Latest Thoughts On The 2012-13 UK & USA Autumn & Winter Seasons (Includes Video!)

Written by on August 18, 2012 in United Kingdom & Ireland with 0 Comments

Image courtesy of Mark Vogan

Well we are now fast approaching the end of meteorological summer 2012 and for many of you, the questions about what kind of winter lies ahead are starting to come in.

There are many aspects which must be considered when looking at long range forecasts and so I shall try to briefly share what factors and drivers play significant roles but I will go into the finer details in the weeks and months ahead which will explain in detail the fundamental role these players have in this fall and winter for both the US and UK.

20-30 Year Warm/Cold Cycles of The Pacific & Atlantic

I am a great believer in the ocean cycles and their role on our climate across the continents. The vast oceans of both the Pacific and Atlantic play a huge role on weather and climate across North America and Europe and when both oceans are warmer than normal, you naturally warm the continents. In 2007 the Pacific flipped following 20+ years of warmth. This ties in well with the Atlantic being warm and the warmer than normal period which followed the cold era of the 60s and 70s when both the Pacific and Atlantic were last cold.

This return to a cold mode in the Pacific tips the balance of warm across the hemisphere and world. So now that the Pacific is now back in it’s cold mode but the Atlantic remains warm so wild swings in temperature deviations from normal become more common across the world. While there’s the overall warm/cold modes in the oceans, there’s embedded warm, cold modes known as the ENSO index in the Pacific and this plays a major role in a global pattern reversals. These modes constitude warmer or colder than normal sea surface temps in the equatorial Pacific. When warmer than normal it’s an El Nino and when cold it’s a La Nina.

The cold Pacific tends to mean fewer El Ninos and more La Ninas and when El Ninos do occur, their often weaker and for all you winter weather lovers out there, we want a cold PDO with weaker El Nino..

Map courtesy of NOAA

Take a look at the above chart showing recent global SST’s. See the horseshoe of cold over the North Pacific indicationg the cold mode of the Pacific.. This by the way leads to drier conditions in the Western US, colder in Alaska and more in the way of drought and heat when the AMO is warm and there’s a la nina into an el nino transition. El Nino’s which are in close to SA in the cold PDO is what supports drought and heat like we saw back in the 1950s.

Now, by his autumn the long range models have a ‘weak’, central Pacific nino. That means the warmest waters compared to normal are positioned over the CENTRAL PACIFIC and not in close to the South America coast. When the warmest waters are nearest SA, autumns and winters in the US tend to be warm but when the ninos are centred in the central Pacific, the winter tends to be colder and snowier in the Eastern and Southern US with ridging over the western US. This allows more frequent blasts of cold from Northern Canada into the Eastern US.

The North Atlantic Tripole in SST’s of Warm-Cold-Warm Leads To More Blocking & Negative NAO’s

The North Atlantic also plays a vital role in the weather pattern for both the US and Europe. Warm modes of the AMO which we’re currently in tends to support more in the way of blocking over Greenland and when high’s build over Greenland thanks to warmer than normal SST’s, this draws a trough over the eastern US and a western Europe trough. Enough cold reading to sink south into the trough and you’ve got plenty of winter. This pattern is known as a negative NAO.

The warm surrounding Greenland, cold in the central Atlantic and warm over the tropical Atlantic known as a tripole favours blocking and this is what we saw strongly in winters 09-10 and 10-11 with 09-10 bringing repeat cold and snowy periods to both Eastern US and Western Europe.

Autumn’s looking cold and stormy overall across US

Autumn is looking cold and stormy across the US with potential for a substantial cold October over the Rockies and perhaps Plains but staying milder in the East

Same for Europe. The weaker nino this autumn and winter looks good for a colder winter for the UK/Ireland and Western continent but warmer than normal over the central and eastern continent.

As for Western Europe, I believe a warm month is in store with even hints of an Indian summer but October may start cold but turn mild with a warm but very wet November which could extend into early or even mid December like we saw back in 2009.

So, a warm autumn for Western Europe and a cold and stormy autumn for the US but warmer than normal in the east. For winter, I believe an overall colder than normal winter like we saw in 2009-10 is in store with periods of bitter cold and snow. Gone will be the memories of the warm 11-12 winter in the UK and particularly warm US winter.

More to come soon.. Stay tuned.

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