Did tropics dictate N Hemisphere winter 18-19? What gave may have also taken away!

Written by on February 5, 2019 in Rest of Europe, United Kingdom & Ireland with 0 Comments

I feel my cold, blocky winter projections keep getting pushed back and so therefore my forecast has busted some. Sure it did turn colder beyond New Year but that came came across the Atlantic rather than Russia as expected.

The reason for the bust? It’s got a lot to do with the fact the NAO has refused to go negative, shutting down at Atlantic ‘pest from the west’ influence. By why? Looks like the MJO had a lot to do with that.

What interesting is that while the MJO went into phases 1, 2 and 3, this may have likely triggered the SSW but from the peaking of the SSW, the MJO has been traversing phases 3 through 6 and as you can see below, this doesn’t promote a -NAO. But we could and I stress the word ‘could’ be going into phases 7 and 8 during the 2nd half of February, so all may not be lost just yet.

You can see in the below NAO chart that the only time it went negative since meteorological winter began was around New Year.

So why have we seen it colder if the NAO hasn’t went negative? It’s not the NAO but the AO which releases polar air south but the NAO is what determines whether it gets cold for a prolonged period of time over the UK. Notice the AO is projected to rocket into positive, hum.

With -AO but +NAO, the displaced polar air has become entrained in the westerly flow so we’ve enjoyed at least some snow and with higher pressure building overhead, we’ve experienced some cold days and nights but the westerlies and Atlantic influence has never been far away.

Put together by Stuart Markham of www.chorleyweather.com, based on a neutral ENSO and phase 7 of the MJO, we get this hemispheric setup.

But for us to really get that -NAO we need to get into phase 8 which would deliver this.

According to the MJO, we’re heading into phase 7 over the week to 10 days and possibly 8 by week 3.

The CFSv2 suggests a continued westerly pattern with Icelandic low continuing to drive over the next couple of weeks. This coincides with a transition from UK block to Greenland block. Note by week 3, the CFSv2 indicates a blockier pattern.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

Credit: Tropical Tidbits

If we based the next 3 weeks purely on the MJO and we all know it’s not that simple, this suggests little winter through till at least Feb 20th, remember what we got at the close of February last year? Keep in mind that you can still see serious cold even into early March despite shortening nights and lengthening days. Of course last years ‘beast from the east’ came in the wake of an SSW and I don’t see another one occurring the rest of this winter. As they say, no two SSW events are the same and even if everything points to something, other players can thwart a seemingly ideal situation.

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