Model Output Discussion - The Start Of Winter

[OldMetMan]

Some interesting remarks spotted this morning in the NWS forecast discussion. It's not exactly clear to me what the implications are for the circulation pattern here, but it looks significant:

"...AND WHAT IS

BECOMING MORE EVIDENT...IS THE LATITUDE FOR THE WAVE TRAIN

MIGRATION. TO ME---IT'S DISPLACED SOUTH OF A 'TYPICAL' LATE-AUTUMN

LATITUDE---CLOSER TO 40N-42N THAN 47N-48N ALONG 140W LONGITUDE. IF

THE ECENS MEAN IS ANY INDICATION OF WHAT CAN BE EXPECTED...ITS

1/12Z DETERMINISTIC RUN AND 250MB JET FORECAST SHOULD BE NOTED

FROM THE SOUTH COAST OF JAPAN TO 40N 140W BY THE END OF DAY 7.

A SECOND FEATURE OF THE PACIFIC---IS THE EARLY EMERGENCE OF THE

SUBTROPICAL JET...AND ACTIVE OVER NORTHERN MEXICO SO EARLY IN THE

LOW-SUN HALF OF THE YEAR. THIS IS USUALLY MORE A LATE JANUARY

THROUGH FEBRUARY OBSERVANCE. AND WITH THE DETERMINISTIC GUIDANCE

SUGGESTING NOTABLE INCREASES IN THE PACIFIC BRANCH OF A JET NEAR

25N...IN CLOSE PROXIMITY TO HAWAI'I NORTHEASTWARD INTO NORTHERN

MEXICO BY THE END OF DAY 7...AM THINKING THIS MEDIUM RANGE

FORECAST PERIOD IS TRYING TO TELL US SOMETHING---AND PERHAPS THE

PATTERN IS CHANGING IN EARNEST...WITH THE DOWNSTREAM EJECTION OF

THE CLOSED LOW OFF THE CALIFORNIA COAST SETTING THINGS INTO MOTION."

I mentioned the unusual appearance of what seems to be some sort of sub-tropical feature by the GFS for this coming weekend, and with each run, the GFS has maintained the formation of this significant feature but has changed it's development. The latest run shows it becoming a major storm system next week.

There has been a great deal of change within the longer term trends of the model output, even more than usual it seems to me and I can't shake the feeling that something important is going to happen within the next couple of weeks.

What NWS are saying about the sub-tropical jet suggests to me a weakening of the northern stream, and subsequent reduction of zonal activity at our latitude. Others more knowledgeable about such things are welcome to comment.

The model output is, in my view, even more unreliable in the longer term than is usually the case and I am struggling to see any consistent trend emerging from recent runs of all the major outputs. The storm system I mentioned above, well the projected development just looks plain wrong to me. As I mentioned in my last post, it looks more likely to introduce a greater amplification to the flow upstream and may be what the NWS is getting at.

For now, things look pretty "normal" but by the end of the week, I suggest we may see the first signs of a major pattern disruption and change towards a colder and more blocked one. I shall have to mull this over in the coming days and come up with a less vague prediction than this! But I will say that when it comes to cold and snow, be careful what you wish for....!

[blizzard81]

Some interesting remarks spotted this morning in the NWS forecast discussion. It's not exactly clear to me what the implications are for the circulation pattern here, but it looks significant:"...AND WHAT ISBECOMING MORE EVIDENT...IS THE LATITUDE FOR THE WAVE TRAINMIGRATION. TO ME---IT'S DISPLACED SOUTH OF A 'TYPICAL' LATE-AUTUMNLATITUDE---CLOSER TO 40N-42N THAN 47N-48N ALONG 140W LONGITUDE. IFTHE ECENS MEAN IS ANY INDICATION OF WHAT CAN BE EXPECTED...ITS1/12Z DETERMINISTIC RUN AND 250MB JET FORECAST SHOULD BE NOTEDFROM THE SOUTH COAST OF JAPAN TO 40N 140W BY THE END OF DAY 7.A SECOND FEATURE OF THE PACIFIC---IS THE EARLY EMERGENCE OF THESUBTROPICAL JET...AND ACTIVE OVER NORTHERN MEXICO SO EARLY IN THELOW-SUN HALF OF THE YEAR. THIS IS USUALLY MORE A LATE JANUARYTHROUGH FEBRUARY OBSERVANCE. AND WITH THE DETERMINISTIC GUIDANCESUGGESTING NOTABLE INCREASES IN THE PACIFIC BRANCH OF A JET NEAR25N...IN CLOSE PROXIMITY TO HAWAI'I NORTHEASTWARD INTO NORTHERNMEXICO BY THE END OF DAY 7...AM THINKING THIS MEDIUM RANGEFORECAST PERIOD IS TRYING TO TELL US SOMETHING---AND PERHAPS THEPATTERN IS CHANGING IN EARNEST...WITH THE DOWNSTREAM EJECTION OFTHE CLOSED LOW OFF THE CALIFORNIA COAST SETTING THINGS INTO MOTION."I mentioned the unusual appearance of what seems to be some sort of sub-tropical feature by the GFS for this coming weekend, and with each run, the GFS has maintained the formation of this significant feature but has changed it's development. The latest run shows it becoming a major storm system next week.There has been a great deal of change within the longer term trends of the model output, even more than usual it seems to me and I can't shake the feeling that something important is going to happen within the next couple of weeks.What NWS are saying about the sub-tropical jet suggests to me a weakening of the northern stream, and subsequent reduction of zonal activity at our latitude. Others more knowledgeable about such things are welcome to comment.The model output is, in my view, even more unreliable in the longer term than is usually the case and I am struggling to see any consistent trend emerging from recent runs of all the major outputs. The storm system I mentioned above, well the projected development just looks plain wrong to me. As I mentioned in my last post, it looks more likely to introduce a greater amplification to the flow upstream and may be what the NWS is getting at.For now, things look pretty "normal" but by the end of the week, I suggest we may see the first signs of a major pattern disruption and change towards a colder and more blocked one. I shall have to mull this over in the coming days and come up with a less vague prediction than this! But I will say that when it comes to cold and snow, be careful what you wish for....!

Great post. Nick Sussex is is very good at extrapolating and analysing these discussions from over the pond. I wonder what his views are on these discussions ?

[shaky]

Some interesting remarks spotted this morning in the NWS forecast discussion. It's not exactly clear to me what the implications are for the circulation pattern here, but it looks significant:"...AND WHAT ISBECOMING MORE EVIDENT...IS THE LATITUDE FOR THE WAVE TRAINMIGRATION. TO ME---IT'S DISPLACED SOUTH OF A 'TYPICAL' LATE-AUTUMNLATITUDE---CLOSER TO 40N-42N THAN 47N-48N ALONG 140W LONGITUDE. IFTHE ECENS MEAN IS ANY INDICATION OF WHAT CAN BE EXPECTED...ITS1/12Z DETERMINISTIC RUN AND 250MB JET FORECAST SHOULD BE NOTEDFROM THE SOUTH COAST OF JAPAN TO 40N 140W BY THE END OF DAY 7.A SECOND FEATURE OF THE PACIFIC---IS THE EARLY EMERGENCE OF THESUBTROPICAL JET...AND ACTIVE OVER NORTHERN MEXICO SO EARLY IN THELOW-SUN HALF OF THE YEAR. THIS IS USUALLY MORE A LATE JANUARYTHROUGH FEBRUARY OBSERVANCE. AND WITH THE DETERMINISTIC GUIDANCESUGGESTING NOTABLE INCREASES IN THE PACIFIC BRANCH OF A JET NEAR25N...IN CLOSE PROXIMITY TO HAWAI'I NORTHEASTWARD INTO NORTHERNMEXICO BY THE END OF DAY 7...AM THINKING THIS MEDIUM RANGEFORECAST PERIOD IS TRYING TO TELL US SOMETHING---AND PERHAPS THEPATTERN IS CHANGING IN EARNEST...WITH THE DOWNSTREAM EJECTION OFTHE CLOSED LOW OFF THE CALIFORNIA COAST SETTING THINGS INTO MOTION."I mentioned the unusual appearance of what seems to be some sort of sub-tropical feature by the GFS for this coming weekend, and with each run, the GFS has maintained the formation of this significant feature but has changed it's development. The latest run shows it becoming a major storm system next week.There has been a great deal of change within the longer term trends of the model output, even more than usual it seems to me and I can't shake the feeling that something important is going to happen within the next couple of weeks.What NWS are saying about the sub-tropical jet suggests to me a weakening of the northern stream, and subsequent reduction of zonal activity at our latitude. Others more knowledgeable about such things are welcome to comment.The model output is, in my view, even more unreliable in the longer term than is usually the case and I am struggling to see any consistent trend emerging from recent runs of all the major outputs. The storm system I mentioned above, well the projected development just looks plain wrong to me. As I mentioned in my last post, it looks more likely to introduce a greater amplification to the flow upstream and may be what the NWS is getting at.For now, things look pretty "normal" but by the end of the week, I suggest we may see the first signs of a major pattern disruption and change towards a colder and more blocked one. I shall have to mull this over in the coming days and come up with a less vague prediction than this! But I will say that when it comes to cold and snow, be careful what you wish for....!

good god we got one hell of a northwesterly blast coming up at the end of high resolution of the latest gfs run!!! Looks pretty dangerous aswell!!

[Hocus Pocus]

Some interesting remarks spotted this morning in the NWS forecast discussion. It's not exactly clear to me what the implications are for the circulation pattern here, but it looks significant:

"...AND WHAT IS

BECOMING MORE EVIDENT...IS THE LATITUDE FOR THE WAVE TRAIN

MIGRATION. TO ME---IT'S DISPLACED SOUTH OF A 'TYPICAL' LATE-AUTUMN

LATITUDE---CLOSER TO 40N-42N THAN 47N-48N ALONG 140W LONGITUDE. IF

THE ECENS MEAN IS ANY INDICATION OF WHAT CAN BE EXPECTED...ITS

1/12Z DETERMINISTIC RUN AND 250MB JET FORECAST SHOULD BE NOTED

FROM THE SOUTH COAST OF JAPAN TO 40N 140W BY THE END OF DAY 7.

A SECOND FEATURE OF THE PACIFIC---IS THE EARLY EMERGENCE OF THE

SUBTROPICAL JET...AND ACTIVE OVER NORTHERN MEXICO SO EARLY IN THE

LOW-SUN HALF OF THE YEAR. THIS IS USUALLY MORE A LATE JANUARY

THROUGH FEBRUARY OBSERVANCE. AND WITH THE DETERMINISTIC GUIDANCE

SUGGESTING NOTABLE INCREASES IN THE PACIFIC BRANCH OF A JET NEAR

25N...IN CLOSE PROXIMITY TO HAWAI'I NORTHEASTWARD INTO NORTHERN

MEXICO BY THE END OF DAY 7...AM THINKING THIS MEDIUM RANGE

FORECAST PERIOD IS TRYING TO TELL US SOMETHING---AND PERHAPS THE

PATTERN IS CHANGING IN EARNEST...WITH THE DOWNSTREAM EJECTION OF

THE CLOSED LOW OFF THE CALIFORNIA COAST SETTING THINGS INTO MOTION."

I mentioned the unusual appearance of what seems to be some sort of sub-tropical feature by the GFS for this coming weekend, and with each run, the GFS has maintained the formation of this significant feature but has changed it's development. The latest run shows it becoming a major storm system next week.

There has been a great deal of change within the longer term trends of the model output, even more than usual it seems to me and I can't shake the feeling that something important is going to happen within the next couple of weeks.

What NWS are saying about the sub-tropical jet suggests to me a weakening of the northern stream, and subsequent reduction of zonal activity at our latitude. Others more knowledgeable about such things are welcome to comment.

The model output is, in my view, even more unreliable in the longer term than is usually the case and I am struggling to see any consistent trend emerging from recent runs of all the major outputs. The storm system I mentioned above, well the projected development just looks plain wrong to me. As I mentioned in my last post, it looks more likely to introduce a greater amplification to the flow upstream and may be what the NWS is getting at.

For now, things look pretty "normal" but by the end of the week, I suggest we may see the first signs of a major pattern disruption and change towards a colder and more blocked one. I shall have to mull this over in the coming days and come up with a less vague prediction than this! But I will say that when it comes to cold and snow, be careful what you wish for....!

You've set the cat amongst the pigeons there OMM.

[LomondSnowstorm]

Really? Looks like a fairly good snow event here for Sunday, at ground level

 

 

Yeah, I do think the whole 'no snow in the next fortnight unless you stand on top of Ben Nevis' type analysis is a bit over the top given we're looking at this in three days time:

While there may not be much precipitation around (as is more the problem with today's 'northerly', as the DP here is sub 0C) the temperature profile still looks pretty conducive to snow:

 

That's before we consider Sunday, when precipitation looks to be more abundant:

 

 

Of course the upper air temperatures may well moderate a bit as we get closer to the time, but it's not that rare to see Polar-sourced northwesterlies deliver - early December 2011 delivered some notable snowfalls for central Scotland with upper air temperatures around -6C:

[blizzard81]

Well, following on from my post last night with regards to colder weather middle third Dec - 10th Dec being the transition, the models really firming up on this. GFS and GFS P 06z carrying on that trend. Like I said last night, nothing frigid but I tell you what, it will probably feel bloomin frigid in that screaming north westerly. Quite a significant wind chill there.

[Man With Beard]

Although there may be bits and pieces of wintry stuff over higher ground coming up, the hunt for cold may need to be put on hold for a bit while we see where this storm is exactly going to go - all too reminiscent of last year - and wouldn't need a great change in track to put millions in its path:

Btw - this chart is for wind gusts - "black" is close to 100mph or higher - even the pinks are 50mph - GFS didn't do too badly last year when forecasting wind speeds IIRC)

[knocker]

Well, following on from my post last night with regards to colder weather middle third Dec - 10th Dec being the transition, the models really firming up on this. GFS and GFS P 06z carrying on that trend. Like I said last night, nothing frigid but I tell you what, it will probably feel bloomin frigid in that screaming north westerly. Quite a significant wind chill there.

 

I find it incredible that you can rattle on about temps and pattern change when the important aspect is the possibility of some extreme weather and wind speeds in Scotland. Yes in your post last night you mentioned a pattern change at day ten. You were wrong then and you are still wrong now unless to would like to offer a different interpretation of this mornings anomalies And actually the temps are above average in England.

Charts courtesy weatherbell

Edited December 2, 2014 by knocker

[terrier]

Not liking the look of the latest gfs run. That storm system look all to reminiscent to last dec. while many seem to be chasing the cold we can't underestimate this storm track. Hopefully it heads further north and misses the uk.

[phil nw.]

Yes a possible storm event across the north is something to watch out for next week.

Naefs and Ecm height forecasts show a noticeable -ve anomaly to the north of Scotland,an area where we can expect lows anyway.

The trend in the 500hpa anomalies keep the seasonal chill with a se aligned upper trough Greenland into E.Europe and Atlantic hts out to the sw.

http://www.meteociel.fr/modeles/ecmwf.php?ech=240&mode=101&map=1&type=1&archive=0

http://www.meteociel.fr/modeles/naefs_cartes.php?ech=240&code=0&mode=0&map=1&runpara=

No sign of any advance west of Russian hts so it looks like we continue with a rather chilly Atlantic pattern with signs of a more unsettled and windy week 2.

Any change I would think would come from upstream of which there is no sign yet.

Edited December 2, 2014 by phil nw.

[Team Jo]

Could I ask that we try and keep to model discussion, as oppose to the somewhat confrontational one liners/woe is me, it's never going to snow - type comments... there's a special thread for that.. so if your post has disappeared from here, it's probably been relocated to there.

 

[blizzard81]

The GFS P offering something much more blocked post day 11 and it should feel very seasonal. The other thing I noticed about the run was the banal nature of the weather over in the States. I think many over there, especially in the north east

may welcome this after the extreme cold of last winter, unless they are a coldie like me!

[IDO]

Those whom are supporting the UKMO have to remember that all the other models are bringing the Atlantic storm into the jet at about T126-T138 and blowing it up into a deep storm by D6:

 

06z P: 06z op:

 

The UKMO at T144: 

 

Not a sign of the storm, in complete contrast to ECM, GFS and GEM. I suspect they are wrong from D3 and that means everything that follows is even more wrong.

 

The control  is one of the worse case scenarios and the eye of the storm:   

 

Timing issues on the GEFS as well as intensity and track but the vast majority agreeing on a deepening storm: http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=168

 

 

 

 

[Nouska]

Hi John and good morning,

I noticed on p. 27, dealing with North Atlantic sea-surface temperature, the following... 'NAO prediction based on this factor alone: +0.5'.

That seems an interesting statement to make; it seems they take the NAO state which they are expecting for the next three months based entirely from one factor (and that with a seemingly not very strong signal too): current North Atlantic sea-surface temperatures.  Am I interpreting this correctly? (- I was!!)  If so, what is it about this particular signal that means it gets to be the only one worth considering? (- now irrelevant, they don't). Also, p. 31 seems to paint a different picture using a hindcast method? (still interested in what the charts there show...).  Slightly (less) confused by this one (now!)...

 

Way back in the early noughties, the May SSTs were used as an NAO indicator in the Met Office's winter forecasts. It wasn't mentioned after they dropped the public seasonal forecasts but seems to have made a reappearance in a paper about the GloSea5 prediction skills. I would offer a tentative suggestion that the long range models are being skewed by very warm oceans, all over the Globe.

 

It is interesting that the NOAA LR forecast, predicated only on SST anomalies, is showing something very different as a forecast for this winter.

[legritter]

good morning posters ,although no real signs of deep cold on todays charts and Data there is plenty of interest out past the 6 day range .every possibility of some newsworthy weather headlines Next week and quite a chance for some of us to see[ Some]Snow and unwelcome wind storms .but as usual at the seven day range many things yet to be sorted on any track and timing of such events .past this it could be a case of repeat and rinse looking at extended Data ,but remember how things changed last year towards mid month ,no guarantee it will this time around, but we are i feel going to have some very interesting Model discussion with some Joy for some depending on your preference of weather type .so to sum it up it looks like our kneck of the woods is going from quiet uneventfull weather pattern to a Quick change artist with a sting  in its Tail ,Mr vortex Has been given the Sack by north american and Canadian upper air space ,Final destination [watch this space ]. Not a very technical post but we all have our way of expression ,  

[Mapantz]

Really? Looks like a fairly good snow event here for Sunday, at ground level

 

While some snow could at lower levels cannot be ruled out, I'm not sure how you can suggest a good snow event at ground level from that chart?

Whilst 850's may support snow, other factors need to be added in. One factor would be the 0C isotherm heights- Here's the chart from the same run and the same time.

Typically, some transient snow (possibly heavy for a time) 200-500m, in heavier showers/bands of precipitation, the isotherm can be dragged down to allow snow to fall at lower levels.

This experimental chart gives the sort of idea in what sort of heights/areas would see accumulations

It's all speculative this far out of course, and I'm not an expert but it's wise not to expect a "good snow event at ground level" from the type of chart you posted.

It'll be fun watching some of those webcams on the Scottish mountains though!

[garbagebags]

While some snow could at lower levels cannot be ruled out, I'm not sure how you can suggest a good snow event at ground level from that chart?

Whilst 850's may support snow, other factors need to be added in. One factor would be the 0C isotherm heights- Here's the chart from the same run and the same time.

viewimage.png

Typically, some transient snow (possibly heavy for a time) 200-500m, in heavier showers/bands of precipitation, the isotherm can be dragged down to allow snow to fall at lower levels.

This experimental chart gives the sort of idea in what sort of heights/areas would see accumulations

viewimage (2).png

It's all speculative this far out of course, and I'm not an expert but it's wise not to expect a "good snow event at ground level" from the type of chart you posted.

It'll be fun watching some of those webcams on the Scottish mountains though!

 

Hi, my reply was moved here - https://forum.netweather.tv/topic/81281-model-banter-moans-and-ramps-autumnwinter-2014/page-49

Thanks,.

[blizzard81]

Is this the major wind storm (sometime in December) that Chio refers to in the winter forecast ?

Misses most of the UK on this run but it's track may change and I wonder if it will herald a major

pattern change ?

 

gfsnh-0-192.png

 

I say it misses us but it may actually hit us later in the run!

Knocker - see my post from yesterday afternoon (above).I was probably the first person to mention the wind storm. This storm and the change to colder weather are intrinsically linked as stated in my post.

[Dr. Astro]

Good morning all,

 

Following on from OldMetMan's comments regarding the NWS discussion, i'd like to add some further information.

 

I'll try and keep this as simple as possible.

 

Firstly though, the current weather situation we have here in the United Kingdom, or "reliable timeframe" as it's commonly known as.

 

This week, Monday to Thursday is looking rather benign, dry, some sunshine and feeling chilly, especially at night time, where frosts may accumilate in favourable places.

 

We can see this from the following charts: (I'll be using the GFS to illustrate in the reliable time frame, as most models agree unanimously)

 

Tuesday

 

 

 

Wednesday

 

 

Thursday

 

 

So, we can see from the above charts (MAX Temperatures) that it will feel rather chilly, especially after the mild(ish) weather we have been accustomed to as of late.

 

The 500-1000hPa charts are of good use, these measure how warm, or how cold a layer is in the atmosphere. Thickness charts are a good way to measure the probability of snow, or other prospects like warm/cold air.

 

The change is coming in from our North West of the United Kingdom, and we can see by Thursday night.

 

We can see on the T850 chart, which measures the upper air temperature's and becomes instrumental to what we recieve on the ground, so to speak. It's also another good tool to use for deciding if you will get snow or not, and the general rule is:

(Maritime flow)

Sea Level: -7c

150m: -6c

300m: -5c

450m: -4c

600m: -3c

 

I say "General Rule" as it can be different depending on what else is happening weather wise.

 

So, anyways, we can see from the following thickness chart on Friday there is potential for snow, albeit mainly at elevated levels.

 

 

The above chart is the 500-1000hPa. What we are looking for here is the "528 DAM Line" or 528 Dacameters. We want this to be as south as possible if you are looking for cold/snow.

 

The 850's are showing at -5C.

 

 

Using the rule we learnt earlier, places above 300-400m could see some snow.

 

We can see from the Snow Risk chart below as the front pushes in, NW Scotland and higher ground 400m + is ideal for snowfall.

 

 

After this time frame, we are really getting into the unreliable time frame, but it's always nice to check what the charts are showing within the reliable timeframe, as people tend to get carried away with silly posts like:

 

"No cold for the next 4 weeks"

"No mild weather for the next 4 weeks"

"No snow in December"

"Charts are crap"

 

Etc etc, you get my point. If anyone can tell you with 100% confidence what the weather will be like in 4 weeks time, then they should be working for NASA/UK Met and running the company. Oh, and placing lottery numbers too.

 

As I mentioned at the start of the post to go on from what OldMetMan was talking about, we can see as per comment from NWS:

 

 

A SECOND FEATURE OF THE PACIFIC---IS THE EARLY EMERGENCE OF THE
SUBTROPICAL JET...AND ACTIVE OVER NORTHERN MEXICO SO EARLY IN THE
LOW-SUN HALF OF THE YEAR. THIS IS USUALLY MORE A LATE JANUARY
THROUGH FEBRUARY OBSERVANCE

 

We can see where the Jet is at the moment in Mexico which attributes to the post above, it usually isn't their at the moment.

 

 

Maybe this does mean a large pattern distruption, I am not sure, but will have a good look at the charts and data available to us and decide from there.

 

If we look at the forecast for the Jet we can see it remains very strong for 14/12

 

 

But after this is where the NWS discussion and what OldMetMan was talking about might change, around the 17th as we see a strong surge from the Jet over Mexico at 180 hours.

 

 

Which looks on course for Central USA & should start to impact upstream around the 17th.

 

Remembering the Jet Stream from earlier, and how powerful it was, we can see around the time of impact C.USA we have a slack Jet coming from Canada and southerly digging:

 

I am unsure if this is related, but will post again when I have done some research.

 

Another thing to keep an eye out on is the potential storm, at the moment it's hitting Scotland, and Western Isles, but needs an eye kept on to track and see how it unfolds, but that's for another post, maybe.

 

Regards,

 

Dr. Astro

 

 

[MR EXTREMES]

So plenty of neg post from lots today it's only the start of winter and a lot have suggested jan to be the month to expect changes.

Whether or not the met office agree with future developments beyond there limits don't mean anything there job is to forecast the near future developments.

I think the comments discounting the OPI index and other dynamic forcings have not even taken affect.

Maybe recent solar activity has helped fuel the vortex and is a worry but really no one can call further into winter but on the flip side a ssw event is without a doubt a possibility this should help unless the trop takes the start on and causes a knock out blow for the rest of winter is another idea more suited for the strat thread.

[winterof79]

Its between D6-10 that the north may see some wintry weather and its about a 20-25% chance at the moment: NW graphe3_1000_232_0___.gif

 

Further south its 5-10% so an outsider: graphe6_1000_306_141___Londres-27.gif

 

As it is coming from the NW and that flow tends to get downgraded as the uppers are modified then all rather uncertain. However it is also to do with how the Atlantic storm interacts with the jet and this changes run to run and amongst the ensembles. 

The 06z ups the % a touch so at least some interest

http://modeles.meteociel.fr/modeles/gens/runs/2014120206/graphe3_1000_268_31___.gif

[IDO]

So plenty of neg post from lots today it's only the start of winter and a lot have suggested jan to be the month to expect changes.

Whether or not the met office agree with future developments beyond there limits don't mean anything there job is to forecast the near future developments.

I think the comments discounting the OPI index and other dynamic forcings have not even taken affect.

Maybe recent solar activity has helped fuel the vortex and is a worry but really no one can call further into winter but on the flip side a ssw event is without a doubt a possibility this should help unless the trop takes the start on and causes a knock out blow for the rest of winter is another idea more suited for the strat thread.

 

 

Its not negativity it is "probability". That is the way I always look at the weather. At the moment it is highly unlikely that we will get a high latitude blocking pattern in the NH in the next 16 days. That is based on current output rather than experience from say the more knowledgeable members. Of course there is still a chance that the pattern will change but looking at the 16 day GEFS I would put that down to <10% for blocking to materialise.

 

 

The 06z ups the % a touch so at least some interest

http://modeles.meteociel.fr/modeles/gens/runs/2014120206/graphe3_1000_268_31___.gif

 

 

Yes some of the GEFS get many of the parameters spot on for transient low level snow. Cannot rule it out. The control is one, though it is nasty with respect to the storm, so hoping this is unlikely. Though in context I cannot remember last winter in my region having too many 10-15% chances of snow so already better than last year if snow is your thing.

[blizzard81]

Good morning all,

 

Following on from OldMetMan's comments regarding the NWS discussion, i'd like to add some further information.

 

I'll try and keep this as simple as possible.

 

Firstly though, the current weather situation we have here in the United Kingdom, or "reliable timeframe" as it's commonly known as.

 

This week, Monday to Thursday is looking rather benign, dry, some sunshine and feeling chilly, especially at night time, where frosts may accumilate in favourable places.

 

We can see this from the following charts: (I'll be using the GFS to illustrate in the reliable time frame, as most models agree unanimously)

 

Tuesday

 

 

 

Wednesday

 

 

Thursday

 

 

So, we can see from the above charts (MAX Temperatures) that it will feel rather chilly, especially after the mild(ish) weather we have been accustomed to as of late.

 

The 500-1000hPa charts are of good use, these measure how warm, or how cold a layer is in the atmosphere. Thickness charts are a good way to measure the probability of snow, or other prospects like warm/cold air.

 

The change is coming in from our North West of the United Kingdom, and we can see by Thursday night.

 

We can see on the T850 chart, which measures the upper air temperature's and becomes instrumental to what we recieve on the ground, so to speak. It's also another good tool to use for deciding if you will get snow or not, and the general rule is:

(Maritime flow)

Sea Level: -7c

150m: -6c

300m: -5c

450m: -4c

600m: -3c

 

I say "General Rule" as it can be different depending on what else is happening weather wise.

 

So, anyways, we can see from the following thickness chart on Friday there is potential for snow, albeit mainly at elevated levels.

 

 

The above chart is the 500-1000hPa. What we are looking for here is the "528 DAM Line" or 528 Dacameters. We want this to be as south as possible if you are looking for cold/snow.

 

The 850's are showing at -5C.

 

 

Using the rule we learnt earlier, places above 300-400m could see some snow.

 

We can see from the Snow Risk chart below as the front pushes in, NW Scotland and higher ground 400m + is ideal for snowfall.

 

 

After this time frame, we are really getting into the unreliable time frame, but it's always nice to check what the charts are showing within the reliable timeframe, as people tend to get carried away with silly posts like:

 

"No cold for the next 4 weeks"

"No mild weather for the next 4 weeks"

"No snow in December"

"Charts are crap"

 

Etc etc, you get my point. If anyone can tell you with 100% confidence what the weather will be like in 4 weeks time, then they should be working for NASA/UK Met and running the company. Oh, and placing lottery numbers too.

 

As I mentioned at the start of the post to go on from what OldMetMan was talking about, we can see as per comment from NWS:

 

 

We can see where the Jet is at the moment in Mexico which attributes to the post above, it usually isn't their at the moment.

 

Jet.png

 

Maybe this does mean a large pattern distruption, I am not sure, but will have a good look at the charts and data available to us and decide from there.

 

If we look at the forecast for the Jet we can see it remains very strong for 14/12

 

 

But after this is where the NWS discussion and what OldMetMan was talking about might change, around the 17th as we see a strong surge from the Jet over Mexico at 180 hours.

 

Jet 2.png

 

Which looks on course for Central USA & should start to impact upstream around the 17th.

 

Remembering the Jet Stream from earlier, and how powerful it was, we can see around the time of impact C.USA we have a slack Jet coming from Canada and southerly digging:

 

I am unsure if this is related, but will post again when I have done some research.

 

Another thing to keep an eye out on is the potential storm, at the moment it's hitting Scotland, and Western Isles, but needs an eye kept on to track and see how it unfolds, but that's for another post, maybe.

 

Regards,

 

Dr. Astro

Welcome Dr Astro, just about the best and most informative first post I have ever seen.

[Man With Beard]

 

 

Etc etc, you get my point. If anyone can tell you with 100% confidence what the weather will be like in 4 weeks time, then they should be working for NASA/UK Met and running the company. Oh, and placing lottery numbers too.

 

 

 

Great opening post Dr. Astro - welcome to the forum - I have highlighted the bit of your post that I particularly liked! 

[summer blizzard]

Well, looks like we have quite a seasonal week coming up which should please many. Not until the 9th do models have tropical maritime air..