Model Output Discussions 12z 08/03/17

[Summer Sun]

The ECM weeklies issued yesterday show temperatures recovering from next week after this week's chilly blip passes - week 2 of May has weaker signals for most of the country

Rainfall remains below average for at least another 4 weeks

Edited April 25, 2017 by Summer Sun

[Eugene]

GFS 06Z ensembles seem very keen on a greenland high towards the end of it's timeframe, ECM 00Z T+240 hrs backs this up big time too. 

[stodge]

10 minutes ago, Eugene said:

GFS 06Z ensembles seem very keen on a greenland high towards the end of it's timeframe, ECM 00Z T+240 hrs backs this up big time too. 

Indeed and so does GEM though the exact placing and orientation of the HLB isn't clear as yet. The key difference is sourced airflow - IF the HP sets up over Scandinavia the air is sourced from Eurasia and will probably be warm at this time of the year but if the HP ends up more to the north the air could be sourced from the Arctic - a kind of indirect Polar Maritime airflow and would be much cooler.

The key to this evolution is what happens at the weekend - IF the trough fails to break across the country, the HP sets up over Scandinavia but as GFS shows if the LP clears to the east and sets up over Denmark, the HP builds further to the west and the air comes from the Arctic.

[knocker]

A quick look at this morning's GEFS, EPS and last night NOAA anomalies. All are okay with the expected pattern change next week albeit with some detail disagreements. The GEFS is declining the east European ridge quicker than the EPS for example.

But they all agree more or less on retaining a fairly active vortex/lobe N. Canada with associated trough into the Atlantic but retrogressing the latter as the amplification downstream increases and the high pressure ridges N/NW in the North Sea area. Thus the UK is encompassed by a slack high pressure cell and becoming quite warm with temps above average but the usual temp and cloud caveats apply with an HP cell vis location The EPS has the surface centre just in the North Sea for example but this is obviously something the det. runs will sort. But still on course for dry and warm next week..

Looking at the later period it certainly looks like we may hang on to the high pressure for a few days. There are some changes upstream with the Canadian lobe/trough weakening and the Russian lobe/trough becoming more influential. This has the effect of shifting the ridging HP further west but the UK still under the surface high which will do likes wise so although the weather remaining dry the temps may well return to average. But to reiterate this is something the det. runs will need to sort but things not looking too bad.

Edited April 25, 2017 by knocker

[Frosty.]

It's increasingly looking like early may will see a change to warmer and settled conditions with high pressure becoming the dominant feature..so says the GEFS 6z mean..plus the latest MO update indicates very warm and fine weather at times next month..so the seasonal models (GloSea5 / Ec32) must be looking good for an early taste of summer next month..fingers crossed

Edited April 25, 2017 by Frosty.

[Frosty.]

The Ecm 00z ensemble mean is looking good too once we get into early May..hopefully leading to a warm / very warm and largely settled late spring with summer like conditions.

[johnholmes]

not forecasting but about the weather now

some wonderful cloudscapes now out to my east and NE, large Cb9 and type 3 along with towering Cu, less convective over and west of me at the moment

[Frosty.]

The good news is the Gfs 12z shows a marked change to warm anticyclonic conditions from next tuesday with temps soaring into the low 20's celsius during the second half of next week.

Edited April 25, 2017 by Frosty.

[Frosty.]

Good news from the GEFS 12z mean too, becoming warmer and anticyclonic during next week..I think we can look forward to a summery spell through early May..hopefully further ahead too!

[Frosty.]

The Ecm 12z also shows a marked improvement next week as high pressure builds in and temperatures respond, soaring into the 20's celsius..what a beauty!

Edited April 25, 2017 by Frosty.

[Longtimelurker]

Frosty, Warmer to the West and North if I'm reading that ECM correctly? That's unusual if so as it's mostly the opposite.

[I remember Atlantic 252]

2 minutes ago, Longtimelurker said:

Frosty, Warmer to the West and North if I'm reading that ECM correctly? That's unusual if so as it's mostly the opposite.

deepest FI no point in details yet, but if that May 4-5 chart comes off like that, then I'd expect western Scotland to have best weather, always a risk for my location, which is very prone to north sea mist, can linger all day, 

[Matthew.]

Please be right for +168 onwards ECM

[Frosty.]

23 minutes ago, Longtimelurker said:

Frosty, Warmer to the West and North if I'm reading that ECM correctly? That's unusual if so as it's mostly the opposite.

Yes you're right but it would be at least warm nationwide with very pleasant surface conditions with high pressure becoming centred over the uk..looks increasingly very nice after BH Monday.  

[Winter Cold]

ECM doesnt look as good as last nights though, the 850s I posted yesterday were higher than its showing tonight. The plume looks to be being deflected NW away from the UK on this run:

 

GFS also showing that next weeks warm up maybe temporary before a return to average. Just like this weeks few days of colder weather, next week may see similar the other way. A clear arc in the ensembles showing it may not last:

Typicaly the worst weather over the next few weeks looks like being the bank holiday with a large spike in the ppn graph!!!

[ANYWEATHER]

Good Evening All. After the unseasonably cold week , a rather unsettled blip this Bank holiday weekend  and a slight warm up is on the cards , The models show something of a ridge building in from the east Tuesday onwards , but whether we can warm things up a lot or little is open for question , but Im expecting a dry May as my forecast suggests in our local monthly magazine, and this looks in situ with model output. But with these conditions ,its too cold and too dry, so far for farmers and growers and the continuing prospective for  dry conditions may and is a concern for crop growers nationwide...

[Scorcher]

7 minutes ago, Winter Cold said:

ECM doesnt look as good as last nights though, the 850s I posted yesterday were higher than its showing tonight. The plume looks to be being deflected NW away from the UK on this run:

 

Well no, but last night's charts were truly sensational, I wasn't really expecting them to be showing again today. But the ECM has moved back towards a strong high pressure build this evening after a relatively disappointing run this morning. These are still excellent charts, particularly for the west of the country. 

It's still a long way off and the positioning of the high is far from certain- we could still see a more favourable position for nationwide warmth as we get closer to the time.

The good news to me tonight is that the models seem to be backing away from retrogression of the high which was being shown earlier.

[Winter Cold]

9 minutes ago, Scorcher said:

Well no, but last night's charts were truly sensational, I wasn't really expecting them to be showing again today. But the ECM has moved back towards a strong high pressure build this evening after a relatively disappointing run this morning. These are still excellent charts, particularly for the west of the country. 

It's still a long way off and the positioning of the high is far from certain- we could still see a more favourable position for nationwide warmth as we get closer to the time.

The good news to me tonight is that the models seem to be backing away from retrogression of the high which was being shown earlier.

True

Yes certainly the dry theme looks to continue except for these blips like the showers today and perhaps a little rain Sun/Mon but after that looks to be dry again. GFS seems to agree.

Even if it doesnt get very warm it still feels nice and pleasant in the mid-teens now if its sunny so I too am hopefull for some good weather in May

[Man With Beard]

Surprised the chart hasn't been posted yet!

Heatwave potential if it sticks in that spot (which it doesn't on this run) - I'm talking maxes 25C-28C. But a chance the high will drift NW with time.

[knocker]

EPS ens 850mb temps means and contours

[Frosty.]

Tonight's Ecm 12z ensemble mean will give those of us looking for an early taste of summery weather during early may a warm glow..it's looking increasingly anticyclonic next week and hopefully beyond.

Edited April 25, 2017 by Frosty.

[damianslaw]

Its the time of year when the atlantic traditionally settles into its spring slumber, and the outlook certainly looks non-atlantic dominated, a northerly followed by a slack cyclonic airstream over the bank holiday weekend (rather unfortunate timing - as the lengthy settled period looks like breaking down just in time for the weekend with rain for many), followed by an easterly to greet May, possibly becoming more of a northeasterly in time... with signs high pressure will retrogress to the NW, and low pressure settles to the SW (but far from certain). We could see more of a southerly feed next week which would pull in some very warm uppers for the time of year, nothing too unusual though with perhaps the NW the best spot for dry sunny conditions (again quite par for the course in May - when the east can often be plagued by sea fret and haar and low cloud with warmest conditions in the NW). 

The main headline is for a continuation of the lengthy dry spell bar a shortlived unsettled blip over the weekend. 

[MP-R]

Looks like quite a varied two weeks coming up in terms of airmasses - from the current Arctic maritime, to Tropical maritime over the weekend, Tropical continental mid next week and most likely Polar continental or even Arctic continental again thereafter. The overall theme, bar the Bank Holiday weekend, looks like a mostly dry one again. Don't know about other people, but this could well be my driest April on record depending on how much falls at the weekend.

GFS brings a brief warm spell next week with temperatures into the low-mid twenties for a few days but then a cool down to average or perhaps below as winds swing northeasterly to northerly - a pleasant change though to the howling westerlies and northwesterlies that so often plague May. ECM is broadly similar out to FI. I was hoping for a more convective easterly like last year but there looks the possibility in FI of a weaker version of what we have now with a slacker but possibly convective northerly.

Bar a few days next week, I wonder if this May will be similar to 2010, which was also quite dry for the main, but with a cool/cold first half and much warmer second half with notably high temperatures around the 20th-24th given such dry ground.

[Nick F]

Morning, not posted in a while. After the unseasonably cold snap this week, although I like cold and snow in winter when it hangs around, it seems a waste of a potent northerly in late April with the strong sun and longer days, though it did bring some dramatic convective skies, hail and even thundersnow for some. But I like many others are probably hunting for a nice warm up. Having spent 10 days on Easter hols recently in Spain with blue skies, temps in the low to mid 20s, getting some colour and vitamin D, it's been a bit of a shock.

The GFS was offering the low 20s for the middle of next week, but seems to have shifted temps downwards on the last few runs. The reason is the orientation of the high which seems to have shifted north and west on last few runs, so we get more of a cool easterly or northeasterly flow rather than light and variable winds. So temperatures not hitting 20s, rather mid to high teens at best. But should be pleasant out the breeze in the sun.

Yesterday's 12z run for 1500hrs next Wednesday:

Same time but from this morning's run, the high further north and west:

 

Edited April 26, 2017 by Nick F

[knocker]

The detail for the upcoming weekend is still a long way from being nailed on as it would appear to be the interval before a major pattern change.

This morning's gfs starts with the familiar picture of the weak ridge of the next two days giving way as the upper trough dominates the eastern Atlantic by 12z on Saturday resulting in this surface analysis which shows lows forming on the associated front lying to the west of Ireland. As can be seen the task of cutting off the cold northerly is complete and temps are back to normal.

From here it starts getting a tad complicated. The main trough in the Atlantic is reinforced by more cold air being ejected SE from the Canadian vortex/lobe (last throw of the dice). This results in a 'tongue' of the trough stretching east over the UK. On the surface this results in the aforementioned front swinging on it's axis and tracking north east across the UK  But at the same time a new low has formed in the circulation of the main trough and is over Lyme Regis by 00z on Tuesday bringing some more wet weather to the south, albeit one wouldn't expect a huge amount of rain from all of this.

It is at this point that the major pattern change gets under way with pressure building rapidly in the vicinity of the UK and the rough shunted further south in the western Atlantic. As ever it's a question of where the surface high sets up shop and the gfs this morning has it way north of the UK  thus an easterly flow with temps around normal

This morning's GEFS anomaly is broadly supportive of this scenario