AFM 101 Lecture Notes - Lecture 5: Royal Meteorological Society, Polar Vortex, Meteorology

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29 Sep 2016
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Winter 2016/17
Tentative weather prospects
UPDATE 15/09/16 now online
UK winter 2016/17 weather forecast indicators
It's a long way off but are there any early pointers to how winter 2016/17 may turn out? Independent
meteorologist Matthew Hugo, BSc, FRMetS, RMet takes a look at what the latest data is suggesting.
After an exceptionally unsettled winter last year, primarily due to the influences of El Nino and the QBO
(Quasi-biennial Oscillation) phase, the coming winter is likely to have different ‘foundations’.
There is some uncertainty over the likely phase of ENSO (El Nino-Southern Oscillation) for the winter
period, but a repeat of last year's ‘strong’ El Nino is not expected.
At the moment ENSO-neutral conditions are in evidence, if not just with a slight trend towards La Nina.
La Nina is favored to develop during the rest of the northern hemisphere summer, with an approximate
75% chance that this will be maintained through the autumn and winter.
When coupled with an easterly phase of the QBO the coming winter may turn out significantly different
to the last one.
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We will start by briefly looking back at the winter of 2015/2016 as a comparison to the coming winter
period. Last winter produced one of the most potent and powerful polar vortex in many years. This
helped produce a relentless period of very wet, very mild and very windy conditions across the UK and a
distinctly +NAO (North Atlantic Oscillation). During last winter we were entering into one of the
strongest El Nino events in many years and this, without doubt, had some influence on the northern
hemisphere’s weather patterns. Equally important was the westerly phase of the QBO. This combined
with solar activity and El Nino helped produce a distinctly cyclonic and unsettled winter period with little
cold weather.
Whilst looking ahead to the winter period at this time frame will produce more questions than answers,
what can be looked at are ENSO and also the likely phase of the QBO. These variables go through
broader changes and evolutions making it is possible to predict with some degree of accuracy the likely
patterns for this coming winter.
After the very strong El Nino of last winter we have now progressed towards near neutral conditions and
with an on-going trend towards La Nina in the coming months. At the moment some of the main
forecast models (see below image) highlight that through the winter period a weak La Nina is expected
to be in evidence. Clearly this will be in complete contrast to the ‘strong’ El Nino of last winter.
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Whilst there is always an uncertain connection between ENSO and the weather across our region of the
northern hemisphere, it is expected that a weak La Nina event wouldn’t aid in strengthening the
northern hemisphere’s polar vortex like the El Nino event of last year did. A weak La Nina can promote
more in the way of northern blocking through the winter period, but this is certainly an uncertain
prediction at any time due to other factors.
The QBO (Quasi-biennial Oscillation) phase this winter is expected to be opposite of last year with an
easterly phase expected. Without going into the details of the QBO too much, essentially think of the
QBO phase as a system that can facilitate the development of a more potent northern hemisphere polar
vortex. A westerly phase QBO essentially adds more ‘fuel’ to the overall winter-setup, whilst an easterly
phase of the QBO is known to promote a more disorganized polar vortex. The more disorganized the
polar vortex is through the winter period the greater the likelihood of colder outbreaks and less in the
way of stormy conditions.
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