Model Output Discussion - 18z - 25th Nov onward

[nick sussex]

MattHugo on twitter highlighting that he expects the 96 and 120 to be modified from the UKMO after discussion- probably negatively

Thats very strange, indeed theres more support for the UKMO tonight at especially 96hrs than there was last night so I'd be surprised to see them do that.

In terms of the 120hrs they might modify that but I can't see them going with the ECM probably a middle ground solution.

UKMO forecasters are well aware though of the fallibility of ensembles regarding undercutting scenarios, its bad enough for the operationals at their higher resolution.

[Weathizard]

To me, ensembles are useless in scenarios like this, I know people say to look at them, but in a lower resolution in this undercutting scenario they are pretty much useless, I haven't looked at any for days, I just hope we get the GFS on board tonight, would take a big back track but something has to give sooner or later surely.

[Gibby]

Good evening. Here is the evening look at the 12z output from the big three tonight and a hint of what weather could be expected from the charts if verified.

All models show Low pressure over Eastern England moving gently East into Europe with an increasingly chilly and breezy Northerly flow blowing down over the UK for the remainder of the week. Tonight will see rain at times over England and Wales with a band of somewhat more persistent rain over Northern Britain and North Wales slipping South to other Southern areas overnight. Scotland will be drier, colder and clearer with some showers around Northern and Eastern coasts. As the week progresses these will become more wintry over the higher hills a little way inland from the coasts. After a breezy spell midweek winds will decrease late in the week and through the weekend with frost and freezing fog becoming problemmatical later making it very cold in places where it doesn't shift through the days.

GFS then shows the Atlantic revving up early next week spilling milder air East ahead of which will be a band of rain and hill snow in the North. Through FI tonight the operational shows a classic case of a High to the South and Low to the North pattern with rain at times, heaviest in the North and West while the best of drier and brighter weather is focussed more towards the South and East in breezy conditions with near normal temperatures. Later in FI the weather starts to turn colder in the North as Low pressure shifts to the East with Northerly winds gradually seeping South towards the South by the end of the second weekend. At the transition point rain could turn to snow and be followed anyway by a cold Northerly wind and snow showers to Northern and Eastern areas in a very cold and wintry NE flow to end the run.

The GFS Ensembles show that the mean for the run stays below the long term mean throughout the run. The operational was both a mild then colder outlier in the second half of the run for the South. After a drier spell this week it shows a return to unsettled conditions with rain at times and no doubt snow over the hills.

The Jet Stream shows a North to South flow over the UK resulting from a ridging North of the flow through the Atlantic recently. The flow breaks down eventually and relocates on a West to East flow South of the UK as we move into next week.

UKMO for midday on Sunday tonight shows an Arctic High north of Norway with Low pressure close to the SE while an Atlantic trough is inching in towards Western areas of the UK as it's energy transfers SE into the cold air. The weather would be cold and bright for many on Sunday with wintry showers of sleet or snow across Eastern Britain. Elsewhere freezing fog could be a big problem in slack winds failing to clear through the day. Cloud would be moving over the top of the cold air with the chance of some frontal boundary snow in the day that follows.

ECM shows a rather different picture to UKMO as a ridge moves into the UK from the West at the end of the weekend with fog and frost aplenty before cloud and rain moves in early next week in association with Low pressure smashing through the block from the NW. It then transfers to Scandinavia later next week. the weather would turn unsettled with rain preceded by snow briefly on the hills with a short milder interlude following before cold and showery NW then North winds return later with wintry showers for all areas with frost again by night. The run ends with a flattening of the pattern with Atlantic westerlies and spells of rain taking over from the colder conditions on Day 10.

In Summary there is still deadlock between the models tonight with UKMO holding firm on its cold feed from the North penetrating into next week with an Atlantic battle becoming possible by Monday. GFS and ECM show the Atlantic breaking through the block relatively quickly, albeit a transitory phase as cold and unsettled weather eventually returns, quite quickly from ECM but much less quickly from GFS. The solution of this war will continue to be fought over the coming days as the models handle new day by day data. My own thoughts are that cold weather once established can prove difficult to budge and I wouldn't be surprised if there are still big differences between the models at the end of this working week. The one thing that is certain there is strong signals for a much drier phase than recently over the UK to enable the flooded field and river catchments to drift down to more normal levels.

[Mark Bayley]

I would say that there is a hint of MJO phase 2 in those forecasts as well, Mark.

Perhaps a blend of both is the right mix.

<Snip>

Yes, more notable on the UKMO and ECM forecasts

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

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

Although taking the three as a whole i would perhaps lean more towards phase one. Interesting outlook none the less as we head into the December though. I'm eagerly awaiting GPs winter forecast!

[John Cox]

This maybe the case for western areas and Ireland however for the east, north east, and south east, A battleground type situation seems the form horse to me. These situations have the potential to bring very large snow events to where ever the battle takes place usually the further east the better.

To add i am not disappointed at all with the evening runs still things are very much unresolved and in the balance. If we do see a breakthrough from the atlantic do not be to downbeat as it is very likely that the cold will return before you know it.

Thanks London-snow

Yes, you are correct when it comes to us here in the west. I am jealous of you guys/gals in the SE of the UK. The continental influence is with you and as you say, very interesting cold/mild battlegrounds might occur with subsequent snowfall for your areas.

I hope you are right about the return of the cold generally

[bluearmy]

Exeter will modify the faxes based on the ecm 12z ens (which matt hasnt seen yet) and the latest mogreps ens.

jma shows one end of the spectrum, gfs the other. It will probably be somewhere inbetween.

[ukpaul]

Thats very strange, indeed theres more support for the UKMO tonight at especially 96hrs than there was last night so I'd be surprised to see them do that.

In terms of the 120hrs they might modify that but I can't see them going with the ECM probably a middle ground solution.

UKMO forecasters are well aware though of the fallibility of ensembles regarding undercutting scenarios, its bad enough for the operationals at their higher resolution.

Forecasters are like pollsters, they don't want to stand out too much just in case they are wrong and their reputation takes a hit. It's not so much a reflection of what might happen but what degree you can safely be away from what others say might happen.

They are both crunching numbers with an enormous amount of variables, sometimes like a few of the pollsters with the biggest reputation in the US elections, their assumptions turn out to be just plain wrong.

[london-snow]

Regarding Matt Hugo and his comments regarding the UKMO. He would say this because most models are going against the UKMO. If i was Matt Hugo and i knew that a lot of people was following him and hanging on what he says then i would keep those thoughts to myself until he is 100% confident in the pattern going forward in which case if he is fair enough but its the weather and it has ways of biting you in the back side.

Goes back to my earlier thought - How many times since data became available have we seen a developing situation as we are seeing now before us.

I think back to the 80s when the data available today was not there and cannot think of any other situation before then.

lets await the fax for this evening going to be very interesting viewing.

Edited November 26, 2012 by london-snow

[Andy Bown]

So many posts hanging on what the models are showing beyond T120. We can bet our bottom dollars that come T120 it will be nothing like what is shown.

5 or 6 days ago T120 for today was showing the current LOW sitting just to out South with a brisk ENE flow and fronts lingering over Southern Britain while the Northern 2/3rds turned much colder and drier. Gibby's updates for several days said virtually the same for the South.

And now that timescale has arrived the LOW is exiting to the East, not the South, and a Northerly flow is developing bringing largely dry and cold conditions nationwide - even in the areas that 120 hours ago were seemingly going to stay under frontal rain.

[Isolated Frost]

72 fax compared to yesterday's 96 fax has introduced a shortwave by west norway, and pulled the trough northwards- more in line with the GFS and UKMO- expect the FAX to go accordingly and the north-easterly turn into a more faint northerly with less shower activity and notably less uppers with a nearby trough-

[nick sussex]

The latest CPC charts look unsettled and cold with troughing and positive anomalies to the north and nw.

http://www.cpc.ncep....10day/500mb.php

This snippet from their discussions is quite positive.

THE AO INDEX WHICH RECENTLY HAS

BEEN NEGATIVE IS FORECAST TO APPROACH ZERO BY DAY 7, BE NEGATIVE AT DAY 10, AND

REMAIN NEGATIVE THROUGH DAY 14.

We just need to get through days 7 to 10 with some trough disruption to the west and any snowmen might not turn into puddles!

Edited November 26, 2012 by nick sussex

[chris55]

Exeter will modify the faxes based on the ecm 12z ens (which matt hasnt seen yet) and the latest mogreps ens.

jma shows one end of the spectrum, gfs the other. It will probably be somewhere inbetween.

Sensible conclusion Nick. (but come on UKMO and JMA whoop whoop)

[Isolated Frost]

Latest CPC 500mb update-- continuing the expectation of ridging by svalbard- but the trough moves into Germany at this juncture- and north/north-west winds feed into the UK- not north/north-east..

Next update says no to the PV again-

[UV-RAY]

The latest CPC charts look unsettled and cold with troughing and positive anomalies to the north and nw.

http://www.cpc.ncep....10day/500mb.php

THE AO INDEX WHICH RECENTLY HAS

BEEN NEGATIVE IS FORECAST TO APPROACH ZERO BY DAY 7, BE NEGATIVE AT DAY 10, AND

REMAIN NEGATIVE THROUGH DAY 14.

We just need to get through days 7 to 10 with some trough disruption to the west and any snowmen might not turn into puddles!

I always struggle to read these Nick I guess it's all those squiggly lines, could you break it down for me please. Where is the troughing? Edited November 26, 2012 by Seven of Nine

[JCP]

MattHugo on twitter highlighting that he expects the 96 and 120 to be modified from the UKMO after discussion- probably negatively

I bet he's wrong. Why would they modify it, when they didn't last night?

If anything the UKMO has more support for the 96/120 time period than it did last night.

I don't understand the obsession with his tweets tbh.

Edited November 26, 2012 by JCP

[Frosty.]

Frosty didnt we have same situation in feb this year where the Atlantic bumped into cold air we got a load of snow where i am good few inches sorry for going off topic

Yes I believe we did, it would probably be more marginal this time but forecasting rain/snow could be knife-edge at the weekend, more chance if fronts stall and then get pushed back west but it looks a cold weekend to me.

[nick sussex]

I always struggle to read these Nick I guess it's all those squiggly lines, could you break it down for me please. Where is the troughing?

They're showing positive and negative anomalies, positive red higher pressure, negative blue lower pressure. I agree they can give me a headache!

[Methuselah]

I bet he's wrong. Why would they modify it, when they didn't last night?

If anything the UKMO has more support for the 96/120 time period than it did last night.

Maybe because things have changed, over the past 24 hours?

[liam300]

I bet he's wrong. Why would they modify it, when they didn't last night?

If anything the UKMO has more support for the 96/120 time period than it did last night.

NOGAPS looks in support for it also.

[SMU]

I bet everyone a sportsman £1 that the UKMO dont modify the output to ECM

S

[UV-RAY]

They're showing positive and negative anomalies, positive red higher pressure, negative blue lower pressure. I agree they can give me a headache!

Thanks Nick.

[Troubleatmill]

MET forecast Cumbria for 1-12-12

Saturday

Cloudy conditions on Saturday with low temperatures and snow falling mostly in the eastern fells at first, becoming more widespread and heavier later. Winds will be fairly light. Freezing level around 300 metres.

Ian

Sharp edge on Blencathra saturday!....should be fun getting up Foul crag!

[cooling climate]

Fantastic synoptics from the UKMO and still the model to follow.

The other big two are slowly, slowly coming back in line with the UKMO in the

five day outlook and with the UKMO being so solid in its output I am sure we will

see this trend continue.

The JMA run is a beaut and shows the possibility of what could transpire further

down the line although it is more fallable than the big three.

[Frosty.]

oh well, its deja vu again, 00z again will be crucial we took 1 step back last night and today we took 1 forward thanks to ukmo 00z and 12z yet again, I wonder how many more times it can rescue the situation.

[Isolated Frost]

I bet he's wrong. Why would they modify it, when they didn't last night?

If anything the UKMO has more support for the 96/120 time period than it did last night.

I don't understand the obsession with his tweets tbh.

Well at 72, you can see the movement of the shortwave nr w norway indicating that a more watered down n'ly should be expected a la GFS...