Model Output Discussion - 05/01/2016 18z onwards

[rory o gorman]

13 minutes ago, summer blizzard said:

Pressure is far too high. You'll struggle to get any precipitation at all above 1030mb and really you want sub 1020mb.

Not a very good way of reading convective precip I'm afraid . SST's are near 10c in that location and 500mb heights approaching -30 . I don't even need a Skew-t to tell me there will be adequate ML  CAPE for convective given the lapse rates.

P.S Dublin Ireland had thundersnow in 2009 with pressure about 1025 Hpa, if memory serves correctly. 

Edited January 6, 2016 by rory o gorman

[bluearmy]

The ecm parallel retrogressed the Atlantic ridge North days 8/10 and pretty well linked up to the Arctic high to form a mega block to our west

steves 552 dam making it into se Greenland by day 10

all conjecture from an op at that range but at least  an ecm op of sorts more in line with the ens

[captaincroc]

Just a question for the experts.... I know the weather can technically go 'tits up' at any time but at what time scale can we safely say that 'something' is going to happen?  To my untrained eyes I take it that if the Greenland block appears then some sort of cold weather will come (with more specifics nearer the time).

Was just wondering when we can be sure of this pattern change? 

 

Cheers

[Zerouali lives]

Amazing looking 06z on the GFS - reminds me of March 2006 when we had a foot on snow in low lying Aberdeen city centre courtesy of a 5 / 6 day northerly

[summer blizzard]

6 minutes ago, rory o gorman said:

Not a very good way of reading convective precip I'm afraid . SST's are near 10c in that location and 500mb heights approaching -30 . I don't even need a Skew-t to tell me there will be adequate ML  CAPE for convective given the lapse rates.

Possible and of course there are micro things to bear in mind but in my decade on here i've only really seen one cold spell deliver reasonable snow on a widespread basis with such high pressure values (Feb 12) so while some locations may get lucky i suppose that it's my mental guideline. I only really look deeper if the dam and pressure vales check out.

Edited January 6, 2016 by summer blizzard

[Day 10]

The gatekeeper has finally gotten off his stool, turned the key to the lock and flung those Arctic flood gates wide open

Edited January 6, 2016 by Minus 10

[Snowboard Tennyson IOW]

Momentum seems to have built from a few days ago, cold looks to be upon us from early next week. Noticeable temperature change down here already, nice to see day time single figures but want daytime low single figures next week please!? If 850s are -10 then that will mean very low daytime temps.  The ground is still warm so a week or so of cold followed by some battle ground action through the channel would be spot on. 

[Rocheydub]

12 minutes ago, rory o gorman said:

Not a very good way of reading convective precip I'm afraid . SST's are near 10c in that location and 500mb heights approaching -30 . I don't even need a Skew-t to tell me there will be adequate ML  CAPE for convective given the lapse rates.

P.S Dublin Ireland had thundersnow in 2009 with pressure about 1025 Hpa, if memory serves correctly. 

I thought it was 1015hpa... I'll have to look it up, but the big difference then was that upper 850's were -9 and -10 weren't they?

[BLAST FROM THE PAST]

1 hour ago, Tamara said:

Can't think who has been boring people for so long posting pages of 2015 atmospheric circulation history - and suggesting  possible July/Jan -AO/NAO connect

 

 

Neither could I, that's why I asked

 

BFTP

 

Edit - Read your edit  @tamara .....I refer to my correlation post...some find if confirmed as per current outlooks

Edited January 6, 2016 by BLAST FROM THE PAST

[craigore]

Can i just ask those in the know... 

Do you think this will be a nationwide cold spell wth snow chances for many even us southeners. 

Or Snow confined to usual areas i.e northern  parts , scotland and areas wth elevation..

Im asking because to the untrained eye those northelys predicted never seem to bring the cold far enough south or the precipitation...

I personally will be hoping for more of a N.Easterly at some point during the coming cold spell..

[Coopsy]

31 minutes ago, summer blizzard said:

Pressure is far too high. You'll struggle to get any precipitation at all above 1030mb and really you want sub 1020mb.

Jan 1987....best sea effect snows in (my) living memory in the southeast.....right on the 1020 line. (that assuming I'm talking same things (new to charts lol)

Edited January 6, 2016 by Nemesis

[rory o gorman]

9 minutes ago, Rocheydub said:

I thought it was 1015hpa... I'll have to look it up, but the big difference then was that upper 850's were -9 and -10 weren't they?

It was certainly above 1020 hpa at one point with a nasty grapel thundersnow streamer with tops about 30k. 850 mb temperatures play a role but not nearly as much as the 500mb . The LFC for a parcel in a streamer here is probably nearing 800mb so buoyancy above that would be the telling factor. 

Edited January 6, 2016 by rory o gorman

[rory o gorman]

4 minutes ago, Nemesis said:

Jan 1987....best sea effect snows in (my) living memory in the southeast.....right on the 1020 line. (that assuming I'm talking same things (new to charts lol)

Southern Ireland was also blasted with 6 inches plus of snow , with thundersnow reported as a streamer setup. Again the pressure is plus 1020 hpa but the SST/upper trough created quite steep lapse rates . 

[Turnedoutniceagain]

10 minutes ago, Nemesis said:

Jan 1987....best sea effect snows in (my) living memory in the southeast.....right on the 1020 line.

I lived in Germany then. -20c for over a week, awesome

[John Badrick]

2 hours ago, LeeSnowFan said:

but what sort of time frame do you look at to say "It's locked and loaded and ready to go"?

T24 

[Weathizard]

Classic model thread - people worrying about snow chances by area when we haven't even got the cold in yet  ensembles in staggering agreement at such long range for a cold spell now but remember how fickle the models can be, let's get the cold in.. Then see who gets lucky.

In all honesty dry weather wouldn't go amiss it in a lot of places! On to the 12z's.

[John Badrick]

MetO  on board 

[nick sussex]

I'm wondering whether we're seeing the different MJO forecasts played out here. The ECM is much more bullish about rushing the signal into phase 8, the GEFS is slower and has the signal meandering around just as it enters that phase.

A key feature of the MJO phase 7 composite in positive ENSO is that Arctic high joining forces with the Atlantic ridge. Interestingly reading the NCEP state forecasts a few days back they mentioned the idea of some cross polar blocking.

So looking  you can see circled black the cross polar blocking, and the blue arrow denoting the joining forces of the Atlantic ridge and the Arctic high:

One would think that looking at the dynamical model forecasts that we're about to enter phase 8 which would be a different composite, the GEFS slower to get to that phase however the smoothed out version reducing ENSO interference and Kelvin wave has the MJO only getting into phase 7, bearing in mind the tropospheric timelag MJO response the MJO is only just in this phase and the strongest impact would start showing within the week.

Now this is where it gets a bit more interesting, bear with me!

We know that MJO trop influence is moderated by ENSO and also its impacts effect different parts of the NH to differing degrees, ie some have a greater/lesser impact dependent on what the El Nino is doing.

 

This quote from some excellent research into ENSO/MJO:

Although the global mean amplitudes of geopotential height anomalies associated with the MJO do not appear to vary dramatically with the MJO phase, the nonlinear component of the global flow associated with the MJO and ENSO might be more substantial in some geographical regions than others. Figures 10a–d show the absolute values of the composite geopotential height anomalies averaged over all the MJO phases during declining, cold, warming, and warm ENSO, respectively. During each ENSO phase, except Nin ˜o-3.4 rising, the largest anomalies associated with the MJO occur over the North Atlantic and regions to the immediate east and west. During Nin ˜o-3.4 increasing trends, the strongest composite anomalies occur over the Bering Sea.

You'll see from those maps the MJO still expected to have a strong impact to the west of the UK even with the positive ENSO, indeed over the last few weeks we have seen a small decline in region 3.4, I don't think enough to call it a declining but at least its moving in the right direction.

PS sorry those maps are so small, I've tried to enlarge, circled red is the area just to the west of the UK!

 

 

 

 

Edited January 6, 2016 by nick sussex

[mountain shadow]

4 hours ago, craigore said:

Can i just ask those in the know... 

Do you think this will be a nationwide cold spell wth snow chances for many even us southeners. 

Or Snow confined to usual areas i.e northern  parts , scotland and areas wth elevation..

Im asking because to the untrained eye those northelys predicted never seem to bring the cold far enough south or the precipitation...

I personally will be hoping for more of a N.Easterly at some point during the coming cold spell..

I think East Kent will do very well, particularly if the cold spell becomes more extended. 

[BarnetBlizzard]

11 minutes ago, craigore said:

Can i just ask those in the know... 

Do you think this will be a nationwide cold spell wth snow chances for many even us southeners. 

Or Snow confined to usual areas i.e northern  parts , scotland and areas wth elevation..

Im asking because to the untrained eye those northelys predicted never seem to bring the cold far enough south or the precipitation...

I personally will be hoping for more of a N.Easterly at some point during the coming cold spell..

 

At this moment in time its obvious Northern Scotland will have the best chances for extensive snow showers or periods of snow as they are closer to the source of the cold. However, it is looking more likely in recent runs the cold will extend to the majority of the UK and stay there (not a toppler). Once you have the cold, then you can look for the snow and in the case of the upcoming cold "spell", troughs and other features could pop up anywhere. 

In December 2010 the cold came from the North yet the biggest falls for Southern england came from activity moving up from the South and stalling, so no point worrying about where and how much snow yet!

[warrenb]

A lot of Kent would do well, we get all sorts of streamers in really cold weather, the thames and the medway acting as tramlines.

In 2010 we did vey well here in West Kent due to  a slight ENE which switched the streamer from the Thames to the Medway. Got 32cm of snow here in Tonbridge.

[Paul_1978]

37 minutes ago, captaincroc said:

Just a question for the experts.... I know the weather can technically go 'tits up' at any time but at what time scale can we safely say that 'something' is going to happen?  To my untrained eyes I take it that if the Greenland block appears then some sort of cold weather will come (with more specifics nearer the time).

Was just wondering when we can be sure of this pattern change? 

 

Cheers

I'd like to get it within T+92 to be sure, but maybe I'm being over cautious. 

 

We've seen some situations go TU within T+92 before and I've no doubt there will be plenty of squeaky bum moments to come yet. 

[terrier]

Just caught up with the gfs 6z what another great run even upgrades on the 00z. But I still don't think this is a given yet. Yes it's going to turn colder. But let's not forget these charts are at 9/10 day range away yet. Think a lot depends on what that Azores decides to do. Hopefully we see the ecm and ukmo move towards the gfs later today. But at the moment keeping feet firmly on the ground as we've seen these types of sypnotics go wrong at t72. 

[Rocheydub]

25 minutes ago, rory o gorman said:

It was certainly above 1020 hpa at one point with a nasty grapel thundersnow streamer with tops about 30k. 850 mb temperatures play a role but not nearly as much as the 500mb . The LFC for a parcel in a streamer here is probably nearing 800mb so buoyancy above that would be the telling factor. 

It was indeed, you are correct. It was 1025 for some of it. Apologies. That was a fantastic night. I was in work in the city centre, and remember the fright I got when the first clap of lightning-thunder came, I was expecting it, but not so close to where I was!!!

[winterof79]

29 minutes ago, Turnedoutniceagain said:

I lived in Germany then. -20c for over a week, awesome

Ditto. -16 inside the Barracks corridor.Breath froze.

When I mentioned in reply to SMs post that we could dream of a link between our Atlantic ridge and the Arctic high, I was thinking further down the line in output not the 06z