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FI Charts (T120+ onwards) Summer/ Autumn 2018 **READ MOD NOTE IN FIRST POST**
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Is there even a sniff of a bit of cold going on in FI ?!
Yes, some GFS runs are showing cold northerlies/northwesterlies in around 2 weeks time. On average, 2/3 ensemble members per suite are showing snow somewhere in the country (some over the past few days have shown widespread snow but we know that probably won't happen - look at Perturbation 1 and 3 ie. 2nd and 4th from the top line to the right showing widespread snow)
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I wrote this for an article so the wording might sound weird.
Recently, the GFS model has been consistently picking up on a northerly to occur around the last weekend of October 2018. It’s been showing this for the past few days but today, it has gone quite extreme with the cold levels by October standards. The charts below are of the 500mb height synoptics and very cold 850hPa temperatures which the midnight and six o’clock runs of the GFS generated today. That is a proper northerly blast with cold air coming straight from the Arctic and a mid-Atlantic ridge setting up ascending to Greenland. Out of the two, the GFS 0z was clearly the more extreme one of the two as it brought the -9 isotherm into Scotland and set up a block of high pressure in Greenland with a centre of around 1065mb.
These kinds of synoptics are among the coldest you could receive for this time of year in the UK and Ireland. October 2008, exactly ten years ago, brought the most widespread October snowfalls since 1974 and for some, their first October snowfall since 1934 showing just how rare such a scenario is. Even London had snowfall in October 2008 which is probably unheard of to some people. Could we have the same pattern occur exactly ten years later? It would be an amazing coincidence but extremely unlikely.
GFS 0z
GFS 06z
The Arctic Oscillation is an index that shows you whether there is above or below average heights over or around the Arctic Circle. The more positive the AO is, the deeper the below average heights are i.e. low pressure thus disallowing cold from descending into the mid-latitudes where the UK and Ireland are. The more negative the AO is, the stronger the above average heights are i.e. high pressure thus sending cold down into the mid-latitudes. The AO has been in an unusually long positive state since the Beast from the East and the Son of the Beast events earlier in the year with only a few temporary blips into negative AO during the period such as late July into early August or late June (see the top of the chart below). Positive numbers (1, 2 etc) reflect positive AO whilst negative numbers (-1, -2 etc) reflect negative AO.
The GFS ensembles (the red lines at the end) are forecasting a drop in the AO into quite negative territory by the third week of October showing there is the suggestion of blocking to occur over the Arctic which will in turn send cold air down into the mid-latitudes. The question though would be, where would it do so? The latest GFS runs highlighted above show the cold air coming to the UK and Ireland via northerly winds. This would be a huge change on the weather since April.
The North Atlantic Oscillation is an index that shows you the difference in mean sea level pressure between the Icelandic Low and the Azores High; two elements which make up the zonal pattern that give the UK and Ireland mild Winters and cool Summers. The more positive the NAO is, the deeper the Icelandic Low is and the stronger the Azores High is. The more negative the NAO is, the weaker the Icelandic Low and Azores High are – sometimes even can be swapped around which many cold Winters have. Positive numbers (1, 2 etc) reflect positive NAO whilst negative numbers (-1, -2 etc) reflect negative NAO. Like the AO, the NAO has been in an unusually persistent positive NAO state since April, in fact, unprecedentedly so. This has been as a result of the very strange North Atlantic sea surface temperature (SST) profile that 2018 has produced.
However, the GFS ensembles are not only picking up on a change in the AO to negative levels, they’re doing the same with the NAO for the third week of October onwards. This would be completely different to anything we’ve seen since April with high pressure forming somewhere near Iceland. This would support the northerly scenarios the above GFS runs show today but no guarantee of course.
Meanwhile on the other side over towards Alaska, the GFS is picking up on a trough to be placed here around the same time it wants to deliver a northerly airflow to the UK. This would be yet another major change on the weather recently as blocking has achieved record heights in this region. This is another thing that would support the northerly verifying for the end of October as the jet stream is not aligned from the north of Alaska going southeastwards into the eastern seaboard of the US. If it were, cold conditions would take place in the eastern US and then blow up the jet stream across the North Atlantic delivering stormy conditions to the UK and Ireland. This would not be the case if the trough were to verify.
There is no doubt that the media will jump on the hype train and release scaremongering headlines such as EARLY WINTER ARRIVING WITH BLIZZARDS COMING TO LONDON or something like that. Ignore them! Do not be heeding any attention to them as they are a complete waste of your time.
This northerly could verify and bring the first widespread snowfalls of the season very unusually early but there is a higher chance of it not verifying especially given how we’re talking just around two weeks away and other models such as the more accurate in terms of verification ECM have yet to generate out as far as when the GFS shows the northerly to occur. Will be keeping a close eye on it as always with everything in weather world. It’s all just for fun right now though the bigger picture itself is very intriguing.Photography site - https://www.sryanbruenphoto.com/
Weather photo portfolio - https://sryanbruen.myportfolio.com/weather-1
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Artane2002 wrote: »^^ That cold northerly on the GFS 12z is now a mild southerly
. Hope we don't get that southerly, I'd be in cold mode by then.
So close yet so far, high pressure would be retrogressing to Greenland if the low weren't so deep in the Atlantic on that run.
Photography site - https://www.sryanbruenphoto.com/
Weather photo portfolio - https://sryanbruen.myportfolio.com/weather-1
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Artane2002 wrote: »This post is just for fun, it probably won't happen this way. Perturbation 15 from the GEFS 6Z has gone totally nuts. It shows most of the country enveloped in -10c uppers and -12c into Scotland!
Syranbruan hinted towards this a few days ago, no?Racism is now hiding behind the cloak of Community activism.
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Artane2002 wrote: »This post is just for fun, it probably won't happen this way. Perturbation 15 from the GEFS 6Z has gone totally nuts. It shows most of the country enveloped in -10c uppers and -12c into Scotland!
That's getting into absolute record breaking territory (would completely smash previous October records). I will bullishly come out and say that is not going to happen, not even close to that extreme especially in the age of a warmer Arctic.
This northerly (which I discussed in-depth the other day) is still being shown for a period at the end of the month to bring quite a chill to the country on some model runs but others have us on the periphery under an area of high pressure (which at the end of October would still be fairly cool especially at night with frost potential ever increasing more widely deeper into the season).
Another GFS 06z ensemble just for fun, Perturbation 5. Proper northeasterly winds with blocking to the west.
Like I said, the above shown was just for fun. What I think is most likely (right now) is we get some kind of a northerly shot sometime at the end of October but it will only lead to frost than wintry conditions rather.
The indexes (AO and NAO) are still predicted to change significantly during this second half of October into negativity which is a complete flip of what has occurred from the extended Summer period.
This is the latest SST anomaly map from NOAA on 18 October. The Atlantic has a very messy profile with a largely cool area to the very north of the Atlantic, neutral through the middle though still very warm over towards the eastern seaboard of the US and a fairly warm to neutral tropical Atlantic. This is not favourable for a negative NAO so unless we see dramatic changes - I discuss the changes that have happened since May below in a second - any negative NAO interludes are likely to be temporary than prolonged. I predicted a positive NAO for Autumn 2018 in my Autumn forecast due to this Atlantic SST profile and so far this season, it has been consistently positive yet again continuing the theme of Summer 2018.
This chart is of the 7-day SST anomaly change that has occurred in the past week over the North Atlantic. We can see that there has been significant cooling going on near the eastern seaboard of the US and Newfoundland which is a big change as the SSTs have been extremely warm there over the year so far (and still are, even at this point; only emphasises how warm they've been). SST anomaly change other than that hasn't deviated much with a lot of regions having little change in the past week. Colder anomalies near the eastern seaboard of the US and Newfoundland is a positive for negative NAO conditions. Will this continue through the rest of October, November and into the Winter? We shall see.
Will discuss more on the bizarre things (and trust me, the tropospheric patterns right now are REALLY bizarre and unique) going on with the weather in the Winter 2018/19 thread when I can: https://www.boards.ie/vbulletin/showthread.php?t=2057903068&page=15Photography site - https://www.sryanbruenphoto.com/
Weather photo portfolio - https://sryanbruen.myportfolio.com/weather-1
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After the HP of next week a cooler spell showing up from around next Fri especially over the weekend being in a brisk NW then N flow. Possibly turning a bit milder again briefly the start of following week. GFS showing cold wetter LP systems coming from the NW after that but too far out in F1 to Know for sure.
Could see some nice convective cloudscapes coming down from the N over next weekend and some showers maybe wintry in Northern counties ?
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Meteorite58 wrote: »After the HP of next week a cooler spell showing up from around next Fri especially over the weekend being in a brisk NW then N flow. Possibly turning a bit milder again briefly the start of following week. GFS showing cold wetter LP systems coming from the NW after that but too far out in F1 to Know for sure.
Could see some nice convective cloudscapes coming down from the N over next weekend and some showers maybe wintry in Northern counties ?
Why is Rathdowney shown on these maps? Not like it's a major town, literlly had to google it.0 -
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Model runs continue to point towards quite a potent cold snap *for the time of year* (remember it's only October), similarly consistent to how the Beast from the East event earlier in the year was picked up in the model output.
Photography site - https://www.sryanbruenphoto.com/
Weather photo portfolio - https://sryanbruen.myportfolio.com/weather-1
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