Model Output Discussion - Spring Has Sprung

[Pauski]

1 hour ago, Mike Poole said:

Yes, high hangs around in some shape or form until the end of the run on the GFS, although drifts slightly northwest later.

GEM 12z run is a cracker through to T240, things starting to properly firm up now:

If you look at the direction of the wind in my place in Finland, it is mostly Northeast. This time of the year idon't actualy like these type of charts, it needs to be june or july(better) when it should hapen. 

Something like this i want  "A warm summer comes to Finland also when there is high pressure in northern Russia, and low pressure over Central Europe and the Baltic Sea " 

[near northampton]

 Pauski 

Edited April 14 by near northampton

[Rain All Night]

11 hours ago, Rain All Night said:

0z deterministic runs, out to Sun 21 Apr (day 7)

The ECM AI model shows the UK high coming under threat from an Icelandic system next Sunday, but it stands alone. All of the other models display splendid frames for next weekend, especially further west.

0z ensemble means, out to Mon 29 Apr (day 15)

You can see that perhaps towards the last days of April, beyond day 10, some member runs in these ensemble suites may be showing outcomes where the blocking breaks down.

12z deterministic runs, out to Sun 21 Apr (day 7)

ECM machine learning model continues its rebellion, and ICON goes for an easterly... otherwise, beautiful charts for next Sunday!

Edited April 14 by Rain All Night

[Rain All Night]

12z ensemble means, out to Mon 29 Apr (day 15)

Is that some kind of trough-type-thing developing just to our east later on? It looks as though the high may ultimately move back out west, but seemingly not northwest.

[Kirkcaldy Weather]

On 07/04/2024 at 19:34, Kirkcaldy Weather said:

Heading toward Mid April I'm watching for a plunge of Arctic air as troughing develops to the North of the UK and moves toward Scandinavia and Europe bringing a flow from the Northwest and North.

Active period of weather with this.

Number of dynamics going on, we have a cold front which will be finishing its journey through Ireland and the UK by midday Monday.

With a strengthening Jet Streak interacting with the cold front there are a few heightened threats these being increased wind gusts with trends for embedded potentially damaging gusts and also a potential for tornadic activities embedded along the cold front I'd suggest parts of Ireland and also Wales and Southwest England being particularly at risk though it's a wide area overall.

To the Northeast of this active Jet Streak we have a deep cold pool moving in at 500hpa, this corresponding brilliantly with a pool of increased instability meaning the showers having a higher expectation of being thundery in nature and combining to the Lowering Isothermic values a wintry mix with snow mostly at high levels though not exclusively with hail and sleet to lower levels. Northwest, North and Northeast England and Scotland seeing the most of this activity.

As this Arctic plunge descends through Europe this brings yet another significant snowfall event across the Alps, a very repetitive and common occurence during this El Ninò. I'm also noticing the signal of a significant snow event in Bosnia and Herzegovina from Wednesday through Friday.

[Andrea]

 Model Output Discussion - Spring Has NOT Sprung. It looks like for another 2 weeks 

[In Absence of True Seasons]

 Andrea it sprung for 24 hours on Saturday

[danm]

9 minutes ago, Andrea said:

Spring Has NOT Sprung. It looks like for another 2 weeks 

It's sill due to settle down again later this week? Subtle differences in the positioning of the high which needs resolving, but the trend is the same across the models this morning. 

ECM:

 

GFS:

 

The GFS then looks dire into the last week of April, but that's a way off. 

 

UKMO:

[Andrea]

 danm ECM looks good if it was January. I'm also checking my hometown in Italy, and it's very interesting to see how it is going from proper summer to winter in 2 days. In a part of the world that is much more stable than here in this period.

[Sherry]

 Andrea spring sprung ages ago we’ve not had a below average month, leaves are open, flowers open, it’s very much a typical spring one day warm one day cold that is spring 

Edited April 15 by Sherry

[Rain All Night]

15 hours ago, Rain All Night said:

12z deterministic runs, out to Sun 21 Apr (day 7)

ECM machine learning model continues its rebellion, and ICON goes for an easterly... otherwise, beautiful charts for next Sunday!

14 hours ago, Rain All Night said:

12z ensemble means, out to Mon 29 Apr (day 15)

Is that some kind of trough-type-thing developing just to our east later on? It looks as though the high may ultimately move back out west, but seemingly not northwest.

0z/6z deterministic runs, out to Mon 22 Apr (day 7)

Three of these are showing ICON's little easterly now, including ECM.

GFS 6z has a different take:

0z/6z ensemble means, out to Tue 30 Apr (day 15)

GEFS 0z wants to take the high northwest, and then the GEFS 6z wants to take it really northwest - too far northwest, look what happens after.

Edited April 15 by Rain All Night

[Cambrian]

Shiver me timbers! 

Looks like we have a retrogressing high before our very eyes, ha ha haar (and other pirate noises) - even before it’s properly arrived.

Whether ‘twill be as shivery as 6z GFS op at day 9, where it withdraws far enough to the northwest to allow a proper cold blast down the frontage with some snow a fair way south, and settling on the hills…

   

or holds close enough nearby to keep the old lunger a bit further east like on the 0z GEM op at day 10 (beware that sea serpent beyond the pole, haar)…

the retrogression and European trough are definitely looking to be features of week 2 - ‘tis here too on the 0z EPS at day 11. Aar.

The CFS weeklies (weeks 1-3) show the Euro trough by week 3 being reinforced by its maritime buddy that’s come romping through the Azores in weeks 1 and 2, while to the north, the Atlantic heights hint at wobbling back east, a tad back our way again…

  

…the big concern for us island landlubbers looking for something to warm our jellies is that rather than a generally quiet but cool outlook, the pattern in the event all heads just that bit further north bringing us back into chilly cyclonic influences that just judder your rafters. More pirate noises….

[danm]

 Cambrian the dreaded Spring, high latitude blocking. A common set up at this time of year, but one that causes many frustrations for those of us looking for more prolonged warmth! 

[Addicks Fan 1981]

 Cambrian wonder if the weather is reacting to the final SSW? Mind you you could say as @WYorksWeather has said that its better to have a later final warming rather than a later one for when the summer arrives.  

[WYorksWeather]

In relation to the previous discussions around the final warming, here is a paper I found recently which discusses this in much more detail. I've summarised a few points below on my reading of it, but I definitely welcome any input from the various pro meteorologists and other experts we have on this forum in case of any misinterpretations on my part.

Skilful predictions of the Summer North Atlantic Oscillation

WWW.NATURE.COM

---

The Summer North Atlantic Oscillation responds sensitively to an anomalous strength of the stratospheric polar vortex in spring, which can be exploited for seasonal predictions, according to large-ensemble...

Details

From my reading of this, the proposed mechanism for a late final warming leading to better prospects for summer (particularly early to mid summer, so June and July) is as follows:

1. A later final warming typically means a stronger than average polar vortex in May at 10hPa
2. This means that at lower stratospheric levels like 50hPa, the polar vortex can persist into late May or even into June
3. This tends to then correlate with a positive phase of the Summer North Atlantic Oscillation (SNAO)
4. A +SNAO correlates with drier and warmer weather for the UK in summer

There is also an additional factoid - a late winter SSW (defined as occurring between 1st February and 15th March, that is not the final warming) correlates quite strongly with the strength of the polar vortex in May, and therefore have a sizable impact as well on the causal chain above.

There is a significant amount of experimentation in the paper that does seem to support the idea that this is causative, not merely a correlation. In years where the vortex at 50hPa in May varies by 1 m/s or more from climatology, the relationship is particularly strong, with a correlation of 0.55 (which if you know your stats means it explains 0.55 ^ 2 = 30% of the variance in the summer NAO, which is quite a lot).

This is of course pretty cutting edge, with the paper only being published in November, but it does seem to make sense.

Summary

So, the upshot for our summer is that we have very positive signs if you're looking for a warm and dry one:

• A late winter SSW promoting a positive May Polar Vortex Index (MPVI, which the paper defines as a stronger than normal vortex)
• If we do get a positive MPVI (as most forecasts of the polar vortex are suggesting), then this correlates, (and may in fact have a hand in causing) a positive summer NAO
• A positive summer NAO correlates with a warm and dry summer for the UK

This is not of course, definitive. No one factor can guarantee a warm and dry summer. But having any predictability is still an improvement - previously prediction of the summer NAO was considered to be essentially impossible even at very short lead time, unlike the winter NAO.

In any case, I hope this fairly deep dive into the final warming and its impacts is useful, and if you are interested the paper is linked.

[Rain All Night]

8 hours ago, Rain All Night said:

0z/6z deterministic runs, out to Mon 22 Apr (day 7)

Three of these are showing ICON's little easterly now, including ECM.

GFS 6z has a different take:

0z/6z ensemble means, out to Tue 30 Apr (day 15)

GEFS 0z wants to take the high northwest, and then the GEFS 6z wants to take it really northwest - too far northwest, look what happens after.

12z deterministic runs, out to Mon 22 Apr (day 7)

Most of the (modest) shenanigans we've seen over the past 36 hours ago have disappeared now. Fine weather for all throughout next weekend looks to be the most likely scenario.

12z ensemble means, out to Tue 30 Apr (day 15)

Interestingly, it looks like the pattern will lapse into something cooler again by the end of next week, but without any Atlantic influence (contrary to this morning's GEFS runs).

I don't have time to wait for the full ECM ensemble to come out, so the abridged version will have to do. It goes just about far enough out to show the appearance of a cold trough to our east, supporting the GEFS and GEM ensembles.

Edited April 15 by Rain All Night

[damianslaw]

For the first time in over 3 months, yes that long, the models show high pressure rather than low pressure ruling the roost in the near term. We are not talking a major blocking high that will fend off frontal features, namely as it is forecast to position to our west at first allowing weak frontal features to flow around its NE flank, it then attempts to build over and through to our east but ultimately becomes thwarted by lower heights which look set to develop into a major euro trough. In these set ups which are very common in the latter half of Spring, chilly easterly and north east winds can bring cool damp showery airstreams to the east and south, whilst the north and west holds onto the driest sunniest weather. The only time in the year when the NW is on the 'fine' side of the NW- SE divide.

More notable is the return to near average means, again something we haven't seen for any length of time since mid January. 

 

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A blustery and chilly morning here, showery with plenty of hail. Not great, but a 1030mb+ high building through the UK and Ireland by day 6 on the 0z ECM op, day 0-6 here, the rise in pressure and its convenient location now well inside the reliable and for once, coinciding with the weekend! Many a lawn will get mowed….

 

An impressive build in heights to the west and north. No doubt some fresh and chilly nights and mornings as it works its way in and settles down. Consistent signs of the high pulling back west thereafter, but for a fair few days, this is going to feel much, much better!

[SunnyG]

 damianslaw In brief, more of the same then.

11 hours ago, damianslaw said:

it then attempts to build over and through to our east but ultimately becomes thwarted by lower heights which look set to develop into a major euro trough. In these set ups which are very common in the latter half of Spring, chilly easterly and north east winds can bring cool damp showery airstreams to the east and south,

 

[CryoraptorA303]

14 hours ago, Addicks Fan 1981 said:

wonder if the weather is reacting to the final SSW?

Almost certainly; a SSW affects the weather sometimes for months after.

[ANYWEATHER]

 CryoraptorA303 not always a SSW to deliver this type of weather which is pretty normal for the time of year. A fragmenting PV is of responsible for changing the default  wind pattern at this time of year , to more of a Northerly or even an easterly which is more common during April and May , than at any other time of year!

[Rain All Night]

13 hours ago, Rain All Night said:

12z deterministic runs, out to Mon 22 Apr (day 7)

Most of the (modest) shenanigans we've seen over the past 36 hours ago have disappeared now. Fine weather for all throughout next weekend looks to be the most likely scenario.

12z ensemble means, out to Tue 30 Apr (day 15)

Interestingly, it looks like the pattern will lapse into something cooler again by the end of next week, but without any Atlantic influence (contrary to this morning's GEFS runs).

I don't have time to wait for the full ECM ensemble to come out, so the abridged version will have to do. It goes just about far enough out to show the appearance of a cold trough to our east, supporting the GEFS and GEM ensembles.

0z deterministic runs, out to Tue 23 Apr (day 7)

0z ensemble means, out to Wed 1 May (day 15)

GEFS diverges early (day 6) by sending low pressure over the top of our high from west to east, and then again subsequently by not sending as much high pressure north-westwards as the other two models do.

Incidentally though, this doesn't make a whole lot of difference to the prognosis for us: a warm(er) settled weekend followed by a change to cooler conditions not of Atlantic origin.

We're not quite yet at the point where we can gain much insight into how the month is going to end, but I suspect we're not too far off.

Edited April 16 by Rain All Night

[Frigid]

Can't recall seeing graphs like this in April since 2021. Both chilly and dry. 

   

Down south are seeing quite the period of below average temperatures.

Edited April 16 by Frigid

[Scorcher]

 Frigid Slightly below average at 850 hPa doesn't necessarily mean 'chilly' though.

Just as high 850 hPa temps don't guarantee 'above average' temps at the surface.

As always there will be local variation depending on wind direction and sunshine.

[raz.org.rain]

 Scorcher indeed. As I recall when we had that near record high 850hPa airmass the other week, the ground temperatures didn't see an exceptional response.