Model Output Discussion 12z 20/04/13

[Frosty.]

A real north-south divide on the GEFS 12z mean with another fine and sunny, increasingly warm weekend and start to next week for the southern half or third of the uk with pressure of 1020 mb but scotland & n.ireland and perhaps northern england again on the wrong side of the polar front jet for much of the time with a stronger zonal cool oceanic airmass which is the familiar story of the spring so far in the north with the northern blocking remaining intact for a while longer. During next week it looks like all parts of the uk will have a much cooler cyclonic spell with strong sunshine punctuated by heavy slow moving thundery showers and also spells of more persistent rain with sometimes squally and variable winds but eventually the trough will fill and the azores/atlantic anticyclone will make another attempt to bring back some late spring warmth.

Watch out tomorrow down the central spine of the uk for scattered heavy showers breaking out, very hit and miss and a lot of sunshine inbetween, it also looks very warm again tomorrow with a general 20-22c and a few spots could reach 23 and possibly 24c which would make it the warmest day of the year so far, scotland looks much sunnier and warmer than today with max temps of 15-18c. Midweek becomes much cooler and windier with rain spreading northeastwards across the uk followed by sunshine and showers, some heavy and thundery.

It looks like the Ecm 12z op run has caught the ukmo 00z disease with a cooler and more unsettled looking weekend but hopefully it's just briefly lost the plot, the gefs mean still looks good enough to me.

So we have the gefs 12z mean, the gfs 12z and ukmo 12z op run onboard (plus the met office update) for a fine and pleasantly warm weekend in the south against this latest ecm 12z op.

Edited May 6, 2013 by Frosty039

[Frosty.]

No ridge for Saturday...Ecm...  

i noticed  it's still outnumbered by data that still shows ridging though.

[IDO]

No ridge for Saturday...Ecm...  

I think its just timing, GFS 12z ridges earlier than ECM, opposed to ECM bringing in the week 2 trough later:

GFS T192: ECM at the same time:

Both still have a milder more settled three days around next weekend for the south.

Edited May 6, 2013 by i'm dreaming of...

[Gibby]

Good evening. Here is tonight's look at the midday outlook supplied by GFS, UKMO, GEM, NAVGEM and ECM for today Monday May 6th 2013.

All models are still supportive of a change to a windy and cooler spell with a period of rain followed by heavy showers from later tomorrow onward. The warm temperatures of today and for a time in the East tomorrow will not be repeated for some time as Westerly winds ensure conditions remain much cooler from Wednesday. There is more reluctance tonight to lift the UK out of the showery spell until later in the weekend as a further showery trough caught up in the West flow passes through late Friday and Saturday, though Sunday does hold a reasonable chance of being drier and brighter as a ridge builds somewhat over the South.

GFS then brings the UK under a further sustained unsettled spell as Low pressure slips SE down across the British Isles with showers or longer spells of rain developing widely through the week in rather cool conditions. It's not until the final frame of the run when this Low pressure complex fills up completely with a ridge replacing it across the South.

The GFS Ensembles show good agreement with quite a tight spread of members that favour a rather cool or normal at best set of conditions. In essence this means rather cool and showery period as the most likely option, given that precipitation spikes are commonplace later in the run.

The Jet Stream is maintained as a split flow for the majority of time over the next week to 10 days. For a short while at the weekend the Northern arm dies as the Southern arm ridges North to the UK. However, it soon reverts back South as the Northern arm strengthens across the Atlantic and over Southern Britain in a week or so.

UKMO tonight shows a showery Saturday and a less showery Sunday. A weak ridge is shown close to Southern England but an upper trough will maintain the risk of showers, especially in the North and inland over England through the daytime. Signs are that on the 144hr chart the following days will see Low pressure and unsettled conditions move down from the NW.

GEM shows a slower transgression towards next week's unsettled spell as the WNW flow at the weekend lasts rather longer gradually being replaced by less windy weather under slack pressure with a gradual trend towards more unsettled weather as we move deeper into next week.

NAVGEM shows a showery period from a Westerly flow at the weekend with most of the showers in the North before they gradually extend to other areas as we move into next week as Low pressure drifts down into Scotland from the North.

ECM tonight has a very showery picture across the UK with the weekend seeing the best of any drier spells between the showers over Southern and Eastern Britain. As we move into next week Low pressure slips down from the NW enhancing the showers in all areas with just brief sunny intervals between times and rather cool temperatures maintained. At the end of the run the showery picture is maintained with warmer air knocking on the door of the East from Europe most likely accompanied by much sea mist and haar.

In Summary the weather looks rather disturbed tonight. The Azores and European High's that Southern areas have enjoyed of late looks like slipping further away from our shores and becoming less influential with Low pressure slipping down over the UK next week with the accompanying showers and outbreaks of rain (with hail and thunder a possibility) becoming the most likely weather type. Once this pattern of Low pressure sets in it may well become slow moving over the UK as GFS illustrates clearly tonight. If there are straws to clutch it's GEM which holds a faintly lit candle as it is more reluctant or delays sending Low pressure down from the North over the UK next week.

[legritter]

Evening all ,iv been mostly lurking lately but enjoying our forum and all the hard work that goes into it .todays charts and data is hinting at some active weather gracing our shores with a mixture of spring weather even autumnalat times .having spent today digging my veg patch its unbelievably dry soil for quite a depth and not a worm in sight ,oh what varied weather we have on our small island .Iwould certainly not want to stick my kneck out past say mid month but what ever turns up im pretty sure that its going to be interesting not normal fair ,i can feel it in me water ,cheers gang ,Fantastic sunset tonight ahead of our incoming trouble ,

[Guest pjl20101]

Looking like a very weak trough on the CPC 8-14 day output tonight over us and over much of western Europe, think the MJO will be the major player in our weather over forthcoming weeks, back to topic and see what I mean by this:

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

[johnholmes]

I would hardly call that 500mb trough as a very weak trough. It is the major player for the UK weather in the time scale 6-15 days.

As predicted by the anomaly charts for about 8-9 May back around 1-2 May.

Edited May 7, 2013 by johnholmes

[Guest pjl20101]

Thanks very much John for that, it does seem a very complex pattern coming up for forecasters indeed. Don't know Matt hugos perception on things john but he seemed to he quite adamant about a dry may and I am not sure with whether he will change his mind or not as I haven't been reading his tweets of late.

[mushymanrob]

a cooler atlantic spell shouldnt worry anyone, the suns still strong and warm and its not going to be wall to wall cloud, so, with some much needed rain normal may weather wont be a bad thing.

 

as i see it, the biggest area of concern now is watching for the evolution of northern blocking early next month. washout summers appear to start with this feature in early june, and dispite seemingly quite reasonable suggestions that 'you cant write off the whole of summer this early', unfortunately you can as last year proved.

[mountain shadow]

A miserable cyclonic looking ECM for the next ten days. Winds mainly from the North West, showery and below average temps.

Looks to raise pressure over Scandi. which would improve things for the West.

[ANYWEATHER]

A very disturbed spell of weather on offer, with Thursday of concern for high winds for the southern Uk, then if we look to the weekend we see any ridging being completely dropped by the models. So in essence then looking at how much high pressure is forecast over the Poles as per previous Summer/years since 2007 and including that year, we may be looking down the barrel of yet another loaded gun!  

[Frosty.]

I'm looking for the positives again this morning, and there are some... the Gefs 00z mean shows weak ridging across the far south of the uk this weekend into the first few days next week which would suggest drier, brighter and pleasantly warm weather for southern england which would then extend a little further north next monday into tuesday. Also, high pressure building to the northeast on the Ecm 00z, that could really shorten the troughs impact on the uk during next week by pushing the trough out into the atlantic, there is also an improvement on the gefs mean later with pressure generally rising.

 

The downside is the ukmo 00z which is again showing a cool and cyclonic weekend with sunshine and showers and the ecm 00z also shows a generally rather unsettled start to the weekend but the gfs 00z shows a slowly improving trend with ridging for the south which lasts into next week so there could be a few fine days for the south and southeast at the end of this week into next week. The gfs then shows a trough taking over by the middle of next week and persisting for some time but it's a sunshine and showers outlook so there would be lots of interest for storm enthusiasts with heavy thundery showers in the outlook.

 

In the meantime, enjoy what looks like being the warmest day of the year so far with 24c possible in parts of central and eastern england with lots of sunshine but there will also be some heavy showers breaking out down the central spine of the uk but very hit and miss, most areas staying fine and warm/very warm, cloudier today for the southwest, wales and ireland with a few spots of rain, sunnier and warmer for scotland. Tomorrow could also be a fine and fairly sunny pleasantly warm day for most of scotland but rain will be spreading north and east across the uk tomorrow and a much cooler and windier few days with rain followed by sunshine and showers, this unsettled mix then continuing into the weekend, especially for the north and west.

 

 

[Gibby]

Hi everyone. Here is the report on the midnight outputs from GFS, UKMO, GEM, NAVGEM and ECM for today Tuesday May 7th 2013.

All models show a change to more unsettled weather on the way with today being the last day of the current warmth and sunshine across England and Wales. Low pressure is forming down to the SW and will become a deep Low complex close to NW Britain by later tomorrow sweeping strong winds and rain followed by showers to all areas. Temperatures will then be much lower than recently with a cool feel to things generally. After tomorrow the weather will be a typical Spring mix of sunshine and well spaced April showers. Parts of the South and East could still have a reasonable amount of dry weather but less likely in the NW. When the showers do come along they could well be heavy and accompanied by hail and thunder locally. It's not until Sunday when a brief window of 24-48hrs of less showery weather looks possible over the South as a transient ridge of High pressure moves across from the West.

GFS then shows a very showery week next week as Low pressure moves South over the UK, close to SW England by midweek with heavy showers or longer spells of rain likely for all by then. There is little cheer through FI with Low pressure ambling around the UK in no particular hurry to either fill or move away maintaining the heavy shower risk but with some warm sunshine between the showers in what will otherwise be a rather cool spell of weather.

The GFS Ensembles show a generally showery pattern through the two weeks with very little spread of note between the members. There are no indications of anything as warm as currently through the coming two weeks though by the sheer nature of showery conditions there will be some places that fair rather better than others, maintaining drier conditions more while other have some heavy if brief rainfall events.

The Jet Stream is not becoming our friend again over the next few weeks with a split flow endorsing a UK based trough next week with the Southern portion dragging ever lower pressure down to low latitudes and keeping the UK on the colder side of the seasonal warmth.

UKMO today shows a blustery and showery weather type over the UK over the weekend with a drier phase on Monday under a weak ridge before renewed Low pressure extends down into the UK from the NW by midweek.

GEM today shows Low pressure slipping South over Ireland through the week and eventually to the South of the UK with rather cloudy and showery weather for many. Some longer spells of rain are also likely with the East seeing the best of any drier and sunnier breaks between the rain.

NAVGEM shows a showery WNW flow at the weekend with a deep Low sinking South to cover the North Sea and Northern Britain by midweek next week. This means heavy showers and ever decreasing sunny intervals as we move through the week with generally cool and breezy conditions.

ECM finally continues the gloom though conditions in the SE may not be too bad for a day or two early in the week. However, Low pressure is shown to migrate South close to the West of Britain with rain or showers here. As the cool uppers then engage warmer uppers to the South of the UK by midweek next week, deeper Low pressure forms close to the SW spilling rain or showers North across the UK to most areas. It may become somewhat warmer and more humid should this pattern develop.

In Summary there is little cheer for those of us looking for a continuation of the current early summer type weather. Low pressure is set to return tomorrow and keep a showery and blustery Westerly flow with temperatures down 5-6 degrees on recent daytime values. There will be some dry weather to be had but not guaranteed as there will also be showers blown through on the breeze, heavy and thundery at times. Through next week the pattern is maintained as Low pressure looks set by all models to slip South over or near to the British Isles with rain and showers continuing for all at times. Coming from the North temperatures will never be overly warm but in any interludes of brightness and lighter winds it will feel pleasant enough. The worrying thing that I can see this morning is the refusal of this pattern to lift out of the British Isles anytime soon once it sets in with pressure becoming High to the North (yet again) and a split Jet flow with the Southern arm encouraging low pressure to sink South to Southern latitudes. It seems a familiar and repetitive pattern of synoptics over the British Isles in recent years.

[Summer Sun]

Going by the 00z ensembles from ECM and GFS its going to be a long road back to anything settled of course during the next 10 days or so its bound to be sunny at times which will make it very fairly pleasant but for something like this mornings weather (dry, sunny and warm for many) its going to be a slow old process to get there

 

ECM and GFS ensembles at t240 both look similar

 

 

Looking further a field and its a mixed signal with nothing really settled standing out

 

 

 

[Frosty.]

It looks like a sunshine and showers outlook from all the models/ensembles this morning, however, this is a very interesting weather type with one area having a deluge but a mile down the road stays sunny and for storm fans it could be a cracking few weeks coming up with a cool cyclonic pattern, we will be into the much cooler, breezier pattern from tomorrow with rain spreading north and east followed by sunshine and showers, the showery spell persisting for the rest of this week and weekend but the far south of the uk still looks like becoming drier, brighter and somewhat warmer, if not by the weekend, then for the first few days of next week but then it's widespread showers, some heavy, squally and thundery but with sunny periods and light winds between the showers and the sun is very strong now so it will feel pleasantly warm but temps dropping several degrees in the showers and overnight where skies clear and winds drop, it looks like being cold enough for a touch of grass frost in prone areas, especially in the countryside.

Edited May 7, 2013 by Frosty039

[Tamara]

There was a mid latitude high pressure solution in reasonable apparent agreement just before the B/H and this has steadily leaked away over the last few days and leaves us with an unpalatable low pressure solution that is indeed reminiscent of recent years, and with the summer slowly starting to approach and unseasonally wet and windy weather never too far away, it gives a feeling of deja vu already.

 

We know that the stratosphere has warmed sharply in accordance with a final warming and there is no doubt that the pressure rise apparent in the models over the pole in response to this seasonal polar stratospheric change is attributable to the process of the low pressure systems being ever adjusted on a more and amore southerly track. However, the question remains whether this is the prelude for a repeat of the synoptics of previous summers or whether this is simply a final burst of HLB in accordace with the final break up of the polar vortex before that energy dissipates and the gradient between residual winter time polar air and the ascendancy of the ferrel cell with sub tropical/tropical air to the south is reduced and neutralised leading to a slacker jet stream.  

 

The polar stratosphere this summer *shoudn't* be as pre-disposed to blocking due to ongoing changes in some background factors of a technical nature  - its a case of whether these are condusive to taking the jet stream further north and thus assisting a closer presence of the Azores High than we have seen in recent years. 

 

I think in light of recent summers and also analogues which show this year as similar to that of 62/63 it might mean that no bets are put forward, if that anlaogue is to be believed  More seriously I think there is greater uncertainty this year based on the changes of weather patterns we have consistently seen and nothing can be taken for granted, whatever the t/c's and techincal factors might point to.

 

The EPS show good overall agreement to 7 days that no return to the current warm temperatures is in sight and an unsettled regime persists as pressure starts to rise above and behind the trough sinking down from the NE atlantic towards us

 

Edited May 7, 2013 by Tamara Road

[Alexis]

Northern blocking is becoming evident, but there are tentative signs that the positioning might be more favourable during the second half of May. Hopefully we'll see a warm easterly and generally higher pressure over Scandinavia instead of what we've experience in the past - northern blocking pushing the jet directly over us combined with extensive cyclogenesis.

[Average Joe]

Going by the 00z ensembles from ECM and GFS its going to be a long road back to anything settled of course during the next 10 days or so its bound to be sunny at times which will make it very fairly pleasant but for something like this mornings weather (dry, sunny and warm for many) its going to be a slow old process to get there

 

ECM and GFS ensembles at t240 both look similar

 

 

Looking further a field and its a mixed signal with nothing really settled standing out

 

I'm sure there's scope for change. Only a week or so ago there was talk of droughts for May. What is that saying about a week being a long time.......!?

[Scorcher]

Northern blocking is becoming evident, but there are tentative signs that the positioning might be more favourable during the second half of May. Hopefully we'll see a warm easterly and generally higher pressure over Scandinavia instead of what we've experience in the past - northern blocking pushing the jet directly over us combined with extensive cyclogenesis.

 

I can't really see any northern blocking in evidence- pressure looks like remaining low over Greenland which is at least a crumb of comfort.

[Summer Sun]

As has been said a week is a long old time in weather terms and things can and do change quickly looking at the permutations for t240 on GFS this morning 12 members go for wet and windy whilst 8 go for something more settled or a sunshine and showers type set up

 

 

The MJO out the the 20th is expected to leave phase 2 and move into phase 3 and 4 which if it does will bring something more unsettled

 

[Frosty.]

There is a window of fine, sunnier weather on the Gfs 06z  across more southern parts of the uk this weekend into early next week with pressure rising a little and showers tending to die out or at least become isolated, temperatures are slow to respond but sunday and monday look warmer for the south and east with 17-19c probable, rather cooler than that further to the north and west where it remains showery. The southeast stays driest and warmest for longest into next week but by tuesday it's trending unsettled and the majority of the uk looks dominated by a trough for most of next week with sunshine and showers, some heavy and thundery and occasionally merging into longer spells of rain, eventually the trough fills but is soon replaced by another trough to maintain the showery outlook, towards the end of the run it becomes drier and a little warmer further east with a lot of high pressure to the east of the uk and the trough eases back to the southwest of the british isles with the western side of the uk remaining generally unsettled.

Edited May 7, 2013 by Frosty039

[Jonathan Lang]

Why is everyone getting down on the upcoming unsettled weather? The general 'sine wave' of air pressure fluctuations shown on the current GEFS would give at least a good balance between unsettled, wet weather and sunny, calm and nice conditions. The T850 also shows there will be at least one warm sunny day next mon/tue so worry not! Any further is FI!  

[Frosty.]

The Gefs 06z mean also shows weak ridging (1020mb) moving east across the far south of the uk during the weekend into the start of next week with increasingly dry, sunny and pleasantly warm weather but most of the uk continues cooler and unsettled with showers and longer periods of rain, some heavy and thundery but with sunny spells too, then all of the uk is in the cool cyclonic trough dominated pattern by tuesday, some improvement in the 6z mean later in the run with a slightly warmer and drier trend from the east.

[Summer Sun]

This afternoon's UKMO doesn't look too good for the weekend with low pressure in charge the best we could hope for at this stage would be sunshine and showers

 

 

Into next week and its a continuation of the unsettled weather I'm afraid

 

 

The only slight hope is if GFS is correct (chances of this are slim) with the low getting kept slightly further north the further south you are the better it would be

 

 

As GFS progress it doesn't get any better I'm afraid in fact it gets worse

 

Edited May 7, 2013 by Gavin.

[Frosty.]

I think the ukmo 12z has improved very slightly from the 00z, there is now a small window of fine weather as weak ridging runs east across the far south but for most of the uk it's cool and unsettled throughout but there is still time for the situation to improve a bit more and it will be the timing of the slight pressure rise as it ripples it's way across southern england that is important as it would give some respite from the cool low pressure dominated outlook from tomorrow onwards.

 

The Gfs 12z is more unsettled for the weekend but there is still a window of opportunity for a fine and warmer day in the southeast on monday before the cool cyclonic pattern sets in across all areas.

 

In summary, I still believe there is a potential window of fine weather for southern england at some point during the coming weekend and next monday before the cool cyclonic pattern locks in.

Edited May 7, 2013 by Frosty039