Model output discussion - 20th Feb onwards

[Gordon Webb]

9 minutes ago, Convective said:

I can remember many a time when the most violent storms broke out over the northern half of England before moving into Scotland, due to the humid continental air mixing with the cooler temperatures the further north. Either way, plumes can deliver storms just about anywhere so its safe to say I'm quite looking forward to the progression of this potential set-up, even more so now that the majority of models have come into agreeance  

The key word is POTENTIAL think some are getting a little carried away a little too early , in 2 , 3 , 4 days time if the charts are more of the same then you can have a little confidence remember 2 or 3 times last year at a 5 or 6 day away windows looked nailed according to some then when the time came was not as was expected or didn't happen at all or were caught out by late changes , not meaning to put a damp squib on peoples expectation just injecting a note of caution especially with the convective expectation some have as that can be especially fickle even with ideal conditions

[Carl46Wrexham]

3 hours ago, William Grimsley said:

Fair play, but every model seems to want to agree of a warm and thundery spell by the end of next week.

You're welcome to them, in fact you can have my quota as well. My soggy grass is badly in need of a cut and thus DRY warm weather much needed.

[Frosty.]

The Gfs 6z op shows we are well on track for a much warmer spell from Friday and especially next weekend and the following week with temps into the 20's celsius, locally mid 20's c which would feel great compared to the cold spring so far. There also look like being an increasing risk of heavy showers and thunderstorms with higher humidity but a lot of dry and sunny weather too, towards the end of the run it looks driest and sunnier across the south and east under a strong ridge of high pressure with temps still close to 70F...hopefully an early taste of summer is just around the corner! 

[Gordon Webb]

3 hours ago, Carl46Wrexham said:

You're welcome to them, in fact you can have my quota as well. My soggy grass is badly in need of a cut and thus DRY warm weather much needed.

 

yep same here

 

yesterday was cold and showery and next weekend may be warm and showery ? and people seem to think that's a weather improvement it isn't , it's just a warmer version of unsettled and apart from storm watchers who may get there wish I suspect this won't be enjoyable for most , been warm and humid and getting soaked is no more pleasureable than been cold and freezing and getting soaked 1 fine day followed by 3 warm wet ones does not good weather make

[March]

Jesus Christ guys, April wasn't even a wet month. 

[cheese]

49 minutes ago, Gordon Webb said:

 

yep same here

 

yesterday was cold and showery and next weekend may be warm and showery ? and people seem to think that's a weather improvement it isn't , it's just a warmer version of unsettled and apart from storm watchers who may get there wish I suspect this won't be enjoyable for most , been warm and humid and getting soaked is no more pleasureable than been cold and freezing and getting soaked 1 fine day followed by 3 warm wet ones does not good weather make

I don't think you've actually bothered to check the model output yourself, have you?

[Paul]

This is the model thread don't forget, if you want to discuss what weather you do or don't like please head over to the spring chat thread. 

[Captain Shortwave]

Certainly a movement to a warm and showery regime as we reach the end of this week as low pressure becomes established to our west and south.

      

Winds between the south and east as well as above average 850s should help temperatures respond (around the 20C mark looks likely in many spots with the potential for higher temperatures if the specific details allow it). It does look like a rather unstable pattern with low pressure quite close by so the risk of home grown showers and thunderstorms as well as the potential for imports from the near continent. 

A warm first half of May looks a decent prospect given recent developments, a definite change from the cool or even cold April we have just experienced.

Lastly can we try and keep to model discussion as there are threads available to discuss potential storm risks elsewhere.

[Vorticity0123]

After an underwhelming end of April in terms of temperature (which I have more throughly described here) May seems to start off quite differently, as alluded to by Captain Shortwave above. What's interesting though, is the confidence which is associated with the pattern change - like also occurred in the end of April with the cold being forseen many days before. Are we again heading towards a blocked scenario? Let's find out!

Unsettled UK

Before we get there, lets take a look at the actual situation. And that situation looks very unsettled for the UK!

ECMWF surface pressure and 500 hPa heights (colours) as of Sunday 00Z.

With low pressure activity to the immediate north of the UK, it is most likely that one disturbance after another hits the UK. However, things are going to change, especially temperature-wise for the southeastern parts. Next Thursday shows this the best:

A quick pass-by of high pressure

ECMWF surface pressure and 500 hPa heights (colours) as of Thursday 00Z.

A building high pressure area passes by the UK from the southwest, causing the weather in the southeastern parts of the UK to be more settled. More notably, with a shifting of the flow to southerly directions the air advected towards the UK also becomes increasingly warm, giving rise to gradually increasing temperatures, especially for the southeast. Yet, low pressure remains close by...

And that will also remain the theme for the rest of the weeks. So a prolonged period of settled weather appears not to be in store. What will change, though, is the general location of low pressure, with some interesting consequences for the UK!

Complete turnaround

To show the turnaround, we now shift towards ensemble forecast (so multiple runs averaged together) for 9 days out.

ECMWF Ensemble surface pressure and 500 hPa heights (colours) as of Tuesday 00Z (9 days from now).

What we can see is that a low pressure area (in white contours) has dropped southward all the way towards the Bay of Biscay. This could cause a flow of warm air from the European continent towards the UK itself. Yet, with low pressure still nearby, such map would allude to an increased risk on showers and thunderstorms as the air gets increasingly unstable.

Surprising confidence

If you realize that the above chart is an ensemble averaged forecast for 9 days out, it is actually surprising how confident the forecast appears to be. Having such a strong signal for a trough to the south of the UK is remarkable to say the least for this time range. To show this, we jump to the GFS spaghetti ensemble plots for about a day earlier (because the plot got too messy after 8 days).

GFS Ensemble 500 hPa heights (colours) as of Monday 06Z (8 days from now).

Spaghetti diagrams show all individual runs of a weather model, in this case the GFS. Every line here represents the height of the 500 hPa surface, being the 5.92 km line (delineates high pressure; located mostly over Africa) and the 5.52 km line (the most important here, lower values often indicates troughing or low pressure, mostly located over the UK).

Often, such spaghetti plots are, as the word says, a spaghetti after about 8 days, showing very little in the way of structure. But thinks are remarkably different now. Almost all models show the trouhging over and mainly to the west and southwest of the UK (blue line), and strong ridging to the east over mainland Europe (red line). From this plot one can quite confidentially say that we will have low pressure activity to the west, high pressure to the east, and a warm southerly flow in between! To what extent this will reach the UK is a matter of details, which cannot be forseen in this timeframe. What one can say, though, is that it is going to be a relatively warm, and most likely unsettled, period to come. Enjoy!

Source:

http://www.wetterzentrale.de/topkarten/fsenseur.html (Spaghetti plots)

 

 

 

 

 

Edited May 1, 2016 by Vorticity0123
Deleted obsolete figures

[knocker]

The influence of low pressure in the south west quadrant is evident though out most of the GFS run staring next weekend when a depression moves up from the Biscay area into the south west/

 

[Frosty.]

There is a lot to like about the Gfs 12z op run, especially with regard to the temperatures which become very summer like with max temps into the 20's celsius and plenty of sunshine and to make it more interesting there are likely to be thundery showers dotted around too...Finally, after weeks of unseasonable cold, those of us who fancy some warmth are going to get some!

[ANYWEATHER]

Good Evening All! Its nice to see the weather turning much milder and eventually warmer as we end this week. Along with that change though given the rather slack area of low pressure predicted by the gfs in a weeks time will spark some heavy downpours with thunder and lightning. So in three words , Warmer And Wetter  looks  the general theme from the models...by later this week.

[summer blizzard]

As much as i like my early season warmth (May-July) i suspect some people may take a too optimistic view. The GFS and GEM indicate quite well the potential pitfalls of such a setup if heights start to build north of us again and the trough pushes a bit east.

In the meantime though, i'll be cheering as with most.

 

[knocker]

The ecm has a pretty fair agreement with the gfs for Saturday with the low nudging north

Edited May 1, 2016 by knocker

[Frosty.]

9 minutes ago, ANYWEATHER said:

Good Evening All! Its nice to see the weather turning much milder and eventually warmer as we end this week. Along with that change though given the rather slack area of low pressure predicted by the gfs in a weeks time will spark some heavy downpours with thunder and lightning. So in three words , Warmer And Wetter  looks  the general theme from the models...by later this week.

I won't be complaining during the very warm spells of sunshine with temps approaching the mid 70's F between the thunderstorms Bring it on!

[Frosty.]

The Ecm 12z shows a very nice warm up with +10 T850's at least reaching the south / southeast so potentially low to mid 20's celsius with increasing humidity and a growing chance of heavy showers and thunderstorms, both homegrown and spreading north from the near continent between very warm sunny spells.. so a much more continental flavour to our weather with above average temps for a change looks to be on the way, no complaints from me if this verifies!

[Cheshire Freeze]

Wow, just checked the GFS 12Z and apart from the increasing temperatures, the first thing I noticed was the extensive N latitude heights into FI with low after low being pushed in on a southerly tracking jet. I could only describe it as 2007 on steroids. Seriously wet for some on that run.

[alr1970]

I think a reality check is needed here. Look at the scatter on the ensembles:

Based on that I take predictions of 24C in Manchester in May and knock off 5 degrees. GFS always exaggerates temperatures, both for cold spells and warm ones. It will still be very pleasant though.

[Methuselah]

1 minute ago, alr1970 said:

I think a reality check is needed here. Look at the scatter on the ensembles:

Based on that I take predictions of 24C in Manchester in May and knock off 5 degrees. GFS always exaggerates temperatures, both for cold spells and warm ones. It will still be very pleasant though.

25c just north of London more likely?

[Singularity]

Remarkable just how consistently the models are now showing the cyclonic SE'rly flow from Friday onward, bringing contrasting wedges of drier and quite humid air, this allowing for some good sunny periods but also some punchy afternoon showers and, yes, a few classic thunderstorms.

Indeed, it could well feel like mid-July by the weekend or at least Sunday, as temperatures approach the mid-20's. Slow moving downpours do mean that there may be some locally very high rainfall totals. Flash flooding is therefore an unfortunate possibility- but for many on here I expect the prospect simply adds to the excitement and anticipation levels. I know I wouldn't mind a few lazy, wandering storms with good electrification, despite seeing a wetter than usual April - as this was the result of several isolated large rainfall events, with conditions seeming a lot drier overall; the topsoil is turning dusty for the first time this year.

 

Yes, one does have to wonder if the mid-high latitude blocking will turn against us again by mid-month, with the walling-off of the Atlantic on the ECM 12z more ominous than the 00z scenario of another sliding low that could pull the trough back to the SW of the UK -  but to be honest I'd rather focus on the preceding summer-like conditions until they're well established!

[Frosty.]

No downgrade to the warm outlook on the Ecm 12z ensemble mean, it looks just as impressive as 24 hours ago and we are still on track for our weather to gradually turn much warmer with a more summer like feel and good spells of very warm sunshine, by far the warmest and humid spell of the spring so far but also a growing chance of thundery showers...I'm ready for a warm spell now!

[knocker]

A quick look at the NOAA and ecm anomalies just to keep an eye on the medium term prospects.

The 5-10 pretty much as we would expect with trough digging south around Iberia, NOAA slightly with a more negative tilt, with HP Scandinavia. Thus the surface analysis remains LP generally to the south west with a S/SE flow with temps above average. Of course the detail weather wise will depend on the smaller scale evolution but the chances are it will be quite interesting.

The later period sees the two systems swivelling around the UK and thus the trough becoming more negatively tilted. The way forward is very dependent on how this pans out. Perhaps the LP transferring west and veering the upper wind or even some slack low pressure over the UK. Either way temps probably remaining a little above average but I think file under pending for the time being.

Edited May 1, 2016 by knocker

[knocker]

The GFS this morning.

Turning warmer and drier during the week as the HP tracks east except for NW Scotland where it may wet and windy for a time. Come the end of the week low pressure starts nudging up from the south which brings outbreaks of rain, possibly thundery,

Thereafter at the beginning of the week the low pressure to the south is briefly influential bring easterlies across the UK before another low travel north up the North Sea to be west of Bergen by Thursday 12th.

So essentially a dry warm outlook with temps a little above average for the next ten days but of course the detail is bound to change. Worth noting the WAA into northern Scandinavia.

 

 

[knocker]

The ecm takes the weekend low just to the west. It's also not keen on the GFS North Sea low and by the end of the period has tha Azores HP ridging in from the south west. Temps generally a little above average as the run progresses but nearer average at the end. I have to say this morning's runs are best described dog's dinnerish.

Edited May 2, 2016 by knocker

[Singularity]

 

While the warm weekend (for the SE in particular) with ample thunderstorm potential for western parts in particular unfolds, GFS (left) had made a significant chance out to the west on the 00z, with a sliding low either very weak or absent. ECM (right) has made no such alterations.

This greatly affects the surface conditions going into the following week;

 

The pressure gradient between the NW Europe trough and Atlantic ridge on the 00z GFS (left) is large enough to bring blustery conditions at times, this holding temperatures down in the low 20's (so not feeling too bad, and very nice in sheltered spots). The reduced surface heating does however keep the number of showers down, which some will like, others despair at (when considering the thundery potential in a slack setup - see ECM summary below).

ECM (right) instead has areas of low pressure breaking through in the Atlantic, resulting in a messy picture with slack pressure gradients in the vicinity of the UK. Maximums Mon-Tue could reach the mid-20's in places (though the raw data only goes for 21-23*C in the SE, but I digress), and there would be a good environment for homegrown downpours - with some thunderstorms for good measure.

Longer term, both models converge on a scenario with lowering heights a little south of Greenland, the Azores High trying to ridge in but having to overcome the Euro/UK trough complex, ECM (below-right) doing a better job of this than GFS (left) as of day 10 and with greater promise going forward as the Atlantic jet does not look to cut through the UK more or less west-east such as GFS depicts out to day 12 or so (the ridge then builds in but a little half-heartedly away from the SW). 

 

Still some blocking highs evident in the longer-term, but tending to drift toward the mid-latitudes and weaken somewhat. Quite a typical mid-May setup by the end of the GFS 00z I think.

Edited May 2, 2016 by Singularity