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

hatrickpatrick wrote: »

Briefly, what are the known biases and caveats of the GEM model? For instance, I do know that where the Atlantic tropics are concerned, it has a reputation for being far more generous in upgrading non-tropical lows to tropical cyclones, which other models don't develop and which ultimately don't end up developing. As in, you can look at a CMC/GEM chart of vorticity in the Atlantic tropics and see two or three tropical storms or hurricanes forming throughout a run, where the GFS and ECM don't see any - and more often than not, the GEM does not verify in these circumstances.

Are there any other known biases with this model which we should look out for in the context of our own part of the world?

I don't know of biases with the GEM but I know that it doesn't have a great verification record.

ECM 12z is a flat zonal westerly and perhaps getting very cool quite quick with the air coming off the cold north Atlantic.

Villain wrote: »

Jesus FI really is all over the place! ECM flipping and flopping too.

I wouldn’t like to try call beyond +120 which makes The Eagles comments too very strange!

I suspect that at least some of the current model uncertainty is related to invest 96-L, a disturbance currently off the US coast which is now formally designated by the nhc to become a tropical depression within the next couple of hours. Models seem to have difficulty with our weather when there's a northward moving subtropical disturbance which is not yet classified as a tropical cyclone and will interact with the jet stream at some stage, so I'd expect them to settle a bit once this system fully develops into a tropical cyclone this evening.

96L denoted by a red X on the left hand side of this image:



Special Message from NHC Issued 6 Jul 2018 20:10 UTC
NHC will initiate advisories at 5 PM EDT on Tropical Depression Three located a couple hundred miles southeast of the North Carolina coast.

Cork Boy 53 wrote: »

What did he say?

Well he nearly guaranteed good weather for the next 10 days and to be little in the way of rain for remainder of the month..he sounded fairly certain of it ...

The air between the Eastern Seaboard of the US and us is stupidly warm as compared to averages, and without looking, you'd imagine SSTs would be slightly above normal.

Warmer water fuels hurricanes and other cyclones and will contribute to their remnants as well.

(Note: this is not and cannot be an Ophelia when it reaches us. Forecast to track thousands of km too far north for that)

That's all I'll say for now other than that the last few months have thrown the rulebook away - and the fact that we're openly discussing an Atlantic Hurricane before it has even been named in terms of its impact on Ireland is quite extraordinary.

GFS 12z is cool, unsettled and cyclonic.

GEM 12z = Summer 2018 lives on.

UKMO starts to turn unsettled at the very end.

Yeah, I definitely think Tropical Depression 3 and Beryl are causing a ruckus in the model output. This is just silly at this stage.

If ECM 12z follows history of previous days, it will be an unsettled run. The ECM 12z runs have had a tendency to be unsettled recently even though the 0z runs tended to be settled.

sryanbruen wrote: »

It does not follow history, staying settled and warm.

Well then obviously this is the correct model and all the others are just worthless pieces of junk which we can safely ignore

Have not done one of these kinds of posts in quite a while now but this is my update on everything and my thoughts on the outlook which in fairness has proved to be a big headache.

To start off, let's have a look at the latest run of the GFS model. What can I say? Well, it's a very different run compared to pretty much every other GFS run we've seen in the past few days. It keeps high pressure going up to and including Sunday 15th (St. Swithin's Day) with further settled and dry weather although some showers possible Thursday/Friday generated by the heat and slacker gradients for a time in the atmosphere. After Sunday 15th, everything goes slack again with average pressure for the third week of July with nothing definitively unsettled or a washout being indicated on this run, just some light rain bands or showers and sunny spells. Temperatures would be going back down towards average over Ireland but as you can see from Tuesday 17th on this run, the cool 850hPa temperatures over the North Atlantic just don't quite get in to Ireland thanks to a continuously anomalous area of above average heights to the east and over the Azores as well as the jet stream splitting into two.

This is a very different run as I said to what we've seen from the GFS these past few days so it's to be taken in isolation as the overall consensus is for a brief unsettled and cooler period - until we start seeing similar runs to this GFS 12z of course.







UKMO keeps things settled and at the end of its run, the high starts to go to the east pulling in a south to southeasterly flow. On this run, this flow looks stable and high pressure dominated so don't expect convection really if the UKMO 12z were to come off. This is different to yesterday's UKMO 12z which wanted things to turn unsettled by that time frame so again like the GFS 12z to be taken in isolation and not very serious until we see trends of it appear.



What is causing all the ruckus? Simply, Tropical Storm Chris. This is the current expected track of Chris up to Friday. It is expected to become extratropical by either Saturday 14th or Sunday 15th as it comes closer to our shores. The exact track of Chris is uncertain. Previous runs showed it coming through us and bringing us a bout of wet and windy weather but today's UKMO and GFS show it well to the north of us barely having an impact on Ireland.

Chris could be the start of an unsettled spell OR it could even prolong the settled weather again! Let's take a trip back to August 2014 and also April this year.

Both lows; ex-hurricane Cristobal on 31 August 2014 and "Irene" on 16 April 2018; promoted ridging over us. The first one, Cristobal, gave away to one of the driest Septembers on record in our countries with barely any rainfall for a lot of places for much of the month following a very wet end to Summer 2014. Meanwhile, Irene gave away to an exceptional warm spell for the time of year (at least in the UK) and later, a very dry May along with a very dry June with lots and lots of high pressure being the dominant influence. Same could happen with Chris this time in prolonging the settled weather again with it helping to ascend more high pressure from the south (which will be bad news). The Azores High is still very strong and ridgey. Add the fact that the GFS was "toying" onto this idea too yesterday well in FI on some runs. I would not be surprised whatsoever if this was to actually happen given how the Summer has turned out so far and with reasons above given light. You could also consider Hector of mid-June.







GFS ensembles seem to have upgraded the warmer than average temperatures too out to Tuesday 17th but we'll see the whole suite soon.

Uncertainty is a big issue out as early as later this week so taking anything serious beyond that time is a bit pointless.

First, I'll start where I finished off from yesterday. The GFS 12z ensembles were an upgrade on the warmth yesterday in FI (they are similar today but the 16th-19th July is quite cool on today's 12z ensembles). They were showing the unsettled spell in terms of temperatures as a blip than a persistent phase with temperatures warming up again after about a week. Precipitation spikes also seemed to lower in FI. But these are just subtle hints more than anything as it's pointless otherwise because of all the uncertainty again.

Now onto today. This is the latest update of Hurricane/Tropical storm Chris. Chris is expected to become a hurricane tomorrow, back to tropical storm status by Friday as it passes by Newfoundland and then become extratropical as it travels over the North Atlantic. The centre of Chris on the latest run of the GFS is expected to be way to the north of Ireland so wind shouldn't be too much of a concern.



The GFS 12z is a changeable westerly flow with rain from time to time and is quite normal Ireland type conditions, nothing overly wet as well as not very dry. Air masses changing different ways with one having warmer than average temperatures and another having average or relatively cool temperatures. The GFS 0z and 06z had a far more unsettled and zonal pattern with unseasonable strong winds along with some quite heavy rain, the 12z seems to have died that down quite a bit but still changeable. These changes from run to run yet again reveal the uncertainty! Giving Thursday's chart (+66 hrs) on this post to show you where Chris is at that stage and watch how it travels up the North Atlantic and combines with the low pressure over Iceland.







UKMO 12z shows everything slack on Sunday 15th and Chris pushing in from the Atlantic.



GFS ensembles are bringing the NAO into negative territory through next week meaning there is signs of the jet stream heading southwards - at least for a time, bringing depressions with it over Ireland. However, the strength of these depressions whether it's the intensity of the rain or the wind is open up to question. GFS 12z suggested light rain over south and eastern regions whilst the north and west would get the bulk of the rain - as you'd expect in a zonal pattern.



I know there will be people throwing their toys out of the pram - there always is some people that do - that Summer is now over, good luck to us next year. I plotted this graph of the daily NAO data for Summer 1976. As you can see, July 1976 had quite a negative NAO index during much of the month in comparison to a positive NAO June and August that year. July 1976 was actually a rather dull and more unsettled month than June and August even though mean temperature wise, it tended to be the warmest month of that Summer.

Basically, plenty more opportunities for more settled weather sometime this Summer and as you've seen, September (even sometimes October) can be an extension to Summer too.

The battle of US and Europe with ECM going very much against the Atlantic but GFS bringing our more usual influence back.

Interesting model runs ahead in the coming days.

hatrickpatrick wrote: »

Either Sryan or Meteorite mentioned a few weeks ago that the GFS has a bias for returning to a typical jet stream / Atlantic dominated regime in FI, so that's probably something to bear in mind.

Yep it does but it's persisting in the last few runs. TBH they all can overplay the lows in FI but the range between is rather big at present

Latest GFS 6z:


ECM 0Z:

Just wrote a big analysis of the latest GFS run, only for Boards to randomly log me out after hitting post and lose the whole thing. :mad:

The 12z looks like a big improvement on the 6z for those who are looking for the settled weather to continue. The low pressure predicted by the 6z for next week has been significantly downgraded.

For comparison:

6z:


12z:



And:

6z:


12z:


Low pressure in the Atlantic continuing to be blocked. Heights lower than we've been seeing over Ireland, but still high.

Further out, towards the end of its run, the 12z shows the jet stream finally coming back into play - but the way things have been going, this seems to be getting delayed repeatedly with every model update.

Definitely still incredibly uncertain, but this run is at least an indication that those who don't want a washout aren't quite out of the game just yet.