FI Charts (T120+ onwards) Summer/ Autumn 2018 **READ MOD NOTE IN FIRST POST**

Wow, the FI GFS 6z is an orgasm for the eyes ��

The jet stream and Polar Vortex are gradually waking up

Interesting ECM chart for next Sunday:



What kind of weather would we get with a chart like this? would that tiny 1015 circle sitting right on the jet stream border to our West be a surface high or low, given its surroundings, and thus would it have fronts etc which might cross Ireland or would it be more like a mini-anticyclone?

https://twitter.com/RyanMaue/status/1029034831777353728

Looks like the 0z GFS got stuck last night, never seen this before O_o

Watching now to see if the 6z overwrites the entire mixed run or gets stuck too

hatrickpatrick wrote: »

@Sryan, can you point to any particular factors which have made this period difficult for the models to get a handle on - compared with the remarkable consistency and accuracy even in FI forecasts during the late Spring and early Summer? I presume the appearance of subtropical disturbances as noted earlier in the thread play a role? Our weather models seem to go completely off the rails as soon as anything with tropical characteristics appears on the scene.

Any other particular factors at play? Or is it perhaps that we've gotten so used to a consistent, unusually predictable pattern so far that the usual level of uncertainty just seems dodgier than usual in comparison?

I have now finally gotten time to sit down and try answer this question in great detail because it involves a lot of explaining to do and complications. I have personally not witnessed a moment like this in my model watching years so far!

Firstly, yes it's multiple factors that are possibly causing this high uncertainty we've been having during the latter part of the Summer after the Atlantic broke through on the 27th July. Before this period, the Polar Vortex was weak and so was the jet stream that throws the Atlantic depressions at us normally. This allowed there to be reasonably high certainty for a long time through Spring into early Summer as there wasn't much to really break down the big anticyclone and all the dry weather even systems like Hector in mid-June failed to do so showing you just how stubborn the conjoined Scandi High and Azores High were which is evident in many of our hot summers. However, as shown by the graph below of zonal wind speeds, the Polar Vortex has gathered pace as it usually begins to do at this time of year anyway. Another view of this is looking at the stratosphere temperatures - you'll find the chart below. The grey line represents the 1981-2010 average stratosphere temperatures at 10hPa whilst the black line is the actual recorded temperatures through the year. As you can see by both lines, they're on their way down. A colder stratosphere equates to an intensified jet stream whilst a warmer stratosphere equates to the opposite with a meandered or weak jet stream (usually involved with sudden stratospheric warming events). This is completely normal as I said and that it happens every year from August into early Autumn whilst numerical weather predictions try to get a grip of how the Polar Vortex is going to behave. However, the question lies in why is it even more difficult (and exceptionally so) this time around even if it is normal. Well I'm using this part as a starting point to the post because whilst it's normal, it plays an important part. Basically, it's a nuisance than anything else :P.





I previously gave a post about the rossby waves which you can find here: https://www.boards.ie/vbulletin/showpost.php?p=107680385&postcount=382

As the rossby wave occurred, it gave the jet stream a bit of oomph and since, we have been in this changeable pattern to which Ireland is known for. I expected this when I theorised about it. These rossby waves have slow motion and as a result, we could be in this changeable pattern for a good while unless something drastic happens like a big Atlantic tropical cyclone ascending high pressure from the Azores (or the back-to-school week phenomena occurs). The changeable pattern is going to bring uncertainty into the question at times because well..... it's in the name, changes happen regularly with interchangeable air masses, in contrast to a blocking pattern like we had from May to early July which has not much going on.

Since the SSW event back in February, the North Atlantic SST profile has been in a position not seen since at least the early 90s. This is the last time when there was a cold Atlantic Multidecadal Oscillation (AMO). The AMO is a climate cycle that affects the sea surface temperatures of the North Atlantic Ocean. When the majority of the North Atlantic is cold, the index tends to be negative whilst the reverse occurs when the majority of the North Atlantic is warm. It is prone to changes on a regular basis like the other indexes but it comes in cycles as an average overall. For example, negative AMO occurred from the early 1960s to the early 1990s but since the early 2000s up to at least 2017, the AMO has been positive. A sign of negative or cold AMO is a horseshoe shape of cold sea surface temperature anomalies as shown below in May 2018. There was theories going around, including by the UK Met Office and myself, that this meant we'd get a hot and dry Summer with a lot of anticyclonic influences as it shared similarities to how May 1976 looked. Well, that theory turned out quite well. However, this may have influenced the uncertainty because of observations struggling to understand the interaction of this with the Polar Vortex gathering pace and not to mention how we have been in the positive AMO phase since the mid-90s. You can see the latest and this time last year's Atlantic SST profile charts below the May 2018 one. They are night and day different in many ways including a warmer tropical Atlantic (which led to an active hurricane season combined with the La Nina event) and to the south of Greenland. This cold AMO is very unusual for modern times and thus, the models don't really have a lot of data for this. It will be interesting to observe. Due to how 1976 went with an exceptionally wet Autumn following the hot and dry Summer, you'd think an unsettled Autumn is the likely scenario especially with the Scandi High broken down which was one of the main elements in developing this hot Summer - similar in 1976.

We would usually be seeing uncertainty caused by Atlantic tropical cyclones and hurricanes at this time of year up to October but this year, there is a possible El Nino forming and there is also the cold sea surface temperatures over the main development region (MDR) for hurricanes in the North Atlantic. In El Nino years, vertical wind shear is increased over the Caribbean and Atlantic and this helps to prevent tropical cyclones forming into hurricanes. The opposite occurs over the Pacific. This is what has happened this year, the vertical wind shear has been above average and it has been a quiet season so far with agencies expecting this to continue through the Autumn possibly making 2018 the quietest Atlantic hurricane season since 2015 at least. This should make the weather straightforward for us but of course it doesn't, mother nature is never that nice to us! ENSO is also proving to be a lot of headaches itself, see the ENSO thread for information on the matters here: https://www.boards.ie/vbulletin/showthread.php?t=2057875863







One common thing that every model watcher knows or should know is that the models do not handle pattern changes well but we've been in this changeable pattern for more than a week now, you would think they'd gain some certainty.

There is a lot of possibilities that are causing the uncertainty to be abnormally high. Let's compare model runs.

This is every GFS run for Friday 24th August during the afternoon since Sunday just gone. Very different from run to run, day to day.



Meanwhile, the ECM has been ok since the 24 August came into its timeframe but look how different today's 12z was to say yesterday's 0z:



It's all really complex and probably a bit too hard to understand but I've tried explaining it as simply as I possibly can without getting a bit "too sciencey". It's only going to get worse into Winter if all these weird phenomena occur. This is not just uncertain because we've been used to high certainty and consistency in model outlooks during the Spring and early Summer but also down to reasons named above with millions of further potential culprits waiting to be seeked. It's a a matter of wait and see. I hope this post has answered your question.

I was looking at some recording last night. I think it was from the UK Met Office. He was talking about a wiggle in the jet stream which was only just starting to happen in the north Pacific. It's going to reach us by about the time of the UK bank holiday. He was saying that it all depends on whether the wiggle goes south of us or north of us on whether we have another blast of hot weather or something cold. But they don't know yet. I think it was meteorologist Aidan McGivern but I'm not sure.

Models today looking wet, cool and autumnal for next weekend.

ECM clusters have all of a sudden began to point towards a very settled and blocked end to August into start of September.... typical, back to school week!

There are 5 different clusters but each are just variation on a similar theme with different positions of the high pressure. The exact high alignment is vital to how warm and sunny it gets.

Looks like starting off similar to September 1995 to me which started warm and dry but then became unsettled and cool especially in the UK more than Ireland.

sryanbruen wrote: »

540 thickness line (late Autumn conditions / feel to the air) near us by Friday on the GFS 0z. ECM 0z delays it and really only gets into the north of Scotland.

Didn't want to quote your other post since it was so huge and image heavy for mobile boardsies, but thanks so much for taking the time to explain the current uncertainty. A lot of the phenomena you described were things I was relatively familiar with as a lifelong hurricane enthusiast but what surprised me most about your post was the polar vortex - you mentioned that it's normal for it to ramp up a bit at this time of year, whereas I had always had it in my head that the PV's reappearance for winter generally happened in Autumn, in and around the end of September / beginning of October.

I'm very interested to see where the AMO goes in the coming years - if we're experiencing a true flip ushering a decade of cooler North Atlantic SSTs or if this is a blip, and how that might behave in relation to global warming and climate change - which has surely increased somewhat since the end of the last cool AMO phase in the mid-nineties. Will be interesting to see how that pans out and if any correlations can be taken from it in a decade or so.

Regarding El Nino, you've mentioned a few times that El Nino is behaving oddly this year and confounding attempts to forecast it - I wonder could this be related to the theory that this year might be a Modoki El Nino, in which East Pacific temperatures cool somewhat and the central Pacific becomes anomalously warm? This type of El Nino tends not to "settle" into this pattern until the year after it emerges, in which case we could expect the Pacific to behave somewhat erratically throughout this Winter and possible settle into a proper Modoki event early next year. If the AMO does not remain negative through this Winter and returns to neutral or positive conditions, a leftover El Nino modoki going into next summer could mean another very severe Atlantic Hurricane Season - the 2004 Modoki event was followed by the infamous 2005 season, and forecasters at the time talked about how drastically lowered Atlantic Wind Shear from that event was playing a large part in fuelling the numerous monster hurricanes which formed.

Today's model runs into FI seem to predict a return to ridiculously high pressure over Ireland after the current period of unsettled weather - both the GFS 6z and ECM 0z show this today from around August 28th onwards, and the GFS is showing the Jet Stream being shoved to our North once again - but from what you've said, we should expect this to change entirely between now and tomorrow, and essentially return to our usual designation of FI as genuinely FI, and not something to base ongoing forecasts on as we've been doing for much of the summer

hatrickpatrick wrote: »

Didn't want to quote your other post since it was so huge and image heavy for mobile boardsies, but thanks so much for taking the time to explain the current uncertainty. A lot of the phenomena you described were things I was relatively familiar with as a lifelong hurricane enthusiast but what surprised me most about your post was the polar vortex - you mentioned that it's normal for it to ramp up a bit at this time of year, whereas I had always had it in my head that the PV's reappearance for winter generally happened in Autumn, in and around the end of September / beginning of October.

I'm very interested to see where the AMO goes in the coming years - if we're experiencing a true flip ushering a decade of cooler North Atlantic SSTs or if this is a blip, and how that might behave in relation to global warming and climate change - which has surely increased somewhat since the end of the last cool AMO phase in the mid-nineties. Will be interesting to see how that pans out and if any correlations can be taken from it in a decade or so.

Regarding El Nino, you've mentioned a few times that El Nino is behaving oddly this year and confounding attempts to forecast it - I wonder could this be related to the theory that this year might be a Modoki El Nino, in which East Pacific temperatures cool somewhat and the central Pacific becomes anomalously warm? This type of El Nino tends not to "settle" into this pattern until the year after it emerges, in which case we could expect the Pacific to behave somewhat erratically throughout this Winter and possible settle into a proper Modoki event early next year. If the AMO does not remain negative through this Winter and returns to neutral or positive conditions, a leftover El Nino modoki going into next summer could mean another very severe Atlantic Hurricane Season - the 2004 Modoki event was followed by the infamous 2005 season, and forecasters at the time talked about how drastically lowered Atlantic Wind Shear from that event was playing a large part in fuelling the numerous monster hurricanes which formed.

Today's model runs into FI seem to predict a return to ridiculously high pressure over Ireland after the current period of unsettled weather - both the GFS 6z and ECM 0z show this today from around August 28th onwards, and the GFS is showing the Jet Stream being shoved to our North once again - but from what you've said, we should expect this to change entirely between now and tomorrow, and essentially return to our usual designation of FI as genuinely FI, and not something to base ongoing forecasts on as we've been doing for much of the summer

In contrast to our discussion, the CFS ensembles are forecasting the Polar Vortex to be weak through this Autumn which means northern blocking will be more likely to occur.

More changes on models this morning with northern blocking forming over Svalbard and the Norwegian Sea. This would bring a cool and wet start to September if it were to happen. I expect more changes before we get any kind of certainty. Scenarios massively changing from day to day.