Europe December 2020 Outlook (opposite of last year)

Written by on November 30, 2020 in Rest of Europe, United Kingdom & Ireland with 0 Comments

Autumn 2020 has been very warm, particularly for north, central and east Europe with a back and forward in temps further west. For the UK and West, September was warm while October was average to below average but November was firmly above average.

2nd highest November Arctic Oscillation of last 70 years, A ‘good’ omen?

Between October 27 and November 27, we observed the 2nd highest positive AO/NAO index for the period in the last 70 years, hence all the warmth and persistent rain.

 

Opposite to last year

Interestingly, November 2020 was opposite to November 2019 when you look at Western Europe.

November 2019

Credit: Michael Ventrice

November 2020

Credit: Michael Ventrice

12 month ago and the polar vortex was revving up to it’s strongest/coldest levels of the last 40 years!

Credit: Andrej Flis

A record strong positive AO followed for the rest of winter 2019-20 after the peak cooling of the PV around New Year.

The record strong vortex last winter may well have been attributed to the record strong positive Indian Ocean Dipole last autumn. Notice that it’s been negative this autumn.

December 2019 temp anomaly

Credit: Tropical Tidbits

Negative IOD + MJO + Strengthening Siberian Aiding A Weak 2020 Polar Vortex?

With the aid of a -IOD (warm Indian Ocean), we depart November and enter December with an MJO pulse, (albeit less pronounced) crossing the Indian Ocean (phase 2-3-4 and enhancing convection over the east Indian Ocean/west maritime-continent region.

This upward heat release (aided by the Himalayas) is helping strengthen the Siberian high and both are influencing the upper troposphere as well as the stratosphere, causing a degree of friction to the stratospheric zonal winds.

The below infrared shows the thunderstorms over the east Indian Ocean.

The below graph shows a strengthening Siberian high.

The EC has the current positioning of the MJO repeating itself later in the month, a sure sign that this restriction to the PV maintains through December.

Credit: WeatherModels.com

Credit: WeatherModels.com

A¬†weaker PV in both troposphere and stratosphere means slower zonal winds and slower downstream polar jet stream. Buckling or amplification of the jet is much more achievable with more northward progression of warm high’s. As your well aware, push warm air north and the cold is forced south.

Notice the strong warming at 50pha on the Asia-Pacific side of the pole in response to the MJO at day 10.

A reduction in mean zonal winds!

What does that mean? AO/NAO goes firmly negative as a result.

There definitely appears to be some sort of signal with cold November’s followed by mild winters. Let’s see what we get following our warm, wet November in 2020. Remember back to November 2009, warm and very wet. We all know what followed.

What’s Ahead?

Even if we don’t get a complete shutdown of the Atlantic, I do think we’re in for at least a cold and unsettled, possibly even stormy at times. By that I mean we get a -AO which allows arctic origin air into the mid latitudes but a +NAO could keep a W or NW flow going rather than W or SW like last December.

As you can see from the below CFSv2 for December, 3 high pressure centres dominate the NH. A Scandinavian block could keep a frequent feed of easterly winds and associated continental air flowing westward over Europe. However, a mid-North Atlantic high with no hook-up with the Scandi high could still allow Atlantic-modified air into Western Europe. The result would be the battle between mild ocean and cold continent over the UK and an interesting wintry fight.

Credit: Tropical Tidbits

Indeed the above is a mean for ALL of December. Given all the above, we have an increasing chance of seeing solid blocking from Atlantic up over Greenland to Scandinavia.

The 850mb temp anomaly chart below shows a core of colder than normal just west of the UK.

Credit: Tropical Tidbits

ECMWF is mouth watering!

Credit: ECMWF

Credit: ECMWF

December looks cold with a mix of rain and snow and under clear skies over snow cover, cold nights (-10 to -15C in Highland, North England/Wales).

GFS 10-day snow forecast

Credit: Tropical Tidbits

Watch this space as we head deep in December. Modelling points to significant pressure put on the PV at 10hpa. The below charts hints at the very least, the continuation of a -AO, perhaps even an eventual SSWE!

Credit: wxcharts.com

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