Model Output Discussion 12z 20/04/13

[AWD]

As the latest GFS shows, as well as to some degree, the overnight ECM Op, the main build of anticyclonic weather looks to build just after the Bank Holiday weekend, with the weekend itself rather more mixed.

Temperatures look rather respectable though, especially towards the South East where it could be rather warm;

with the 70F value likely to be broken, although how much sunshine and how much cloudcover there will be is open to debate at this early stage;

This is because the 06z throws a front up from the Biscay area later on Sunday and more especially Monday;

bringing a band of moderately heavy rainfall to some parts of England and Wales on Bank Holiday Monday;

So BH Monday could be a fly in the ointment for those with outdoor plans, one to keep an eye on there in future runs, and also maybe for convective fans. Although on this particular run the instability thrown up stays south of the front and heads NE into France, this could change on future runs and provide some interest in this department;

Something to watch here, especially for those further south. This is about as exciting as it gets for us convective/storm fans over the coming couple of weeks, so if we are to see something less settled on Monday, perhaps a change in the distribution of energy could be arranged to allow for some interest for some here.

A respectable BH weekend likely then, not completely dry but much better than previous BH weekends. Looks warm for the south, cooler for he north and a small chance of some storm interest maybe, which would be nice after a relatively quiet convective period to date so far.

Edited April 28, 2013 by AWD

[SP1986]

The outlook looks a little confused at the moment, with outlook changing on daily basis it seems, it's really hard to know where this one will settle. 

 

On one hand the GFS and it's ensembles seem to be implying high pressure will dominate, but on the other hand there are so many cut off lows, shortwaves, little areas of high pressure, that the outlook is near on impossible to define at the moment.

 

I think the general message is, 'more runs needed'

Edited April 28, 2013 by SP1986

[Milhouse]

Thats very true Stephen. Thats the trouble with weak highs and shallow lows. Its very hard to pin down the specific details.

[Frosty.]

The latest GEFS 06z mean is showing a very anticyclonic outlook, even better than the 00z mean in my opinion and rather more like the ecm 00z ens mean. One of the issues will be how quickly the pesky trough to the nw/n of the uk will be broken down to allow high pressure to gain the upper hand and then assume complete control but the 6z mean is as good as could have been hoped for at this stage. 

Edited April 28, 2013 by Frosty039

[phil nw.]

It will settle down to a fine anticyclonic spell eventually-the mean outputs have continued to show an improving outlook from the BH weekend.

The Op runs with their higher resolution are picking up on the lingering upper cold pools as the main trough starts to warm out later in the week.

It`s all a matter of timing as to when these little features finally fill out and any showery activity finally dies away so there is a day or two`s difference on this in the various runs.

It still looks like a very dry,fine and increasingly warm spell in the BH week.The only caveat on that will be the placement of the high cell which may give coastal districts facing onshore winds some low cloud and mist,especially if we get an easterly which has shown up on some recent runs.

[phil nw.]

Just to illustrate the strong signal for an anticyclonic outlook these are the 00z NAEF`s and ECM 500hPa height anomalies for day 10-around the middle of the BH week.

The ens.continue to show another 2 weeks of low rainfall for the south and at the moment even further north the only notable amount may be from that small low that is modeled to affect northern areas around Friday.

[legritter]

Iv been a lurker lately as our friends from Canada have been here for past 3 wks and travelling around our small island we have seen a big range of temp ,and been in the right places for the best weather . onto the charts and data and it looks to me as May will deliver below average temp but nothing of big note ,atleast the first half .as always any high pressure that sets up at this time of year could bring us mirk warmth or even cold so at the moment looking too far ahead would be unwise ,but a nice warm spell would be welcome by many .

[Milhouse]

GFS12z vastly different to the 6z with low pressure remaining to the west of the UK in the run up to, and including the weekend with temperatures rising under a light southerly. Chance of some more unsellted conditoons affecting western parts towards the weekend on this run.

[Frosty.]

Very nice 12z output so far from the ukmo and gfs 12z, the Bank Holiday weekend is currently looking rather warm and increasingly fine but still a risk of showers in places, pressure looks higher away from the far northwest. The Gfs 06z was a cool run but the 12z is a warm run with max temps from next weekend onwards being in the 17-20c range, there would be some areas which get into the 70's with the set up shown. All in all, a much warmer outlook and generally anticyclonic with long sunny spells and well below average rainfall, all parts of the uk having a taste of summer with some peachy looking FI gfs 12z charts.  

[AWD]

If it wasn't for these little shortwaves/troughs etc hindering the build of "proper" high pressure, then the BH weekend could be excellent. We have consistency regarding the temperatures, which look warm for many, especially so further south and east where temperatures are very summery;

But you can see below little "kinks" showing small disturbances, enough to produce showers or weak rainbands for some;

This also shown by the admittedly, not too reliable GFS PPN charts below too, but it does sow the general gist;

Saturday;

Sunday;

BH Monday;

These are the sort of disturbances that will get shown in the FAX charts nearer the time (if of course, the Met Office believe them to be true) and have the potential to be a spoiler for the folks who are under the rain/showers. Will be interesting to view the FAX outputs nearer the time as to the amount of instability the Met Office believe there will be left over from the fading trough before pressure rises enough to kill anything off.

[049balt]

Hi everyone, have been a lurker for a while so this is my first post. We are desperately needing some good weather in Ireland and all indications point  to just one more horrid week left of this weather and then May looks fine.

 

http://wxmaps.org/pix/prec4.html

[Milhouse]

ECM not great but as there are so many possibilities tonight that i'm not going to take one run seriously. On the 12z theres a small feature which develops over northwestern France next weekend which cuts off the warm flow off the continent and eventually brings down a cooler northeasterly.

 

 

 

On the other hand the 12z GEFS ensemble mean is a definite improvement over what the 0z showed this morning with high pressure staying over the UK for longer and little sign of a northerly in FI that quite a lot of ensemble members supported this morning.

 

[Frosty.]

The Ecm 12z operational shows pressure rising through the Bank Holiday weekend but there is a fly in the ointment in the form of a pesky shallow trough,  on holiday monday it's just to the south of the uk but then it expands a little and pushes into the southeast, the run ends with this trough covering much of southern and eastern uk, and with a high pressure cell to the northwest we have a NE'ly flow so not as warm or as settled as the Gfs 12z op run during the same timeframe. So this run looks rather more unsettled with showers around and cooler than the ecm 00z but generally it's still an improving picture (minus that trough) from next weekend onwards with more in the way of sunshine and generally becoming warmer, this trough will hopefully disappear on future runs.

 

The week ahead looks fairly pleasant across the south with sunny spells and mainly dry weather, just a few showers dotted around tomorrow in southern britain but then tuesday & wednesday look fine, perhaps a few showers returning on thursday and friday but still a lot of fine weather, temps near average, in the 13-15c range but chilly overnight with a touch of frost. Northern britain looks more unsettled and cooler in the next five days, very showery tomorrow, tuesday drier and brighter with just a few showers. wet and breezy midweek and then colder and showery later in the week, hopefully a big improvement by next weekend.

Edited April 28, 2013 by Frosty039

[SP1986]

The ECM situation looks like a volatile one to model, therefore as it stands I cannot see the ECM situation actually occurring. We will probably eventually see a simplification of these outcomes; ie many of these little features will be removed. That's my experience of it anyway!

Edited April 28, 2013 by SP1986

[Gibby]

Hi everyone. Here is tonight's review of the midday output on the expected pattern of weather events over the next 10-14 days from the five big super weather computers.

All models show a chilly West to NW flow over the UK with a cold front clearing the SE overnight leaving a showery WNW flow over the UK. Not many showers in the South as High pressure slowly builds from the SW over the coming days. Through midweek any Low pressure influence will be restricted to the far North with England and Wales seeing benign and dry conditions with sunny spells by day but chilly nights with grass frost for many. Towards the end of the week Low pressure close to the NW sees the models divide on the outcome of events thereafter.

GFS shows Low pressure moving towards Northern Ireland on Friday before being absorbed by a deeper Low well to the NW. A showery trough is left down across the UK giving the risk of unsettled weather with showers over the weekend more especially in the West. Over FI tonight the trend remains for High pressure to build strongly across the UK bringing fine and eventually somewhat warmer conditions for most. Late in the run the High pressure migrates further towards the NW with a light to moderate NE flow setting up across most areas with some scattered showers developing in a return to rather colder temperatures.

The GFS Ensembles show good solidarity on a warm up tonight, especially in the South with a warm spell looking likely in the second half of the run and in the South. Rainfall amounts look quite restricted once more especially in the South while the operational was one of the warmest options on offer in it's warmest phase.

The Jet Stream shows the main arm of the flow continuing to blow West to East across the Atlantic and the British isles in a weakening form over the coming week or so.

UKMO tonight shows slack Low pressure over the UK early next weekend but with Low pressure close by to the NW. Many areas will stay dry but there will be some showers scattered about heavy in places but most prevalent in the NW later.

GEM tonight shows the Low pressure at the weekend as a more significant feature developing late in the week near NW Scotland and sinking South over western areas and then to the South maintaining a very showery feed over the holiday especially in the west and later the South.

NAVGEM tonight is not so dramatic in not developing the Low as much instead bringing a shallow upper trough South which develops enough energy in the South late in the weekend for a few showers before signs of a strong High pressure belt develops over the North at the end of the run.

ECM shows a cold pool from a filling Low pressure at the start of the weekend with some heavy showers almost anywhere over Friday and Saturday. Later in the run the main concern for long term prospects is the amount ocf cold air over the Atlantic with all the Sping warmth bottled up well South of the UK and in Eastern Europe. The final days of the ECM run shows shallow high pressure moving further NW away from NW Britain as the showery Low near the South sets up a chilly NE flow with heavy and thundery showers for most, especially in the South and East.

In Summary things are still not clear cut on the weather events of the Bank Holiday weekend with various solutions which would offer very different weather at the surface. At least it doesn't look like a write off weekend with a showery Low looking the most likely fly in the ointment for many at least at the start of the weekend and possibly longer ala ECM. For those looking for a heatwave anytime soon I'm afraid to disappoint you in stating that although things will feel pleasant enough in the sunny spells between the showers things will be average at best and often rather chilly, especially at night.

[Frosty.]

The GEFS 12z mean is as good as could be hoped for with a very strong signal that we are heading towards a major anticyclonic spell with a taste of summer for all areas, stick with the mean, it shows a more realistic picture and so far today, the gefs and ecm mean have been rock solid behind a warm and settled outlook, hopefully the ecm 12z ens mean will keep things heading that way.

[Guest pjl20101]

Looking very +ve across the UK according to this link here. My only concern is that there is above average heights towards Greenland. Anyway here is the link:

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

Looking good and a tad perplexing situation to be honest guys.

[snowking]

Awaiting the 12z ensembles but it should be noted the general trend from the ECM over the past 48 hours has been to reduce the mean from slightly above average to below average (Red is the 0z from today, then Blue, Green, Black):

 

 

At the same time the 0z in particular showed an uptick in mean precipitation projection:

 

 

I'll have to report tomorrow what the subsequent 12z and 0z runs following on from this suggest, but nothing above average currently looks on the horizon to me, and we may be made to wait until the second half of May before we see such an occurrence

 

SK

Edited April 28, 2013 by snowking

[Guest pjl20101]

By the way snow king I know its not relevant but have more Enso and QBO years entered the analogue matches my friend?

[Mark Neal.]

GFS keen on high pressure over the british isles for 2nd week of may! 

[AWD]

Frosty & Gavin will be loving the latest GFS Op with a developing High pressure cell over the UK for pretty much the whole of the BH weekend, turning it increasingly warm and sunny;

[mountain shadow]

GFS is à cracker for sustained settled spell kicking in this weekend. The op has full support from the GEFS for à large pressure rise over the uk.

Hopefully the ECM will go the same way.

[IDO]

GFS looking good for the Bank Holiday Monday: Away from East coasts should feel warm: . 17 out of the (22) GEFS members have the UK in some sort of high setup. Still quite a variance with regard to position: http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=180. The other five members show a partial high.

Last night's ECM op was another outlier (precipitation): with one of the coolest options (temp.): ...best ignored. Still a settled week or so of high pressure looks the call from the Bank Holiday.

The GEFS pressure charts show a steady fall for the end of the Bank Holiday week: The GEFS stamps confirm this with only four members having the UK under total anti-cyclonic conditions at T384 (12 under a trough, 6 mixed).

Rainfall totals next 8 days good as well, that is for most:

This week and the SE hold onto the settled mild temps till late Friday: 18.00 Friday:

The trough passes within 24 hours (south) and by 18.00 Sunday temps very good again: and by Monday UK wise:

Edited April 29, 2013 by i'm dreaming of...

[mushymanrob]

The outlook looks a little confused at the moment, with outlook changing on daily basis it seems, it's really hard to know where this one will settle. 

 

On one hand the GFS and it's ensembles seem to be implying high pressure will dominate, but on the other hand there are so many cut off lows, shortwaves, little areas of high pressure, that the outlook is near on impossible to define at the moment.

 

I think the general message is, 'more runs needed'

 

nail on the head.... from my pov its pretty useless trying to get a grip on anything past thursday as there are so many options, it only takes one small shift in data to produce something completely different, and without much of a concensus between the big three its unwise to pin hopes on a favoured chart.

 

even if we do get a anticyclonic spell, the exact position/orientation will make a huge difference in the weather we actually get.

[Frosty.]

The GFS 00z is an excellent run from the Bank holiday weekend onwards as high pressure builds from the southwest and a major anticyclone then covers the uk, generally becoming centred just to the west but most importantly the weather becomes warm, temps nudging a degree or so higher each day and eventually into the 70's. It turns into a near perfect run with light winds and lots of sunshine for just about all parts of the uk, later in FI there is retrogression and a dramatic change to cold, showery northerly winds at the end of the run with frosts and even snow showers for northern hills in mid may, but most of the run is sunny and warm.

Edited April 29, 2013 by Frosty039