Model Output Discussions 12z 01/09/2016

[Frosty.]

The GEFS 6z mean shows there is plenty of support for what would be our first cold outbreak during early November with high pressure drifting out into the atlantic and a scandi trough (below is just a sample)..I think we are on track for a colder spell developing next week from the north with frosts becoming more widespread and even a risk of showers turning wintry, especially in the north and on hills / mountains where snow should be expected..more interestingly is the MO expect it to turn colder with a N / NWly airflow next week and even beyond!

Edited October 24, 2016 by Frosty.

[phil nw.]

3 hours ago, knocker said:

I'm sorry I'm not sure I follow what you mean and would be grateful for a quick illustration if possible. I ask because to my untutored eye it looks very much like the energy shooting out from the north Canadian vortex that is creating the very tight thermal gradient and the 160Kt west-east jet and not allowing the HP to ridge into Greenland.

Yes agree with that Knocker.That is a surge in the northern jet which rides through the downstream ridging.In spite of all the +ve anomalies across the Pole this is always something to be aware of.Certainly more than a shortwave!

[carinthian]

Long term tendancies ? Cold November ?  Looks like strong positive temps differentials in the Oceanic Arctic/ SE Greenland, Continental fringes of Africa and to a lesser extent Iberia. Most of European land mass including British Isles average to lower than average temps.  but looking at the map temp profile appears for the blocking scenario to continue into November.

 C

[Seasonality]

5 minutes ago, carinthian said:

Long term tendancies ? Cold November ?  Looks like strong positive temps differentials in the Oceanic Arctic/ SE Greenland, Continental fringes of Africa and to a lesser extent Iberia. Most of European land mass including British Isles average to lower than average temps.  but looking at the map temp profile appears for the blocking scenario to continue into November.

 C

Liking those temp anomalies Carinthian. A clear signal for a cool spell over central and eastern europe, including Warsaw I am pleased to add. All the better for helping to start off a nice cold pool for the UK to tap into further down the line.

[knocker]

52 minutes ago, Singularity said:

Hi Knocker, thanks for the question.

What we've seen is a change to the behaviour of that little low to the west of the main one situated just N of Iceland; last night's 12z (left) had it absorbed into the parent low without causing trouble, while today's 00z (right) keeps it independent, which means it can interact with the low to the S of Greenland, their combined effect producing the undesirable jet stream alignment by the next day:

 

Gone is the buckling jet arcing back to the NW in favour of a flat one heading NE - albeit not with all that much strength.

The strong jet that you've picked out is a part of the equation of course - a slight increase in its intensity has allowed the low S of Greenland to progress further east at the time that the shortwave low offers to dance. Without that, the two may still have been having nothing to do with one another in the model output.

With that shortwave's behaviour, it's actually not the most classic of examples to be honest, that being a shortwave on the eastern flank of a trough, but it may be the second or third-most classic, so to speak? 

Anyway - I'm not yet seeing reason to rule out the low S of Greenland being slower, or the shortwave low being absorbed into the parent low after all, either of which could prevent their interaction and reintroduce the colder outcome for the earlier part of next week.

I think I'm following what you are saying Singularity but I'm having a bit of trouble sorting why a small shortwave is having such a big impact on the jet

Regarding the period you posted. I'm not going to analyze the two runs because as far as i can see it can be covered by just looking at last nights 500mb charts for around the period you mentioned

At T114 we have HP ridging NW into Iceland with the vortex over Canada and two upper lows, one to the NW of the ridge and the other to the NE with a tough running south from the former. The jet runs around the trough and then NE strengthening considerable with the rapid increase of the thermal gradient between the trough and the ridge, (the cold and warm air)

As we move on 24 hours or so everything is more amplified The ridge is now extended to the east of Iceland with the trough just to the west with a new ridge into Greenland. This development, particularly the trough and the ridging to the west severely disrupts the jet. In a nutshell I'm still failing to see how a shortwave can do all of this.

Edited October 24, 2016 by knocker

[Singularity]

2 minutes ago, knocker said:

I think I'm following what you are Singularity but i'm having a bit of trouble sorting why a small shortwave is having such a big impact on the jet

Regarding the period you posted. I'm not going to analyze the two runs because as far as i can see it can be covered by just looking at last nights 500mb charts for around the period you mentioned

At T114 w have HP ridging NW into Iceland with the vortex over Canada and two upper lows, one to the NW of the ridge and the other to the NE with a tough running south from the former. The jet runs around the trough and then NE strengthening considerable with the rapid increase of the thermal gradient between the trough and the ridge, (the cold and warm air)

As we move on 24 hours or so everything is more amplified The ridge is now extended to the east of Iceland with the trough just to the west with a new ridge into Greenland. This development, particularly the trough and the ridging to the west severely disrupts the jet. In a nutshell I'm still failing to see how a shortwave can do all of this.

 

You're right about how the jet becomes so strong - my focus is on the fact that whereas previously a gap was able to open up between the two areas of low pressure N of Iceland and S of Greenland into which a ridge was able to push, greatly raising heights over Greenland (see the 'nose' of the jet into the far-S of Greenland on the left-hand of the jet stream charts I posted), in the 00z GFS run this is unable to happen due to the lows combining into one elongated system. Note that the strong section of jet stream was present both before and after the adjustments, though it too has seen changes to the orientation as a knock-on effect of the alterations in the N/NE Atlantic.

Essentially, it's a relatively short-term development that delays proceedings by changing the configuration of the jet as we go into the weekend. My apologies for the confusion over this matter, especially if it remains after this post is read  Work beckons so I must leave it here.

[Frosty.]

Well, no sign of a Northerly on the Gfs 12z into next week, indeed it still looks anticyclonic and unseasonably warm across the southern half of the uk..very pleasant, cooler air slowly filters south but it stays settled.. what a lovely early November this would be!

Edited October 24, 2016 by Frosty.

[Ali1977]

2 minutes ago, Frosty. said:

Well, no sign of a Northerly on the Gfs 12z into next week, indeed it still looks anticyclonic and unseasonably warm across the southern half of the uk..very pleasant 

Can't believe how much the models have changed, the only plus is that it isn't mid winter and we're not missing out on a snow fest  - and it will still feel relatively nice in the sun at this time of year.

[Barry12]

Big differences at just day 6 on the GFS and UKMO

Nothing is settled yet...

[Frosty.]

The Gfs 12z shows colder and more unsettled weather arriving from the NW towards the end of next week with snow for the hills and mountains of Scotland..it's set up for reloads and an Arctic blast finally arrives, scotland becomes wintry and the way the run ends suggests more to come through November.

Edited October 24, 2016 by Frosty.

[Ali1977]

FI teasing again, i'd definitely trade the 1st predicted Northerly for this set up - even 1 week later helps it have much more punch. 

Edited October 24, 2016 by Ali1977

[swfc]

tbh im at a loss on the 12z to see such big changes since this morning let alone yesterday.im know expert on the strat ete and the effects of tropical storms but is the atmosphere in such turmoil and flux that a 12 hour forecast isnt accurate !!!!!

[Singularity]

Just flying through but this is a classic example of trough disruption with lows sliding into the base of a Scandi trough, resulting in a clash of mild and cold air that by mid-Nov is often capable of producing a band of snow along the leading edge of the front (which may then occlude to become mostly or entirely snow).

This is a +16 day chart so it's main purpose is to serve as a guide as to what sort of thing newcomers to chart-watching should be looking out for if they are seeking (or fearing!) snowy weather. Note that for better results snow-wise there typically needs to be none of the yellow shading (mild air) and only an increasingly thin line of green shading (arcing toward the centre of the low pressure system; a 'warm' sector), this surrounded by the blue shading (cold air).

[fergieweather]

6 minutes ago, swfc said:

tbh im at a loss on the 12z to see such big changes since this morning let alone yesterday.im know expert on the strat ete and the effects of tropical storms but is the atmosphere in such turmoil and flux that a 12 hour forecast isnt accurate !!!!!

I don't see any major change of emphasis for the week ahead...albeit boundary layer detail will be the main day-to-day headache.

If, however, you refer to extended medium range wax and wane lately... that's why we use ensembles/clusters at that range, not deterministic runs! 

[swfc]

1 minute ago, fergieweather said:

I don't see any major change of emphasis for the week ahead...albeit boundary layer detail will be the main day-to-day headache.

If, however, you refer to extended medium range wax and wane lately... that's why we use ensembles/clusters at that range, not deterministic runs! 

yes sorry ian the plus seven day period

 

[Gael_Force]

9 minutes ago, Singularity said:

This is a +16 day chart so it's main purpose is to serve as a guide as to what sort of thing newcomers to chart-watching should be looking out for if they are seeking (or fearing!) snowy weather. Note that for better results snow-wise there typically needs to be none of the yellow shading (mild air) and only an increasingly thin line of green shading (arcing toward the centre of the low pressure system; a 'warm' sector), this surrounded by the blue shading (cold air).

Would you not be better showing a thetaE chart for this illustration?

[fergieweather]

2 minutes ago, swfc said:

yes sorry ian the plus seven day period

 

Pattern remains prone to amplification through the 1st half of Nov (at least), with currently scant sign in either ECMWF or GloSea of pronounced zonality/deep lows/strong westerly flow, at least for now (EC's monthly suite runs again this evening). As previously discussed, where we ultimately see respective high/low centres positioned remains open to considerable uncertainty (eg as per model flux last 24hrs) but given the amplified tendency, will continue to offer potential for northerly outbreaks. I wouldn't be at all surprised to see this sort of muddle repeating on through the next fortnight (or more).

[gottolovethisweather]

2 hours ago, Frosty. said:

The GEFS 6z mean shows there is plenty of support for what would be our first cold outbreak during early November with high pressure drifting out into the atlantic and a scandi trough (below is just a sample)..I think we are on track for a colder spell developing next week from the north with frosts becoming more widespread and even a risk of showers turning wintry, especially in the north and on hills / mountains where snow should be expected..more interestingly is the MO expect it to turn colder with a N / NWly airflow next week and even beyond!

 

I haven't been following the models or model output discussion thread of late, but I think November will bring some quite widespread cold and wintry Synoptics to all. I like most others like to attempt their pattern match routines, and so far this Autumn and in part the Summer CET mean comparisons lend themselves to a 2010 situation developing. Given the blocking and deep cold bottled up under the stubborn upper high, it wouldn't take much for the cards to fall right for once. Please regard this, simply as a "gut feeling" post from gottolovethisweather, and not much else. A frosty bonfire night would be a good bet right now, I feel.

[Ali1977]

The GEFS are way better looking at day 10 for blocking at Northerly flows...I expect a swing the other way could be right round the corner. Some examples below at day 10, there are others too.

 

[knocker]

22 minutes ago, Gael_Force said:

Would you not be better showing a thetaE chart for this illustration?

Or better still a 1000-850 thickness and precipitation chart and make if 5 days not 15.

EDIT

Just for fun the 1000-5000 shows the airmass boundary quite well

Edited October 24, 2016 by knocker

[Gael_Force]

8 minutes ago, knocker said:

Or better still a 1000-850 thickness and precipitation chart and make if 5 days not 15.

Surely matters not the range if purely for educational purposes. Do we have 1000-850 thickness charts available on the free sites?

[Frosty.]

The GEFS 12z mean shows the high slowly retreating w / sw next week with lowering heights from the NE which indicate a colder and more unsettled trend from the N / NE later next week onwards.

[knocker]

Just now, Gael_Force said:

Surely matters not the range if purely for educational purposes. Do we have 1000-850 thickness charts available on the free sites?

Yes that's fair comment. I'm not sure to be honest

[feb1991blizzard]

8 minutes ago, Gael_Force said:

Surely matters not the range if purely for educational purposes. Do we have 1000-850 thickness charts available on the free sites?

 

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=ukuk&MODELL=gfs&MODELLTYP=1&BASE=-&VAR=th85&HH=3&ARCHIV=0&ZOOM=0&PERIOD=&WMO=

Edited October 24, 2016 by feb1991blizzard

[damianslaw]

Trend in the models continues to be ridge over the country retrogressing out towards mid atlantic leaving us exposed to an airflow from between NW and NE. The models continue though to show quite a slow evolution - with the extra energy in the jet perhaps putting a little hold on such a set up verifying within the next week, but more definately likely later next week.

In the meantime, lots more dry weather for many especially the south and east, the NW seeing cloud and outbreaks of mostly light rain or drizzle, the usual NW-SE split, but not something we have seen much this October. Another late October ending on a notably mild note, but not especially so, and nightime temps could still be quite low where skies clear, though it looks a mostly cloudy affair.