Model Output Discussions 12z 08/03/17

[stodge]

2 hours ago, knocker said:

People keep talking about upgrading this and downgrading that but the detail for the Easter weekend was never pinned down and in fact still isn't. People expect far too much from the models, outside of the reasonable time frame, forgetting, or deliberately ignoring their current scientific limitations. In winter you can say this in spades when the cold cabal are in full hysterical mode.

That's a fair point, Knocker.

I certainly don't think the Easter weather is in any way "settled" as yet and intra-run variation adds to the confusion.

I do think the key is the extent to which the trough digs SE over the North Sea on Saturday. Some earlier modelling suggested quite a plunge into the southern North Sea which encouraged a height rise to the west oriented more North-South and maintaining a N or NE flow - something like P10 on the 06Z GEFS.

What we are now seeing is a more ESE'ly drift into southern Scandinavia which restricts the N'ly plunge and keeps heights to the SW and these build back across keeping the Easter weekend fairly benign before a second attempt at what I shall call "the plunge" after Easter.

At T+168 (Easter Monday), there's broad agreement in the GEFS for a new LP to develop south of Iceland and it's what happens to this that drives the FI evolution.

Move out to T+240 and you can see the OP and the majority lowering heights to the E and SE over Europe and introducing a cool N or NE'ly but the big spread is Eastern Greenland - this is between those Members which develop Greenland heights and a ridge S or SE and those which build heights from the mid-Atlantic NE but lower heights over Greenland. The latter option leads to the jet sinking the HP while the former locks in the colder airflow.

At T+324, this divergence becomes enormous - look at P12 and compare with the OP for example.

The modelling has consistently shown the possibility of Greenland heights in low-res but they've rarely come into high-res so caution is very much the watchword. The repeated plunge of Arctic air with associated Greenland heights has been consistently and persistently modelled in high-res but has not so far come into low-res. This may be because of the continued persistence of PV energy over NE Canada and NW Greenland - this has, throughout spring, encouraged MLB rather than HLB but as it dissipates (final SSW anyone ?), there is the potential to import that warmer air into Greenland and encourage blocking and I wonder if the record snowfall recorded might strengthen that blocking as we move further into spring but that's an observation for another place.

Yet, it hasn't happened - the PV energy has persisted and held back the development of HLB - once again, until we see it strongly in low-res I would be cautious. For now, it looks as though Easter will be unremarkable - neither warm nor cool, probably near average with perhaps a warmer day or two in the south but also a little rain for all at some point and perhaps something a bit more defined for NE Scotland and NE England.

 

[knocker]

42 minutes ago, snowray said:

 But in the last couple of years its been 0 out 10 and I have lost count of the number of times that a northerly has been showing up in that time frame, what signals do the models keep picking up for the D7-D10 range that are always wrong then? In fact everything is usually shifted many hundreds of miles to our east, surely there is a way of correcting these errors.

 

Well if your brief analysis is correct I sincerely hope not as it's a trend that should be encouraged.

[Summer Sun]

Well UKMO is quite a bit different for Easter Sunday from it's 00z...

00z

12z

 

[Frosty.]

Yes the ukmo 12z looks more settled by Easter Sunday and the Gem 12z improves too with high pressure gradually taking over.

Edited April 10, 2017 by Frosty.

[Frosty.]

I actually don't think the Easter weekend will be bad at all, at worst it's likely to be sunshine and April showers, some heavy with hail and thunder but they would die out if high pressure nudges in as shown on the ukmo / gem 12z and any cooler / colder air would be negated by the increasing strength of the sun which is already as strong as early september.

Edited April 10, 2017 by Frosty.

[comet]

40 minutes ago, Frosty. said:

I actually don't think the Easter weekend will be bad at all, at worst it's likely to be sunshine and April showers, some heavy with hail and thunder but they would die out if high pressure nudges in as shown on the ukmo / gem 12z and any cooler / colder air would be negated by the increasing strength of the sun which is already as strong as early september.

I think it is almost a given that any pronounced colder weather will be post Easter weekend. Quite a few of the gefs showing -8c 850 temps pushing down across much of the country post Easter.

Edited April 10, 2017 by comet

[snowray]

10 minutes ago, comet said:

I think it is almost a given that any pronounced colder weather will be post Easter weekend. Quite a few of the gefs showing -8c 850 temps pushing down across much of the country post Easter.

You don't mean at D10 there by any chance do you comet?

In fact I think I'll book my trip down to Bournemouth after all for the Easter break, its looking pretty good on todays runs.  UKMO best of all..

[Frosty.]

The Ecm 12z looks unsettled and chilly for most of the Easter weekend, and it stays chilly beyond Easter with high pressure to the west and lower heights to the east / northeast..a locked in pattern.

Edited April 10, 2017 by Frosty.

[knocker]

Still not complete agreement between the gfs and ecm over the weekend. The ecm is still liking a shortwave spawned by the upper trough near Greenland at T120 tracking east and impacting Scotland Sunday night with some quite wet weather A slight variation on the previous run.

[ANYWEATHER]

Hello! Tonights gfs and ecm ops suite suggest a continuation of the benign drier than average conditions ,with temperatures below average , so lets not use the word cool, cool cool at this time of year , it feels cold ,cold cold  with the latest synoptic outlook

[Scorcher]

1 hour ago, ANYWEATHER said:

Hello! Tonights gfs and ecm ops suite suggest a continuation of the benign drier than average conditions ,with temperatures below average , so lets not use the word cool, cool cool at this time of year , it feels cold ,cold cold  with the latest synoptic outlook

Nothing to me that suggests 'cold, cold, cold' in the reliable timeframe- looks at worst slightly below average for many, and not even below average further south. Pretty sure 15C is above average for London for this stage of April in fact.

[snowray]

Our cold blast has moved a few hundred miles further east it would seem on the 18z, could be quite mild by easter Monday now. Getting close to 20c on the south coast at this rate.

[Frosty.]

13 minutes ago, snowray said:

Our cold blast has moved a few hundred miles further east it would seem on the 18z, could be quite mild by easter Monday now. Getting close to 20c on the south coast at this rate.

Doesn't look cold, cold, cold for the south does it. 

[snowray]

14 minutes ago, Frosty. said:

Doesn't look cold, cold, cold for the south does it. 

Looking lovely and mild to me, I would expect a few places pushing up around 18c/19c in the S and SE by monday. 

Ahhhh nooooo whats this I see, here comes our next D10 northerly teaser.

Edited April 10, 2017 by snowray

[Frosty.]

Here comes the snow!!!!

[knocker]

As per last night's anomalies, and in that case not altogether surprising. the EC46 update is agreeing with the upcoming pattern change. That is, upstream, Alaskan ridge into the Pole and a quite intense vortex lobe N. Canada with associated trough into the western Atlantic.Downstream very strong surge of the Azores in the Atlantic with the trough to the east. This gets underway this weekend, intensifies next week, and quickly declines starting around the 24th as the amplification weakens. So confidence in the broad picture is relatively high but the detail as ever will depend on the precise orientation and position of the high pressure. Certainly the surface temp will in all probability below average but it could be quite dry still, depending on the above caveat.

Meanwhile back at the ranch. Saturday 00z sees the main low east of the Faeroes on it's way to eastern Europe with the UK in a NW showery airstream which gives way to a drier regime during the day as the ridge nudges in from the south west.

The ridge is briefly squashed on Sunday as the next trough rushes through, again en route to Denmark and points east, which brings some wet weather and some quite lively winds to to Scotland. Following this the HP regains influence and Monday looks like being a much quieter and pleasant day for all with temps not too bad before the high pressure slips away south east and the aforementioned pattern change gets underway.

Thus by midday Wednesday we see the Azores surging in mid Atlantic and consequently the next trough tracking south east over the UK  Best left there I feel

So Easter in a nutshell, starting off showery but, apart from the odd blip in Scotland, improving as the weekend progresses, Best of the weather all told in Cornwall.

And just to confirm where we are probably going with this this morning's GEFS anomalies

Edited April 11, 2017 by knocker

[knocker]

The ecm still has a little shortwave breaking off from the main low to the west and tracking it N. Ireland/central England on Sunday to be East Anglia midnight Monday. Thus fairly wet in the aforementioned areas. From that point the Azores surges and high pressure dominates proceeding and nary a rain drop in sight. This may well become a concern as I believe others have mentioned and was discussed on Farming Today this morning.

Edited April 11, 2017 by knocker

[Frosty.]

Again the Gfs is showing a risk of snow on the 00z for scotland this weekend..

[Summer Sun]

A chilly start to the easter weekend but by Sunday and Monday temps do recover a bit especially for the south so if you can get some sunshine and light winds it would be pleasant enough given the sunshine is getting stronger

[Singularity]

  

As GEFS is way more vigorous with some MJO activity starting just 3-4 days from now than the other models, I am skeptical of it's extensive Arctic blocking scenarios with a focus to the W/NW of the UK. The composites for phases 7-8 tie in very well with the model's trends of late.

 

That ECM has toyed with some blocking too has raised an eyebrow at times and suggests the model is not totally adverse to a bit of MJO action, but of course it may also have been having some of the old feedback issues with amplification. This morning has really backed off though, with the 'limpet vortex' by Canada trying to do us a favour in diverting the cold air to our east - but given the time of year, it's not able to prevent a raw easterly affecting the south for a time.

It soon slackens off, but I'd be interested to see how the strong sunshine interacts with that cold flow and whether it can overcome the high SLP values.

Given the general tendency of the past 4-6 months I'd not be surprised to see this favoured over blocking to the NW even without the MJO considered. Ridges seem very inclined to lean our way - but can we hold onto that for the summer I wonder?

 

[knocker]

And this morning's ecm ens anomalies The only change in the 10-15 period is the pattern is a tad further east.

 

[Frosty.]

Looking at the GEFS 00z mean, the Easter weekend shows an improving picture following an unsettled start as high pressure slowly builds in and temperatures don't look too bad, feeling pleasant in the sunshine but chilly nights. Further ahead, high pressure generally dominates but eventually pulls further west with hints of a Northerly later in April.

Edited April 11, 2017 by Frosty.

[Frosty.]

Those of us looking for a return of the glorious Sun kissed weekend just gone are likely to be disappointed with the Gfs 6z which for most of the time looks rather cool / cold and unsettled, especially for the north and east, the s / w faring slightly better at times. 

Exeter is saying colder than average conditions to dominate the outlook until the end of April, especially for the n / e with wintry showers and night frosts at times which suggests Northerly incursions..however, still feeling pleasant in sunny spells. The s / w occasionally faring better due to higher pressure nudging in, similar to what the Gefs 00z mean shows.

 

Edited April 11, 2017 by Frosty.

[Frosty.]

The Gem 12z shows a window of fine weather across southern uk on Easter day and Monday but thereafter it really goes downhill, becoming very unsettled and cooler during next week with strong winds at times.

[Frosty.]

The Gfs 12z follows a similar route to the Gem as I described above but then changes course and becomes more anticyclonic during low res with pleasant spells of sunshine and lighter winds before ending unsettled and much cooler with snow on scottish hills and mountains. 

Edited April 11, 2017 by Frosty.