European Snow Forecast

Will it snow this winter??

If climatologists and meteorologists could predict the harshness of the winter season with any accuracy airlines, hydropower plants, fuel suppliers, road maintenance teams, and us, the general public, would all save a great deal of time and money. How much antifreeze to buy, how many power peaks to plan for, fuel and road salt to stock, wood to chop. Aside from all these eminently practical concerns, what we actually want to know is HOW MUCH SNOW THERE WILL BE! For the rest, others may wonder, but we’ll live without knowing….

The problem is that forecasting is always easier on a large scale (northern hemisphere, eastern USA, Europe) than it is on a small scale (French Alps, Pyrenees). And predicting general temperature trends is easier than trying to predict how much snow will actually fall, as that means taking precipitation into account, and then trying to figure out if precipitation events will coincide with cold bursts to produce the magic white stuff.

AccuWeather gives the easiest to read winter forecast with the following graphic. But they don’t have much explanation of the science behind their forecast.

Winter forecast accuweather europe

Having a read of both French and English weather blogs there seems to be a mix of factors that feed into winter weather, and therefore the seasonal winter forecast:

¤ El Niño: A central Pacific El Niño event (where the warmest anomaly is in the Central Pacific as opposed to an eastern Pacific) means more chance of a cold winter in both central and northern Europe (2-3° colder). In the UK generally it is only about 1° colder, because the ocean tempers the cold. At the end of November there is a weak, but definite El Niño signature, pointing to a central Pacific El Niño for the winter.

¤ The Siberian snow cover in Autumn: more snow over Siberia in Autumn means the jet stream meanders south, the polar vortex is not so strong and warm air moves into it, so the Arctic winter is warmer and the northern and western European winter is colder. Mediterranean areas could be warmer. Judah Cohen’s seasonal forecast uses this measure, along with the El Niño signal, as the main determinants of his winter forecast. An article from the New York Times explaining further is found here.

Judah Cohen Winter Forecast 2014-15The graph to the left shows Judah Cohen’s predicted winter surface temperature anomalies for the Northern Hemisphere in Dec-Jan-Feb 2014/2015 in degrees Celsius. The model is forecasting cold for much of the Central and Eastern United States and Northern Eurasia, with warm in Western North America, Southern Europe and North Africa. The model uses October Siberian snow cover, sea level pressure anomalies, predicted El Nino/Southern Oscillation anomalies and observed September Arctic sea ice anomalies. The strongest signal in the model is the October Siberian snow cover, which is the second highest ever observed in the record. This is an indication of an increased probability of a weakened polar vortex or a sudden stratospheric warming and a predominantly negative Arctic Oscillation during the winter. Credit: Judah Cohen, AER, Inc.

All this is good news for the European ski season.

¤ Arctic Sea ice loss: Some forecasters suggest that more sea ice cover in the Arctic at the end of summer will mean a colder winter, but evidence has been building for a couple of years that in fact low sea ice cover in the Kara and Barents Seas (above Scandinavia) in autumn mean a change in the pressure systems over northern Europe and Russia which lead to outbreaks of very cold air, in particular at the start of winter before the sea ice fully rebuilds. This year the ice loss not as much as in 2012, but is below average. See an excellent article explaining the mechanism behind this.

¤ Sunspot activity: high sunspot activity favours more westerly flow (so a more zonal jet stream, more storms coming into western and northern Europe and generally milder conditions) and weaker sunspot activity encouraging the jet stream to meander more, making it more meridional, which encourages blocking events, and means generally colder in northern and western Europe. We are coming out of a period of maximum sunspot activity (which was only a weak maximum) so solar activity should be weaker as the winter progresses.

¤ Quasi-Biennial-Oscillation: Quoting directly from the webpage of the Dept. Meterology at the University of Reading to explain what the QBO is, “The eruption of the Krakatau volcano (6 ° S 105 ° E) on August 27th 1883 led people to believe that the stratospheric wind above the equator blew in a westward direction. Dust from the eruption took 13 days to circle the equator and this upper air wind became known as the Krakatau easterlies. In 1908 Berson launched observational balloons above Lake Victoria in Africa and found westerly winds at about 15km (120mb). These westerly winds are called Berson’s westerlies. These conflicting results were resolved through the work of Reed (1961) and Veryard and Edbon (1961), who showed that the wind above the equator oscillates in direction. It was shown that the wind in the stratosphere changed direction on average every 26 months and that the alternating easterly and westerly wind regimes descend with time.” From Wikepedia – Westward phases of the QBO often coincide with more sudden stratospheric warmings, a weaker Atlantic jet stream and cold winters in Northern Europe forecasting-stone-euws-blogand eastern USA whereas eastward phases of the QBO often coincide with mild winters in eastern USA and a strong Atlantic jet stream with mild, wet stormy winters in northern Europe (Ebdon 1975). After reading a bit further things don’t appear to be so clear. Currently we are in an easterly phase, but it is weakening, and apparently this may favour a negative North Atlantic Oscillation which is one of the key indicators of cold winters in northern and western Europe.

The science is very interesting (and complex). An unfailing forecast model could be the one to the left. But is is not much use to us!

Final seasonal forecasts should come in right at the end of November. We’ll keep you posted!