Model Output Discussion - cold spell to end Autumn

[Cheshire Freeze]

Just now, tight isobar said:

Any anti-coldie..

Couldnt have picked this shortwave by hand and placed it better!

..

Distrupting the flow north...

And aiding a southerly feed!!!!

Comical!!

That's the UK and its weather for you-

It's why I always remain sceptical these days. Been burnt many times over.

I do get the feeling though that this next phase of weather i.e next week, will determine where we go long term. If this block fails then it could well let the westerlies return without much interference to the strat. The same happened last year where a Greenland HP episode failed- it set the tone for the rest of winter.

[Summer Sun]

ECM saves the day at the end for any long lasting cold it is charts like this we need to see with pressure down over Spain and Portugal much lower

 

[Derecho]

Afternoon, here is my interpretation of the 12z GFS, ECM and UKMO

Only interpretations upto T240 are made

So it seems (!) we finally have the UKMO on board!. This gives the opportunity for retrogression and I breathe a sigh of relief. At least until that spoiler shortwave appeared on the ECM!

GFS                                                          UKMO                                                      ECM

As mentioned earlier, two key things need to happen:

- The low in the central Atlantic needs to remain rooted
- Pressure to our south needs to be sucked up to Greenland like a vacuum

The GFS is again great as it sends WAA up to the west coast of Greenland, seriously disrupting the jet over North America, many recent cold winter months in the UK have seen notable warmth in these regions. UKMO would likely see something similar.

At T192 we build a stunning Greenland high and cold air inevitably moves down from the north, ideally we want to see lower pressure to our south to head into classic territory but it’s still really good, especially for northern areas. The ECM however cuts off the WAA somewhat and part of the high sinks into Spain. Leaving the UK potentially facing mild SW'lies but we still have a strong Greenland High to fend them off.

Such an outcome though leaves the risk of a west based -NAO so hopefully we can avoid it.

GFS                                                           ECM


At T240 with the GFS, we see an incoming low threatening to bring a snow event to the UK. The potential for a channel low is a big advantage of these setups though the ECM shows how it can go awry, so best to stay grounded yet again for a little while. Despite this the Greenland high wins on this one.

GFS                                                          ECM

In summary it is very pleasing to see the UKMO fall in line, hopefully we will see Newfoundland hit by mild easterlies to lock blocking into place and avoid heights to our south. If we do this could be a superb cold spell but still a long way to go.

Here are the ratings

UKMO 8/10 snowflakes – Upto T144 falling in line with the others an potential thereafter
GFS     8.5/10 snowflakes – Impressive heights over Greenland with cold waiting to our north
ECM  6.5/10 snowflakes – Still produces a cold outcome in the medium range but we would be treading a fine line if that shortwave pops up in the future!

[bluearmy]

The behaviour of the lows is not going to be correct at this range so the micro scale is unpredictable 

however, looking at the 00z spread and current op tells you that the upper ridge placement is predictable from run to run

  

 

  

 

[tight isobar]

Well its gets through and we are back in the game...

A very knife edge run...

But still makes the waa evolution...

So much to be resolved-yet-

[Cheshire Freeze]

1 minute ago, Summer Sun said:

ECM saves the day at the end for any long lasting cold it is charts like this we need to see with pressure down over Spain and Portugal much lower

 

It's a horrid run Gavin.

Ends with a mid latitude feature rather than anything high latitude based.

[Dean E]

ECM paints a different picture tonight compared to last night, we do get back into the freezer by +240hr but its a messy route and one I'm not liking.

As @CreweCold and others have been mentioning, the sheer resistance of heights over the Mediterranean is a big danger for our winters currently. Unit I see lower heights pushing into that area, everything is on the table right now. 

[karlos1983]

It’s almost as if all routes lead to Rome, just when it looked like there was no way back on the ecm at 192, staring down the barrel of south westerlies, and we end up with this.

[Frosty.]

Was i worried??? Nah

[Paul_1978]

6 minutes ago, Zakos said:

very encouraging from the ECM

 

16 minutes ago, karlos1983 said:

Eeesh, dreaded west based 

 

10 minutes ago, Had Worse said:

Wow.

Freezer to Sauna in 12 hours. 

Such a range of opinions and emotions!

Edited November 27, 2017 by Paul_1978

[Dean E]

1 minute ago, Paul_1978 said:

 

 

Such a range of opinions and emotions!

Basically don't look past +192hrs for now and if you do, take it with an incredibly small pinch of salt! 

[karlos1983]

1 minute ago, Paul_1978 said:

 

 

Such a range of opinions and emotions!

Well It was a bit of an up and down ecm to be fair. I’m not one to sit and wait, never been a virtue of mine. 

Plus the stakes are pretty high... I don’t see the problem. Just comentry 

[mulzy]

Just now, Dean E said:

Basically don't look past +192hrs for now and if you do, take it with an incredibly small pinch of salt! 

Why 192 hrs?  Take everything after 120 hrs as JFF.  Having said that we have all been burnt within the 120 hrs mark!

[frosty ground]

I mentioned this morning about that low cutting through causing issues and 12 hours later it' already proven correct for this run at least.

 

[Paul_1978]

4 minutes ago, CreweCold said:

It's a horrid run Gavin.

Ends with a mid latitude feature rather than anything high latitude based.

Weren't you wanting low heights to the south a few minutes ago? You have low pressure over Portugal and Spain there.

[nick sussex]

The ECM is saved because we don’t see a west based neg NAO , the high cell is forced east which helps force the pattern se.

I hope tonight’s ECM goes some way to explain why regardless of earlier outputs the CSAC Cold Synoptics Action Committee unanimously voted to keep a Code Red advisory in action ! 

Edited November 27, 2017 by nick sussex

[ACCOUNT DELETED]

13 minutes ago, Ryerson said:

The JMA isn't great either.

I'd take this high pressure over wind & rain any day. If we can't have snow, I'll settle for dry & mild personally myself  

[ArHu3]

Just now, mulzy said:

Why 192 hrs?  Take everything after 120 hrs as JFF.  Having said that we have all been burnt within the 120 hrs mark!

168h verifies 3 out of 4 times (according to ecmwf themselves)  but it's quickly downhill from there 

[blizzard81]

3 minutes ago, karlos1983 said:

It’s almost as if all routes lead to Rome, just when it looked like there was no way back on the ecm at 192, staring down the barrel of south westerlies, and we end up with this.

If anyone is fearing a toppler after day 10, I would advise caution. I don't believe we would suffer one as the low off the US eastern seaboard travels northwest back towards the US coast between day 9 and 10. 

[Dean E]

1 minute ago, mulzy said:

Why 192 hrs?  Take everything after 120 hrs as JFF.  Having said that we have all been burnt within the 120 hrs mark!

Yeah I think that is the better assessment, Clearly all this model reading is making me forget time scales! 

[Frosty.]

The Ecm 12z snatched victory from the jaws of defeat in the 3rd minute of injury time!

[Cheshire Freeze]

1 minute ago, Paul_1978 said:

Weren't you wanting low heights to the south a few minutes ago? You have low pressure over Portugal and Spain there.

Having low heights to the S is a basic requirement but not guaranteed to produce the goods for the UK. You need a decent upstream profile too. The ECM day 10 chart isn't bad, but the core of blocking heights are mid Atlantic to our west- they need to be further N for anything sustained. 

Also pertinent to point out that the ECM sees us chasing synoptics at days 9&10 now...whereas the spoiler is days 6-8.

[Zakos]

2 minutes ago, karlos1983 said:

Well It was a bit of an up and down ecm to be fair. I’m not one to sit and wait, never been a virtue of mine. 

Plus the stakes are pretty high... I don’t see the problem. Just comentry 

I agree with you mostly.

I think paul is right in a sense though that many posters are overreacting to each and every model run.

Just because a run shows mild weather, that has no effect on the weather itself, and there is nothing to say that it will not swing back to showing cold weather on the next run.

 Ive seen cold spells appear out of nowhere at 96 hours, sometimes less. i personally feel that you really shouldn't pin too much hope on any output beyond 144, as you will suffer in the long run..the models love to tease!

plus, the end result on the ECM is still a significant cold shot. all to play for IMO.

[comet]

8 minutes ago, Frosty. said:

Unbelievable in here, you would think this week is going to be mild but it certainly isnt!.. The Ecm 12z indicates, windchill, frost, ice and Snow in the reliable timeframe!

 

 

Yes it is going to be rather cold to cold with some lucky locations seeing snow but it is a long way from a big freeze. Even on the coldest days to come IE Wednesday to Friday any lowland snowfall over England will not hang around for long with max temps of 3 or 4c, Having said that the charts and the weather are 100 times more interesting than what we have seen the last few years and of course there is a real possibility of a potent cold spell (perhaps freeze ) in the not to distant future.

[knocker]

A look at the ecm through the week.

At midday tomorrow the low is over Denmark with the front that brought about a lousy day in these parts today  lying across central France. To the west the high is centred south west of Iceland with some ridging NE and thus the wind has a north easterly component over Scotland with snow showers. Elsewhere a northerly flow with wintry showers along the coast.

Twenty four hours later the high cell is south of Iceland as the low to the east loses it's identity with the UK still in the cold northerly regime, Wintry showers in Scotland but pretty dry elsewhere albeit cold with max temps around 4-5C generally in England and Wales and only 1-3C in Scotland

Thursday midday see the high starting to ridge north east across the Faeroes which reactivates our low somewhat which drifts back into the eastern North Sea which initiates an onshore flow across the east coast a a front which could well produce some fairly significant snowfalls spreading inland. Temps generally only around 3C in England but 8C in God's Little Acre.

Overnight Thursday and into Friday morning the low drifts south west into Holland which introduces strong NE winds and the possibility of some significant snow to the south east.with some negative dew points around. By 1800 Friday this should have cleared and by Saturday 00 the ridge is extended over the UK with energy whipping around the top.

Over the weekend the high continues to deflect any troughs to the north east and also the colder air so by Sunday lunch time temps are back to around average .

The UK remains under the influence of the high during the beginning of the week but by Tuesday 12 things are getting not a little complicated so best left there for the moment but just to mention energy has slipped under the ridge.

.

The aforesaid energy

 

 

 

Edited November 27, 2017 by knocker