Model output discussion - after the beast, what next?

[Leon1]

16 minutes ago, Summer Sun said:

06z GFS getting the milder air a bit further north early next week

06z

00z

I just want that red bit to come up to us then it'll be pleasant. Cold or warm at this point I don't mind which one.

[stodge]

Morning all

Considerable divergence in the output at even quite short ranges yesterday suggesting lack of clarity in extremis. Both colder and milder options in play yesterday and plenty to suggest the battle between colder and warmer air masses was intensifying with the British Isles pretty much in the line of fire.

With such large differences in the output, the medium range analysis should, in all honesty, be considered with an even larger bucket of salt than usual but perhaps the trends are what we're really looking for. Yesterday GFS continued its signal for warmer and more "typical" conditions going into April with the jet moving back north and the Azores HP coming into play while both ECM and especially GEM kept the winter/spring battle going well into the new month.

Today's analysis takes us to Saturday April 7th and for a change we'll start with the GFS 00Z OP at T+240:

A much colder outlook from GFS for Easter and beyond this morning. The immediate post-Easter period sees first an E'ly and then a N'ly but by T+240 signs the Greenland ridge is easing but LP remains close to the south of the British Isles and with -8 uppers and a chilly NE'ly breeze it will still be a long way from spring for southern Britain. Further north and north west an Atlantic ridge promises drier weather under lighter winds.

Further into FI and there is a rapid transition to much warmer conditions. The Atlantic returns but as the trough approaches the British Isles heights to the east cause it to disrupt to the north and south leaving the British Isles in a mild if not warm SSE'ly flow with dry conditions to the east but less settled and often wet weather for western parts.

GFS 00Z Control at the same time:

The Control is also unsettled and cold through much of Easter but by this time the cold is starting to ease as the LP drifts SW into Iberia and fills and a ridge from the Azores moves up and over the LP and across the British Isles so by this time dry and settled for most but a risk of night frosts. Further into FI it remains settled with HP close to or just to the east of the British Isles but not really advecting any significantly warmer air.

The ECM 00Z OP at T+240:

Strangely, it looks very similar to the GFS 00Z OP at the same time (see above) but the journey there is very different. To be fair, ECM has hinted at a mini warm up on Easter Monday but the warms nap quickly gets displaced by returning colder air and essentially that is what happens. As the post-Easter LP approaches it slows and forces warmer Southerly air over the British Isles in advance of its arrival while the GFS this morning doesn't have this "gap" between the LP systems and maintains the colder air in situ. By T+240 the LP is still to the south with a chilly NNE'ly flow over eastern and southern parts but lighter winds to the west with a ridge of HP moving in from the Atlantic.

GEM 00Z OP at T+240:

Having been the coldest of the model output so far this week, GEM signals an end to the colder weather with a ridge from the Azores HP and a positively aligned trough so a return to more normal conditions with SW'ly winds. It may just be a matter of timing and GEM may be more progressive than either GFS or ECM in a return to Atlantic conditions on or around the second week of April.

Back to the GEFS 00Z at T+240:

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

A mixed bag as you might expect but overall colder than Tuesday's equivalent and a significant group bringing E'ly winds over the British Isles. Some milder Members too it has to be said.

In summary, a degree of turn round and a degree of model alignment this morning. GFS was the mildies' friend yesterday but it's the coldies' friend this morning with a prolonged spell of cold and unsettled weather likely through and beyond Easter with winds from the east or north and a clear risk of snow for northern hills and perhaps some transient snowfall for lower ground as well. ECM handles the LP differently so there's a brief warmer spell around Easter Monday while GEM keeps the LP over rather than to the south of the British Isles so unsettled yes but not as cold as GFS.

All three models show the cold easing at the end of next week - the long influence of the Greenland HP is waning and heights are starting to come NE from the Azores. Now, that offers two alternatives, either a return to a traditional pattern of LP to the NW, HP to the SE and SW'ly winds or, as GFS Control suggests, an MLB setting up close to the British Isles. The UKMO longer term forecast suggests the latter as a possible option so fine days but frost and fog at night and slowly rising temperatures. That's all a long way off and at the moment we have to see the end of the cold pattern come into the hi-res and I'm reminded that in 2013 the models persistently and consistently showed an end to the cold pattern but only in low-res.

As ever, more runs are needed.

 

[Summer Sun]

GFS 06z is certainly a milder run for the south compared to the 00z still hanging on to the colder temps further north

06z

00z

Some parts of Wales are at least 9c warmer on the 06z than they were on the 00z

Edited March 28, 2018 by Summer Sun

[frosty ground]

2 hours ago, bluearmy said:

Karl - a couple hours of wet snow ? Is that what people are chasing ? 

I dont think so

a snowfall where you can go for a tramp or build a proper snowman - otherwise I’m not sure it’s of any note.

anyway, I still maintain that current modelling shows away from elevation (and Scotland) that there is little to be excited about. 

I don't know what people are chasing at the end of March.

The only person that mention the ability to build snow men is you, you are arguing against your own comments.

The fact remains there is a possibility of snow, that's what the models show, of course it may only materialise over northern scotland and over the higher hills, but you dismissed it out of hand, and to justify it you made a point to argue against something that no one had mentioned. 

[Eastnorthwest]

Honestly, in all the years I've been model watching i don't think I've ever known them to change so freaklently as they do these days and currently only up to 3 days out ,I wouldn't mind betting the next GFS run puts us back into the colder side of the border line by Easter 

Fascinating in a way and I wouldn't right off a white Easter till Friday at the mo

[Man With Beard]

Couldn't get to the weather models yesterday - just shows you can't stay away from the charts for long! The D5 and D6 charts this morning look a not insignificant risk of snow events in the north, but I would argue that the set-up does not allow southerners to put away the sledge either:

   

In my opinion, the UKMO and ECM charts are the type that could possibly see more of a northerly influence than is currently shown. The UKMO could well pull colder air down from the north as the low moves through the UK. The ECM, and possibly even the GFS, could see a wedge of heights form from the UK towards Greenland.

So northern areas are already at risk of seeing snow between D6 and D9 - but southern areas, whilst not really being borderline, are let's say bordering on being borderline

However, the possibility of warmer conditions between D10 and D15 looks to have survived since I last looked 48 hours ago:

  

It's the clusters with the straight lines up from Europe towards Scandi that suggest a flow from between the W or SSW. Sure, not total agreement, and clusters remain that keep the UK trough dominated, or even under an easterly influence (not sure an easterly from this would be significantly cold). 

Overall, I'm placing my bets on sledging incidents next week (probably north of Manchester but possibly a surprise north of the M4 event?!?) and then warmer weather the week after.

Edited March 28, 2018 by Man With Beard

[stodge]

45 minutes ago, sebastiaan1973 said:

I wonder what the impact will be of the reemerging MJO in the Western Pacific. The composites show high pressure in the Atlantic west of the British Isles and phase 8 around Greenland. 

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/mjo/composite.html

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/foroper.shtml

Indeed, yesterday's forecast hinted at a 7-8-1 progression starting now which would perhaps explain the colder signal in the GFS output this morning. However, all the models are hinting at a return to a more traditional pattern during the second week of April so perhaps the progression will be quite quick. OTOH, the models may simply be playing the "default" game in lieu of a stronger signal. I wonder if Phase 2 or 3 in April would support an MLB close to the British Isles.

[Summer Sun]

Cracking end to GFS with higher pressure building to our east allowing the door to open to warmer southerly air 

[Eastnorthwest]

4 minutes ago, frosty ground said:

I don't know what people are chasing at the end of March.

The only person that mention the ability to build snow men is you, you are arguing against your own comments.

The fact remains there is a possibility of snow, that's what the models show, of course it may only materialise over northern scotland and over the higher hills, but you dismissed it out of hand, and to justify it you made a point to argue against something that no one had mentioned. 

Anything is possible according to GFS recently from  heavy rain to blizzards, to below average temps to the edge of the first Spanish  ploom of the season fascinating if you think about it ,no one would bet their house on it ,I know I wouldn't ,easier winning the lottery than forecasting the weather at the moment 

[frosty ground]

12 minutes ago, Summer Sun said:

Cracking end to GFS with higher pressure building to our east allowing the door to open to warmer southerly air 

Looks colder than the run from yesterday.

[Summer Sun]

After viewing the 06z it comes as no surprise to see the 7-day trend turning warmer from a line around north wales south still a bit below normal in the north

The first hints of the milder air arrive early on Easter Monday in the southwest

Edited March 28, 2018 by Summer Sun

[Eastnorthwest]

25 minutes ago, Summer Sun said:

After viewing the 06z it comes as no surprise to see the 7-day trend turning warmer from a line around north wales south still a bit below normal in the north

The first hints of the milder air arrive early on Easter Monday in the southwest

2 gueses what the 12Z will show ,either colder or much the samey, I'm going for colder ,who's with me?

[Eastnorthwest]

Will be interesting to see the latest AO update this afternoon from what' it's showing now which is diving into negative again

[mb018538]

Whatever happens, it doesn’t look great for the next 7-10 days. Plenty of unsettle weather around....and as usual, when we don’t want a southerly tracking jet we get one!

[Purga]

42 minutes ago, Summer Sun said:

After viewing the 06z it comes as no surprise to see the 7-day trend turning warmer from a line around north wales south still a bit below normal in the north

The first hints of the milder air arrive early on Easter Monday in the southwest

Wishful thinking..... no not SS... never....

[Summer Sun]

22 minutes ago, Purga said:

Wishful thinking..... no not SS... never....

Do those Climate Outlook maps update for the 06z and 18z or just 00z and 12z?

[stodge]

Afternoon all

It's the reverse of what generally happens in winter. There's an E'ly or a N'ly in low-res and some people get excited because it's the weather they want but it stays in low-res so we get the eye candy T+276 or T+324 charts which look wonderful but which don't materialise.

Now we get some individuals talking up warmer charts in low-res but in truth the 06Z OP isn't much different from the 00Z OP.

The 06Z OP at T+234:

The 00Z OP at T+240:

Minor differences at best. The signal for a change to a more traditional weather type is still a long way off in low-res. Yes, it will get warmer at some point - it's called spring and it happens most years - but whether that is via the Atlantic or via a suitably-placed MLB is much less clear.

[Summer Sun]

Easter day currently looks like it will be mostly dry but the odd light shower can't be ruled out but on the whole plenty of usable weather even if the temps are on the cooler side of normal

Later in the day, we see a more substantial band of rain moving into the south-west this slowly moves north and there is the potential for this to turn wintry into Easter Monday as it moves out of Devon and Cornwall into the colder air 

[phil nw.]

Yes it's that time of year where the weather is topsy turvy over the Uk.

As the Polar vortex starts to shrink and split around this time of year we can get an undulating jet across mid-latitudes,often across the Uk, as the current models show.

GFS 06z op.

 

The following are from the latest gefs 06z set.

Day 5/10 means

so we see an ongoing battle between the polar and sub-tropic air streams with often quite cold temperatures and Winter hanging on in the far north but signs of warmth on some days further south.

A look at the 2mt.average temperatures expected in 3 locations,north to south underline this.

It must be said none of the above are showing any notable warmth as yet.

Needless to say It promises to be quite a changeable and sometimes quite cold andwet period as lows continue to track across or near the UK whilst this battle continues to be fought.

The London rainfall graph

showing an upward trend during the coming 2 weeks,although it's fair to speculate there will be some days of brighter and drier weather across the country between the bands of rain and showers with just a hint of some improvement in week 2 on the pressure ens.

 

[Derecho]

 

Block to the NW looking stronger to our NW on the 12z GFS, this may keep the easter weekend drier, but it could make things colder later on. Or the high could sink over Central Europe

[SMU]

UKMO 96 120 is a dont look now if you like Spring....

WOW...

[Leon1]

Just now, Steve Murr said:

UKMO 96 120 is a dont look now if you like Spring....

WOW...

why?

[Summer Sun]

UKMO 12z has cold air spreading to all parts from Saturday

GFS 12z has milder air pushing into the southwest on Monday

Edited March 28, 2018 by Summer Sun

[cheshire snow]

Snow from the South Midlands Northwards Monday according to the GFS12z

As SS posted above less cold air getting into the far SW On Monday

C.S

Edited March 28, 2018 by cheshire snow

[reef]

The reason the GFS is milder is that it winds up the low to south-west much more than the UKMO, which sees it weaken and sink southwards. I wouldn't be surprised if there is quite a spread on the GFS ensembles at this range depending on how this low deepens.

The models are notoriously poor at forecasting lows approaching from the south-west so it might be a few more runs before its more concrete, even at this close range.

Edited March 28, 2018 by reef