Europe October 2020 Outlook (Lookback at Sept & What’s Ahead)

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

Like August and much of the summer, September has been a month of mixed fortune with settled spells interrupted by more unsettled. May and September are often thought of as being the ‘best month’s of the year’ but this didn’t really apply in 2020. Despite the UK see it’s first September 30C in 3 years and other ‘summery mid 20s’, we also witnessed the UK’s coldest September night, like we did back in May, since 1997. In May Kinbrace hit -6.7C while Altnaharra did it in September with -5C.

Credit: Met Office

An unseasonable spell of particularly wet, windy and cold over East Anglia produced the coldest September day on record to parts of the region just 4 days after enjoying 26C. A month’s worth of rain, strongest regional wind since 1997 and highs under 10C brought very chilly late October weather early to Norfolk and Suffolk.

Katesbridge Does it again!

A couple of morning’s after Altnaharra observed the UK’s lowest September temperature since 1997, Katesbridge, Co Down does it again. Like back in May, Katesbridge takes ‘unusual cold’ a step further compared to the mainland UK! A low of -3.7C not only set a new September cold record for Northern Ireland the island as a whole.

May 2020

Credit: BBC Weather

September 2020

Credit: Met Office

In May, while the UK had it’s coldest since 1997, Katesbridge saw NI’s coldest May night since 1982.

This little hamlet in County Down just continues to firm up it’s frosty reputation and has certainly been getting a bit of a habit at breaking if not threatening Northern Ireland monthly records lately. The previous September record low for NI was recorded just two years ago and it was at this very place. Katesbridge did it in August 2015 and nearly did it in July that year also.

See my related articles

Visit to Katesbridge weather station, Northern Ireland’s icebox

Towns in Scotland, England, Wales Endure Coldest May Night’s in 20-40 Years But Northern Ireland Takes The Prize!

September 2m temperature anomaly

Credit: Mike Ventrice

Has Hyper active period of Atlantic Tropical Cyclones Shaped The Hemisphere’s October Pattern?

It may be pure coincidence or we are now seeing the atmospheric response to the hyper active spell of tropical cyclones in the Atlantic 10 days ago. There’s a ‘lag time’ from event to downstream atmospheric response right? Well we are ending September and beginning October with a significant developing high latitude blocking pattern over the east Arctic Ocean and Ural Mountains.

Credit: NASA

I believe this at the very least could be an atmospheric response to the tremendous northward heat release from the tropics 10-15 days ago forcing a -AO/NAO and cold, wet open to October for the UK and France.

My reasoning behind this idea takes us back to the basic fundamental. What is the physical purpose for tropical cyclones? They take heat out of the tropics and REDISTRIBUTE it north into the temperate regions. The sheer amount of ‘heat lows’ spanning the tropical Atlantic about a week ago was about as many as you’ll EVER see at any given time. This high latitude blocking we’re seeing develop now nicely coincides with a lag period of about a week to 10 days. Time for that heat to pile up over the polar region.

Take a look at the CFSv2 500mb height anomaly for October looking down over the Northern Hemisphere.

Credit: Tropical Tidbits

GFS ensembles show a negative Arctic Oscillation through at least the first half of October.

Europe 500mb height anomaly for October

Credit: Tropical Tidbits

2m temp anomaly

Credit: Tropical Tidbits

Precip anomaly

Credit: Tropical Tidbits

What’s interesting is the string jet stream in a sea of blocking HP. These stones in the stream force incoming air into the troughs and forces rapid deepening of LP’s. We shall see a classic example of this as a low deepens at the base of the trough and has nowhere to go but eventually north up over the UK this weekend bringing heavy, persistent rain and gales.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

This piling up is nicely seen when looking at the 500mb height anomaly charts and the low deepens with strong surrounding HP.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Lot’s of rain to come next 2 weeks.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

GFS ensemble firmly has below normal temps for the UK and warmer than normal further east through the first half of October.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Taking the positives from the current pattern

For me, this is most interesting because it’s not so much what the pattern may produce during the next 3-4 weeks but more what it could be telling us about later down the road when it really matters.

First and foremost, based on the above charts, I see a cool and wet October in the west, warm and dry in the east but we’re likely to see the return of a neutral to even weak positive AO and NAO during the 2nd half of October so possibly a spell of more settled or at least milder. The reason? That highly active period in the tropics last about 10 days, so too may the blocking before we turns around.

What’s important about this setup as we head into October is that with arctic blocking, this should keep the westerlies somewhat weaker than normal. A weaker jet makes for a greater chance at blocking and a weaker polar vortex. A weaker PV also brings a better chance for sudden stratospheric warmings.

A negative AO is good news for October snow building throughout the NH. A greater coverage of reflective snow cover means less incoming solar rays and stronger cold. A big Eurasia snow cover during October is said to increase the likelihood of a -AO/NAO winter. A weak solar cycle at around the minimum too is said to increase a -AO winter.

Other factors to take into account? Low arctic sea ice, more warm water exposure which can lead to higher than normal pressure over the pole? The extreme wildfire season of 2020 and large quantity of smoke circling the planet is said to have a ‘similar’ effect as volcanic eruptions. In 2017 a study stated that the vast levels of smoke released into the atmosphere actually reached and effected earth’s stratosphere. Another influence which could trigger an SSWE or at least a weaker PV?

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