Model Output Discussion - heading into April

[stodge]

Afternoon all

ECM swung dramatically toward GFS overnight and this morning's GEM plays a very similar tune.

While we might get a true E'ly, there are two other thoughts which are cropping up in the Ensembles across the board:

1) IF the northern blocking is too far north the south gets closer to the European trough and we'll import rain or showers from the Continent leaving the fine weather for the far north. The response to strengthening heights to the north is a broad but shallow trough from the Atlantic through Europe. IF the heights across Scandinavia are robust enough the British Isles is in the E'ly flow with the continental influence felt only in the Channel Islands and along the south coast as a strong wind - if not, pressure falls to the south and the instability manifests in the form of areas of rain or showers.

2) What often happens is the heights drop out of Scandinavia and retrogress to Greenland so we get a new LP developing to the north of Iceland which swings SE and introduces a cool/cold NNW'ly airflow so the flow is E then NW then N as the HP re-consolidates over Greenland/Iceland which is effectively what 06Z Control shows.

The 06Z Mean tells you all you need to know:

 

[Man With Beard]

48 minutes ago, knocker said:

Allowing for the limitations of the map projections  I would have said the det run is pretty close to main cluster at 168 and the jury is still out at 192

Should also be added, when looking at the individual ensemble members, there are by T168 about 20% members which are even more progressive than the op run in their dealing with the trough, in that they fuse the trough between the Atlantic and Scandinavia to a far greater depth, with the UK being the dividing line between ridge to the north and ridge to the south. This pattern would make mid-range forecasting for the UK very difficult as the local conditions would depend on exactly where the balance between north ridge and south ridge would lie.

[Frosty.]

Looking at the GEFS 6z mean, the longer term trend continues to indicate high pressure being sucked towards Greenland with potential for a chilly less settled late April, perhaps with some arctic influence but by the cusp of May, any wintry weather would be very watered down / toothless and there’s no guarantee it would work out that way, there are a few warmer options but the main theme is of a blocked slow moving pattern with some pleasant benign surface conditions for most of the time.

[mb018538]

Rainfall chart for the next 10 days shows the expected patten well - drier to the north closer to high pressure, further south (and west) you go the greater risk of rain pushing up from the south.

[damianslaw]

There were hints from the models a few days back, that we might be looking at northern blocking surfacing in the longer term. Today's models continue this theme. In the near term, high pressure anchoring itself over the UK, meaning more dry sunny weather for many, with temps climbing again, but nowhere close to the heady heights of the weekend. However, instead of sinking south into the continent, developments over the NW Atlantic aid warm air advection into Greenland and this sets up cold air advection over NE Europe, thus heights elongate and get sucked north collapsing in on the trough to the NE and becoming a very substantive feature, whilst heights lower to the SW and some form of weak shallow trough develops. In the interplay of trough to the SW and NE and behaviour of the main longwave trough out of NE USA, enables heights to build NW to Greenland something we haven't seen for a long time.

What would the outcome be? Tricky to say, chance we may become influenced by the shallow trough feature which could develop into low pressure and bring chilly showery/wet conditions more so to the south, or instead see a generally cool often cloudy interlude with showery outbreaks more so in the NE. ECM is showing a very long drawn cold NE flow.

For the winter cold lover these are the king of synoptical evolutions you long for. Door firmly held shut on the atlantic, alas they are far less likely to happen in the depths of winter, and far more likely as we move ever deeper into spring, especially by late April. Easterlies are preety common at this time of year, and at any other time of year, I would be cautious of the synoptics on offer verifying, but at this time of year - far less so.

Edited April 13, 2020 by damianslaw

[Allseasons-Si]

17 minutes ago, damianslaw said:

ECM is showing a very long drawn cold NE flow.

 

I suspect you where talking about this morning's run?

the 12z is a vast improvement,i just hope it's not a warm outlier just like the gfs op/control

 

gefs ens and the gefs mean at 240

That's an impressive mean for day ten and we would be drooling at a mean like that in winter.

[damianslaw]

3 minutes ago, Allseasons-si said:

I suspect you where talking about this morning's run?

the 12z is a vast improvement,i just hope it's not a warm outlier just like the gfs op/control

 

gefs ens and the gefs mean at 240

That's an impressive mean for day ten and we would be drooling at a mean like that in winter.

Yes this mornings run, but the evening run still shows the source being from a long way NE - a cold source, but with less of a wind, wouldn't be quite so bad.

[Frosty.]

A very decent ECM 12z operational with plenty of high pressure which becomes even stronger towards the end as it’s reinforced from the Azores, following all the low pressure of recent months, it’s nice to see high pressure predominantly in the ascendancy bringing largely pleasant weather!

 

[knocker]

It's day ten so academic but a cold source is not a done deal

[damianslaw]

1 hour ago, knocker said:

It's day ten so academic but a cold source is not a done deal

Ensembles picture is a colder source than the ECM one output. Trend at least from today's ensembles is something colder from the NE. All about trends rather than  individual runs.

[Allseasons-Si]

10 minutes ago, damianslaw said:

Ensembles picture is a colder source than the ECM one output. Trend at least from today's ensembles is something colder from the NE. All about trends rather than  individual runs.

I think what Knocker was referring to is that we shouldn't take that time frame as gospel as we know how quick models can and do change from now until that said date but you also have a point as to what the ens show(bearing in mind the 12z not out yet) and there doesn't look to be a warm up anytime soon and looks to become more unsettled after days 3/4

also the anomaly's show a cool picture out to day ten and beyond with height's centered to the N/NW of the UK

cpc 6-10 and 8-14 day 500mb height anomaly's

lastly,if we where to look where the source of the wind direction is coming from then check out the De-built wind direction chart,it shows predominantly winds coming in from 45 degrees NE.

so at this moment in time,the ext models/ens and anomaly's show a cool picture so make the most out of the fine conditions for the next few days.

 

[Cloud 10]

Cracking synoptic day 10 chart from the 12z GEM,with a clear 3 wave pattern across the Northern hemisphere.

 

[shaky]

Gfs 18z dry and breezy all the way to 240 hours so far!!!astonishing dry output at the moment!!no sign of any meaningful rainfall as far as i can see!!

[knocker]

7 hours ago, damianslaw said:

Ensembles picture is a colder source than the ECM one output. Trend at least from today's ensembles is something colder from the NE. All about trends rather than  individual runs.

I am well aware that det runs should never be taken in isolation, unless in a short time frame. I'm also aware that recently a colder regime has been indicated down the line, but from where I'm sitting, the source of the colder air has yet to be determined

[Methuselah]

GFS 00Z not looking too horrendous: maybe not as cool as some have feared, and there are even some very tentative suggestions of a southerly evolving with time...?

T+168          

T+240          

T+312          

T+384          

It's all a very long way off, so I'll no' be getting excited!

[Frosty.]

Again the ECM 0z operational is showing heights sucked NW towards Greenland and the day 10 would be an absolute cracker...if it was WINTER!
 

 

[SLEETY]

Perfect winter charts showing in Spring again.How predictable is that.

If the end of the ECM run verifies,then I wouldn’t rule out snow for anyone.

Towards the end of April has had several notable snow events in the past.

[knocker]

9 minutes ago, SLEETY said:

Perfect winter charts showing in Spring again.How predictable is that.

If the end of the ECM run verifies,then I wouldn’t rule out snow for anyone.

Towards the end of April has had several notable snow events in the past.

Do you not think it a tad warm.? Not that it is worth the bother

[DavidS]

1 hour ago, knocker said:

Do you not think it a tad warm.? Not that it is worth the bother

Yes, and the uppers don’t look conducive to snow, apart from maybe the very north of Scotland.

 

[Djdazzle]

Snow at the end of April for lowland Britain is incredibly rare. The ECM does not support it and once again, it’s so far into FI that’s it’s not worth bothering. A few days ago the ECM was showing a heatwave. I think we can be confident that HP will be in charge, but how cold / warm the airmass will be is far from certain.

[Zak M]

Pretty decent GFS run I must say. It has a high sticking on top of the UK up to 210 hours - bringing signs of settled and warmer weather.

Then after 210 hours it has a northerly - bringing more unsettled weather with temperatures below average for the time of year.

[MATTWOLVES 3]

Who do we believe... ECM or GFS... look at those heights over Greenland come the later frames... Even in April that would bring some very chilly conditions.. I'm soaking up the sun right now... Come day 10 I could be ice lake fishing..  

And do stay safe, and try and not have nightmares. 

[stodge]

Evening All

The 12Z output is still coming but the E'ly or SE'ly continues to firm up.

That's the T+144 from UKMO, GEM, GFS Control and GFS OP.

Some differences in HP positioning and the Atlantic profiles as you'd expect at this range but the net effect is the same with an airflow from the east or south east across the British Isles. Nothing too dramatic to be honest.

Moving toward the end of the month both OP and Control keep northern blocking but the OP brings the trough much closer from the south. This broad but shallow feature would bring disorganised bands of rain and showers to southern parts but keep it on the warm side and even humid.

The 12Z Mean at T+240 hasn't changed that much:

I don't think there's much chance of a NE'ly blast from Scandinavia at this time though whatever happens the best of the weather look to be points north and west. The key is how close the trough gets to southern parts as we approach the end of the month. 

 

[stodge]

I couldn't resist this:

12Z JMA at T+180.

How often do we see a 1075MB Greenland HP any time and certainly in winter? 

[Methuselah]

57 minutes ago, stodge said:

Evening All

I don't think there's much chance of a NE'ly blast from Scandinavia at this time though whatever happens the best of the weather look to be points north and west. The key is how close the trough gets to southern parts as we approach the end of the month. 

Thank you, God!