Model Output Discussion 12z 20/04/13

[phil nw.]

A new thread for the 12z model runs then.

A typical Spring outlook it seems with some warmer sunshine during the next few days before a change to a cooler and more unsettled period at the end of the week.

As ever please post on topic and be polite to other members.

[Summer Sun]

So far tonight GFS is wanting to bring high pressure back in from the west quickly later next week making the change to unsettled weather a very short blip

 

 

Caution is needed though we need to wait till ECM is out later on to see if there is any support. UKMO and GFS at t144 are miles apart

Edited April 20, 2013 by Gavin.

[phil nw.]

The 12z GFS T96hrs. chart shows the approaching colder air coming from the north west.

heralding that change.Wednesday looks like the last of the warmer days as that colder air spreads south and east to all areas by the end of Thursday.

[Frosty.]

The Gfs 12z operational shows a straightforward change from warm and settled to cooler and showery by thursday once a weakening band of rain has cleared southeast, we will all be in the same boat with a cooler nw'ly airflow and scattered showers with sunny spells , this pattern persists through next weekend and overnight it would be cold enough for a touch of frost.

[Frosty.]

The cool snap is fairly brief with the weather soon turning milder into the following week with some showers & sunny spells and winds going around to a light to moderate easterly, the pattern beyond that becomes rather slack with lots of blocked looking charts with high pressure but not totally settled as there are shallow troughs dotted around, the main one being to the southwest of the uk but temps look alright, going into the low to mid 60's, not a bad gfs 12z overall.

Edited April 20, 2013 by Frosty039

[Carlrg]

Is this the warm (ish) easterly you mentioned earlier Gav?

 

Would the undercut also help pull even more of the warm continental air in?

 

http://176.31.229.228/modeles/gfs/archives/2013041918/gfs-0-288.png

 

http://176.31.229.228/modeles/gfs/archives/2013041918/gfs-6-312.png

 

http://176.31.229.228/modeles/gfs/archives/2013041918/gfsnh-1-312.png

Edited April 20, 2013 by Carlrg

[Frosty.]

The ukmo 12z is significantly better than the gfs 12z and keeps the weather dry and warm for longer into thursday but by friday it's turning much cooler although the far south and southeast remains moderately warm through into friday, so there are going to be timing issues next week with the breakdown from warm and fine on tues/wed to cooler and showery by thurs or friday at the latest. The ukmo 12z indicates an arctic flow coming down into scotland during friday and into the weekend, rather colder than the gfs shows, the position of the atlantic high will make the difference between a cool nw'ly and a colder n'ly by next weekend.

[Methuselah]

Is this the warm (ish) easterly you mentioned earlier Gav?

 

Would the undercut also help pull even more of the warm continental air in?

 

http://176.31.229.228/modeles/gfs/archives/2013041918/gfs-0-288.png

 

http://176.31.229.228/modeles/gfs/archives/2013041918/gfs-6-312.png

 

http://176.31.229.228/modeles/gfs/archives/2013041918/gfsnh-1-312.png

One thing worries me about a 'warmish easterly', however: WAA over the cold North Sea can only result in one thing - cold, grey and misty conditions spreading as far inland as East Wales overnight...Not very promising for areas bordering the North Sea.

[Frosty.]

One thing worries me about a 'warmish easterly', however: WAA over the cold North Sea can only result in one thing - cold, grey and misty conditions spreading as far inland as East Wales overnight...Not very promising for areas bordering the North Sea.

it is worrying since the north sea is colder than normal and the met office made a point about this in the extended outlook recently, some ne coastal areas could end up being very cold and misty with temps of 6-7c which is the temperature of the north sea, I believe it should be a few degrees warmer than that in early to mid may. It would be pretty good to the nw of high ground though, such as nw scotland, the western isles and parts of nw england including n.ireland and isle of man.

[Carlrg]

it is worrying since the north sea is colder than normal and the met office made a point about this in the extended outlook recently, some ne coastal areas could end up being very cold and misty with temps of 6-7c which is the temperature of the north sea, I believe it should be a few degrees warmer than that in early to mid may. It would be pretty good to the nw of high ground though, such as nw scotland, the western isles and parts of nw england including n.ireland and isle of man.

I agree but is this outcome not the lesser of two evils? IMO better than weeks and weeks of Atlantic driven washouts which we had last year.

Edited April 20, 2013 by Carlrg

[Frosty.]

I agree but is this outcome not the lesser of two evils? IMO better than weeks and weeks of Atlantic driven washouts which we had last year.

it depends, those who live in counties bordering the north sea would be cold and dull, so they would prefer winds from a sw'ly point with more shelter from hills to the west, location is key.

[Summer Sun]

I remember a few years ago when we got an easterly around May time i think it was and every day here was lovely once the early morning cloud burnt back to the coast 25 miles or so further east and they were stuck under cloud and sea fog right on the coast with single figure temperatures whilst here it was close to 20c

 

Anyway back to the here and now and ECM has the 1020mb line slightly more north than UKMO does at t120 so this extends the warmth and drier weather by another day

 

 

By Friday its all change as we lose the high and introduce a cooler air flow if the high edged further east we'd be in a northerly flow for a time

 

Edited April 20, 2013 by Gavin.

[Frosty.]

The Ecm 12z is looking similar to the ukmo 12z in keeping the weather warmer and drier for longer, it's the gfs which is currently looking too progressive, so the ecm holds back the change to colder and showery for a while longer. The southeast of the uk in particular looks like having a nice warm spell next week with tuesday warm and sunny, even warmer on wednesday and now even thursday could be warm and dry but with pressure falling on thursday, a chance of showers breaking out after a sunny morning, cooler and more unsettled for nw britain though.

[Methuselah]

The Ecm 12z is looking similar to the ukmo 12z in keeping the weather warmer and drier for longer, it's the gfs which is currently looking too progressive, so the ecm holds back the change to colder and showery for a while longer. The southeast of the uk in particular looks like having a nice warm spell next week with tuesday warm and sunny, even warmer on wednesday and now even thursday could be warm and dry but with pressure falling on thursday, a chance of showers breaking out after a sunny morning, cooler and more unsettled for nw britain though.

That's great news, Frosty: as we all know, the GFS is always wrong... 

[Summer Sun]

At 168 the high does indeed move further east so that sets up a north to north easterly flow for a time

 

 

T192 sees the high getting forced south west wards

 

 

By t240 we`re in what looks to be a SEly flow with lots of heat building on the continent

 

Edited April 20, 2013 by Gavin.

[Carlrg]

A cool northerly on the NAVGEM at T144.

 

 

http://www.wetterzentrale.de/pics/Rnvg1441.gif

 

 

What's the chances of the HP in the Atlantic drifting over us?

Edited April 20, 2013 by Carlrg

[Frosty.]

A cool northerly on the NAVGEM at T144.

 

http://www.wetterzentrale.de/topkarten/fsnvgeur.html

 

What's the chances of the HP in the Atlantic drifting over us?

i'm not so sure it would drift over us, more likely to occasionally ridge into the uk before toppling southeast with the jet aligned nw/se for a little while at least. The shape and position of the atlantic high will have an impact on whether we get a polar maritime nw'ly or an arctic northerly next weekend.

[Carlrg]

i'm not so sure it would drift over us, more likely to occasionally ridge into the uk before toppling southeast with the jet aligned nw/se for a little while at least. The shape and position of the atlantic high will have an impact on whether we get a polar maritime nw'ly or an arctic northerly next weekend.

 

Only just seen Gav's post. 

Edited April 20, 2013 by Carlrg

[Frosty.]

Rather cold and showery by the end of next week on the ecm 12z but then temps starting to recover towards the end of next weekend onwards but showers would be wintry for northern hills for a while and the scottish mountains would have some snow showers but some ridging pushing southeast so drier and sunnier in central and southern parts at times with less showers, most of the showers across the northwest nearest the centre of the low, cold enough overnight for slight air frosts where skies clear and especially under the ridge conditions but even the showery areas having some sunny spells.

What's happened to the thunder within heavier bursts of rain caused by an active cold front interacting with residual warm air mass with shallow trough somewhere....can't remember the rest of it risk?

 

Resolved?

I blame the models, they keep changing.

[Gibby]

Hi everyone. Here is tonight's look at the midday output from the big models, namely GFS, UKMO, GEM, NVGEM and ECM for today Saturday April 20th 2013.

All models still support the pattern on previous recent output of a cold front moving SE across the UK over the coming 24 hours followed by a Westerly flow with some rain at times, restricting to the North as we move into the new week. High pressure moving East close to Southern Britain then brings a potential period of warm and bright weather with some sunny spells and light winds. The North remains susceptible to rain at times and later in the week colder and more unsettled conditions begin to push down from the NW reaching all areas by the weekend.

GFS then shows the end of next week and next weekend with a chilly North or NW flow with sunshine and showers on the menu for most with some cold nights under any clearer skies. The cold quickly moderates as we move into the new week with pressure becoming slack over the UK for a time before the pattern settles with High to the North and low to the South by midweek. The North would become largely dry from this point on while the South would remain at risk of showers as various Low pressure jostles around to the South of the UK. By the end of the run temperatures are back up to respectable levels for early May.

The GFS Ensembles continue to show a colder interlude late next week and weekend with a slow recovery in uppers with time to the long term mean. Rain is not a huge ingredient of the menu tonight, restricted largely to the cooler and showery phase next weekend.

The Jet Stream powers across North America and the Atlantic and over the UK for the next week or so with a weaker development in the flow by next weekend.

UKMO shows a slack Northerly flow developing by next Friday displacing the warm air over the South with rather colder conditions in light winds and the risk of some heavy showers in places.

GEM shows a cold and showery Northerly too over the end of next week and weekend for all of the UK.

NAVGEM too shows the same chilly northerly with the flow backing Westerly later in the weekend as new Low pressure sinks SE towards Scotland.

ECM tonight shows a Northerly flow developing by next weekend with showery and rather cold conditions for many but in any sunshine in the South it will feel OK between the showers. A weak ridge is then shown on Sunday ahead of a new low slipping SE from Iceland to be centred over the the Northern Isles by Day 10 which is a departure from recent runs and would mean a recovery in temperatures for many as winds back Westerly and showers become more restricted to the North.

In Summary tonight there are a few changes from this morning. The cold may not be as pronounced as shown in recent runs but it will certainly be noticeable in the South after the rather warm conditions likely there around midweek. Any rainfall looks to be of the showery variety, some of which will be heavy with hail and thunder and it will probably be cold enough at night for ground frosts where skies clear. However, having said that ECM has retracted the deeply unsettled and cold conditions of recent runs by Day 10 and in general the models seem to be reducing the longevity of the colder weather when placing tonight's operationals with tonight's GFS and previous runs ensemble data.

[Frosty.]

 

 

Resolved?

yeah it should be resolved by early next week due to the large differences between the gfs and the euro models

Edited April 20, 2013 by Frosty039

[Carlrg]

yeah it should be resolved by early next week due to the large differences between the gfs and the euro models

 

Around midweek according to Gibby.

Edited April 20, 2013 by Carlrg

[Zenarcher]

My summary on the models this evening,

24 hours Sunday - Mostly cloudy with showers and only South Eastern England seeing the best of the weather with sunshine for most of the day. Gales over Ireland and Scotland but a light breeze for Wales and England. Temperatures on the mild side especially for Southern parts of England.

48 hours Monday - Continues the theme of cloudy weather but dries up for most parts although maybe a few showers around in the West. Fog patches are also likely anywhere in the UK as well. A strong breeze for all of the UK with Northern and Western Scotland seeing gales. Temperatures staying mild with around 15c possible in Southern parts of England and Southern Ireland.

72 hours Tuesday - Looking a great day for England and Wales with clear sunshine in control. The same cannot be said for Northern England, Ireland and Scotland with it starting cloudy in these parts and eventually showers and heavy rain moving in later. A calm wind over most of the UK but a strong breeze across Scotland with gales in the West and North. Temperatures for Southern England are looking high at around 18c and Southern Ireland not far behind at 14c.

96 hours Wednesday - All models agree on high pressure sitting across the South of the UK meanwhile low pressure continues over the North. The weather will be similar to previous days mostly cloudy with some showers around. Temperatures still well into the double figures for the Southern parts of the country.

120 hours Thursday - All models agree on the weather pattern to look more blocked than what it has been recently with a large high pressure system moving into the Atlantic around 1040mb most of them have it at. This may bring some classical spring weather to the UK, sunny spells with showers. Temperatures in the South would still remain mild but for Scotland it may turn colder.

144 hours Friday - Models all show something different here but they do agree on the high pressure staying in the Atlantic with low weak pressure over the UK.

Edited April 20, 2013 by weathermaster

[Frosty.]

Around midweek according to Gibby.

yes that sounds about right, the fine and warm spell is growing longer again on ecm and ukmo, I have a feeling the gfs is being over progressive again, hoping the good weather can last as long as possible next week.

[Frosty.]

You investing in a time machine, Frosty? I thought it could only be resolved as-and-when it either happens or doesn't happen, as Pete said.

 

Recent model output hasn't budged wrt thundery breakdown (or absence of); there is no change there. Sensing some subtle maneuvering away from original assessment. Hmmmm.

it wiil be resolved when we have cross model agreement within a few days of the change, and I was going to ask to borrow your time machine since you have already resolved the outlook this afternoon.