Quid à propos de l'hiver 2018-2019 (20/10/18)

Long Range Forecast : Winter 2018-2019 outlook

Update 3 from TWO  (The Weather Outlook)

Long range and seasonal models

A brief overview of the long range model output for Winter 2018-19.

  • ECMWF: Still pointing towards the chance of a cold Winter especially in December with easterly potential but backtracked from its massive easterly domination in last month's update of the seasonal model.
  • Perhaps milder later on showing the chances of a front loaded Winter.
  • CanSIPS: Backloaded Winter with a relatively mild, unsettled December, anticyclonic January and a very northeasterly February which would be cold.
  • JAMSTEC: Colder than average Winter signalling northerly or northeasterly winds whilst the east of Europe is much milder.
  • Méteo France: Close to average temperature and wet .
  • Glosea5: Mild and zonal with an increased risk of westerly winds.
  • IRI: Warmer than average over Greenland indicating northern blocking Near UK with no temperature deviation.
  • CFSv2: Anticyclonic January but stormy December and February. Very mild.

Indexes and teleconnections (20/10/18)


North Atlantic Oscillation (NAO)

Positive this winter. That suggests an increased chance of mild and wet periods.

Quasi-biennial oscillation (QBO)

The QBO is currently transitioning back to positive (westerly) phase and that is expected to continue through the winter. A positive QBO is associated with an increased chance of a +North Atlantic Oscillation (NAO) and milder winter weather.

El Niño Southern Oscillation (ENSO)

El Niño is favoured to form in the next couple of months with 70% to 75% chance and continue as a weak event through the Northern Hemisphere's winter. A correlation between a weak El Niño and an increased incidence of cold periods during the late winter has been established. The TWO view is that a strong El Niño increases the chance of a mild and wet winter.

Since the Sudden Stratospheric Warming (SSW) in February

there has been an ongoing signal for high pressure blocks to have more influence on the UK's weather than normal. In the late winter and early spring northern blocking led to widespread snow as the Beast from the East made its presence felt. That was followed by one of the warmest (it could turn out to be the warmest once all of the data has been collated) summers on record in the UK due to the persistence of anticyclonic conditions. As we head through the meteorological autumn the elevated signal for high pressure still appears to be present.

Solar Activity

The solar minimum is expected next year and current levels of activity are very low. There is a suggestion that cold winters occur more frequently in the UK shortly after a solar minimum is reached and that low levels of solar activity generally increase the likelihood of colder periods.


Summary

Since the last update in September the TWO view is the chance of winter 2018/19 being cold has increased.

Despite recent climatology favouring milder conditions, some of the seasonal models, background signals and the increased propensity for high pressure blocking to form since the Sudden Stratospheric Warming (SSW) event in February suggest otherwise.

At this stage the TWO view is there an elevated chance of winter 2018/19 being colder than average.