Maison Jaune Blog

Ed. note:  This was for Winter 2010/11 – However, you can read my latest long-range forecast for Winter 2011/12 for Chamonix and the French Alps here.

As the long range weather forecast for Winter 2010-11 in Europe, the French Alps and Chamonix is not yet out, I’ve put together my own prediction.  Ok.  It’s not very scientific – but it is WAY early for a decent reliable forecast.

“La Nina” is a phenomenon that occurs when the tropical seas of the Pacific off the coast of Latin America are anomalously cool, while the waters become warmer towards Australia, the Philippines and Indonesia.

The strongest effects are felt in the Pacific basin, but meteorologists are increasingly confident that it can affect weather systems around the world.  For instance, La Nina has already been implicated in Britain’s dismal summer of 2007.

The Multivariate ENSO index (El Nino Southern Oscillation) is a measure of the sea and air temperatures, wind, pressure and cloud cover across the tropical Pacific.

This data is combined and normalised to produce an average figure and a monthly value.

“El Nino” is the abnormal warming of the cold ocean waters off the coast of Peru and appears on the index as positive differences above the average – marked in red on the graphic below.

.. and La Nina is when there is a negative  variation – marked in blue on the graphic below.

Unlike El Nino, La Nina events tend to be rather brief – lasting only a year.

El Nino (ENSO) analysis 1950 - 2010

It is a useful measure as the condition tends to persist for several months at a time and has a big influence on northern hemisphere weather patterns.

Tony Crocker, skier and actuary writes, “the El Nino of 2009-10 was strong through FEB/MAR (the 6th highest El Nino in the past 44 years), but has swung radically to a La Nina value of -1.166 as of JUN/JUL 2010. The northern spring months are the historically most likely time for an El Nino or La Nina to break up, so there is already some confidence that the current La Nina will persist through the northern winter season of 2010-11”.

The Climate Prediction Center (http://www.cpc.noaa.gov) has also just put out an advisory on the 9^th September which predicts a moderate to strong La Nina through Winter 2010-11.

La Ninas cause slightly warmer winters in Northern Europe than usual, often with cold spells early on.

However, the presence of the Atlantic ocean moderates the affect that the Pacific ocean has on us here in Europe.

The North Atlantic Oscillation is a climate phenomenon of fluctuations in the differences of atmospheric pressure at sea level between Iceland and the Azores.

In other words, it is a measure of the strength and direction of the westerly winds across the North Atlantic.

The permanent low-pressure system over Iceland, and the permanent high-pressure system over the Azores control the strength and direction of the prevailing westerly winds into Europe.

When there is a big difference in the pressure at the two stations (NAO+), this produces increased westerly winds, and thus cool summers and mild and wet winters (large snow pack) in Central Europe.

Impacts of the North Atlantic Oscillation (NAO)Source: http://bit.ly/c5WPrR Investigations into Seasonal Predictability of North Atlantic Winter Climate by C.G. Fletcher

However, when the index is low, (NAO-), westerly winds are suppressed and these areas suffer cold winters and storms track southerly toward the Mediterranean Sea resulting in increased storm activity and rainfall to southern Europe and North Africa

Last winter, 2009-10, there was an El Nino condition and an extremely negative NAO, which some meteorologists believe led to the unusually cold winter (coldest in UK for 30 years, with over 7 consecutive days where the temperature was sub-zero).

North Atlantic Oscillation 1950 - 2010

Looking at the graph above, I think that the ongoing negative NAO is starting to diminish, and as it is the longest period of sustained negative NAO since 1968, I believe that it is most likely to reverse to be a NAO+ winter.

Thus, I think the pattern for the start of this winter will be a La Nina and a positive NAO.

As these are characterised by cold spells early on then mild, wet winters, one might expect this coming winter to be excellent.  The ground will freeze early, and the higher ski resorts such as Chamonix will receive abundant precipitation, i.e. snow!!!

Editors note: Massachusetts-based Weather Services International (http://bit.ly/93CFmB) has just put out a forecast release confirming the trend towards a NAO+ winter. They write, “As we head into the autumn season, most of the main climate drivers are suggesting that a return to the positive phase of the North Atlantic Oscillation (NAO) will occur. This would be associated with above-normal temperatures across Scandinavia and the northern mainland, with below-normal temperatures across the South. By November, the combination of the warm Atlantic and cold Pacific suggest that the below-normal temperatures will become more widespread. However, there is uncertainty in the forecast given the recent multi-year persistence of the negative phase of the NAO. While our strongest climate signals indicate that the NAO will trend towards more positive values, we are somewhat concerned that the persistence of the negative NAO may continue through the autumn, which would result in cooler temperatures across much of Scandinavia, UK, and the northern mainland,” said WSI Chief Meteorologist, Dr. Todd Crawford.

It should be noted that Bertolini et al, found in their study, “Interannual variability of winter alpine precipitation”, that there was no clear NAO signature in the interannual fluctuations of precipitation in the Alps.  Likewise the Arctic Oscillation had no great statistical significance, however the East Atlantic West Russia appears to have an influence on the first part of winter; a negative however statistically significant impact on the Western Alps where we are located.

Winters with La Nina : 2009, 2008, 2000, 1999, 1995, 1989, 1998, 1985, 1976, 1975, 1973, 1972, 1971, 1970, 1967, 1968, 1964, 1963, 1962, 1961, 1956, 1955

Winters with NAO+ : 2007,2004, 2002, 2000, 1999, 1995, 1994, 1993, 1992, 1991, 1990, 1989, 1983, 1976, 1973, 1972, 1967, 1959, 1954

Winters with La Nina and NAO+ in bold.

Winters with La Nina & NAO+: 2000, 1999, 1995, 1989, 1976, 1973, 1972, 1967

Anecdotal Evidence…
One of the previous years where there was a La Nina and a NAO+ was 1999 – mid-way through the strongest La Ninas since 1955.

1999 was the winter of severe storms in France where over 100 people died, and we had record snow conditions in Chamonix.  It had fabulous early season snow – then in late January, it snowed 1 metre overnight , the following week it snowed non-stop for three days, and put down more than 2 metres in Chamonix.  Then sadly, the Montroc avalanche occurred which killed 12 people in early February.

Snow Totals for Mont Aigoual. Post-1950 years with La Nina and NAO+ are in green. Source: pistehors.com Red line shows 5th order polynomial trend line

1995-6 – was in the top 5 wettest Januarys in the UK…London received 224% of normal January rainfall…. The Alps had one of the snowiest since records began in 1894, with a total of 10.39 metres of fresh snow on Mont Aigoual to the South of the Cérvenne mountains.

1989 Exceptionally mild&dry in the UK  One of the warmest winters.

1976  January gales in UK…  big drought though….

1973  Severe gales in UK april..  notably dry year..

1967  One of the coldest New Years in 16 years with many roads blocked by snow in the UK…

Number of Days with Snowcover. years with La Nina and NAO+ are in green. Source: pistehors.com Red line shows 5th order polynomial trend line

There is some great weather information here:
http://www.weathercharts.org/
Climate Logic’s seasonal weather forecasts
US National Weather Service’s Climate Prediction Center
Tony Crocker’s US Ski Resort Snow pages
Interesting article about the effects of global warming on skiing in the French Alps

Gorgeous day today in Chamonix…
Crystal clear blue skies – been out taking lots of new photos of the chalet for the website.

Aircraft contrails above the Aiguille du Midi