Model discussion highlights

[Bricriu]

8 minutes ago, Quicksilver1989 said:

But snowy weather in early March isn't unusual looking back historically. It's just that March over the last 20-30 years has been so much milder then in decades gone by.

Yes,  when i was growing up the period around the Cheltenham Festival was often cold and snowy. It's just that in more recent times it has been milder.

[BlueHedgehog074]

A little peak at the models for Tuesday mid day this week, they set free a chilly North-Westerly over the UK. This of which dragging some pretty cold 850 hPa temperatures and low heights and thicknesses (via the UK/Western Scandinavian trough) further South/South-East:

06Z GFS

0Z ECMWF

0Z UKMO

 

0Z GEM

06Z ICON

Still could bring some blowy weather, particularly early on into Tuesday,

 

Isobars quite tight over the UK above. A chance for this to bring some squally wintry showers and some squally areas of rain, sleet and snow as Monday’s Low escapes into the North Sea. 

Some models above, such as the UKMO and ECMWF, look a touch flatter with the North-Westerly for Tuesday, particularly towards the Southern part of the UK.

Seems to depend really as to the speed that Atlantic/Azores ridge builds in from the South-West and how it tries to dislodge the North-Westerly flow into, and through, Wednesday. The -5*C 850 hPa temperature line struggles to get to the far South-West of the UK on the ECMWF which could make showers less wintry, except perhaps over the hills, such as those in Dartmoor. 

The GFS and GEM perhaps the most amplified with the North-Westerly on Tuesday, but overall when looking at the above charts there’s not much give or take to it. It could be fair to say GFS is the most ambitious with how far South it floods those cold 850 hPa temperatures reaching Northern France! (The GFS, however, can be prone I feel to overdoing the cold depth of the 850 hPa temperatures a little). 

Having said that, it looks to be a day of wintry showers for places, particularly over North-Western areas and over high ground to the North and West. Some are likely to stream South-East through the Cheshire Gap ganging up on the Midlands too - especially Northern parts of the Midlands from the charts above that show more of a West-North-Westerly flow over the Southern/Central parts of the UK.

With the strengthening March sunshine, some could pop up inland, plus with the heights being low, especially further North over the UK, some of these wintry showers are likely to be beefy. These bringing snow across the hills, and to lower levels at times too, particularly Midlands Northwards, although I expect there to be some sleet, hail and graupel showers in the mix as well. 

While it looks to be a cold and, at times, blustery day, where the sun shines between the showers it could feel fairly pleasant. Some places, perhaps more so down the fairly far South, may miss a lot of the showers. It is also worth saying that with many of the operational models above showing some kinks and little troughs in the flow, there could be a chance of more organised wintry showers and longer spells of sleet and snow sinking South through parts of the UK during Tuesday.

It may not be a Northerly/North-Westerly flow of -10*C hPa temperatures (with far North-West of Scotland maybe having a chance to get into the -10*C’s briefly), but that day does provide a chance for a return of wintry weather. For a North-Westerly, it looks to be a rather potent one. One that could bring a good amount of interest. As well as some of the strong winds it’s likely to bring earlier on in the day. 

Original post: https://community.netweather.tv/topic/98485-model-output-discussion-snow-watch-limited-edition/?do=findComment&comment=4830919

[SLEETY]

Another cold outbreak from the N/Ne again later on this month is looking possible.You would not rule it out.CET for March in Northern Scotland going to be way below normal if that comes off.

 Very cold air in the Arctic.Iceland been having a very cold winter and now Spring.

[SilverWolf]

1 hour ago, Quicksilver1989 said:

But snowy weather in early March isn't unusual looking back historically. It's just that March over the last 20-30 years has been so much milder then in decades gone by.

I agree with that. I remember snow in April in the early 80’s in Gloucestershire a few times. But that ‘normal’ really ended in the mid 80’s. There’s been far more snowless winters since then, let alone March. But I think people are comparing this March to 2018 only, which was exceptional and rare regardless of the decade..  

Edited March 12, 2023 by SilverWolf

[MJB]

Control looks chilly

 

 

 

[Nick F]

14 minutes ago, SLEETY said:

Another cold outbreak from the N/Ne again later on this month is looking possible.You would not rule it out.CET for March in Northern Scotland going to be way below normal if that comes off.

 Very cold air in the Arctic.Iceland been having a very cold winter and now Spring.

Central England Temperature in northern Scotland, how does that work?

Hadley CET 3.4 or an anomaly of -2.3C up to the 11th. 

Met Office Hadley Centre Central England Temperature Data Download

WWW.METOFFICE.GOV.UK

 

[SLEETY]

17 minutes ago, Nick F said:

Central England Temperature in northern Scotland, how does that work?

Hadley CET 3.4 or an anomaly of -2.3C up to the 11th. 

Met Office Hadley Centre Central England Temperature Data Download

WWW.METOFFICE.GOV.UK

 

I meant the average temperature for Northern Scotland for the Month is going to be way below Normal if we get another very cold outbreak of air from the North or North East!

Edited March 12, 2023 by SLEETY

[Methuselah]

2 hours ago, mushymanrob said:

agreed, all i can see on the ops and the anoms is "normal" cold for March mixed with milder slots. I very much doubt now we can get anything Wintry (as in deep cold/ice days/widespread lying snow) without importing some extremely cold air... and there no sign of that.

It seems to me that the SSW has created something of a retro-season... Cold and snowy Arctic blasts were much more common back in the day. So far, this spring reminds me of 1975; I just hope it doesn't spoil the cricket! 

Edited March 12, 2023 by Methuselah

[Derecho]

1 hour ago, SilverWolf said:

I agree with that. I remember snow in April in the early 80’s in Gloucestershire a few times. But that ‘normal’ really ended in the mid 80’s. There’s been far more snowless winters since then, let alone March. But I think people are comparing this March to 2018 only, which was exceptional and rare regardless of the decade..  

I would class 2013 as the most notable March in recent times. To get a second half as cold as that again would be very challenging.

The BFTE was seriously impressive but was also short-lived. Most of March 2018 was rather mild and very wet with 2 short and sharp cold spells enough to bring the CET below average.

The first halves of 2005 and 2006 I remember saw a fair bit of snow. The former ended up being a well above average month CET wise despite the cold first half. If we get a southerly in the second half of the month, something similar could happen again with all the heat bottled up to our south.

[Rob 79812010]

CET didn't change much last couple of days due to big temp rises in South regardless off depth of cold further north. Still think well end up below cet average and well below 91 to 2000 average. Models and forecasts seem to be showing mild flipping to cold next couple of weeks with. Last week of march looks like it might flip cold again. 

[Rob 79812010]

2 hours ago, SilverWolf said:

I agree with that. I remember snow in April in the early 80’s in Gloucestershire a few times. But that ‘normal’ really ended in the mid 80’s. There’s been far more snowless winters since then, let alone March. But I think people are comparing this March to 2018 only, which was exceptional and ra. re regardless of the decade..  

Our weather is so interesting and varied depending on location. Your recollection of the 80s was a number of good snow years. Where I am the 80s were awful. 81 was a few inches. Other than that we had some snow I think winter 85. It was a snowy breakdown though and the thing I most remember was a week of frozen slush which was treacherous.  Here in Manc we've started having more Irish Sea snow showers which are perfect for our neck of the woods. Pretty but only ever a couple of cm. We've probably had more snowfalls in last 2 years than the whole of the 80s honestly.  Last weeks weather system never does well for for low level west of pennines. Models and forecasts were showing this nearer the time. The classic was Feb 47 where swathes of the country were deluged with snow and drifts. I believe the max snow depth in Manchester that month was 5 cm. Different story 63 though 

[Rain All Night]

The 06z GFS ensemble run is the keenest I've seen yet on the idea of a spell of chilly northerly/north-easterly winds reaching the south coast starting about a week from now:

But the ECM ensembles have been showing little interest in this, the 00z run a case in point:

(19th - 26th)

In the much shorter term, tomorrow lunchtime looks windier down here than we've seen in ages...

It might then have a sting in its tail for the southwest overnight as it clears away and Tuesday's northerly comes in...

The northerly will bring us down here a welcome chance to see some sunshine. Just spotted that the UV levels are starting to creep up for the Spring.

Edited March 12, 2023 by RainAllNight

[Ladyofthestorm]

Going to be close to record breaking cold March for my area .

Temperatures midday barely above freezing . 

Snow on ground even at sea level for past 7 days and trend looks set to continue. 

On a par with March 2006 and 2013. 

 

 

 

[Northernlights]

4 hours ago, BLAST FROM THE PAST said:

Too many writing off the potential cold spell incoming and the recent cold, the other day the CET daily mean for 8th March was the coldest for 50 + years.  
 

BFTP

I know its the north of Scotland but we had snow on the local beaches for four days last week the cold in both the December and March cold spells has been equally cold at sea level even more remarkable in  December.  Temperatures of -8c  is not usual in March.  Daffodils here only at Bud stage on south facing areas and just coming through the ground in north facing spots.   Unless we have a very warm April there will still be odd ones flowering at the beginning of May. Just to add we are currently 4c with heavy rain

Edited March 12, 2023 by Northernlights

[Methuselah]

Well, I'd rather have what we've got this year (alternating between cold and mild) than endless weeks of cold, dry cack, as we saw in 2013!  

[Rain All Night]

The UKMO looks pretty representative this afternoon, things slackening up in our vicinity as the TPV moves away...

[Stuie]

7 hours ago, Methuselah said:

It seems to me that the SSW has created something of a retro-season... Cold and snowy Arctic blasts were much more common back in the day. So far, this spring reminds me of 1975; I just hope it doesn't spoil the cricket! 

Looking at the AO across the pond, agreed, messy stuff (all forecasts) and has to be SSW related.

[damianslaw]

Mmm the atmosphere seems primed to swing between cold and mild for some time yet.. and there are hints we may see more concerted pressure rises to the north as the scandi trough weakens and the PV pulls away further east. I'm not sensing any marked change in fortunes if you want something sustained warmth springlike wise, the milder incursions most likely to be wet thanks to southerly tracking low pressure becoming slow moving and temporarily pulling in shots of tropical maritime air - briefly..  cold/dry, cold/wet and mild/wet - but not dry/mild, take your pick.

Edited March 12, 2023 by damianslaw

[Blessed Weather]

The outlook suggested by the majority of members from this morning's ensembles - both GEFS and ECM/ENS - supporting the analysis from Damian above. A look at the T240 charts (for 23 March) suggests:

• the NH pattern at mid latitude predominantly meridional so jet stream amplified (alternating low/high/low etc)
• the tPV more likely to have located on the Siberian side of the NH
• there are hints of a pressure rise over or to the north of the UK

Meridional jet stream:

Ensemble means T240: GEFS  ENS

But a look at some of the GEFS members shows the range of options within the T240 mean:

In a nutshell, for the UK an unsettled outlook, sometimes the jet to the south, sometimes to the north, providing temperature swings as the airmass swings between cool/cold polar maritime and tropical maritime.

Although worth noting that the UK - as is often the way - located in the part of the NH where there is the most uncertainly. 

Spread at T240 GEFS  ENS

 

[ANYWEATHER]

The unsettled mode continues ,with an undulating jet stream ,so plenty of rain and wind continuing for the majority with some wintryness in the usual places for this time of year...

[Rain All Night]

Can we get from here...

To here...

With this mean..? 

[mushymanrob]

21 hours ago, Methuselah said:

It seems to me that the SSW has created something of a retro-season... Cold and snowy Arctic blasts were much more common back in the day. So far, this spring reminds me of 1975; I just hope it doesn't spoil the cricket! 

More like March 1970 to me, as 75 didnt produce lying snow here, just endless cold Northerlies. Either way, June 70 was great and summer 75 was great...

[Methuselah]

1 hour ago, mushymanrob said:

More like March 1970 to me, as 75 didnt produce lying snow here, just endless cold Northerlies. Either way, June 70 was great and summer 75 was great...

Aye Rob, you're right. March 1970 was indeed snowier. 

[Eagle Eye]

After the brief intrusion of polar maritime (it appears) air we should start to see the downstream influence of the retrograde Alaska-Kamchatka high and the influence of that when combined with the forward progression (linear forward progression e.g no real Wavebreaking on a temporal synoptic scale) of the wave come off the central-northern part of the eastern seaboard. This is the first sign that the Atlantic is waking up slightly. A full on zonal start to Spring is not what this means though. Initially, the low's win out but there's still some MJO-+VE AAM influence and a neutral ENSO background and that allows the Hadey cell expansion that aims towards UK-Scandi and that may set up the summer pattern given some seasonal forecasts with a UK-Scandi sitting high pressure.

The w'ly wind burst (WWB) in the Pacific came from a holding extension of the Alaskan ridge and undercutting Pac low and that caused a especially tropics based WWB in the ENSO region which is a typical response to that holding pattern. It appears that this came as initially a reaction to the +VE EAMT double event that may or may not have been influenced by Strat circulation but the SSW likely influenced the length of AAM in strong +VE territory given SSW MJO-AAM circulation influence. This WWB likely destructively interfered with the holding pattern signal as the SSW's influence weakened into just the retrogressing RWT and that' where we begin to see the North Pacific return to the low pressure above the ridge given the shift towards jet retraction given the -VE EAMT over the coming days supporting a return to semi-zonal/UK-Scandi high to be more influential as we move towards April.

And as I'm starting my A-Level paper for Geography (if I get in, bear in mind I haven't done my GCSE's yet but wanted to get ahead) for the formation of Cyclone Freddy and am also starting reading Dr Mike Ventrice's PHD Dissertation, I thought I'd share a bit of what I've done so far here.

"

One forecasting and analysis tool for the formation and supposed life of a tropical cyclone is by using convectively coupled Kelvin waves (CCKW) which have higher wavenumbers than Rossby waves and are only equator-tropics waves characterised with typically smaller waves and weaker wave fluctuations than Rossby waves. Generally, for forecasting cyclogenesis you tend to get pre-CCKW easterlies followed by the convectively-active phase of the CCWK. They most frequently occur 2 days after the convectively-active phase passes through. CCKW’s affect the zonal wind structure along their passage as well as the convection in the inter-tropical area. They affect the general environment in terms of moisture shear and vorticity in the tropics.  

It is likely that the CCKW train (CCWKT) helped to increase the convection triggers with advection of moisture with the stream of warm unstable air off the Hamersley mountain range and great sandy desert area in western Australia. A wave off warm air was likely to have been lifted due to the kelvin waves passage through. With the convectively active phase and weakening of vertical shear that became a recipe for cyclogenesis. 

CCKW’s have been noted to interact with the feedback convective envelope of the MJO due to typically having stronger feedback in terms of convection. Enhancing the dynamical processes of inter-tropical forcing and it appears that this time these two worked together with Indian Ocean convection linked with the lag of phase 3 moving the convection envelope slightly further east and the timing was perfect for the exit of easterlies and the return of westerlies and weak shearing just north of Australia. Eventually, the inter-tropical forcing and convective action between Australian heat forcing and the eastwards moving convection. Eventually, these dynamics combined to become cyclone Freddy. 

If we look on the Hovmoller diagrams below we see the 850-hPa zonal wind anomalies and the 850-hPa velocity potential anomalies in the 20S-10S area. Looking at the zonal wind and we can see the pre-CCKW easterlies quite strong between 60E-150W around the 28th January and then the westerlies favourable for cyclogenesis around the 150E area in early February with the CCKWT moving west over time as the tropical cyclone also moves west. 

On the velocity potential diagram you will notice that the diagram base area is changed with 180 instead of 0 being on the left. We are looking at the 28th January onwards for CCKWT effects. Notice the dashed blue line just after the 28th; that is the convectively active phase of the MJO with the red outline being the convectively supressed phase of the MJO (the MJO-CCWK are coupled somewhat). Notice the divergence (negative) part of the kelvin wave between the 10th and 17th of February and that’s a sign of kelvin-wave enhanced convection along with MJO enhanced convection. Though divergence and shearing towards the centre of that part of the CCWK meant that the intensification would’ve happened on the border between the suppressed MJO convergence and enhanced MJO divergence. As that border made its way through the area that tropical cyclone was in, it became the first large intensification phase for the tropical cyclone by modifying the horizontal shear, moisture and low-level vorticity characteristics of the local area to be favourable for intensification for a couple days. There is a similar evolution in early March for the second major intensification of Freddy. 

At the time of disturbance formation in late January, the MJO was transitioning between phases 3 and 4 with the Indian Ocean to Maritime Continent convection in the tropics area transitioning eastwards between the two. The synoptic scale convection patterns associated are both modified and change the structure of Kelvin waves. A short-period active phase MJO modification and changing of slow moving CCKW’s in the Troposphere likely led to the initial cyclogenesis as talked about before. The active response of the CCKW to the warm pool regions of the MJO phase 2 (though typically a weak warm pool, the strength of the RMM phases negate that) was a distortion of the inter-tropics symmetry. An asymmetrical response known as a ‘Gill response’. 

An example of the ‘Gill response’. 

The dynamical structure of these CCKW’s are affected by the meridional winds. These winds affect the tilt of the Kelvin waves at the different levels and of course they change differently at levels due to surface friction and geopotential height factors. Low-level convergent winds preceding upper-level divergence in the wave structure which Is also affected by temporal phase speed. 

Specifically for tropical cyclone development and there isn’t a lot of research to do with them but some research does suggests they form with strong potential vorticity via diabatic heating processes and a number of synoptic-scale CCKW’s with the active convective envelope needed for the thunderstorms needed to help with very early-stage disturbances formation in the first place.  

At the time around formation and initial intensification of the disturbance, the eastwards moving MJO convection envelope (negatives show outflow from convection) and similarly moving Kelvin wave. Shearing tends to be strongest in the centre of the outflow but on the edge between the outflow-divergence and the supressed convection convergence is where cyclogenesis is most likely. You see the area between them on the Kelvin wave where cyclone Freddy NW of Australia. 

"

[Rain All Night]

1 hour ago, Eagle Eye said:

After the brief intrusion of polar maritime (it appears) air we should start to see the downstream influence of the retrograde Alaska-Kamchatka high and the influence of that when combined with the forward progression (linear forward progression e.g no real Wavebreaking on a temporal synoptic scale) of the wave come off the central-northern part of the eastern seaboard. This is the first sign that the Atlantic is waking up slightly. A full on zonal start to Spring is not what this means though. Initially, the low's win out but there's still some MJO-+VE AAM influence and a neutral ENSO background and that allows the Hadey cell expansion that aims towards UK-Scandi and that may set up the summer pattern given some seasonal forecasts with a UK-Scandi sitting high pressure.

The w'ly wind burst (WWB) in the Pacific came from a holding extension of the Alaskan ridge and undercutting Pac low and that caused a especially tropics based WWB in the ENSO region which is a typical response to that holding pattern. It appears that this came as initially a reaction to the +VE EAMT double event that may or may not have been influenced by Strat circulation but the SSW likely influenced the length of AAM in strong +VE territory given SSW MJO-AAM circulation influence. This WWB likely destructively interfered with the holding pattern signal as the SSW's influence weakened into just the retrogressing RWT and that' where we begin to see the North Pacific return to the low pressure above the ridge given the shift towards jet retraction given the -VE EAMT over the coming days supporting a return to semi-zonal/UK-Scandi high to be more influential as we move towards April.

And as I'm starting my A-Level paper for Geography (if I get in, bear in mind I haven't done my GCSE's yet but wanted to get ahead) for the formation of Cyclone Freddy and am also starting reading Dr Mike Ventrice's PHD Dissertation, I thought I'd share a bit of what I've done so far here.

"

One forecasting and analysis tool for the formation and supposed life of a tropical cyclone is by using convectively coupled Kelvin waves (CCKW) which have higher wavenumbers than Rossby waves and are only equator-tropics waves characterised with typically smaller waves and weaker wave fluctuations than Rossby waves. Generally, for forecasting cyclogenesis you tend to get pre-CCKW easterlies followed by the convectively-active phase of the CCWK. They most frequently occur 2 days after the convectively-active phase passes through. CCKW’s affect the zonal wind structure along their passage as well as the convection in the inter-tropical area. They affect the general environment in terms of moisture shear and vorticity in the tropics.  

It is likely that the CCKW train (CCWKT) helped to increase the convection triggers with advection of moisture with the stream of warm unstable air off the Hamersley mountain range and great sandy desert area in western Australia. A wave off warm air was likely to have been lifted due to the kelvin waves passage through. With the convectively active phase and weakening of vertical shear that became a recipe for cyclogenesis. 

CCKW’s have been noted to interact with the feedback convective envelope of the MJO due to typically having stronger feedback in terms of convection. Enhancing the dynamical processes of inter-tropical forcing and it appears that this time these two worked together with Indian Ocean convection linked with the lag of phase 3 moving the convection envelope slightly further east and the timing was perfect for the exit of easterlies and the return of westerlies and weak shearing just north of Australia. Eventually, the inter-tropical forcing and convective action between Australian heat forcing and the eastwards moving convection. Eventually, these dynamics combined to become cyclone Freddy. 

If we look on the Hovmoller diagrams below we see the 850-hPa zonal wind anomalies and the 850-hPa velocity potential anomalies in the 20S-10S area. Looking at the zonal wind and we can see the pre-CCKW easterlies quite strong between 60E-150W around the 28th January and then the westerlies favourable for cyclogenesis around the 150E area in early February with the CCKWT moving west over time as the tropical cyclone also moves west. 

On the velocity potential diagram you will notice that the diagram base area is changed with 180 instead of 0 being on the left. We are looking at the 28th January onwards for CCKWT effects. Notice the dashed blue line just after the 28th; that is the convectively active phase of the MJO with the red outline being the convectively supressed phase of the MJO (the MJO-CCWK are coupled somewhat). Notice the divergence (negative) part of the kelvin wave between the 10th and 17th of February and that’s a sign of kelvin-wave enhanced convection along with MJO enhanced convection. Though divergence and shearing towards the centre of that part of the CCWK meant that the intensification would’ve happened on the border between the suppressed MJO convergence and enhanced MJO divergence. As that border made its way through the area that tropical cyclone was in, it became the first large intensification phase for the tropical cyclone by modifying the horizontal shear, moisture and low-level vorticity characteristics of the local area to be favourable for intensification for a couple days. There is a similar evolution in early March for the second major intensification of Freddy. 

At the time of disturbance formation in late January, the MJO was transitioning between phases 3 and 4 with the Indian Ocean to Maritime Continent convection in the tropics area transitioning eastwards between the two. The synoptic scale convection patterns associated are both modified and change the structure of Kelvin waves. A short-period active phase MJO modification and changing of slow moving CCKW’s in the Troposphere likely led to the initial cyclogenesis as talked about before. The active response of the CCKW to the warm pool regions of the MJO phase 2 (though typically a weak warm pool, the strength of the RMM phases negate that) was a distortion of the inter-tropics symmetry. An asymmetrical response known as a ‘Gill response’. 

An example of the ‘Gill response’. 

The dynamical structure of these CCKW’s are affected by the meridional winds. These winds affect the tilt of the Kelvin waves at the different levels and of course they change differently at levels due to surface friction and geopotential height factors. Low-level convergent winds preceding upper-level divergence in the wave structure which Is also affected by temporal phase speed. 

Specifically for tropical cyclone development and there isn’t a lot of research to do with them but some research does suggests they form with strong potential vorticity via diabatic heating processes and a number of synoptic-scale CCKW’s with the active convective envelope needed for the thunderstorms needed to help with very early-stage disturbances formation in the first place.  

At the time around formation and initial intensification of the disturbance, the eastwards moving MJO convection envelope (negatives show outflow from convection) and similarly moving Kelvin wave. Shearing tends to be strongest in the centre of the outflow but on the edge between the outflow-divergence and the supressed convection convergence is where cyclogenesis is most likely. You see the area between them on the Kelvin wave where cyclone Freddy NW of Australia. 

"

Thank you very much for the forecast and for the "sneak preview"!

The Hadley cell expanding towards the UK from April onwards sounds good to me!!

In the nearer term the models seem to be toning down the height rises to our north as the TPV moves away, and are showing what just looks like a modest amount of "disruption" (I think that's the word?!) to the Atlantic trough to our west.

This week...

Next week...

You can see how this might re-aim the "Atlantic firehose" further south and possibly into Europe, the GFS going much further with that idea than the ECM...

Unfortunately that seems to be about as much interest as we are getting for the time being...

Are we going to see any effects (not snowmageddon ones obviously) from the second stratospheric reversal episode that peaked at the beginning of March?

Edited March 13, 2023 by RainAllNight