seb
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Posts posted by seb
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23 minutes ago, Daniel* said:
Can you actually support that? GFS has maxes barely double figures on Sunday in London mostly single figures across UK.. similarly ECM not much higher.
also lows forecast Monday AM a widespread air frost… this night is clearly going to be a frosty one, with a cold air mass, very light winds and clear spells. I think we should return to this once it passes.
Of course we can return to this at some point on Monday
I've explained in a few of my subsequent posts why I don't believe the ECM Op raw figures for Monday morning (or indeed Sunday) - GFS sits comfortably several agrees above; more than half of the ECM members are above; high SSTs are not taken into consideration (along with several other factors) and the ECM more often than not puts nighttime minima several degrees lower than actuals, especially in autumn.
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10 minutes ago, Addicks Fan 1981 said:
It has a very close tie with what Exeter are on about actually, the met office 6-15 day outputs are pretty reliable and offer information that is second to none.
Well quite. And the elephant in the room that so many don't want to see is that this isn't just shown on the most recent GFS run but also the previous one... and the one before that. And the ECM.
That's what I mean I say that there's wide confidence levels and that this is when you switch to probabilities of what is more likely on balance.
The mean is in sync with the LT average or above, apart from a very short period starting Saturday. The scatter is off the scale starting from Tuesday next week.
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31 minutes ago, Quantock said:
The ‘airmass’, (presumably 850hpa temps) will be much colder than average as currently modelled on the ensembles charts. Whether that translates to lower/higher than average 2m temperatures is a rather different matter and will not become clearer until nearer the time or sometimes on the day/night itself.
Of course it is a different matter but that is exactly what doesn't seem to be understood. I don't know how much clearer I can explain it - there is currently nothing to indicate that there will be widespread out of the ordinary cold 2m temperatures. There may be two mornings where some areas will experience temps which are a little below average for this time of the year but even that is far from guaranteed. People seem to forget that we are an island which is 300 miles wide at its widest point. SSTs are still higher than they should be and that will affect 2m temps and is not accounted for by models.
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3 minutes ago, Addicks Fan 1981 said:
Does the op have support from the control and the mean?
See for yourself...
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41 minutes ago, Daniel* said:
Not sure what some are failing to understand we’re expecting a much colder than average air mass. It’s more than slight deviation. The likelihood of frost into next week is high it’s only cloud which can prevent this.
For 1 or 2 days which is exactly what you are showing; and which is in line with MetO, and with what I (and others) have said. It's also not "much colder than average".
London October average night time temps are 8 degrees and average daytime temps are 14. Even on Sunday which so far looks to be the "peak" of the "colder" air, the low for London is 5 degrees and the high is 14 degrees. Add to that the ECM more often than not underestimates night time temps and it could well be 24 hours with bang on average temps.
As for frost - a few areas north of Manchester on Sunday morning and the same area (roughly) again on Monday morning (unless you want to take the ECM for Monday morning at face value where some patches show up across the central parts of country... but this is of course not supported elsewhere).
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1 hour ago, MattH said:
Morning. These kinds of posts here are the ones that just don't help people learn or gain clarity on the outlook and the content here is highly misleading.
There are no 'wide confidence levels', whatever that means, and using terminology like 'foolish' when it comes to making forecasting predictions at a time frame that actually requires a forecast, is foolish in itself...
That aside back to the forecast and what we see is good clarity on the initial transition to cooler weather mid-week, this has been well documented and forecasted for several days. The process for the south is obviously delayed because of the frontal wave and system from the SW that brings the risk of a sharp thermal boundary and resultant significant rainfall totals on Friday. Therefore, it is a more 'step change' to cooler weather across parts of England and Wales, a more straightforward one elsewhere.
The building ridge to the W and NW then ushers in an air mass that couldn't be any more different than what is in place now (850mb temps fall 20 degrees, see below!) and temperatures WILL end up below average, widely, by this weekend with overnight frosts, especially ground frosts and depending on the longevity of the air mass from the N or NW, snow showers are likely across the hills of Scotland as well. The flow is likely to be cut off and we then end up with a building area of high pressure over the UK early next week (cold and crisp) which then looks to become a potential Scandinavia high, it is at that point confidence falls away more significantly.
The story for the next 5 to 7 days can be told very well on the 00Z GFS ENS... N England is used in this instance as the example.
Regards, Matt.
You are free to disagree with my assessment, just like anyone else. This is however a discussion so I don't see the need for your labelling of posts as misleading.
If you wish to nail down your forecast despite everything shown, then that is your prerogative.
The generally accepted definition of "wide confidence level" is higher uncertainty. Where uncertainty is high, as it arguably currently is x-model at a much earlier point than what we are used to (and as it has been for months), it is foolish to to state that x will happen on Monday, which is what some members have done and which is what I referred to in my post.
Whenever such a scenario presents itself then forecasters apply terms such a "likely", "probably" or something like "more likely ... than"; they often also add "confidence is low" or "confidence is lower than usual".
At this moment in time, it is almost certain that temperatures will drop to more seasonal values after Friday, albeit even at this range it is not clear whether they will be below October average for a time or not (this is more likely in central and northern parts). Any output for the period post Monday currently suffers from increasing uncertainty, between models and also from run to run as demonstrated by the 00z ECM vs it's 12z run; this uncertainty increases more than usual the further into the modelled period we go.
This uncertainty is perfectly reflected in the latest MetO update for 15-24 Oct from this morning which states that temps (nationwide) will be a little below average at the start of that period, rising to little above average. The extended outlook (through to 7 Nov), although from yesterday afternoon, states that temps are generally expected to be a little above average with frost less likely than expected for the time of year.
While you may disagree with that assessment, I happen to fully agree (and I'm not someone to hold back with criticism of the MetO). As it stands, temps will drop but the likelihood of anything cold is low. In fact I wouldn't even be surprised if save for some areas in Scotland and possibly the very far north of England, we will not see any frost even on the "coldest" nights in the next 7-10 days.
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7 hours ago, Daniel* said:
Open your eyes Seb
My eyes are wide open and they see wide confidence levels, average or above average temps and when looking at ensembles and comparing models a whole lot uncertainty across the board.
Whoever wants to be foolish enough to make a call on what the weather will look like exactly from Sunday onwards, be my guest. I’ll stick to cooler, somewhat more unsettled but unlikely to be cold or below average.
Again, probabilities, confidence levels and many other factors matter. Personal preference does not.
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34 minutes ago, WYorksWeather said:
I think taking the period overall you may be right. Again I make no judgement at this stage regarding the length of the cold spell - it's too soon. The most I'd be prepared to say is that it's warm up until Wednesday, bit of a N/S battleground through Friday, then cooler than average for most from Friday through Sunday and possibly quite cold further north. Agree though that at your location you're likely to be closer to average than most of us.
Beyond Sunday is still FI I think. GFS ensembles are out and it is a massive outlier once it goes into FI, but the broad pattern through Sunday is reasonably well supported:
Oh yes, all FI and more so this year. But looking at that scatter probabilities look to be above average for now. Too early to make any calls.
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1 hour ago, WYorksWeather said:
Yeah it is important to take the OP runs with a pinch of salt - as I've been pointing out over the past few days the operational runs have been close to the bottom of the ensemble packs lately. However, tonight it does seem that the 12z runs are mostly singing from the same hymn sheet (pending ECM), and so it does look like there'll be a period of cooler weather.
I also think given the tropical features at this time of year, anything beyond T+120 is iffy, and beyond T+168 is FI. Strictly for fun only.
Cooler yes but nothing to suggest something cold and also not for long.
Blended output for my location literally has 12 days of temps between 12 and 17 degrees. That’s far from cold and still mainly above October average.-
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42 minutes ago, Addicks Fan 1981 said:
The update from Exeter doesn't agree with what you say there as they are going for near average temps and warmer in the south.
Which really is what model output, taken together, is showing. Probabilities matter in forecasting which is why I really never understood why some here still take individual runs as gospel… regardless of scatter in the ensembles and constant chopping and changing of the op runs.
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2 hours ago, Josh Rubio said:
Definitely some marked contrasts in areas according to the ECMWF. This is the expected total precipitation amount up until Sunday 00:00, with the east generally staying the driest.
Though I still think this isn’t a done deal in regards to which areas will receive the highest rainfall amounts.
Yes there will definitely be chopping and changing re the areas that get decent rain and the amount generally is likely over-egged at this point.
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5 minutes ago, MattStoke said:
Even on the warmest ensemble members, a clear downward trend in temperatures following this warm spell.,
Each spring and autumn there is often a point where we have a seasonal switch from warmer to colder conditions or vice versa. Perhaps this is it. Although, with so much anomalous warmth still to our south, it would be foolish to completely rule out the odd warmer spell.
Yes. Although still decent and above average temps southeast of a line Cardiff - Birmingham and not much in the way of rain until next weekend. So let’s see where we end up. There would have been times where 17 degrees with sunny spells on 13 October would have been considered amazing weather.
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42 minutes ago, Cambrian said:
Interesting developments towards next weekend as the low pressure “washing machine” spinning around for days over the mid Atlantic suddenly makes a move eastward over Ireland and UK around days 6 and 7. This is the 0z UKMO, but the ECM and GFS ops show similar.
It’s a shallow feature by then but brings another pulse of warm air with it as it phases with the complex low pressure near Iceland, effectively becoming a wave depression along the polar front, triggering another incursion of colder air on its western flank as it departs.
The warm air brings a lot of moisture with it, and with the north-south temperature contrast set up over the UK and Ireland, a very good recipe for a lot of rain, here on the 0z ECM op through to day 7. So heavy rain over Scotland today, but likely to be the turn for those further south later in the week, as the polar front oscillates north and south.
The Theta E charts for 120-168h show the high instability of the incoming airmass and the formation of the extra centre of low pressure at 156h.
This feature looks like it’s very much got our name on it, a full day of heavy rain for many and has the potential for further development in the models over the coming days.
Yes potentially a lot of rain for large parts of the UK and surprisingly good x-model agreement.
Obviously a lot of variables at the moment that may change the outcome but this scenario has a much higher chance of actually happening than the apparent cold wave some got excited about
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@ANYWEATHER as you disagree with my post, would you point to any output which contradicts what I’ve said?
Just so I can make a final decision on whether to take your input seriously going forward or if better to disregard (which would be a shame).-
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Maybe, just maybe those who (for whatever reason) take the GFS as gospel will have learned their lesson.
If GFS and ECM don’t agree at 7+ days there’s usually a 50/50 chance of one being right (simplified).
However, if the GFS goes off on a wild ride at 72 hours while none of the other models show anything even close to it, even the professionals know what to disregard. But I guess some here always know best.
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51 minutes ago, Wimbledon88 said:
Two day wonder now at best down here. Certainly nothing of note Midlands northwards.
Not really sure what charts you're looking at but even the GFS which does something strange and goes against the other models, has 4 days with temps significantly above average.
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11 minutes ago, alexisj9 said:
Didn't get rain yesterday, or before that either.been very dry again.
Same. Well there was a bit of drizzle this morning which I could feel in my face but it didn't even make the ground look wet (or the garden furniture). Bone dry out there.
59 minutes ago, ANYWEATHER said:Eh...? What charts have you been looking at in the last week?
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Cross-model support of warm and dry weather for South and East; less so the further North and West you go. This doesn't change until Monday at the earliest but even further out the the split remains in place. No rain at all to be seen southeast of a line from Plymouth-Cardiff-Birmingham between now and next Wednesday.
Anything after that, safe to ignore. Common sense of course would indicate that we should, at the very least, expect this latest late push of very warm air to be the last of the season... but who knows. There were people here who claimed September would be washout and autumnal after the heatwave in the first days of he month.
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1 hour ago, alexisj9 said:
Heavy stuff is coming up from the south now. So lots of rain is expected soon along the front.
Interestingly the latest UKV doesn't bring much rain to East Kent until around 9PM! All seems to stay NW of a line from Brighton - Tunbridge Wells - Maidstone - Sittingbourne until later on.
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Definitely feels like one of those days where it will storm later and for hours. Was muggy and now the sun is back out. Temps up too.
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4 minutes ago, ANYWEATHER said:
Not so sure as severe to be honest ,the windiest spell looks later into Tuesday and even this is subject to change! Just a normal ordinary, Autumn spell of weather coming up ,without the paraphernalia of overhyped record breaking weather which we are constantly bombarded with☺
For September with trees full of leaves still and in the southern parts of England, ECM and more so ICON look pretty severe I’d say. But no x-model consensus even as to location which isn’t a surprise right now.
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Model Output Discussion - Mid Summer Onwards
in Forecast Model Discussion
Posted
Someone shared a document with me in the summer but I can't find it now. It explained that the SST data used for the daily model runs is normalised data which comes from SST forecast rather than raw data. The current way of normalising the SST data, if I remember correctly, outputs values that are too low compared to actuals.
Don't quote me on it; maybe someone here has more details.
Having said that, just looking at the temp maps it would appear that both ECM and GFS simply do what they've always done and add a couple degrees for a very narrow strip along the immediate coast. To me that doesn't look like doing much with the fact the the SSTs around the UK are currently several degrees above where they should be.