Model Output Discussion - Into Summer 2020.

[mb018538]

A long way off, but the end of the clusters look good too - a big upper ridge covering the UK. Settled weather more likely.

[Zak M]

Now that's a tasty 06z GFS 

[Tamara]

14 hours ago, offerman said:

That's great. Thank you MBO for the reply and good explanation . Much appreciated . 

Yes, it was good and helpful he replied

You will possibly have seen some of us posting these diagnostic wind-flow plots which in essence measure the strength and path of the jet stream. Much of the wind-flow inertia, though not all, comes from propagation of these wind-flows between the tropics and the extra tropics via torque mechanisms which essentially create a turning force action on the jet stream and alter the strength and direction of the jet stream according to whether greater westerly energy (via positive torques) or greater easterly loss of momentum is weakening forward westerly momentum in the tropics (via negative torques).

The inflection point of these torques is determined in large part by where low frequency tropical convection forcing is positioned in the tropics - and how active the high frequency MJO tropical signal is in terms of whether it augments the low frequency signal or creates a, usually transitional and temporary, a-typical relationship through the atmospheric circulation to the ocean base state.

To deliberately greatly over simplify for purposes of not overcomplicating things - as we know, ENSO phases switch periodically in the Pacific and these phases fluctuate according to various cyclical and intra seasonal phenomena.    When wind-flow inertia overall is lower than average in the atmospheric circulation, then easterly (negative) trade winds dominate across the tropics and through the ENSO zones. As determined by the laws of conservation of angular momentum, this puts compensatory forward energy into the extra tropical jet which flows downstream from the Pacific to the Atlantic. The inflection point of the negative torque usually propagates around 20N to 30N in the Equatorial Pacific and the divergence of decelerating wind-flow creates amplification and sub tropical anticyclonic responses which are amplified poleward into the extra tropics. The displaced westerly momentum in the extra tropics flows across the top of this anticyclonic response according to the downstream trough/ridge response - which is the downstream sub tropical Bermuda and Azores ridges likewise intensified and amplified in the central and western Atlantic. The downstream jet loops across N America and then likewise around the flank of the high pressure response in the Atlantic  - with downstream trough signatures across NW Europe and Scandinavia.

This is the kind of default scenario we saw play out at times during June, and is set to continue, at times, during July. However, as posted recently there are various other factors (already covered in some considerable detail in previous posts) which are periodically interfering with this typical low angular momentum La Nina type summer pattern response, and which allows the Atlantic ridge to adjust eastwards into the UK and other parts of NW Europe periodically. This also happened in June, as we know, and looks like it will be a theme as well during the upcoming month

So this is duly playing out once more in the modelling - with the Azores ridge advertised to return eastwards into the second full week of July. Assuming that the high frequency tropical forcing aiding this shift plays out sufficiently to diffuse the low frequency tropical signal as it propagates eastward across the tropics, then the risk of the ridging being adjusted back into the Atlantic at this timeframe is reduced. During the next few days it will be possible to monitor this and report back on progress - but at this time it looks promising for summer weather to make a return, at least for a time, during the following week

That means I agree with @bluearmycomment, on the basis of the above analysis, that chances of extended country-wide heatwaves are unlikely - but if one is prepared to be sanguine over a mixed pattern of relatively shorter warm spells, potentially thundery breakdowns of interest (such as end of last week) back into cooler more changeable spells when the low frequency tropical signal re-dominates, then it is a reasonable seasonal outlook

 

Edited June 28, 2020 by Tamara

[NApplewhite]

2 hours ago, Zak M said:

Now that's a tasty 06z GFS 

Looking a bit better on Thursday this week as a nose of higher pressure (try's to move) in from the Azores never establishes though.  NW/SE split. Further attempt on Sunday 5th July 2020  . Tomorrow is a washout across the UK (last image) Jetstream doesn't look great though on the 6th July so a lot of strong high level winds even under the higher pressure.  La Nina has a 50% chance of developing over the next few weeks. Causing a US heatwave in the MidWest and cooling across N Europe

 

Edited June 28, 2020 by NApplewhite

[MATTWOLVES 3]

Thanks for that insightful post @Tamara I've got to agree with that also, and what Blue states as well.. The GFS 6z mean tends to ebb and flow with that Azores High Pressure. We see the extension of it building in at times and especially for Central Southern parts, before a little breakdown and trough bring rinse and repeat scenarios moving forwards. This looks like a potential trend for July in general with plenty of usable conditions, and at times probably very warm. The EC46 seems to highlight this type of pattern quite well with the ridge building in at times before receding back SW after a few days. All in all the long term trend is pretty good and more especially away from those NW locations.

 

 

[Northwest NI]

16 minutes ago, MATT said:

Thanks for that insightful post @Tamara I've got to agree with that also, and what Blue states as well.. The GFS 6z mean tends to ebb and flow with that Azores High Pressure. We see the extension of it building in at times and especially for Central Southern parts, before a little breakdown and trough bring rinse and repeat scenarios moving forwards. This looks like a potential trend for July in general with plenty of usable conditions, and at times probably very warm. The EC46 seems to highlight this type of pattern quite well with the ridge building in at times before receding back SW after a few days. All in all the long term trend is pretty good and more especially away from those NW locations.

 

 

Would NE locations not fare worst with Azores ridging, I would have thought?

[offerman]

3 hours ago, Tamara said:

Yes, it was good and helpful he replied

You will possibly have seen some of us posting these diagnostic wind-flow plots which in essence measure the strength and path of the jet stream. Much of the wind-flow inertia, though not all, comes from propagation of these wind-flows between the tropics and the extra tropics via torque mechanisms which essentially create a turning force action on the jet stream and alter the strength and direction of the jet stream according to whether greater westerly energy (via positive torques) or greater easterly loss of momentum is weakening forward westerly momentum in the tropics (via negative torques).

The inflection point of these torques is determined in large part by where low frequency tropical convection forcing is positioned in the tropics - and how active the high frequency MJO tropical signal is in terms of whether it augments the low frequency signal or creates a, usually transitional and temporary, a-typical relationship through the atmospheric circulation to the ocean base state.

To deliberately greatly over simplify for purposes of not overcomplicating things - as we know, ENSO phases switch periodically in the Pacific and these phases fluctuate according to various cyclical and intra seasonal phenomena.    When wind-flow inertia overall is lower than average in the atmospheric circulation, then easterly (negative) trade winds dominate across the tropics and through the ENSO zones. As determined by the laws of conservation of angular momentum, this puts compensatory forward energy into the extra tropical jet which flows downstream from the Pacific to the Atlantic. The inflection point of the negative torque usually propagates around 20N to 30N in the Equatorial Pacific and the divergence of decelerating wind-flow creates amplification and sub tropical anticyclonic responses which are amplified poleward into the extra tropics. The displaced westerly momentum in the extra tropics flows across the top of this anticyclonic response according to the downstream trough/ridge response - which is the downstream sub tropical Bermuda and Azores ridges likewise intensified and amplified in the central and western Atlantic. The downstream jet loops across N America and then likewise around the flank of the high pressure response in the Atlantic  - with downstream trough signatures across NW Europe and Scandinavia.

This is the kind of default scenario we saw play out at times during June, and is set to continue, at times, during July. However, as posted recently there are various other factors (already covered in some considerable detail in previous posts) which are periodically interfering with this typical low angular momentum La Nina type summer pattern response, and which allows the Atlantic ridge to adjust eastwards into the UK and other parts of NW Europe periodically. This also happened in June, as we know, and looks like it will be a theme as well during the upcoming month

So this is duly playing out once more in the modelling - with the Azores ridge advertised to return eastwards into the second full week of July. Assuming that the high frequency tropical forcing aiding this shift plays out sufficiently to diffuse the low frequency tropical signal as it propagates eastward across the tropics, then the risk of the ridging being adjusted back into the Atlantic at this timeframe is reduced. During the next few days it will be possible to monitor this and report back on progress - but at this time it looks promising for summer weather to make a return, at least for a time, during the following week

That means I agree with @bluearmycomment, on the basis of the above analysis, that chances of extended country-wide heatwaves are unlikely - but if one is prepared to be sanguine over a mixed pattern of relatively shorter warm spells, potentially thundery breakdowns of interest (such as end of last week) back into cooler more changeable spells when the low frequency tropical signal re-dominates, then it is a reasonable seasonal outlook

 

Hello Tamara, 

Crumbs!  You're certainly well versed in Meteorology!  Thank you so much for your detailed response which I greatly appreciate for taking the time and effort to reply to a bit of a numpty such as moi. My knowledge is far below par compared to many here and especially yours looking at your reply . 

Can I ask , was the PV in part to blame ( in a good way if you like long dry periods)  for the unprecedented dry sunny weather as soon as lockdown started right up to latter June bar two rainy days in April.  What enable such huge high pressures almost encircling the globe at mid latitudes especially towards and over the UK for Such a long period of time ? 

Another question which I have always pondered, do you think there is any correlation between the inner workings regarding metals under the core and certain large strong high pressure cells ( Hadley I think ) that make them tremendously difficulty to shift at times ?  One of note often seems one off the Portuguese coast and extends over Spain although this year Spain doesn't appear to have this but instead a constant slack low pressure producing many thunderstorms over the country this year. 

Many Thanks again Tamara.  

 

[Mike Poole]

That’s some measly high nosing in at the end of the  ICON, T180:

Here’s to a good set of 12z runs, all the best everyone

Edited June 28, 2020 by Mike Poole

[damianslaw]

Some good posts in here today. Models continue to show the azores high building to the SW, and making inroads into southern parts at least as we move into the second week of July. 

A fairly typical pattern of summer weather, NW-SE divide in evidence. Always wettest coolest and cloudiest further north and west you go.

Longer term, will La Nina imprint itself with the Atlantic gaining the upper hand and the azores high forced into a mid-Atlantic high position. 

Edited June 28, 2020 by damianslaw

[Mike Poole]

UKMO off to a flyer, T120, unsettled spell should be done and dealt with by end of the week:

 

T144:

Gets flattened a bit here, not sure actually what weather would be best for Super Saturday

[mb018538]

GFS is a bit of a car crash on the 12z compared with 06 and 00z - very unsettled into Sunday and Monday. Hopefully an outlier.

[Mike Poole]

1 minute ago, mb018538 said:

GFS is a bit of a car crash on the 12z compared with 06 and 00z - very unsettled into Sunday and Monday. Hopefully an outlier.

Yes, it is horrible, and wrong, i would expect, T168 and T192:

I don’t believe that low will happen, and anyway, it will end the same with an Azores ridge, so no cause for concern...

[Djdazzle]

1 minute ago, Mike Poole said:

Yes, it is horrible, and wrong, i would expect, T168 and T192:

I don’t believe that low will happen, and anyway, it will end the same with an Azores ridge, so no cause for concern...

No clue what it's done there!

[northwestsnow]

GFS looks fine to me..

Azores high on the move, timing of arrival will wax and wane.

Edited June 28, 2020 by northwestsnow

[Methuselah]

Not sure I much like the look of the GFS's rendering of a week Tuesday?

    

But, I might start to like it should it try for an Azores-Scandi link up.

[mb018538]

GEM says nope to the GFS - high pressure in by Monday.

[Mike Poole]

All roads from the Azores lead to the UK, it seems, great run from the GEM tonight, T192:

And this one has some longevity about it I think....

Edited June 28, 2020 by Mike Poole

[Zak M]

12z GEM drags uppers in excess of 16c too for parts of S England

[Mike Poole]

3 minutes ago, Zak M said:

12z GEM drags uppers in excess of 16c too for parts of S England

18s in to the far south by the end with unstable airmass, Zak, cracking run, T240:

[Methuselah]

GFS 12Z is looking better longer-term: warm but not hot:

    

[NApplewhite]

2 hours ago, MATT said:

Thanks for that insightful post @Tamara I've got to agree with that also, and what Blue states as well.. The GFS 6z mean tends to ebb and flow with that Azores High Pressure. We see the extension of it building in at times and especially for Central Southern parts, before a little breakdown and trough bring rinse and repeat scenarios moving forwards. This looks like a potential trend for July in general with plenty of usable conditions, and at times probably very warm. The EC46 seems to highlight this type of pattern quite well with the ridge building in at times before receding back SW after a few days. All in all the long term trend is pretty good and more especially away from those NW locations.

 

 

GFS 12 Z is a horror show for summer lovers look at Monday 6th July 2020  - instead of high pressure we now have low pressure over the UK - weak ridge on Wednesday at 03:00.  Even further out in two weeks time another low pressure over NE Scotland/Northern England 

 

Edited June 28, 2020 by NApplewhite

[NApplewhite]

41 minutes ago, General Cluster said:

Not sure I much like the look of the GFS's rendering of a week Tuesday?

    

But, I might start to like it should it try for an Azores-Scandi link up.

We have been trying to get an Azores / Scandi High link up for several months - it never happens!  As Tamara says the Pacific ridge is influencing the jet stream downstream - heatwave in Mid West USA causing the jetstream to power out of Canada then the deep dive south in the Atlantic so we always remain to the South of the jet.  Look at the low temperatures over the UK / France for the next 16 days. 

[carinthian]

Think the UKMO is showing some uncertainty in the intensity of the low formation to the NW of Britain. This model and others have the low filling rather than deepening at 144t . Lets see how ECM handles this low development. So think based on this run ,  very uncertain forecast for next weekend. Could end up better than the chart would envisage below .

 

C

[Mike Poole]

10 minutes ago, NApplewhite said:

GFS 12 Z is a horror show for summer lovers look at Monday 6th July 2020  - instead of high pressure we now have low pressure over the UK - weak ridge on Wednesday at 03:00.  Even further out in two weeks time another low pressure over NE Scotland/Northern England 

 

Yes, it is a horror show, it’s also wrong.  It is better to try and take a cross model view, so you can see the outliers, like this one!

[NApplewhite]

3 hours ago, NApplewhite said:

Looking a bit better on Thursday this week as a nose of higher pressure (try's to move) in from the Azores never establishes though.  NW/SE split. Further attempt on Sunday 5th July 2020  . Tomorrow is a washout across the UK (last image) Jetstream doesn't look great though on the 6th July so a lot of strong high level winds even under the higher pressure.  La Nina has a 50% chance of developing over the next few weeks. Causing a US heatwave in the MidWest and cooling across N Europe

 

GEM is slightly better - but we still end up with a trough next weekend.