Winter Model Discussion - 11/01/13 00z Onwards

[phil nw.]

Can we try to keep reactions to the MO further outlooks to that thread please folks.

Let`s keep this one for the model outputs-thanks.

[bobbydog]

Would agree entirely. The pattern is being driven by the the big global teleconnectors presently of which the biggest is the strat. The positioning and strengths of these vortices is dependent on the wave feedback from the trop and subsequent warmings. A slight shift to the vortex 'upstairs' will have a slight shift to the vortex 'downstairs' and this will have a determination over surface ridge and shortwave formation. Which is critical when we are right on the border of the cold mass that one little shift can predetermine whether we will see rain or snow.

i suppose then, we are unlikely to see any consistency from the models until the strat reforms to its usual 'calmer' pattern.

[chionomaniac]

i suppose then, we are unlikely to see any consistency from the models until the strat reforms to its usual 'calmer' pattern.

Yes and that still hasn't occurred by T+384!

[Frosty.]

Monday into Tuesday really needs watching, according to the models, an active frontal system will spread southeast across the uk and disruptive snowfalls are likely, just about all of the uk is probably going to have a covering of snow by early next week and some will have it before then, especially in the east as snow showers blow in from the north sea on sat night and throughout sunday, the southeast could end up being the snowiest by the end of the weekend and then the north joins in with snow spreading south. Next week then looks like remaining cold or very cold with scattered snow showers and severe frosts with frequent ice days and some more persistent sleet and snow at times, any mild intrusions look confined to the far west of the uk at times.

Edited January 11, 2013 by Frosty039

[Wadey]

Here is one of the great images from NW extra - slp spread and mean ( cheers Paul) which highlights the uncertainty of the GFS ensembles at T+144. I guess the 'Shannon entropy' is greatest where the red area is and this is the area we are most likely to see most changes in the future output (yes it is the UK)

is this a good chart for us? And why ? Im still learning sorry for the one liner

[Troubleatmill]

Im Guessing then Chio that the models are a bit like a car on an ice at the moment?, slip sliding and fish tailing all over the place unable to get a grip on whats going on and waiting to hit some tarmac?

[chionomaniac]

is this a good chart for us? And why ? Im still learning sorry for the one liner

It's not a good or bad thing. It just highlights the area of greatest uncertainty in the GFS ensembles by T+144. So the sea level pressure (slp) has the greatest spread in those regions between all the members. And that is just one model.

[Captain Shortwave]

is this a good chart for us? And why ? Im still learning sorry for the one liner

The chart just shows the amount of spread and uncertainty around the Northern hemisphere. You can see that the areas with the highest uncertainty are the eastern US and over us, there is no coincidence as how lows exit the states will have a huge effect on our weather, the flatter the pattern, the more likely wet and more mild the weather. More amplification in the states will tilt the jet to give a more favourable weather either polar maritime/Arctic flow or lows going underneath us keeping the weather cold. Pretty much the model has no idea how things will pan out in this run.

Edited January 11, 2013 by Captain shortwave

[Troubleatmill]

is this a good chart for us? And why ? Im still learning sorry for the one liner

Not sure if Chio is still here, but its showing neither, where the red is that is where there is the greatest uncertainty...typically its over us lol

[Panayiotis]

is this a good chart for us? And why ? Im still learning sorry for the one liner

Hopefully Chiono wont mind me answering your questions for you.

Its not good nor bad, its just showing that areas around the UK are likely to see change as that is where (the red) most of the uncertainty is, so looking at the chart for that timeframe is useless as they will probably change

Ha he beat me to it lol and we have basically the same reply, no worries though! 4 posts to answer your question hopefully we have improved your knowledge and understanding!

Edited January 11, 2013 by Panayiotis

[bluearmy]

NOAA expect a colder pattern to set up for the eastern USA , this is in relation to that PV lobe dropping into Canada.

Without a signal for a pressure rise to the north or ne then a pile of energy will just move east and flatten the pattern over Europe. The subject of that seems to have come up over recent long term discussions with the teleconnections saying one thing but the models saying something else.

Historically NOAA cant find a match for what the models had originally suggested and perhaps we're seeing that play out ie east Pacific ridge and Greenland high mismatch.

Of course history doesn't mean it can't happen, theres always a first time !

Looking at all the output so far today I think we just draw a blank in terms of having any certainty as to what the weather might be like in a weeks time.

which is why this becomes so 'knife edge'. i also expected the greeny blocking to downgrade given the cpc comments on the leleconnection issue. however, a weak sustained block iceland locale will do the trick in deflecting the jet far enough south. that would make the next fortnights model watching fraught as each run raises and then drops the 'snow line'. across the uk.

[BLAST FROM THE PAST]

What I can see through this mirky period ahead is that there is no strong signal to come through for a STRONG block until last week to thrird of Jan, which leads us down the path of high drama. Some will be disappointed but I suspect many will do rather well out of this. More snow and cold than not I suggest as a general theme.

BBC SE suggests ice day on Monday with risk of significant snowfall Mon eve....any front bumping into such cold air any precip will no doubt be snow. Fax shown by Phil is very good for central south, SE.

BFTP

Edited January 11, 2013 by BLAST FROM THE PAST

[Jayces]

The subject of that seems to have come up over recent long term discussions with the teleconnections saying one thing but the models saying something else.

Historically NOAA cant find a match for what the models had originally suggested and perhaps we're seeing that play out ie east Pacific ridge and Greenland high mismatch.

Of course history doesn't mean it can't happen, theres always a first time !

Nick or for that matter anyone who might know, if I am reading that correctly you are suggesting that what is being modelled is a scenario that in the history of computer model forecasting hasn't happened before.

Is this because it's just not possible or where you allude to there always being a first time can it actually happen?

I mean the models are just a very complex computer program with specific parameters in them, surely they can only produce outcomes that we know are possible because we have programmed them, ie we know hurricanes weaken over land and without wind shear strengthen over warm water so no model will show the opposite ever as they aren't programmed to I guess.

But are there unknowns in the weather world still (like the strat effects) that are maybe being added now to computer models and giving us a better understanding of what is really going on and showing scenarios we thought were not possible?

Or am I waffling?

[phil nw.]

which is why this becomes so 'knife edge'. i also expected the greeny blocking to downgrade given the cpc comments on the leleconnection issue. however, a weak sustained block iceland locale will do the trick in deflecting the jet far enough south. that would make the next fortnights model watching fraught as each run raises and then drops the 'snow line'. across the uk.

Yes this setup has the UK very much on the edge of the cold block-especially further west.

The GFS Ens Means for the 850hPa anomls still ok though for keeping us generally cold-a snapshot at day 7 and then day 10.

of course even these will move around run to run but it illustrates that any Atlantic systems moving towards us will create some snow chances somewhere over the UK as it comes against the cold air.

Monday`s shortwave on the fax looks a good example.

Quite a decent pattern for snow as long as we retain enough of a weak block further north.

This is quite an interesting setup to me with these potential battleground events but of course it means high risk in seeing if the cold block holds firm enough.

[BLAST FROM THE PAST]

NOAA expect a colder pattern to set up for the eastern USA , this is in relation to that PV lobe dropping into Canada.

Without a signal for a pressure rise to the north or ne then a pile of energy will just move east and flatten the pattern over Europe. The subject of that seems to have come up over recent long term discussions with the teleconnections saying one thing but the models saying something else.

Historically NOAA cant find a match for what the models had originally suggested and perhaps we're seeing that play out ie east Pacific ridge and Greenland high mismatch.

Of course history doesn't mean it can't happen, theres always a first time !

Looking at all the output so far today I think we just draw a blank in terms of having any certainty as to what the weather might be like in a weeks time.

Nick

an you clarify, are NOAA anticipating us to move into a flat pattern?

BFTP

[Frosty.]

What I can see through this mirky period ahead is that there is no strong signal to come through for a STRONG block until last week to thrird of Jan, which leads us down the path of high drama. Some will be disappointed but I suspect many will do rather well out of this. More snow and cold than not I suggest as a general theme.

BFTP

Yes Fred, BATTLEGROUND UK it looks like, I think RJS earlier said the most sustained severe wintry weather will be towards the end of the month and could dominate february, next week and beyond looks like the atlantic will try to break through but will meet strong resistance from the resident cold block, only really the southwest and far west are likely to flirt with milder air, most areas stay cold or very cold for many days once established and with snow at times, some large dumpings likely and next monday could bring widespread disruption to northern, eastern and southern england.

Edited January 11, 2013 by Frosty039

[Josh Taliesin Gibbens]

There are some nice cold temperatures at 850hpa, but with growing uncertainty after monday.

Looking towards monday there is a good chance of snow, but as always there is a chance that this could change, depending on the track of the weather system from the west.

And out on Fantasy Island some beautiful charts .

And finally the precipitation charts.

[BLAST FROM THE PAST]

Yes Fred, BATTLEGROUND UK it looks like, I think RJS earlier said the most sustained severe wintry weather will be towards the end of the month and could dominate february, next week and beyond looks like the atlantic will try to break through but will meet strong resistance from the resident cold block, only really the southwest and far west are likely to flirt with milder air, most areas stay cold or very cold for many days once established and with snow at times, some large dumpings likely and next monday could bring widespread disruption to northern, eastern and southern england.

I think probably when the strongest and sustained blocking will kick in. The period ahead though could be the main story of the winter. If we get a month like Feb 86 it would be amazing, but it was just bitterly cold and dry for many hence its never really remembered. Sometimes a very strong and robust block doesn't produce the goods for most barr being..well, just v cold

BFTP

Edited January 11, 2013 by BLAST FROM THE PAST

[nick sussex]

Nick or for that matter anyone who might know, if I am reading that correctly you are suggesting that what is being modelled is a scenario that in the history of computer model forecasting hasn't happened before.

Is this because it's just not possible or where you allude to there always being a first time can it actually happen?

I mean the models are just a very complex computer program with specific parameters in them, surely they can only produce outcomes that we know are possible because we have programmed them, ie we know hurricanes weaken over land and without wind shear strengthen over warm water so no model will show the opposite ever as they aren't programmed to I guess.

But are there unknowns in the weather world still (like the strat effects) that are maybe being added now to computer models and giving us a better understanding of what is really going on and showing scenarios we thought were not possible?

Or am I waffling?

Hi Jayces perhaps this clarifies things a little, from last nights NOAA discussion:

THE MODELS ARE IN VERY GOOD AGREEMENT ON THE 6-10 DAY, 500-HPA HEIGHT PATTERN.

MODEL SOLUTIONS DEPICT A RIDGE, CENTERED IN THE BLEND AT (47.5N, 135W), OVER

THE GULF OF ALASKA, A TROUGH OVER CANADA, CENTERED IN THE BLEND AT (54N, 85W),

EXTENDING INTO THE GREAT LAKES, AND A WEAK RIDGE OVER SOUTHEAST CONUS, AND

STRONG + 500-HPA HEIGHT ANOMALY OVER GREENLAND CENTERED IN THE BLEND AT (36W,

76N). AS WAS THE CASE YESTERDAY, THE TELECONNECTIONS ON THE PACIFIC, HUDSON

BAY AND GREENLAND ANOMALY CENTERS ARE SOMEWHAT OUT OF PHASE, POSSIBLY

INDICATING THAT THE PREDICTED PATTERN IS NOT YET A CLOSE MATCH TO PATTERNS

OBSERVED IN THE HISTORICAL RECORD. ANALOG CORRELATIONS BETWEEN PREDICTED

500-HPA HEIGHT PATTERNS AND HISTORICAL MAPS IN A 35-DAY WINDOW CENTERED ON THE

FORECAST CENTERED DATE, ARE IN THE VICINITY OF 0.85, WHICH IS NOT HIGH FOR A

WINTERTIME PATTERN. THE MANUAL BLEND FORECAST WEIGHTED THE GFS 06Z AND THE

ECMWF 00Z ENSEMBLES THE MOST, FOLLOWED BY BY GFS 00Z ENSEMBLE AND THE 00Z

CANADIAN.

What NOAA are saying is that when we look back through past set ups theres a conflict from what the models wanted to do with the pattern and what historically teleconnects.

Now if you look through the last few days we've seen a slow erosion of those heights to the north in the outputs, you never want to say something can't happen in weather because you're likely to end up with egg on your face but the last time we had this mismatch the models were indeed barking up the wrong tree.

This time because of the strat warming it doesn't need to end in tears as BA mentions early we can just about get away with a weakish high pressure near Iceland but as for a proper higher latitude block perhaps thats unlikely until we see something that matches previous teleconnections.

[Met4Cast]

I think probably when the strongest and sustained blocking will kick in. The period ahead though could be the main story of the winter. If we get a month like Feb 86 it would be amazing, but it was just bitterly cold and dry for many hence its never really remembered. Sometimes a very strong and robust block doesn't produce the goods for most barr being..well, just v cold

BFTP

Important to remember too that many of the big snowy winters were down to battleground setups, although they had slightly stronger blocks I expect if we had more high resolution data like we do now, we'd have seen similar marginal setups as frontal systems push in. Hell, in 1963 forecasts were suggesting a thaw but instead further snow and cold came

[Frosty.]

I think probably when the strongest and sustained blocking will kick in. The period ahead though could be the main story of the winter. If we get a month like Feb 86 it would be amazing, but it was just bitterly cold and dry for many hence its never really remembered. Sometimes a very strong and robust block doesn't produce the goods for most barr being..well, just v coldBFTP

I liked the part where roger said severe cold compared to the cold or very cold we expect to have before then, also ties in with what GP is indicating for late jan and through feb with a big push of severe cold from ne europe. I'm glad the meto rejected the idea of the 6z of a flatter more average pattern after midweek, it looks to me as though our cold block, once established will prove to be stubborn to shift and may only crumble slightly on the western edges, thrilling times ahead for coldies and especially snow lovers. Edited January 11, 2013 by Frosty039

[nick sussex]

Nick

an you clarify, are NOAA anticipating us to move into a flat pattern?

BFTP

Fred the last I read was a drop down of the PV lobe into the ne USA, some uncertainty though with whether we were going to see a full latitude type trough or something flatter.

They do expect a colder pattern to set up in the eastern USA, for that reason we need a friendly ridge to the north anything to help deflect that energy further south.

[Jayces]

Thanks Nick, it does beg the question though, why are the models barking up the wrong tree?

I am going to guess that they are dealing with data entry at the start of the run that doesn't match up to what they are used to and defaulting to what they have done i the past in those situations and thus the end result is unexpected output?

Will be quite a coup I guess for the human LRF's who predict the correct weather if it goes against the computers.

[rory o gorman]

not looking good for Ireland and the S.W thus far . gfs ens scatter is promising though .

[Josh Taliesin Gibbens]

As TEITS pointed out earlier. All depends where you live. This cold spell might not even happen in large areas of SW and Western UK.

Your quite correct I've learned from what people are saying especially with snow it could run to the line on where and when it will fall. Hence on the charts for later in the week they are most certainly on FI. It could also be the perfect scenario for snow we just don't know.