Model output discussion - cold spell approaching?

[Scott Ingham]

So weather warnings out for 5-15cm above 150m and locally 30cm in northern england wednesday.

Who needs severe cold for snow haha!

[mountain shadow]

6 minutes ago, mushymanrob said:

Well this post wont be very popular, lol..

According the the NOAA charts, there is no sustained deep cold from the Northeastern quadrant in the next two weeks, although this could change of course.

There is a positive pressure anomaly over Greenland, and some ridging, There is a negative pressure anomaly over Europe along with some troughing. But the mean upper flow remains in the Northwest, so IMHO any of that cold to our Northeast isnt likely to be paying us a visit apart from transient blasts. So until/unless these charts shift to allow a prolonged flow from the North or Northeast, im not buying the deep freeze some runs suggest.


 

Now, i do struggle to read these, but how are you seeing a mean upper flow from the North West on these, surely the dashed lines are on an NE to SW axis?

[MATTWOLVES 3]

13 minutes ago, Loadsa2000 said:

Been a long time viewer (probably 15 years plus)

Quick question and a thought reference models

Do you think there will come a day where the models are 100% accurate?

If that would happen how boring this thread would be become.

I never post on here but fascinated how different people have different thoughts about the same models (that is apart from the few who just try to wind posters up)

Good lord don't even go there,we get manic depression in here viewing the output as it is..just imagine if all the models were 100% accurate all the time...the NHS would most definitely run out of sedatives..But in the hear and now we have at least exciting times ahead...I really do hope this Central Northern areas risk gets pulled South though...share the Snow and all that...

Edited January 11, 2021 by MATTWOLVES

[Kirkcaldy Weather]

9 minutes ago, mushymanrob said:

Well this post wont be very popular, lol..

According the the NOAA charts, there is no sustained deep cold from the Northeastern quadrant in the next two weeks, although this could change of course.

There is a positive pressure anomaly over Greenland, and some ridging, There is a negative pressure anomaly over Europe along with some troughing. But the mean upper flow remains in the Northwest, so IMHO any of that cold to our Northeast isnt likely to be paying us a visit apart from transient blasts. So until/unless these charts shift to allow a prolonged flow from the North or Northeast, im not buying the deep freeze some runs suggest.

On the positive side (for cold) its not going to be mild either, its looking (normal) cold and unsettled to me.

 

Hi, this isn’t having a go at you I am just trying to understand as I haven’t used that websites charts before but I rotated it and tried to make out how I’m reading it  which fits in with the outlook

[mountain shadow]

14 minutes ago, feb1991blizzard said:

it screams a shift to west based though, although granted the 240 chart is decent, if not as good as the 0z suite, anyway i am more worried about the EPS collapse of the ridge at 240 than the GEFS west based -nao

And that can be what causes a West based -nao by squeezing the cold out into the Atlantic

 

The chart shows virtually the whole of Europe in a deep freeze North a of a line from Midlands England across to Ukraine. I West based NAO would have milder air moving into Central Europe. This is not a West based -NAO

[mountain shadow]

1 minute ago, Kirkcaldy Weather said:

Hi, this isn’t having a go at you I am just trying to understand as I haven’t used that websites charts before but I rotated it and tried to make out how I’m reading it  which fits in with the outlook

That's what i'm seeing too. Unless the dashes don't imply air mass direction.

[SLEETY]

15 minutes ago, mushymanrob said:

Well this post wont be very popular, lol..

According the the NOAA charts, there is no sustained deep cold from the Northeastern quadrant in the next two weeks, although this could change of course.

There is a positive pressure anomaly over Greenland, and some ridging, There is a negative pressure anomaly over Europe along with some troughing. But the mean upper flow remains in the Northwest, so IMHO any of that cold to our Northeast isnt likely to be paying us a visit apart from transient blasts. So until/unless these charts shift to allow a prolonged flow from the North or Northeast, im not buying the deep freeze some runs suggest.

On the positive side (for cold) its not going to be mild either, its looking (normal) cold and unsettled to me.

 

How can you get a flow from the NW with that chart ,its impossible the wind would be going around the high pressure clock wise,so NE 

[Vikos]

11 minutes ago, mushymanrob said:

Well this post wont be very popular, lol..

According the the NOAA charts, there is no sustained deep cold from the Northeastern quadrant in the next two weeks, although this could change of course.

There is a positive pressure anomaly over Greenland, and some ridging, There is a negative pressure anomaly over Europe along with some troughing. But the mean upper flow remains in the Northwest, so IMHO any of that cold to our Northeast isnt likely to be paying us a visit apart from transient blasts. So until/unless these charts shift to allow a prolonged flow from the North or Northeast, im not buying the deep freeze some runs suggest.

On the positive side (for cold) its not going to be mild either, its looking (normal) cold and unsettled to me.

 

Would agree if we where somewhere around mid-to-end of February, but hey, it's still (begin) of January. We had a (by now in detailted outcome unpredictable) SSWE with great NH-patterns wich show more cold then mild outcomes, even without a PV-Split, wich is to come by the 3rd decade of January if more minor warmings (like predicted) attack it.

Regarding cold to the Northeastern, Sibiria is facing record colds...

[feb1991blizzard]

5 minutes ago, mountain shadow said:

The chart shows virtually the whole of Europe in a deep freeze North a of a line from Midlands England across to Ukraine. I West based NAO would have milder air moving into Central Europe. This is not a West based -NAO

Has turned into a very good set, yes - i admit, needs the eps to follow suite.

[Singularity]

11 minutes ago, mushymanrob said:

Well this post wont be very popular, lol..

According the the NOAA charts, there is no sustained deep cold from the Northeastern quadrant in the next two weeks, although this could change of course.

There is a positive pressure anomaly over Greenland, and some ridging, There is a negative pressure anomaly over Europe along with some troughing. But the mean upper flow remains in the Northwest, so IMHO any of that cold to our Northeast isnt likely to be paying us a visit apart from transient blasts. So until/unless these charts shift to allow a prolonged flow from the North or Northeast, im not buying the deep freeze some runs suggest.

On the positive side (for cold) its not going to be mild either, its looking (normal) cold and unsettled to me.

 

I'm afraid I must red flag this; it's not entirely accurate analysis.

The contour lines show the flow at 500 mb, which dictates the movement of surface weather systems, not the mean direction of surface flow.

The upper ridge to the west supports surface ridges with northerly or north-easterly flow on their eastern flank. The trough to the east of that supports areas of low pressure over mainland Europe, much as we've seen in a good few model runs so far today, which also support spells of northerly to north-easterly flow in the vicinity of the UK.

Now, it's true that the ridge-trough setup is not pronounced enough to lend confidence to a sustained N to NE flow across the UK, but there's a reasonable chance that it occurs for long enough to move some notably cold air in our direction. How far it makes it, is anyone's guess.

[Man With Beard]

38 minutes ago, Daniel* said:

Bugging me that EPS has gone even further in wrong direction. We need this on our side fast.

Yes you're absolutely right - whilst the GFS and to some extent the GEFS seem on balance to favour a colder outcome, the ECM ensembles on the whole are far less interested in creating a long-lasting block to the NW. Spread is still fairly large though.

I'm content with predictions of at least a temporary northerly flow around 18th/19th/20th, but we're a long way from predicting something like a 7 or 10 day freeze with blizzards in summary of the output of the last 24 hours, regardless of what the GEFS is coming out with right now.

On the other hand, although the potential bonus snowfall for later this week isn't far off the marginal point away from northern areas, confidence is very slowly increasing that something will might about from this.

[DanDorsetUK]

For me the heights are only going to amplify on upcoming runs untill downwelling ends.

You can already see mirroring taking place and the trends to drop the PV into Europe and then head west. It's all going to plan. 

The downwelling is still taking place, models will only run with the data it sees. I'm pretty sure the models have yet to take into full account the full impacts of the downwelling. 

The greater the downwelling the more they will run with greater heights, and i feel there is some even better runs yet to come.

For me were just seeing the start of the pattern developing. Heights pushing in from behind the PV in future warmings will only help to drop the PV even lower and push west. I'm very confident were going to be slammed possibly even right through Febuary.

I dont see much stopping this now the momentum is gaining. Maybe a delay here and there with some drama along the way but overall your not going to stop the shift.

Looking for waa up into Greenland is not the only driving factor here but will help with link ups.

There is pressure being forced from above down not just from waa and that I feel the models have yet to fully factor into runs yet.

The Siberian express has already left the station, it may have a few stops on the way but the final destination for me remains the same how ever long it takes to get here.

[Continental Climate]

19 minutes ago, mountain shadow said:

That's what i'm seeing too. Unless the dashes don't imply air mass direction.

That's what I saw too a nor Easter from scandi/Russia. Could be wrong though. 

[johnholmes]

14 minutes ago, Singularity said:

I'm afraid I must red flag this; it's not entirely accurate analysis.

The contour lines show the flow at 500 mb, which dictates the movement of surface weather systems, not the mean direction of surface flow.

The upper ridge to the west supports surface ridges with northerly or north-easterly flow on their eastern flank. The trough to the east of that supports areas of low pressure over mainland Europe, much as we've seen in a good few model runs so far today, which also support spells of northerly to north-easterly flow in the vicinity of the UK.

Now, it's true that the ridge-trough setup is not pronounced enough to lend confidence to a sustained N to NE flow across the UK, but there's a reasonable chance that it occurs for long enough to move some notably cold air in our direction. How far it makes it, is anyone's guess.

Interpreting differences about the 500 mb anomaly charts;

within the next 2 weeks these will be the closest we get as to what the upper pattern is likely to be. The interpretation as to what may happen below 500 mb is never easy. I'll check the daily outputs I do on my weather file and drop my ideas in here sometime this afternoon.

[johnholmes]

19 minutes ago, SLEETY said:

How can you get a flow from the NW with that chart ,its impossible the wind would be going around the high pressure clock wise,so NE 

I suspect that you are wrong, the best advice I can offer to those not used to using the 500 mb anomaly charts is IGNOE the anomaly part and just look at the contour flow. The dahsed lines as some one has quoted as 'following the wind direction' is quite wrong. What the dotted lines how is how much the contour lines are above or below what the average value of the contour line is.

Hope that helps.

 

[johnholmes]

That's what i'm seeing too. Unless the dashes don't imply air mass direction.

 

See my comment above, no hey do not.

 

[mushymanrob]

27 minutes ago, mountain shadow said:

Now, i do struggle to read these, but how are you seeing a mean upper flow from the North West on these, surely the dashed lines are on an NE to SW axis?

 

23 minutes ago, Kirkcaldy Weather said:

Hi, this isn’t having a go at you I am just trying to understand as I haven’t used that websites charts before but I rotated it and tried to make out how I’m reading it  which fits in with the outlook

 

21 minutes ago, mountain shadow said:

That's what i'm seeing too. Unless the dashes don't imply air mass direction.

 

18 minutes ago, SLEETY said:

How can you get a flow from the NW with that chart ,its impossible the wind would be going around the high pressure clock wise,so NE 

Hi guys

The red/blue dotted lines are pressure anomalies, not flow lines , the green lines are the mean upper wind direction from West (left) to East (right).

Being the mean over that period allows surface winds from other directions, but the further away from the mean, the shorter their duration. So we could have a Northeasterly, but it wont be sustained, and to balance out the mean, for every Northeasterly there needs to be a westerly.

Im msure my mentour @johnholmes will correct me if this is inaccurate.

[johnholmes]

I will try and find the basic guidance on this from about 8-9 years ago. It may take some time as I file my ideas on these charts daily every day winter and summer!

 

[wiltshire weather]

34 minutes ago, Singularity said:

I'm afraid I must red flag this; it's not entirely accurate analysis.

The contour lines show the flow at 500 mb, which dictates the movement of surface weather systems, not the mean direction of surface flow.

The upper ridge to the west supports surface ridges with northerly or north-easterly flow on their eastern flank. The trough to the east of that supports areas of low pressure over mainland Europe, much as we've seen in a good few model runs so far today, which also support spells of northerly to north-easterly flow in the vicinity of the UK.

Now, it's true that the ridge-trough setup is not pronounced enough to lend confidence to a sustained N to NE flow across the UK, but there's a reasonable chance that it occurs for long enough to move some notably cold air in our direction. How far it makes it, is anyone's guess.

I am only just trying to work out how these anomaly charts work after getting some pointers from @John Holmes, so just to illustrate the example to aid in my understanding to see if I'm grasping it correctly, here is the GFS 500MB Wind Chart for the 21st Jan which roughly matches the solid green lines on the NOAA chart (edit: I know the anomaly charts are showing the mean flow over a number of days but it seems to correlate quite well with this chart from the middle of the period!)

And now the GFS 500hPa Geopot. Height Chart for the same date/time which gives an idea of how the pressure patterns at the surface might look:

As far as I know I think the dotted lines show the pressure anomalies rather than the actual surface pressures.

Hopefully I'm interpreting that correctly!

WW

Edited January 11, 2021 by wiltshire weather
Typos and clarification

[mushymanrob]

22 minutes ago, Singularity said:

I'm afraid I must red flag this; it's not entirely accurate analysis.

The contour lines show the flow at 500 mb, which dictates the movement of surface weather systems, not the mean direction of surface flow.

The upper ridge to the west supports surface ridges with northerly or north-easterly flow on their eastern flank. The trough to the east of that supports areas of low pressure over mainland Europe, much as we've seen in a good few model runs so far today, which also support spells of northerly to north-easterly flow in the vicinity of the UK.

Now, it's true that the ridge-trough setup is not pronounced enough to lend confidence to a sustained N to NE flow across the UK, but there's a reasonable chance that it occurs for long enough to move some notably cold air in our direction. How far it makes it, is anyone's guess.

Hi

Im not sure theres much of a difference between " The contour lines show the flow at 500 mb, which dictates the movement of surface weather systems, not the mean direction of surface flow." after all , doesnt the 500hpa strongly dictate the surface?

Agreed about the second para, but as these charts are the mean, surely for every northerly theres a westerly if the mean is northwesterly?

Well im not sure we are that far apart tbh, far be it for me, an amateur to argue against someone with qualifications, im not so sure theres much difference in what we are saying.

[mountain shadow]

13 minutes ago, mushymanrob said:

 

 

 

Thanks Mushy.

I don't suppose you have an archived one of these with what a North Easterly would look like then?

Would help in future analysis maybe?

[NewEra21]

Poorest in terms of deep cold towards the end of the run for a few runs, not that it's correct of course. Op once again one of the coldest.

Edited January 11, 2021 by NewEra21

[mushymanrob]

2 minutes ago, mountain shadow said:

Thanks Mushy.

I don't suppose you have an archived one of these with what a North Easterly would look like then?

Would help in future analysis maybe?

We had pne a few days ago when we had the northerly at the beginning of the year... hold on... theres a website ill find an example..

[johnholmes]

Well I've found 'some' of these example, one has 16 yes 16 pages, there are two others but I'll see if I can persuade Paul to allow me to do something in the Learning area so that there is something in there to have a look at. I don't pretend to be the final arbiter in this either. The original data goes back to 2010 when Ifirst started to use them, so some of you may find errors in there.

Anyway its lunch time but I will try and post a first simple guide to see if it helps. They do work, in a 9-10 month check I did back in, I think somewhere between 2010 ans 2012 the 6-10 Noaa showed about a 70-75% accuracy for the upper pattern and 65% fr the 8-14 day. So much higher than the 2x or 4x synoptic output. That is the easy bit one could say, the more difficult part is creating the surface flow from them. Anyway I'll be back later. 

Thanks mushy

 

[chionomaniac]

10 minutes ago, mushymanrob said:

Hi

Im not sure theres much of a difference between " The contour lines show the flow at 500 mb, which dictates the movement of surface weather systems, not the mean direction of surface flow." after all , doesnt the 500hpa strongly dictate the surface?

Agreed about the second para, but as these charts are the mean, surely for every northerly theres a westerly if the mean is northwesterly?

Well im not sure we are that far apart tbh, far be it for me, an amateur to argue against someone with qualifications, im not so sure theres much difference in what we are saying.

Hi Mushy, If you average the flow out over 6 days and then place as 500hPA mean heights then there can be quite large differences between the 6 day 500hPA mean flow and the surface flows during that period. Th0se means were never meant to be read like that. The pressure anomalies are more important when working out likely stearing upper and surface flows as Kirkcaldy showed.