Met Office Warn Cold Weather Could Return In February
By Paul Homewood
The Met Office 3-month outlooks more often than not tend to be pretty bland affairs, as of course our weather is most of the time. One of my criticisms in the past has been that they usually fail to spot the more extreme events that come our way, such as the wet winter of 2013/14, the wet summer of 2012 and the snow in December 2010.
They have just issued the latest outlooks, and for a change have stuck their necks out, with a warning of much colder weather in Feb/March.
A strong, mature El Niño event continues in the tropical Pacific Ocean and is currently at its peak. This El Niño is comparable in strength to the 1997-98 and 1982-83 events and is highly likely to rank among the strongest on record.
El Niño is already creating wide-ranging weather impacts across the globe. The influence on UK weather, however, is more subtle. El Niño moderately increases the probability of the positive phase of the North Atlantic Oscillation (NAO) in early winter. At this time of year, the positive phase of the NAO is associated with milder- and wetter-than-average conditions, whilst the negative phase is associated with colder- and drier-than-average conditions. In late winter El Niño increases the probability of sudden stratospheric warming events occurring. These events disrupt the stratospheric polar vortex and, more often than not, bring cold weather to the UK.
The Quasi-Biennial Oscillation (QBO), an oscillation of the equatorial winds in the stratosphere, remains in a strong westerly phase. The QBO influences winter conditions over Western Europe by modulating the strength of the stratospheric polar vortex and thereby the phase of the NAO at the surface. The westerly phase of the QBO tends to favour a stronger stratospheric polar vortex, leading to a higher likelihood of a positive phase of the NAO. This effect is primarily seen in the early winter but its influence will gradually diminish during this outlook period.
During January, the factors described above suggest a continuing likelihood of positive NAO. This has consistent support from predictions by the Met Office seasonal prediction system along with systems from other global forecast centres. The left-hand graph in figure T2 shows a clear shift towards milder conditions. Although milder than average conditions are expected overall, this does not preclude temporary incursions of colder weather. At the start of the 3-month period, milder-than-average conditions are more likely than colder-than-average. However later in the period, particularly from February onwards several seasonal forecasting systems, including the Met Office system, are in good agreement in suggesting a shift towards more blocked weather patterns; these patterns increase the chance of cold northerly or easterly winds affecting the UK.
Watch this space!