FI Charts ( T120+ onwards) Autumn 2021 **READ MOD NOTE IN FIRST POST**

Can someone briefly explain what one should look for with regard to the MJO when it comes to northern blocking and cold for Ireland? I've only been getting to grips with the MJO in recent years, and as such the charts which define its location by numerical phase are still a little confusing to me - however, the VP200 charts which give you a visual representation of it are now within my ability to interpret :D 

For the uninitiated, or those who have only ever viewed the MJO through the simplified spiral phase/time diagrams, the chart below shows areas of enhanced convection / rising air (green) and suppressed convection / sinking air (red). What I'm wondering is, what do we want this chart to look like if we're hoping for the MJO to give us a kick into a blocking pattern? Where would we want the rising and sinking cells to be? As you can see from the chart, the MJO is currently very firmly in the Indian Ocean, or (I think) Phase 1-3 for those who are more familiar with viewing the MJO in this way. As far as I can remember, we need it in Phase 7 to boost our chances of cold - so the main rising cell (green) centred over the date line, more or less?

I’d fecking love that to happen again, unreal memories of it. Getting pished on Xmas eve and the hangover wasn’t long clearing once you went for the Xmas day walk. The highlight for me was a few lads playing ice hocking on the rivers in kanturk! Totally frozen over. If I remember rift-16/17 was the temp that night

Yeah I tend to refer more to the diagram showing amplitude of particular phases rather than VP200 charts as they are quite a straightforward way of seeing what the MJO is doing relatively speaking. But generally, what one should look out for at this time of year for high latitude blocking to occur is a strong MJO passage of phases 4-5-6 (activity moves from the maritime continent towards the west Pacific) which leads to wave breaking in the Atlantic and helps amplify a mid-Atlantic ridge which may become a Greenland high dependent on how strong this wave breaking is.

It should be noted that of course the MJO or tropical amplification is not the be all and end all, and other things such as a major SSW event or favourable SSTs being conducive to building high pressure out to the west and northwest of Ireland blocking off the Atlantic. Late 2010 occurred with a weak MJO (it was driven by a textbook tripole pattern in the North Atlantic which favoured a southerly tracking of the jet stream) - not surprisingly as it was a La Niña and a moderate to strong one at that in which La Niñas typically reduce MJO activity as compared to warm ENSO events (El Niño) or neutral. This is particularly the case, historically, when the La Niña is in a central based state that I've mentioned in prior posts. This is why weak eastern Pacific based La Niña events are often touted as the most favourable to blocked patterns. Studies have also shown that major SSW events, which have proven to develop high latitude blocking if downwelling occurs from the stratosphere, occur most often in easterly QBO/La Niña or cold ENSO neutral winters and less so westerly QBO or El Niño seasons. However, there are exceptions as always with any teleconnection or driver as other chains of events may have led to such in that given season. MJO phases can have differing correlations dependent on ENSO event too as well as the time of year.

This is a simplified analog diagram on the height anomalies one should expect for each MJO phase during a particular ENSO event. This does not go into the month by month variation that can occur but gives good guidance - there's more in-depth analogues out there going by month. Nor does this guarantee anything as there's other drivers that can significantly change the patterns. Gotta love meteorology and the weather!

ECM mean is much better than the OP. So there's a still a bit of hope. What's your thoughts on that Syran?

😂😂😂😂 you have one poster saying cold never comes til after December and another saying by Jan it’s almost Spring. Gotta love opinions. Gonzo is right though. Jan and Feb are always our best hopes for cold, Feb / March best for snow.

Lads were riding scramblers on the lakes in the Midlands

Was epic alright

Has everyone disembarked the polar express?

Was gonna say the same thing here's hoping anyway that Christmas will be a cold but dry day

EC clusters this evening provide more positive light for prolonging the risk of cold weather (if that's what you seek) with any kind of Euro heights on most vanishing through late November into maybe early December. What this means is that even with only a mid-Atlantic ridge or a displaced Azores High into the Atlantic, low pressure systems can dive from Iceland towards the continent and give numerous "ninja snow" events, commonly called slider lows. On their western side, the winds can veer northerly or easterly helping to advect cold air into the country although again, with the lack of proper high latitude blocking, don't expect a severe cold airmass being streamed this far south. These events are largely marginal with inland areas such as the midlands or high ground favoured for the highest risk of sleet and snow. Think of the likes of December 2017 and late January 2019 for recent comparison.

I must note too that there is a small signal for a stronger MJO push of phases 5-6-7 through early December which could end up reinforcing blocking to develop to our NW sometime in December but this is unlikely. What is most likely is that high pressure will continue to sit out to our west and give toppler type events consistently with milder days separating them as the airflow around the high turns around more to the tropical Atlantic. Typical stuff we have seen time and time again in many winters. Still nothing clear cut to suggest very cold weather.

My brain hurts. Any chance of translating that into layman speak?

I remember on 22nd December 2010 cavan had a maximum temperature of - 9.9c now that's cold

The latest CFS Christmas forecast on Gavs videos showed a cooler pattern alright. Roughly

Cool and windy at end of week

Dry with mist n drizzle but a bit milder early to mid December

Cooler and changeable in run up to Christmad. Windy with maybe wintry showers in North

An easterly has appeared towards the end of the GFS run this morning!