK Met Office is pointing towards a milder than average winter.

Seasonal forecast models
European Centre for Medium Range Weather Forecasting (ECWMF)
The available data from the ECM  is pointing towards a milder than average winter.

International Research Institute (IRI) seasonal charts (see here)
The available data from the IRI is pointing towards a colder than average winter.

Climate Forecast System (CFS) (see here)
At the time of writing the NOAA CFS model is suggesting a colder than average winter across most of Europe (including the UK). It seems to  have been fairly consistent during recent weeks. 

So the seasonal forecasts models are presenting a mixed picture. The CFS does seem to have been quite consistent during recent weeks in forecasting northern blocking (high pressure to the north of the UK) for the winter. Northern blocking does increase the chances of cold weather in the UK during the winter months. 

Pattern matching
Comparing Autumn 2007, 2008 and 2009.

Comparing surface pressure and 850hPa charts with the first half of autumn 2007 and 2008.

 

September 21 2007
//theweatheroutlook.com/twodata/gfs/2007/09/21/00_0_mslp850.png

 

September 21 2008
//theweatheroutlook.com/twodata/gfs/2008/09/21/00_0_mslp850.png

September 21 2009
//theweatheroutlook.com/twodata/gfs/2009/09/21/00_0_mslp850.png

More early cold pooling building over Greenland than in the previous 2 years. 

 

October 1 2007
//theweatheroutlook.com/twodata/gfs/2007/10/01/00_0_mslp850.png

October 1 2008
//theweatheroutlook.com/twodata/gfs/2008/10/01/00_0_mslp850.png
October 1 2009

//theweatheroutlook.com/twodata/gfs/2009/10/01/00_0_mslp850.png
Fairly similar to 2008 with more extensive cold pooling to the north than in 2007.
 

October 15 2007
//theweatheroutlook.com/twodata/gfs/2007/10/15/00_0_mslp850.png

October 15 2008
//theweatheroutlook.com/twodata/gfs/2008/10/15/00_0_mslp850.png
October 15 2009

//theweatheroutlook.com/twodata/gfs/2009/10/15/00_0_mslp850.png
Similar to 2007 with less cold to the north and more warmth to the south than in 2008.

No clear signal from these charts with the early development of cold to the north easing off during October.

Temperatures in the UK this year
Our own central England temperature index shows:
September 2009 was about 0.7C warmer than September 2008 and about 0.4C warmer than September 2007
August 2009 was about 0.3C warmer than August 2008 and about 1C warmer than August  2007
July 2009 was about 0.2C cooler than July  2008 and about 0.9C warmer than July  2007

September 2009 14.7C
September 2008 14.0C
September 2007 14.3C

August 2009 17.1C 
August 2008 16.8C
August 2007 16.1C
July 2009 16.7C
July 2008 16.9C
July 2007 15.8C

Local temperatures from our weather station in the Chilterns, Hertfordshire.
Readings from our weather station show that :

1) September 2009 was generally warmer and a lot drier than September 2008
2) The first half of October 2008 has seen less temperature variation than the first half of October 2008

The national and local readings show that September was warmer and drier than in 2008, but not anomalously warm. The link between September and the following winter is disputed, but my view is that anomalous warmth in September is more likely to be followed by milder conditions during the winter.

ENSO
The winter is expected to bring El Niño conditions. The link between these and the winter in western Europe is tenuous, but there is a feeling El Niño  conditions are more likely to bring milder weather early in the winter.

Solar activity
This is very controversial, but it has been suggested that lower solar activity leads to a less active jet stream. Recently level of solar activity (measured by the number of sun spots) have continued to be low. If this is believed it may be argued colder conditions are more likely this winter.

So what about winter 2009/10?
My view at the moment is that a very mild winter is less likely than has often been the case during recent years. Winter 2008/09 was the first cold one we'd had since the mid 1990s, and it's quite usual for cold winters to arrive in clusters. So there are reasons which support the argument that this winter may be cold again, but there are also some signals such as ENSO and the weather patterns during the first half of this autumn which point towards average or even milder conditions.
TheWeatherOutlook winter forecast will be issued in late November. 

Issued 15/10/2009 © Brian Gaze