Europe November 2020 Outlook

Written by on November 1, 2020 in Rest of Europe, United Kingdom & Ireland with 0 Comments

Despite some record cold morning’s, September was a mild month while October is wound up slightly below average and significantly wetter than normal, particularly for east and southeast parts of the UK.

September temp anomaly

Credit: Michael Ventrice

October temp anomaly

Credit: Michael Ventrice

While Western Europe has seen somewhat of a temperature seesaw, the blowtorch has been relentless, particularly surrounding the Black Sea where all-time monthly record highs have been achieved both months in some areas.

Back in the west of the continent and the warm September and cold October nicely reflects in the positive then negative phase in the AO/NAO.

Connected or not, the positive then negative followed by a return to a positive AO/NAO (more active, unsettled Atlantic pattern) also fits well with the rise then fall of Atlantic tropical activity. Did the ‘hyper active’ September within the tropics force the -AO/NAO and cold 1st half to October? Then positive AO/NAO which brought a more turbulent 2nd half of October as the tropics shut down early October?

A cold 2nd half to November?

November is opening relatively mild, wet and windy but things are set to settle down quickly by the end of week 1.

What’s interesting is that we’ve just had another ramp up in tropical activity. Two cyclones in particular have tracked northeastward, taking tropical heat with them. I believe it’s no coincidence that the models are showing another spell of high latitude blocking week 2 into 3.

What would the return to a negative AO/NAO suggest? A weaker, less zonal jet stream, more amplification which pulls warm air north and cold air south. A potentially cooler or cold pattern.

The CFSv2 weeklies show the large scale flip in height field from negative to positive over the arctic very nicely from week 1 to 2 and holds it through the rest of November.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

The signal may flip back to a more +AO/NAO during the final week of November as I don’t expect this setup to hold beyond 20 or so days IF the blocking including Scandinavia/Greenland block develops maturely.

While it’s hard to say how cold because that depends upon where the ridge/trough settles but one thing I am more confident on is a drier pattern and less of an Atlantic influence. We have potential to get quite cold IF we manage to turn our winds northerly or better still, easterly. Scandinavian blocks can do this, so too can Greenland blocks and the models have both these scenarios on the table.

The reason for a return to positive AO/NAO? The good old stratospheric polar vortex which appears to be strengthening and unlikely to weaken much during November. It’s currently NOT connecting with the troposphere hence why we’re getting a negative AO/NAO but as we head deeper towards winter, a strong PV is likely to begin controlling the pattern more and a strong vortex only means one thing, a mild, moist west-east flow.

10mb temperature (stratosphere) forecast now vs Nov 17th.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Nov 17th

Note it’s forecasted to get stronger and colder.

Writing off winter? Certainly not and one cannot go solely by modelling to predict long range the strength or weakness of the polar vortex. Factors including the behavior of the MJO can change things quickly, especially if the MJO finds itself over the Indian Ocean. Last year, it was stuck in the warm 6-7-8 phases (west Pacific).

The GFS has the MJO entering phases 2-3 and if that can hold and keep coming back to these phases then we have a better shot at pumping heat north against the Himalayas and into the stratosphere.

There may or may not be a longer term feedback from the tropical Atlantic which could help with high latitude blocking in the coming months.

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