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A cold winter incoming?

Winter 2018/19 update 3


19/10/2018

Overview

For more context and background information please read:

Winter 2018/19 weather, Long range forecast signals issued on July 28th 2018

UK winter 2018/19 - Update 2, issued 14th September 2018

For the latest news please see:

Winter forecast prelude - Update 4, Issued 13th November 2018

Snow at Berkhamsted railway station

September and October

When producing the winter forecast the autumn weather patterns are considered. A cool and cyclonic September is counted as a weak factor in favour of a colder winter. On the other hand a warm and anticyclonic month is considered to favour a mild winter. The correlation between warm Septembers and milder than average winters is not accepted by many, but the TWO view is that it has existed in recent decades.   

This year the September Central England Temperature (CET) finished at 13.7C which 0.1C above the 30 year average. The provisional UK mean temperature was 12.4C which is 0.2C below the 30 year average. Rainfall was 108% of average but in the south and east it was drier. As a result the month will be considered to marginally favour a cold winter.

The CET for the first half of October was close to 1.4C above the 30 year average. Weather patterns were very mixed but on balance the first half of the month will be considered to favour a cold winter. 

Seasonal model updates

A number of seasonal models now cover the December, January and February period.

UK Met Office GloSea:
Regional variations are present but for most of the country average or milder than average temperatures are favoured. There doesn't appear to be a strong signal for precipitation levels.

Meteo France
Colder than average in the north and west of the UK, but no signal for the south and east. Wetter than average in the south and east, but no signal for the north and west.

ECWMF
No temperature signal. No precipitation signal for most of the UK but perhaps drier relative to the average in the north.

Jamstec
Colder than average in all of the UK and much of northwestern Europe. Drier than average in the north but wetter in the south.



IRI
No signal for temperature across the UK but warmer than average in Greenland. Drier than average.

CFS v2
The current update is mixed and suggests the possibility of colder conditions in January and perhaps February. (Check the latest CFS v2 charts on TWO).

A lot of the forecast variables are showing no signal. However, on balance there seems to be a developing trend away from milder conditions.

Jamstec Nov Dec Jan 2m temperature anomaly

Jamstec surface temperature anomaly, Dec, Jan, Feb. (Source: Japan agency for Marine-Earth Science and Technology)

Regardless of what they show, the skill level of seasonal models for the UK and north western Europe is still low. In other words they are not very accurate.

Indexes and teleconnections

See the July update for more background information.

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.

Snow thawing,  March 2018

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.

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 or very 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 (or possibly much colder) than average.

From Brian Gaze, TWO founder
Since establishing TheWeatherOutlook over 15 years ago the site has grown enormously and running costs have risen. I intend to continue expanding TWO and keeping it free if possible. If you find it useful and would like to contribute to its development please consider making a donation.

Regular updates will be issued before the TWO winter forecast is released at the end of November.

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