Model Output Discussion 12z 20/04/13

[NeilN]

Does this mean that it won't be dramatic come Weds/Thur with the cool temps or that warm run never happening?

[SP1986]

Certainly not liking the look of the gfs predictions for the weekend for overnight temps. If these frosts come off there is likely to be major damage to outside crops, especially given the last few warm days...

The GFS always exaggerates temperatures at this time of year, this will not happen I'm sure of it.

Edited April 25, 2013 by SP1986

[weather_it_will]

Still looking good for a pressure build at day 10...

 

10 days away is too far away to be reliable.

[Methuselah]

Does this mean that it won't be dramatic come Weds/Thur with the cool temps or that warm run never happening?

Can you pop your location into your profile, please?

[NeilN]

Can you pop your location into your profile, please?

 

It's Weston-super-mare

[Frosty.]

Even before we get to the major anticyclonic spell which the models are continually showing in FI, there looks to be some high pressure within the reliable timeframe, combining the gfs and ukmo 12z this weekend we have a toppling atlantic ridge which is likely to bring a pleasant but cool spell on sunday in the south with long sunny spells for southern britain, and then on monday, the south may escape most of the showers as pressure looks that bit higher near the south coast, tuesday sees a nice atlantic ridge pushing northeast into the uk and wednesday has a high just to the east so despite a cold showery outlook according to the ensemble mean, there should be some decent weather for most areas at times. The gfs 12z charts further into FI look very settled and temperatures inland would become pleasantly warm at 16-18c, cooler on eastern coasts with a brisk easterly wind.

Edited April 25, 2013 by Frosty039

[Summer Sun]

From the first full week of May the ensembles become very clear with the warmer uppers arriving

 

 

A continued clear trend is for precipitation to remain low what a difference 12 months makes rainfall wise

[London Ed]

Hello. I've not posted for a while but I was interested in people's thoughts on the jet stream forecast. Looking at it the jet stream it appears very weak indeed and split, south across north Africa where it's been most of the winter and north across mid and north Atlantic. 

 

Am I correct in this interpretation?

[Gibby]

Good evening. Here is tonight's assessment of the 12 noon output issued by GFS, UKMO, GEM, NAVGEM and ECM for tonight Thursday April 25th 2013.

All models show the dying embers of the warm snap leaving the SE this evening as a cold front crosses SE over the South of the UK overnight. Following on behind will be a mix of sunshine and showers with temperatures well down in the South than of late with frosts at night becoming a real hazard for gardeners and growers from tonight in the far north and elsewhere too from tomorrow night. The weekend keeps the general Northerly feed going with further showers before they die out on Sunday as a ridge moves South over the UK. By Monday a new Low to the North pushes a trough down over the UK with some rain for most before clearer conditions with a mix of sunshine and showers return on Tuesday.

GFS then shows a ridge of High pressure building across the UK for a time towards midweek with some dry, bright conditions before a spell of slack Low pressure brings a return to showers towards the Bank Holiday weekend which looks like remaining showery in a Westerly wind in association with Low pressure to the North of the UK. Then as the Bank Holiday passes High pressure builds from the South with dry fine conditions developing for all with a cool East wind carrying North Sea haar and cloud across Eastern areas with the best of the brightness and warmth reserved for the far West and NW with the risk of some thundery rain edging into the far SW by the end of the run.

The GFS Ensembles show a rather cold period now for the next 5-7 days before the slow recovery shown in previous runs continuing to achieve uppers above the long term average by the end of the run, well supported by most members. Rainfall will be patchy, falling mostly as showers through the colder period of the next 4-5 days.

The Jet Stream shows a slowly weakening West to East flow across the Atlantic and the UK over the next week or so.

UKMO shows a slack pressure area over and around the UK next Wednesday. With uppers rather Low and warm sunshine heavy showers could well develop inland through the day with local hail and thunder while the nights remain clear and calm with a frosts overnight.

GEM shows changeable conditions through next week with showers scattered about at times with Northern areas seeing the largest share of them by the end of the week as High pressure nudges close to the South by the Bank Holiday weekend.

NAVGEM too looks broadly showery next week with low pressure crossing slowly East close to the North with a showery Northerly flow early in the week backing Westerly later with temperatures still largely suppressed for late April.

ECM finally backs up the Met Office mid range forecast today as it shows a generally showery week as slack pressure areas over the UK give light winds, sunny intervals and slow moving downpours for most of next week before pressure builds to the East of the UK and falls deeply to the NW with showers or outbreaks of rain becoming more restricted to more NW areas by the long weekend though with troughs crossing East for a time at least a little rain is possible in the South too for a time.

In Summary after a cool and showery weekend it looks like next week will also be a largely showery one. The distribution of showers will vary from day to day as weak upper troughs get hung up in the light winds over the UK. Temperatures will stay a little below average for the first half of the week but recover somewhat later, especially in the South. Frosts though could still feature up to midweek in places and nowhere looks like it's going to be very warm this coming Bank Holiday though having said that it may not be too bad in places with some sunny intervals from gently rising pressure the most likely end result before a High pressure based Easterly flow develops once most go back to work the following week.

[Milhouse]

I see a little low will slide southeast out of Iceland to distrupt the northerly for next week. That could mean a spell of settled weather with daytime maxima around average which in light winds will still feel suitable for late April. As the uppers are still forecast to be cold for the time of year we will still have the threat of some nighttime frosts.

 

[Milhouse]

UKMO 12z has a very slack pressure pattern at T+144 with the UK under relatively cool, high pressure.

 

[Frosty.]

All things considered, the Ecm 12z operational run looks rather good at times with high pressure either close to or over the uk at times, there is a brief wobble at T+216 hours but by T+240 it's all systems go for a prolonged spell of anticyclonic and warmer weather. The south of the uk does ok on this run with high pressure ridging in from the southwest and pressure generally being higher to the south of the uk so it looks like the driest and sunniest weather will predominantly be across the southern half or third of the BI with the cold and showery weather more likely in northern britain, just occasionally the colder showery weather will penetrate further south such as tomorrow and into saturday, and then again on monday but with high pressure or at least ridging holding the upper hand on sunday and then again next tues/wed and beyond with just the occasional unsettled day, the ecm is still a cool run with a risk of slight frosts for a while but the main focus of showers/persistent rain looks more likely in the north/nw of the uk.

 

So on the whole, the 12z runs don't look too bad, yes it will be cooler than average with ground frosts and slight air frosts but also a lot of dry and sunny weather at times, especially further south.

[Geordiesnow]

Slightly better outlook than the models were projecting yesterday with the easterly feed not being as obvious as it was yesterday and we get into a cool slack pressure set up. Its hard too tell whether the UKMO/ECM has got any frontal rainfall mixed in the charts they are showing because sometimes charts on paper may look reasonably dry are in reality not the case. 

 

Certainly the potential for a cool bright outlook with the risk of frost at night. Don't think any frosts will be all that severe for the time of year though. 

[Milhouse]

ECM mean has pressure generally remaining high over the UK next week with upper temperatures on the cool side due to the absence of a proper pronounced area of high pressure. Then later on pressure rises further from the south as a warmer southerly/southeasterly develops

[Milhouse]

The GFS 18z brings a return to the mild settled conditions as early as the middle of next week with high pressure nosing in actually on Tuesday. However Tuesday looks a particularly cool day for the time of year before high pressure asserts itself and temperatures creep up to average values. High pressure continues to build over the SE of the UK through next week with temperatures into the mid teens by Friday. FI sees high pressure controlling the weather situated to the NE of the UK. Warm for western parts but cooler in the east.

[summer blizzard]

A consistent ensemble trend for a pressure build in 9/10 days, i dare say it may feel like summer.

[mountain shadow]

A consistent ensemble trend for a pressure build in 9/10 days, i dare say it may feel like summer.

The GFS 0z looks cyclonic throughout with the odd better day. The pressure build has gone to be replaced by cool north westerlies.

[mushymanrob]

A consistent ensemble trend for a pressure build in 9/10 days, i dare say it may feel like summer.

 

unfortunately thats far from certain, looking at the mjo and anomaly charts dont now seem to support pressure rise in 9-10 days time.

[Frosty.]

The latest 00z gefs mean shows some improvement as time goes on but the trough to the northwest looks more persistent, but pressure does rise to the south and east so it's still slowly trending in the right direction, I think we are heading towards a northwest-southeast split during the next 10 days but i'm still hopeful that beyond that, we will see a nationwide fine spell.

Edited April 26, 2013 by Frosty039

[mountain shadow]

ECM hold the Atlantic trough further North West at day ten than the GFS buy no réal late Spring warmth in the overnight runs.

[IDO]

The GFS 0z looks cyclonic throughout with the odd better day. The pressure build has gone to be replaced by cool north westerlies.

Looks finely balanced to me, with HP never far away from the SE. No strong indication where the trough will be. The GEFS mean highlights this, with a very messy setup (T180): Euro high and Atlantic trough close to the UK. Yesterday, most later runs favoured an anti-cyclonic outcome. The op was close to the mean on the pressure charts:

This morning the op drops pressure in relation to the mean pressure:

May have picked something up, and has the support of the control, but not convinced yet. Especially with the ECM op and mean from yesterday's 12z showing a milder outlook:

Again there is a split in members so a nearer average, cooler regime is still on the table, rather than the warm op, though I suspect it will still be mainly HP dominated, but the further south the better to benefit. The CFS for May marries up with this:

So something settled and around average may be the call with the south benefitting more from the warmer interludes.

Edited April 26, 2013 by i'm dreaming of...

[Frosty.]

ECM 00z operational run still looks very promising at T+240 hours and is setting up an anticyclonic spell but before then looks mixed with some cold and showery days to come and just a couple of fine days, the ukmo 00z shows a few days next week with high pressure across the south. It also looks cool next week with slight frosts and plenty of heavy showers with hail and thunder. Today will see some big april showers across the uk and a 10c drop in tempeature for the southeast compared to yesterday but tomorrow it should be less showery with more in the way of sunshine, on sunday the weather will be turning unsettled from the northwest but the toppling atlantic ridge across the south could give southern areas a fine day with sunny spells after an early frost.

[Gibby]

Good morning. Here is the early morning report on the midnight output from GFS, UKMO, GEM, NAVGEM and ECM for today Friday April 26th 2013.

All models show a cold and showery Northerly flow over the UK today and tomorrow. A ridge of high pressure moves South over Scotland tomorrow and the South on Sunday killing the showers but giving a strong risk of overnight frost. Early next week a deep Low moves East towards Scandinavia to the North of the UK. A trough is shown to move SE on Monday carrying some rain and followed by bright and fresh NW winds and scattered showers, largely in the North where they could be wintry.

GFS then takes us through the midweek period with High pressure building across Southern Britain with drier and less cold conditions while the North continue to be affected by a Westerly flow in association with Low pressure to the North. Then through the holiday weekend showers look likely to develop as Low pressure becomes more influential from the NW with a windy spell developing in the NW. Temperatures by this stage wll be back to average levels for most in a SW breeze. Through the rest of this run the weather remains changeable with the Atlantic never really lying down giving some rain for all at times with some longer drier and warmer spells possible in the South.

The GFS Ensembles show a cold spell for 4-5 days from now before a steady warm up to nearer to average conditions look likely. there is a lot of spread towards the end of the run though with some unwelcome colder options shown balanced by some warmer ones too so some indecision shown. Rainfall amounts are fairly insignificant anywhere so a lot of dry weather seems likely.

The Jet Stream currently travelling from the west or NW over the UK weakens next week and breaks up in the vicinity of the UK with a new arm forming out of Newfoundland over the Bank Holiday weekend and a very much slacker flow drifting East over North Africa.

UKMO for next Thursday shows slack pressure over the UK with an upper cold pool creating a catalyst for heavy showers to develop over the UK through the day.

GEM today is not a pretty sight for those wanting a dry and warm Bank Holiday weekend as low pressure to or over the North is the driving force over the period with wind and rain or showers commonplace on all days over the UK out to the end of the run.

NAVGEM too is pretty poor with Low pressure sliding South over the UK late next week with heavy showers and suppressed temperatures the order of the day. Some of the showers under this setup would no doubt be heavy with hail and thunder likely in places on each daytime.

ECM finally leaves improvements to the UK weather until May Day itself (6th) with the previous days seeing the UK under the influence of shallow and showery Low pressure before a deep Low to the NW brings cloud and rain East across the UK over the weekend before warmer and more settled conditions arrive from the South just in time for everyone's return to work.

In Summary the outlook remains very mixed. The cool and showery weekend is still a certainty before a drier phase develops early to the middle of next week, especially in the south though frosts at night remain a threat until midweek. A more showery phase then looks to develop later next week UK wide as slack Low pressure meanders over the UK. The Bank Holiday weekend is not looking too special this morning from most of the output with Low pressure over or to the NW of Britain carrying rain bearing troughs and a breeze, at least across the North and probably the South too. Longer term GFS doesn't really kill the Atlantic off this morning while ECM gives us a beacon at Day 10 as warmer and more settled conditions develop from the South.

Edited April 26, 2013 by Gibby

[Summer Sun]

The ENS continues to support a pressure rise this morning

 

 

[Purga]

The warm dry spell is looking shaky this morning with the ENS showing more scatter in the longer term and some cold solutions more prevalent

 

The Op takes a dive at th end with a cool NWly

 

 

The means of both GFS & ECM supporting a cool / average temp & unsettled regime