Model Output Discussion 12z 20/04/13

[Frosty.]

The latest Ecm 00z ensemble mean brings a crumb of comfort next monday with what John Kettley used to call a suckers gap but apart from that it looks cool and unsettled with lots of showers, some squally, heavy and thundery with hail and merging into longer periods of rain at times with a chance of local flooding  but also some good sunny spells at times, temperatures maxing out in the low to mid teens across the south but lower than that for northern britain. There is a slight warming at T850 hPa, the ecm mean tends to centre the trough further west which may allow warm and humid continental air to make inroads into at least eastern britain later next week but in general it's a cool cyclonic showery outlook for all areas with  slow moving trough (s) dominating our weather until later in the month.

[Purga]

Temps down to -5C in the Welsh borders next week & -3C in the south soon after on the GFS 06z!

 

 

 

 

 

Extensive Northern blocking again in FI

 

Edited May 9, 2013 by Purga

[Tamara]

I also wonder what the signal was that made the models ditch the strong high pressure we were supposed to under right now. Monday's warmth was supposed to be just the start of a settled spell according to what they were predicting 10 days ago.

I think much as I suggested in my post above, they suddenly picked up the signal for the final warming of the stratosphere which occured quite sharply after the brief re-grouping of the polar vortex once the SSW feedbacks from late winter and early Spring had disappeared.  This signal is for a repeated  -AO profile and heights rebuilding to the north. In a nutshell we are seeing the consequences of the seasonal demise of the polar vortex reflected in the current modelling - this is happening quite late in the Spring once more

Edited May 9, 2013 by Tamara Road

[Evening thunder]

Temps down to -5C in the Welsh borders next week & -3C in the south soon after on the GFS 06z!

 

 

 

 

 

Extensive Northern blocking again in FI

 

 

Those min temp values are very unlikely to happen IMO, the GFS does seem to have an issue with predicting minima too low in pockets where it predicts very light winds these days. The 850hpa temps we are getting at that time are below average but not especially unusual either, have seen colder in May in recent years.

Edited May 9, 2013 by Stormmad26

[William of Walworth]

here we go again.... time to write off summer?...

Definitely not yet!

I understand what everyone is saying about Northern blocking being a strong feature, but surely only the very rash would predict that this, and a Southerly tracking Jet, are locked on features indefinitely.

Edited May 9, 2013 by William of Walworth

[Frosty.]

The Gfs 06z op run shows a drier and brighter day across southern britain on sunday and for the far south on monday and then an atlantic ridge pushing across the uk later next week bringing one fine day followed by a slight air frost  but apart from that it's a very disturbed pattern with low pressure (s) in control for much of the time with widespread showers, some heavy and prolonged with hail and thunder but also persistent rain at times and there is also a risk of local flooding as the ground becomes saturated but between the rain and showers there will also be good spells of pleasant and very strong sunshine so it's not all doom and gloom. Later in FI it becomes drier in the far north as an anticyclone across northern scandinavia ridges southwest but most of the uk would remain under the influence of cyclonic and rather cool conditions but temperatures slowly beginning to recover across the south later with temps back to the 15-17c range but much cooler than that across scotland apart from occasionally in the highlands where some sheltered areas could be warmer than average at times but generally cool on east and north facing coasts throughout. There is also a risk of grass frosts throughout the period of cool cyclonic domination where skies clear and winds are light, especially in rural areas.

Edited May 9, 2013 by Frosty039

[mushymanrob]

Definitely not yet!

I understand what everyone is saying about Northern blocking being a strong feature, but surely only the very rash would predict that this, and a Southerly tracking Jet, are locked on features indefinitely.

 

true. but if anyone was rash enough to write off summer in the first week of june last year...theyd have been correct. so it is possible, and trends over that last several years have been one of northern blocking establishing in early june... then sticking, and ruining the heart of summer with only a few decent days in august at best.

 

IF northern blocking establishes in the next few weeks, it would be a fairly safe bet to 'write off' june and july in terms of a decent widespread settled spell. 2012 has proven this (as did 07, 08 )

[Frosty.]

The GEFS 06z mean looks about as cool and unsettled/cyclonic as it could do at this time of year, for example, the middle of next week shows a trough directly over the uk which is a recipe for torrential downpours developing after early sunshine, it doesn't change much until very late in the run but there is growing support for the trough to eventually fill and drift away westwards with high pressure to the east/ne of the uk becoming more influential towards late may with a drier and sunnier trend and warming up slowly.

[bluearmy]

I think much as I suggested in my post above, they suddenly picked up the signal for the final warming of the stratosphere which occured quite sharply after the brief re-grouping of the polar vortex once the SSW feedbacks from late winter and early Spring had disappeared.  This signal is for a repeated  -AO profile and heights rebuilding to the north. In a nutshell we are seeing the consequences of the seasonal demise of the polar vortex reflected in the current modelling - this is happening quite late in the Spring once more

 

note GEM and ECM ahead of gfs on the northern blocking and ecm in the driving seat on the retrogression of the trough.

[William of Walworth]

Rob : Yes I do understand, but you rightly posted that IF in bold. One can only hope ths suggestions in recent runs of the trough regressing away and a more warming tend from the south later on, really do come about ...

As write offs go though, next weekend (that of Sat 18th) is currently looking very much like one should those GEFs charts posted by Frosty, or anything like tham, verify as shown ...

[Frosty.]

When we get the first mention of thundery rain moving up from the continent, it's a sign that summer is just around the corner and the latest met office update is signalling a possible very interesting pattern change with the north becoming drier and brighter but for humid and thundery weather to possibly spread up from france eventually. I can only assume this would occur if the trough through next week was to slide south to the west of the uk with building pressure to the east of the BI and warmer/humid air would be drawn up from the continent evenually mixing out the residual cool north atlantic/oceanic airmass, so the outlook is full of interest, be it cool cyclonic with heavy showers or the chance of humid and thundery weather coming up from the south/se in the 6-15 day range.

[Bottesford]

Lets try to keep a little more positive - its only the 9th of May and things can & will change.<br />Just because last summer was mostly dire doesn't mean this one will be too. We berate people for the 'winters over' posts popping up in an early November Atlantic driven spell so lets try to stay a bit more realistic. This sort of weather isn't unusual in May - we need the rain if nothing else anyway. Lets keep an eye on the models and await that pattern change...

[Paul]

Latest from Michael Fish - cool and unsettled about sums it up..

 

 

[Paul]

Can we bring this back to model discussion please

[phil nw.]

Come on everyone we are going way off topic in discussing Summer prospects in here-all ifs and buts anyway.

 

It`s only early May and the models indicate a cool and unsettled period for the next week/10days and that`s about it.

A long way to go so let`s talk around what the outputs are actually showing in this thread to keep it factual.

 

You all know there are other threads including the Summer one if you want to speculate.

Ok thanks all and back on topic now please.

Edited May 9, 2013 by phil nw.

[Methuselah]

Following from Phil, here's the Summer 2013 thread: http://forum.netweather.tv/topic/76293-summer-2013/page-16#entry2691656

[Frosty.]

Considering how cool and unsettled the weather is expected to be in the next few weeks, the Gfs 12z op run is showing some reasonable weather at times, sunday could be a drier and brighter day for southern britain with temps around 15-16c but cooler and more unsettled for northern uk, then later next week we get weak atlantic ridges sliding southeastwards on a nw/se aligned jet so we don't just get a trough over the top of the uk for days and days, the weather pattern keeps mobile and we see decent dry and brighter spells between the showers and more persistent rain next week, all things considered, this run is a lot better than I expected with the azores anticyclone ridging towards the uk in FI and pressure generally rising with a lot of fine and rather warm weather later.

[weather_it_will]

Back to the models, and GFS shows nothing but low pressure all the way to FI.

UKMO is the same at day 6.

ECM also same story.

Edited May 9, 2013 by Hot Wet Windy Cold No Snow

[Frosty.]

The Ukmo 12z shows a weak atlantic ridge pushing eastwards across the south on sunday  ( similar to the gfs 12z) and then only the far south of england holding on to a fairly dry and bright day on monday before the large trough swings down from the northwest with a very cyclonic and rather cool showery pattern taking control through tuesday and especially by midweek with torrential slow moving downpours with hail and thunder after sunny starts, I don't think the ukmo 12z would evolve like the gfs beyond T+144 hours.

Edited May 9, 2013 by Frosty039

[phil nw.]

Just to let the relevant posters know i have moved the posts discussing Summer prospects and matters relating to the Summer thread here

http://forum.netweather.tv/topic/76293-summer-2013/

 

This is because members are coming onto this thread and responding to those that were here.

 

Ok back to the Models -thanks

[Milhouse]

Potential for 2 decent days on Sunday and Monday showing in the ECM with pressure still fairly high in the south. But its downhill from then on.

[Frosty.]

The GEFS 12z mean looks much more unsettled than the gfs 12z operational run with no atlantic ridging indicated, it looks very cyclonic and rather cool for a while but gradually becoming a little warmer and drier later from the east as the trough fills in situ and then begins to retrogress towards iceland/greenland with the uk becoming more settled later in the month, this has been a trend which has been showing on the gefs mean for some days now. So a spell of cool showery weather with sunny periods seems like the main weather type for the next 10 days or so and then gradually drying up and warming up.

[Frosty.]

The main difference between the Gfs and Ecm 12z is the ecm has the main troughing modelled further west so there would be no chance of an atlantic ridge getting even close to the uk later next week, the whole pattern is further west on the ecm which again brings up one of the main flaws of the gfs which is it's eastward bias. With the trough being further west it allows a little of the warmth further east across europe to head west towards the uk so although it would initially be a cool cyclonic pattern next week, there would be some warming at T850 hPa which would eventually have more of an effect near the surface so temps would very gradually recover after a rather cool start. There is also a good chance that through the second half of the weekend and into monday, southern britain would have a more settled interlude with mostly dry and bright conditions with temperatures close to average but then cooler and unsettled weather taking over, most northern parts of the uk look unsettled and cool throughout but then that possible warming trend later next week and a risk of thundery rain pushing north from the continent by the end of next week as the met office update mentioned earlier. It also looks like it could become wet and windy across the far northeast at the end of next week with that low off northeast scotland and some warm/humid air within that system.

Edited May 9, 2013 by Frosty039

[phil nw.]

I am probably sticking my neck out on this but in view of some earlier pessimism on the next couple of weeks i thought i would look for some light at the end of the unsettled looking tunnel.

There, is i believe,just a hint that we may be seeing an eventual end of the unsettled period after next week. The later GEF`s 500hPa mean.

 

 

Ens graph

 

Thickness levels starting to rise from the south as the UK trough starts to warm out.

 

Yes it`s a while away but note too that low heights are still to our north and the Azores heights are waiting in the wings.Every chance the PFJ will go north later.

 

Some improvement starting to show up around next weekend as the upper trough becomes cut off from the parent polar vortex as it continues to shrink with pressure rising over the top.

Both Operationals show this but GFS a little earlier

http://www.wetterzentrale.de/pics/Rtavn1681.png

http://www.wetterzentrale.de/pics/Recm2401.gif

 

This would fit in with a sign for mid-latitude heights building across the UK indicated by the MJO forecast to continue it`s eastward progress along the equatorial pacific into phase 5.

Composite pattern for this

 

My only concern is this pattern may be somewhat modified if the MJO signal weakens nearer the time.Something to monitor there.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/NCPE_phase_21m_small.gif

 

For now though an unsettled and showery week or so to come but a trend to something warmer and more settled beyond may just be starting-let`s see if the overnight runs build on this.

 

 

 

 

 

[Gibby]

Hi everyone. Here is the evening digestion of the 12 noon outputs from GFS, UKMO, GEM, NAVGEM and ECM for Thursday May 9th 2013.

All models continue to paint a generally unstable spell of weather over the UK from Low pressure transferring NE away from the UK over the next 24 hours. Left behind will be an unstable WNW flow with embedded disturbances enhancing the occasional showers to something more organized at times as they pass West to East. A brief drier interlude is indicated over Saturday night and Sunday under the weakest of ridges moving through before renewed fronts and rain from Low pressure to the NW moves across late Sunday and early next week in maintained fresh and chilly Westerly winds.

GFS then takes us through the middle of next week with the Low sinking SE over the UK and away to the South before the weekend. A spell of very showery weather with thunder a possibility looks likely before slow improvements move down from the NW under a slack ridge over the weekend. Though not killing showers off entirely and keeping things none too warm some good dry spells with some sunshine would be likely at times especially towards the West. Late in FI the progression of successive Low pressure areas drifting down from the NW continues at times though there will be increasingly longer dry spells occurring later as High pressure ridges edge towards SW Britain at times.

The GFS Ensembles are still very uninspiring for this time in May with plenty of rainfall spikes shown from uppers that are never far from normal for most parts of the UK. Given the frequency of rainfall events temperatures at the surface will feel cool while conversely in the sunnier spells between the rain it may feel quite warm.

The Jet Stream shows the flow to the South of the UK for the coming few days. It ridges North and then digs strongly South to the West of Britain all the way to North Africa next week before turning East across the Med. The UK and NW Europe remain locked in a deep trough.

UKMO tonight shows a deep UK based trough filling slowly in the middle of next week with rain or showers at times in rather cool conditions overall but with some warm sunny spells between the thundery downpours and lighter breezes late in the week.

GEM is very disturbed tonight with Low pressure circulating the UK throughout next week with showers or longer spells of rain for all areas on most days.

NAVGEM also keeps the UK firmly under the control of Low pressure centred close to Northern Britain with an extensive trough South from it over the UK and NW Europe. As with GEM frequent heavy showers or more general sometimes thundery rain will be maintained over the UK.

ECM tonight shows Low pressure moving down over the UK with thundery showers or more prolonged rain at times almost anywhere. At least the winds will become light as the pressure gradient becomes slack over the UK so in any sunnier breaks it will feel reasonably warm. Towards the end of the run it looks much like this morning's run with Low pressure ending up somewhere near Eastern England with cold and grey weather with rain and strong winds wrapped around the system. By Day 10 very little has changed with Low pressure all over NW Europe with rain and showers continuing for several more days to follow at least.

In Summary tonight the output shows the weather remaining very unsettled with Low pressure in total domination of conditions over the UK. GFS does show some more acceptable weather interludes late in it's operational run but it is not widely supported by other members within the ensembles. There is very little else of note which suggests anything other than occasional sunny spells between the showers or rain with temperatures never exceeding normal values although in any sunnier spells it will feel quite warm given the time of year.