Model Output Discussion - Spring Has Sprung

[LetItSnow!]

The GFS 12z sees a different, though not inconceivable route to high pressure. With such a wad of unusually warm air over Europe for April and a return of the warm SST anomalies around the Azores, it's entirely possible this could promote a ridge of high pressure to develop into a more substatial feature.

Day 10 shows the first 20C appearing on the temperature projection map in the London area. I think if we do see high pressure develop from our south it would easily get us into the range of 19-23C providing there is ample clear sky. The sun is getting stronger very quickly and the continent is warm.

All very un-April like patterns though, it has to be said. Indeed, the charts look very similar to late January and much of February when persistent high pressure to our south kept us bathed in south-westerly winds. At times (late January) it ridged high enough to bring in inversion cold in the extreme south-east; this time though it's April and that increase in pressure would bring our first proper warm spell of the year. Not from a Scandinavian high like usual though. Indeed, without steering the conversation elsewhere it's got a very "new normal" look to it, though for now it would probably be very welcomed by almost the entire UK... you might even convince me into it! 

The devil is in the detail though and the previous run had cool N/NW winds for the same date so it is not a guarantee at this time, but a possibility, and as explained, probably not an unlikely possibility with such a loaded atmosphere. 

Don't send me hateful messages if low pressure is still dominating on the 12th! 

Edited April 2 by LetItSnow!

[sunnijim]

Probably already been said here but the last reversal in early March has thrown up nothing but mediocrity with the block too far NW to bring us any colder weather.

Not that it would have been much more than cold rain and snow on Northern hills at this late stage of proceedings had the block been better positioned.

The misery here would have been palpable had the warming synoptics been wasted like this in  January!

[Kirkcaldy Weather]

 

On 27/03/2024 at 03:06, Kirkcaldy Weather said:

As this initial troughing clears Eastward this will open the door to colder conditions from the North during April week 1 with current trends for this to be most prominent across Northern areas of the UK.

Starting with the above, with a Lowering Isotherm there will be multiple areas of snow particularly across Scotland mostly for higher elevations though mixing occuring at lower levels will be likely, with the first seeing the ongoing rain gradually becoming increasingly wintry > snowy then as a stronger area of frontal precip comes in during April 4th and 5th with the lowest Isotherm values a snow event occurs as this moves through Scotland. 

On 27/03/2024 at 03:06, Kirkcaldy Weather said:

With further trough developments into the latter part of April week 1 in the North Atlantic this will bring an increasingly above average precipitation setup adjusting further north through Ireland and the UK.

 

On 19/03/2024 at 21:11, Kirkcaldy Weather said:

We'll begin to see an increasing influence from blocking further East which could push the Atlantic trough further west and perhaps an opportunity for a plume type setup given past experience and the time of year becoming more supportive.

During Friday and Saturday we get the first great example of the above as a cyclone begins to deepen west of Ireland with increasing high pressure across Europe to the South Southeast of the UK this gives a plume style setup with trends this will draw up highly anomalous PWAT values which indicates very heavy rainfall and a resulting flash flood risk.

This will see a large portion of Europe extending from Africa experiencing surface and upper level temperatures above - significantly above average I'd expect further temperature records potentially tied and broken.

Looking at the setup across the Northern Hemisphere by this weekend some of the most noteworthy events

• Developing Rossby Wave Break Event across America [see global thread for more info] 
• As discussed above plume setup builds across Europe
• The -NAO event connects into the + Arctic Oscillation 

With the teleconnective pairing of the move from a strong -NAO toward positive NAO values with recent stronger +AO values we'll see a focus of troughing and cyclonic developments more centering effects for Northwest and Northern UK and Ireland with a building of higher pressure having greater impacts toward southernmost UK and Europe.

This will also pair with the MJO progressing from our region of the globe ie Western Hemisphere, South America and Africa into the Indian Ocean although at a lower amplitude again feedback shows cyclonic systems trend more Northwest and Northern trackways and I would suggest further plume opportunities are plausible given feedback signal of high pressure to our East and Northeast with similar trough placements to our west and southwest most likely.

Cheers. KW ️

[WYorksWeather]

ECM and GFS 12z runs both flirting with our first 20C or 21C over the weekend. Not as extreme as some prior solutions but the GFS operational still gets a very impressive plume of air with the +10C isotherm over many southern and eastern areas overnight Friday into Saturday, peaking at +14C in the SE corner. The ECM solution is very extreme, with the +10C isotherm up to the Scottish Borders, +15C as far as Yorkshire, and +17C for the south coast!

The pattern is associated with low pressure so will underachieve its potential by a significant margin - with surface conditions more conducive to heating this would have the potential for mid or even high twenties, especially with the ECM solution. In any event, record-breaking minima on Friday night may be more likely than any notably warm surface temperatures.

Nevertheless, whilst GFS knocks temperatures back to around 17-18C, which might mean we'd struggle to achieve the first 20C of the year, but ECM achieves it even on the raw figures, suggesting that in reality we might hit 21-22C somewhere in eastern regions, probably most likely in Yorkshire, the Midlands, or East Anglia.

Main uncertainties are around the timing of the plume and its exact west-east position, small variations in which could still significantly affect the ultimate temperatures we achieve on the day.

Regardless of whether we achieve any notable warmth at the surface, a notable 850hPa level plume is likely even with the GFS solution, and the ECM solution would be completely unprecedented for this time of year.

[Penrith Snow]

Poor GFS this morning with no sign of high pressureeven into FI, the flow becomes more westerly zonal with depressions on a more northerly track which should allow drier weather into the SE.

However, areas further north and west are relentlessly wet with northern England and Scotland receiving 100mm of rain by day 10.

High pressure is over France in FI but just not close enough and certainly not the proper spell of high pressure we are looking for.

Couldn't really be any worse, indeed, I don't like the look of GFS FI because as mid Month approaches much of Europe is enjoying a early heatwave while the UK and Scandinavia remain under an Atlantic influence, we have seen this scenario play out many times in recent years.

Andy

[ANYWEATHER]

 Penrith Snow And ,looks like we are back to square one again after Gfs phantom promise of high pressure.

[Mike Poole]

1 hour ago, Penrith Snow said:

Couldn't really be any worse, indeed, I don't like the look of GFS FI because as mid Month approaches much of Europe is enjoying a early heatwave while the UK and Scandinavia remain under an Atlantic influence, we have seen this scenario play out many times in recent years.

But surely, this heat in southern Europe shown on GFS 0z FI has to be a necessary first step, from where we are now, before there is any reasonable chance of seeing some sustained heat here? 

By the way, I’m still not expecting much to write home about in the UK before the last third of April.

Edited April 3 by Mike Poole

[Cloud 10]

Looks to be an improvement in the weather in the 8-10 day time frame,at least for Southern and Eastern UK as pressure rises over mainland Europe,hopefully providing less rain and higher temperatures at least for some.

 

[Rain All Night]

23 hours ago, Rain All Night said:

0z deterministic runs, out to Tue 9th (day 15)

GFS, you utter troll.

0z ensemble means, out to Wed 17th (day 15)

We can be hopeful of a visit from the Azores high during the latter half of next week, but it doesn't seem it would stick around for very long. GEFS isn't interested, which is a concern.

0z deterministic runs, out to Wed 10th (day 15)

I've dug deep looking for another run that looks like the UKMO, but have come up short.

0z ensemble means, out to Thu 18th (day 15)

The second half of next week still looks decent, and it appears we have some prospect of not falling straight back into an Atlantic trough situation afterwards.

[lassie23]

Surely this weather cannot carry on through the summer months.......can it?

[Sun Chaser]

GFS keeps on with this ridge to our south next week as it becomes more influential with every run.  It seems there could be a way out of this rut as soon as day 7-8. Just in time for my birthday

It could still be somewhat westerly (in the south at least) but ultimately it's high pressure so it would be dry and pretty warm, and with the LP to our west there's potential a day or two later for low twenties under southerly winds.

Inevitably the low swings by afterwards but what's encouraging is that, for the first time in what seems like decades, GFS is repeatedly showing high pressure ridging in from the Azores in FI. The Greenland high is also completely gone by then which can only be a good thing. Don't want to say anything too early but I think there's signs of at least a less offensively wet pattern on the way!

 

Just to add, the ensemble mean pressure has shot up to 1020 out of nowhere! A couple of days ago we were looking at 1010 all the way to the end and now we have relatively good agreement on a build of pressure from the 10th onwards. Huge progress.

Edited April 3 by Sun Chaser

[danm]

 

[Sherry]

Looking at the gfs ensembles they are showing far less rain spikes down here in London and with above average temps could see some nice weather at times 

[danm]

Some continued signs of an improvement next week?

[Cambrian]

Attempting to piece together (as we are inclined to do!), emerging trends of the outputs from different models, here the 12z GEFS and UKMO at day 4:

 

And then, taking it through to day 7:

 

That is one very welcome surge in heights from the southwest early next week, resulting in a 1030mb+ high pressure cell making a visit on the UKMO. 

A tad optimistic perhaps and probably not that long-lasting in the event, but the contrast is striking and very good to start seeing all the same. Have a good one. 

[damianslaw]

 Cambrian Yes the models are showing a change of sorts into next week, thanks to the erasing of heights to our NW, courtesy of an unusually deep low for this stage in the year tracking north to our west pulling a feed of very mild moist air from the south, the pressure gradients promote heights building strong on the SE flank nosing into the UK.

However, this does not seem to be the start of any major pattern change in context of significant dry high pressure influence, the PV is moving to the siberian side and this will leave a space for pressure rises to our NW, seems logical any azores/euro heights building through the UK in time will either sink south or more likely advect west and we pull in more westerly/north westerly airstream with weak fronts on the NE flank of mid atlantic heights. 

Welcome thoughts from those who have more knowledge and gleaning of likely developments deeper into spring, and sign of any significant drying out, and when might we lose these south west airstreams, April and May typically bring more northerly / easterly and anticyclonic influences, these SST values and El Nino phase seem prone to a locked in pattern it seems, and any SSW has had minimal effect. 

Edited April 3 by damianslaw

[minus10]

Yes more encouraging gfs12z run for warmer and drier weather towards mid month....

..mean 850s a healthy plus 5 for almost 5 days and the op/ control north of that at times..

..mean pressure now upto 1025mbs..

..both geo potential and mslp anoms showing more of a traditional weather pattern ..

...resulting in a more traditional nw se rain distribution..

...and somewhat warmer temps..

...this is a trend that has been increasing for a while now so...here's hoping for some good drying weather ...ecm....

 

[WYorksWeather]

A couple of posts tonight - firstly I want to really focus on Saturday's plume event.

The 12z GFS solution has the peak of the plume at 8am Saturday, with the 15C isotherm clipping the far SE corner, and more importantly the +12C across much of central and eastern England from the NE coast, down through parts of Yorkshire, the East Midlands, East Anglia, and the SE of England. Resulting surface temperatures peaking at 19C raw, so in practice more like 20-21C.

The 12z ECM is, as yesterday, the more extreme solution. The plume sits a little further west at 8am, and the +16C isotherm clips the south coast. This means that ECM achieves higher temperatures. We have a 21C raw temperature on the map at 2pm - hence 22-23C is a likely max in reality.

UKV is also in range now, so worth having a look at that as well. The 15z UKV again peaks the plume at 8am Saturday. We have the +15C isotherm clipping in again. Raw surface maxima reach 21C later in the afternoon, so closer to the ECM solution. UKV usually doesn't underestimate temperatures as much, so probably 22C is a good guess for the actual maximum.

Note

Worth noting yet again how unusual this plume is. At the 850hPa level, as far as I am aware (and nobody has yet posted a counterexample), a +15C isotherm even clipping the UK in early April has never happened before. In fact, forget early April, I'm not sure it has even happened in April at all!

If it were associated with surface conditions more conducive to heating (less cloud), it would likely achieve mid 20s as an absolute minimum. We would expect a temperature differential of around 10C from the 850hPa level to the surface at this time of year under fairly decent conditions. At the upper end, at a similar time of year, 25.6C was achieved on 3rd April 1946, with only around a +11C isotherm. However, this came after a much drier start to the year, and as a continuation of a longer warm spell that began in late March.

But in short, if you transplanted those surface conditions, and replaced the +11C with a +15C to +16C isotherm, something truly extraordinary could have occurred this weekend - 28-29C in early April! That is how anomalous the airmass is.

This weekend will likely pass without notice for most - the surface temperatures will be warm but unexceptional, and it may even feel a bit chilly in the presence of strong winds and little in the way of sunshine. But regardless of whether it is reflected in the surface temperatures or not, a milestone has been crossed here with such extreme warmth at 850hPa so early in the year, and multi-model agreement on its occurrence.

EDIT: Worth noting that per a further comment by LightningLover below, a +16C isotherm at this time of year (or even slightly earlier!) is not entirely without precedent. However, it is still extremely rare, and I believe still worth commenting on.

 

Edited April 3 by WYorksWeather
Clarified due to correction by LightingLover.

[LightningLover]

 WYorksWeather Don't forget this once happened!

[WYorksWeather]

Not going to cover the medium range look ahead, partly because I think there's too much uncertainty at the moment, but worth keeping an eye again on the ECM sea surface temperatures. As I mentioned previously, the Azores SST anomalies appear to be making a comeback. We also have a warm anomaly just to our east. Temperatures are still near normal or even slightly cooler than average to our west and north for the most part.

However, given the prevailing wind direction over the next few days, this explains why south-westerlies are able to deliver significantly higher temperatures than we would normally expect. This is the pattern that has been driving consistently above average temperatures for the UK despite synoptic patterns you wouldn't necessarily associate with particularly warm weather.

Days 0, 5, 10 and 15, in anomaly terms:

[WYorksWeather]

 LightningLover Well, I didn't forget, so much as I never knew this had happened! Great find by the way. Did you know about it already, or if not, how did you go about finding it?

Therefore, I revise my previous statement slightly. A 16C isotherm in early April is not unprecedented, but is still very highly unusual, and well worthy of comment nonetheless. I believe the 18-19C which was on some ensembles earlier would have been unprecedented, and thought a 15-16C would still be so.

Again though, thanks very much for finding this - I have no issue with being proven wrong.

 

[Kirkcaldy Weather]

Leading onto the above.

Signals here for a multitude of potential severe weather impacts with this cyclonic system during Friday and Saturday in particular, though I already discussed the flash flood threat I wanted to show that there is a tropical moisture inflow into this cyclone which can be tracked back into the Ninò style Jet with moisture inflow really from the Pacific and Mexico. This moisture inflow starts downstream into the severe weather and ongoing snowstorm in America which leads into an increasingly strengthening Jet Streak helping our cyclone to undergo deep cyclogenisis.

As the cyclogenisis occurs I'd expect wind warnings to be required heading into Saturday with potential for damaging gusts with current signals trending toward Ireland seeing the highest gusts initially with this area transferring possibly across the Irish Sea and impacting Northwest England and Scotland with high gusts continuing into Sunday in the North.

Beauty of a Rossby Wave Break Event as discussed prior this weekend in America. There is likely to be further cyclonic development during the beginning of next week with a dip in the upper level dynamics however discrepancies on the track with some indicating the Bay of Biscay wheras others pull it into this weekends cyclonic developments with movements toward the UK.

[Jordan S]

Just a quick one today

 

Yes @WYorksWeather 

A surge of unusually high upper air temps for Friday/Saturday in the southeast/east of England.

An impressive low pressure system for April set to move north to our west later Friday and into Saturday party responsible for the surge in upper air temperatures, the low spreading heavy rain northwards through western and northern parts of the UK where it will be cooler, with over 3 inches possible in some areas exposed to the southerly wind, southern and eastern England generally drier though some outbreaks of rain could occur at times especially from a cold front on Saturday, very windy with gales in the west and north. Quite cloudy in the south and southeast of the England with surface temperature in the east of England upto around 19-21c in any sunshine, a bit less warm in cloudier parts of the east, though these drier conditions brushed away eastwards by that cold front, some drier weather at times on Sunday before a low pressure system brings more rain for many at times early next week, thunderstorms possibly following behind weather fronts into the south of England with the risk of hail.

 

[LightningLover]

 WYorksWeather I recall @Weather-history mentioning it a while back, and I had to see it for myself! 17c 850's in February is TRULY exceptional, I really can't think of anything that comes close so it's very much an extreme edge-case. And no worries, I just thought you'd be stunned like I was haha!

[WYorksWeather]

 LightningLover What is strange about it is surface temperatures maxed out that day at 17.8C, so an average lapse rate of effectively zero. Must have been something very weird going on that day. Especially in late February, it's not like if you got a similar plume in December when you'd expect very little solar heating. At a minimum, I'd have expected that day to produce 20C somewhere. Looking at the reanalysis it does look like the plume cleared away very quickly to the east, but it's still quite surprising that we didn't achieve 20C.

Anyway, possibly a discussion best taken elsewhere so as not to clog up the model thread too much, but what a remarkable set of circumstances that must have been!