EUROPE: EXTREME SEPTEMBER TO OCTOBER FLIP, IS THE SCANDINAVIA BLOCK A PRECURSOR?

Written by on October 15, 2016 in Autumn 2016, Rest of Europe, United Kingdom & Ireland with 0 Comments

We know September was a warm month and in fact the UK’s second warmest on record but have you noticed how it’s felt chilly? Thank or blame that Scandinavia blocking high, the strongly negative Arctic Oscillation and in turn weak polar vortex.

total-obs

Just look at the incredible flip in where it was warmest during September, it so happens to be coldest in October thus far.

Credit: Michael Ventrice

Credit: Michael Ventrice

Credit: Michael Ventrice

Credit: Michael Ventrice

There is said to be linkage, where it rains heaviest in autumn, that’s where the cold goes in winter but a weak polar vortex, strong negative Arctic Oscillation and positive Scandinavia block during October? This is certainly a strong cold signal during the winter months but during October, well I’m afraid there doesn’t appear to be much suggestion either way. Negative AO’s in October sure will help build the Northern Hemisphere snowpack quickly and ahead of schedule.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

However this doesn’t automatically suggest a bad winter. Last winter saw fast snow growth in Eurasia but the El Nino flattened it’s effects, especially once into late autumn and winter.

The PV both last year and the year prior held strong through autumn and winter over our side of the Arctic, thus the Icelandic low was most influential for particularly Western Europe.

Check out the strong Scandinavia blocking just last October.

eastern-europe-high

The ENSO is very different now compared to then though.

Where the warming and weakening of the PV did occur, it benefited North America, a lot of that was down to the warm Gulf of Alaska.

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The persistency and strength of the Scandinavia blocking pattern of late has caught my attention and made me think whether this could signify a particular upper air setup for later down the road.

Here’s the standardised positive phase of the Scandinavia pattern which we’ve witnessed strongly here this October.

scand_correlation_map

scand_tmap

scand_pmap

Looks like there was a lot of Scandinavian blocking in the 1950s, 60s and 70s then little through the early 80s but a sharp increase during the late 80s. The 1990s and 2000s appear to be more evenly spread.

scand_timeseries

Unfortunately there are October’s which saw little blocking but had a bad winter or multiple spells of cold and snow and there are others with no blocking and a bad winter still occurred and vice versa.

In the long term, solar is undoubtedly the biggest player but years between maximums and minimums, it’s regional drivers which decide the warm or cold fate of a winter season.

2nd to the sun, it’s probably the multi-decadal positive and negative or warm and cold phases of the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) followed by the El Nino Southern Oscillation (ENSO) as a close 3rd. The super El Nino of last year undoubtedly whipped out the changes of a cold winter.

Another driver and player, the Maddan Julian Oscillation (MJO) which is a pulse which circles the tropical ocean and enhancing convection. This can have significant influence not just on hurricanes but warm and cold distribution across the mid latitudes.

With the ENSO being near neutral and solar near the midway point and SSTA’s similar to the previous two winters along with a similar Siberia October snow growth, my suspicion remains unchanged. Overall mild and wet for Northwest Europe but not without significant spells of snow and cold.

Based solely on the current SSTA profile, the below DOES NOT FAVOUR a cold Europe winter.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Why? As stated previous, that warm pool in the Gulf of Alaska (GOA) with less warm ENSO region favours more of a trough and cold winter for the Eastern US which would mean greater thermal gradient and stronger jet stream coming off North America. The cold central North Atlantic and warm ring surrounding favours more of a zonal WESTERLY flow into Europe like we’ve seen the last 2 winters.

Latest CFSv2 monthly through winter 2016-17

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

No video today.

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