I thought I would join up both North America and Europe posts today and take a closer look at some aspects regarding the winter forecast and my long term ideas. When it comes to winter and looking at the big global drivers, there is often a strong teleconnection between North America and Western Europe and with the right setup, there can be warm or cold pools positioned on both sides of the Atlantic.
I mentioned already that the long range models, particularly the CFS and CFSv2 have been jumping back and fourth and I guess the CFSv2 has been trending warmer for North America while it’s been stubbornly warm from central and eastern Europe with equal chances more for the UK and Ireland. The Jamstec has been predominantly warm with cooling now over western North America while it’s been persistently cold for the UK and western Europe. That’s despite a signal for cold on both side of the Atlantic. In other words there are some contradictions to the Jamstec forecast. While I agree with the cold for Western Europe I disagree with it’s warm over Eastern North America, based on it’s water temperature profile as well as the warmth it has over Greenland.
The thing is, as a forecaster, I CANNOT depend on modelling to produce a long term theory or idea as modelling is not enough and it’s not consistent. It should only be used as a tool and confirmation as to whether your on the right track or not. If you go purely by modelling, well your winter forecast may have changed every day or two for the last 4 or 5 months.
We must pay attention to the overall pattern globally, hemispherically and regionally. For example, what kind of summer did we have, what reaction has that had on our surrounding water temperatures, afterall water temperatures play a significant role in feedback to the atmosphere. Where have the biggest rains compared to normal fallen, what’s the behaviour of the NAO, PNA, AO over the last 6 months and what’s the projections ahead as well as what is the arctic sea ice conditions, snow cover and also solar cycle.
Speaking of warm water feedback, we’ve seen that during the late summer here in the UK boosting upper heights with the help of relatively dry ground which has held onto the warmth long into September and early October with the backing of the POSITIVE Arctic and North Atlantic Oscillation. Now that those indexes have went from positive to negative back to positive as the season changes and cold air expands forcing the sub-tropical ridge to weaken, then the warm waters surrounding the UK are now fuelling wetter, stormier than normal conditions.
I want to take a closer look at the current cold PDO vs El Ninos and of course we’ve been generally in a cold PDO now since the late 1990s. Of course in a warm PDO, we tend to get more El Nino’s and during a cold PDO you get more La Ninas but during cold PDO’s, there is of course El Nino’s which develop but their typically weaker and shower lived. They also have a far different response to the atmosphere globally than during a warm PDO.
The below chart shows the various temperatures expected across the US with a positive/neutral/negative NAO/AO against a La Nina/La Nada/El Nino.
This upcoming winter looks to produce a La Nada or neutral ENSO BUT both ECMWF, CFS, CFSv2 and some other models show warm water positioned over the CENTRAL equatorial Pacific. What does that mean? If could mean a warm La Nada and some may even argue a weak El Nino. A weak El Nino or warm La Nada with warm water out over the central Pacific favours COLD over North America and to a lesser extent, Western Europe. Have the warm waters in close to South America and you tend to get a warmer winter.
Check out the reanalysis showing some significantly cold central and eastern US winters when the PDO was cold and there was a central Pacific based weak El Nino.
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In terms of water temperatures not just in the Atlantic or Pacific but globally, both CFS and CFSv2 as well as the Jamstec, persistently show the right profile for northern blocking.
Current water temperatures
Note the slightly warmer pool in close to South America, that during the winter would note bode well but keep in mind that this chart is for October 31. Also note the warm waters indicative of the warm AMO across the North Atlantic but the cold tongue extending from Canada out into the central Atlantic with warmth above and below. As we progress through the rest of the month and storminess continues across the North Atlantic with a stronger than normal jet, that tongue of cold water should push towards the UK but early and mid December which is a classic water temperature profile for a blocking high to setup over Greenland.
Take a look at the below water temperatures for December 1, 2009 and notice the cold tongue extends right the way across the North Atlantic while the warm water currently up against the South American coast has shifted into the central part of the ocean. Of course the winter that was ahead was a brutal one for eastern North America and Western Europe.
December 1, 2009
Now check out the projected water temperature forecast from the CFSv2 for the upcoming winter and see how similar it is to 2009.
The Jamstec shows more of a flat neutral ENSO
As for the solar cycle, while it may be just past a peak in cycle 24, the overall cycle is much weaker than the previous but what’s interesting is the warm winter of 2011-12 for the UK as well as the US can be traced back to when the solar activity, although relatively weak, was however reaching a peak.
Now it’s trending downwards. The last tanking was when right when the cold, snowy 2009-10 winter occurred.
The winter of 2003-2004 was a cold and snowy winter on both sides of the Atlantic and it was during a cold PDO, centrally positioned weak El Nino and if you notice in the chart above, in terms of sunspot count, it’s right in line with where we are right now.
Here’s the CFSv2 upper pattern for November and I believe it’s on the right track with positive NAO/AO, note the largely zonal flow with strong jet across the Atlantic and negative over Greenland.
Also it interestingly shows a positive along the North America West Coast which favours a trough and cool in the East. While I believe the West is cold and stormy to start the month, the middle half becomes zonal or west to east with less cold but a build-up of cold occurs over Canada setting the stage for a cold December. I think there’s a flip for the UK and Europe too with a turn to much colder with height rises mid to late month.
Note the CFSv2 for December shows northern blocking with negative heights over Europe and North America.
January too shows the blocking over the pole and ridging poking it’s nose up into Alaska and the Yukon which supports a trough and the southward decent of the polar vortex into the eastern US while the mean trough is positioned close to the UK.
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