LOW SEA ICE, WEAK VORTEX, RAPID EURASIA SNOW GROWTH MAY FAVOUR COLDER WINTER

Written by on October 21, 2016 in Autumn 2016, Rest of Europe, United Kingdom & Ireland with 0 Comments

As we enter the final 10 days of October I continue to gather the remaining evidence in order to put forward my 2016-17 winter forecast.

The latest information regarding Arctic Sea Ice states that for the time of year, we have the lowest levels on record as you can see from the below chart.

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Look at how negative the AO has been this October but note the NAO has been positive, reinforced by the influence of Nicole driving into Greenland!

total-obs

That negative AO is in response to strong tropospheric warming seen in the below chart.

hgt_ao_cdas14

A -AO in October is a cold and more importantly, snowy pattern which will build reflective snow cover early, hence supporting cold within the mid latitudes this cold season hopefully.

I find it very interesting to see the difference in hemispheric 500mb height pattern this year compared to last with the opposite 500mb Arctic pattern.

By this time last year we already had strong and still strengthening polar vortex with low pressure centred over the pole while warmth dominated the mid latitudes. This year, in the wake of the El Nino, we have a weak polar vortex and with warm arctic ocean, record low sea ice, blocking is the response above.

Plenty of ‘warm’ open water within the arctic…

cursnow

Credit: Tropical Tidbits

Credit: Tropical Tidbits

The atmosphere feeds back producing strong high latitude blocking.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Just look at Eurasia and the increase in snow cover over just the last 10 days.

ims2016283_asiaeurope

cursnow_asiaeurope

The fact we have low sea ice and above normal snow cover in Eurasia, cold builds fast at the source (Siberia) and this correlates to a more -AO and NAO winter.

screen_shot_2016_10_21_at_7_33_03_am

The strength of -AO and Scandinavia blocking this month is certainly grabbing my attention as this may, may be the atmosphere’s way of showing where the blocking will setup this winter. But it doesn’t always happen and what you get in autumn doesn’t always repeat in winter, in fact it can be the opposite.

Winters which follow strong El Nino’s tend to be cold in the northern hemisphere.

HOWEVER, a colder mid latitude during winter doesn’t necessarily mean a cold Western Europe.

I still have my concerns over the warm pool in the Gulf of Alaska and cold pool in the central North Atlantic. As a counter argument, you could say that a weaker polar vortex could support a weaker jet and more strat warming events.

The CFSv2 SST forecast for the Dec-Feb period shows a similar upper air pattern to the previous two winters but there are other factors, likely bigger which say otherwise…

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CFSv2 for December and January.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

With a warm AMO (Atlantic Multidecadal Oscillation), you typically see less sea ice in the arctic and in response more -AO/NAO winters. The stronger, more persistent -AO’s tie well with solar minimums just like we saw in 2008 through 2010. We’ve another 3-5 years before reaching another minimum and until then, I believe winters are mixed rather than relentlessly cold and snowy. However the ‘run-up’ winters prior to the minimum can be very exciting nonetheless.

Credit: WxBell

Credit: WxBell

Credit: WxBell

Credit: WxBell

See today’s video.

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