swfc
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Posts posted by swfc
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15 minutes ago, That ECM said:
Why is it called fi?
Indeed, a lot of chuckle bros stuff and knee jerk reactions to the ops. Give it time and relax a bit, please
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11 minutes ago, NorthYorksWeather said:
Me viewing the afternoon runs
And NWS hyperventilating behind sofa
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These attempt at ridging into Greenland are like my blood pressure. Up and down like a fiddlers elbow
hopefully get the eventually 
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Just now, sheikhy said:
Big ecm coming up!!!if it backs ukmo then gfs probably struggling with split energy!!!!but being on here for the last 2 decades i know how these situations normally work out!!we end up chasing and chasing and eventually nothing turns up and winter is done with!!!this year thankfully ive taken a step back knowing there nothing genuinely exciting happening in terms of snow!its just rubbish rain and wind like most years!!!i been on the edge just watching over and hardly any posts but trust me if snow and cold were to happen for defo then i go from being on the edge to ecstasy like a flick of a switch!!!!!!
It's not a big ec tho mate. Its 31st of December
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Just now, Scott Ingham said:
Yeah it’s the best way! Stick to the means background signals and trends and not unpick every run! For me mid Jan cold is still way way more likely than Atlantic dross!
Thanks man, happy new year pal
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Just now, Scott Ingham said:
You’ve hit the nail on the head Phil. The posting this year has been bi-polar over reactive with nothing but operational runs to back up a return to Atlantic weather. I believe the GFS is definitely not handling the split flow correctly
Thanks Scott ive moved away from the ops and crazy 10 min intervals. End of day forecast from you mid January cold and
Uto
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Just now, Cheshire Freeze said:
The SSW was critical IMO but what do I know, others are saying that isn’t the case. IMO it would have aided a more -AO as it was happening just like the 2013 event did.
It wasnt and nothing has changed ie the strat. Give it time
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4 minutes ago, Eagle Eye said:
All images are screenshots because that's the only way I could get them to work. I think I downloaded them in the wrong format and I can't be bothered to find all the original images.
Alright, well the AWB appears o have changed to initially an equator-ward evolution on the latest GFS before a secondary poleward AWB evolution occurs. Anyway, it's sort of an outlier and still results in the same kind of result. However, I've talked about this for a while, lets go to what I feel I know best. The Stratospheric evolution.
Let's talk about general synoptics for SSW's first as there's still a chance long term with about 20% of EC46 models supporting it.
First off, there's a link between extreme cold in Scandinavia and northeast Europe being pre-SSW, especially pre-Winter and then the few days/weeks before an SSW. Generally you want a stronger anomalously cold daily maximum than daily minimum and SE European warmer than average. Also drier along the NE'rn Europe coasts. Generally that seems to be the setup although the daily temperature cycle
https://repository.library.noaa.gov/view/noaa/25923/noaa_25923_DS1.pdf
I'll initially be using the December 30th 12Z's, will revisit with recent updates.
Generally on the forecasts however, the Scandi cold setup isn't favouring colder anomalies either day or night. So, using the climate extremes here, you need to be wary, it's definitely a cold extreme and a SSW would continue the cold extreme. However, it doesn't look like it's the proper link between climate. Of course, it doesn't ned to be an exact link with the climate extreme and SSW onset, however, I'm still quite cautious of using this.
Explanation of some stuff from my own explanations before the next bit.
"AAM (atmospheric angular momentum)
AMB - Angular Momentum Budget
AAM - Atmospheric Angular Momentum
MT(mountain torque)
GWT(gravity wave torque)
FT(frictional torque)
If AMB increases in the atmosphere it must have been transferred from another source since AMB is always conserved. The sources for AMB are from the Earth, the Oceans and the Atmosphere.
One major aspect in affecting AAM are torques. A torque is the rotational force in the atmosphere.
The 3 main torques affecting the atmosphere are:
Mountain torque (MT) - The turning force applied with the effect of pressure systems on mountains.
Frictional torque (FT) - Boundary layer dynamics.
Gravity wave torque (GWT) - Subgrid (local) torque, upward movement and downward movement to do with the buoyancy.
If there is a net westerly surface wind, the atmosphere speeds up the Earth's rotation and transfers angular momentum to the earth and so there is a net decrease in AAM. The reverse happens with a net easterly wind.
In the NH Winter:
Global MT anomalies are constructed by sypnotic waves that scatter energy across Asia and North America. These sypnotic waves trap the SLP anomaly and push them towards the south. Driven south and east of mountains. Sypnotic wave centres amplify aloft. MT associated with anomaly air parcel transportation in terms of momentum into latitudes its next to. More angular momentum is therefore moves to the 20-20N band. This is where the AAM anomaly appears significant. The anomaly quickly becoming equally uniform leading to a global FT that weakens the AAM anomalies. An anomalous distribution of mass accompanying the MT acting to balance the zonal winds in the 20-30N region. In the mid latitude, Eddy's are the physical link between those two torques."
Unstable inertia - Is the tendency to keep the same atmospheric state with a different disturbance replacing the initial one in the same rough area. So a Greenland high weakening that is fed into and is 'replaced' and strengthens again for example.
Eurasian influence
Then looking at the Eurasian signal, there's a clear retraction of the wave as the AAM falls especially in the area w/an AWB equatorward and appears to help force the return to a -VE EPO. Until another omega high is forced up through the Ural area. Generally, an initially Tibetan forced wave can rise vertically and the polewards cyclonic wavebreaking occurs. That retraction isn't necessarily bad for the surface pattern as it could help uphold/force a return to the -VE NAM due to pushing up the north Pacific +VE heights and the extension of the -TNH pattern occurs. The north Atlantic jet gains AAM from this energy distribution w/the loss of AAM over Eurasia transferred west and that in turn disconnects the Pacific and Atlantic jet streams further when combined w/the natural jet retraction and split over the next few days to further amplify the AAM pushing into the north Atlantic jet by day 10. With the jets seperated, retracted over the north Pacific and the energy over the southern USA jet backing east w/the transfer of energy over the Pacific, it's complex. However, that could be what the 18Z GFS was realising.
Modifications of momentum
The recent +VE EAMT and the slow reaction to the wavebreaking is clearly going to have a large effect along with the MJO phase 3 to drive the pattern. The energy distribution of both the MJO and AAM are obviously going to modify the pre-set pattern but unironically, the unstable inertia rules here due to the distribution of AAM appearing to continue to force the -VE NAM imprint on the Trop. Generally, a supportive sign for Stratospheric imprinting as well. As we go into mid-Winter, the built up momentum through the north Atlantic holding up the -VE NAM pattern is opposed by a loss in momentum budget over the Pacific where we see flip of the north Pacific mode also flipping the north American pattern. This recent evolution appears to be occurring backwards to usual with the AO leading the north American pattern (linearly, it's more of the AO being flipped before the north American pattern due to the pre-supportive AO pattern flip that managed to work through the base US pattern due to the north-south split and the US pattern flips to an east-west distribution that works to being a positive feedback loop for the Greenland-Iceland pattern.
So as the AAM weakens in response to the frictional torque loss after the +VE EAMT event, the momentum that's been forced poleward and is cycling for the next couple weeks, holds the -VE AO pattern in place and forces poleward waves. However, there is therefore less built-up wave distribution as you go up in the atmosphere. Leading to an upper-Trop to lower-Strat recovery for the time being, sort of disconnecting with the upper vortex? So the recovery of the Strat despite the flipped pattern is possible. The recovery will either budge up to previous levels or overcompensate and go further towards the average. That should mean that, they become increasingly -VE NAM and w/being downwards forcing is easier than upwards forcing, the -VE AO could well lose it's inertial grip on the surface-mid Trop.
However, w/rising AAM possible and an already set up Omega block rising over Eurasia right at the end of the 12Z (30th December run) then the recovering tropical-extratropical forcing could eventually re-force it's way towards the north Atlantic. Taking this run at face value, the re-cycling of the Eurasian wave could lead poleward forcing over the north Pacific and pushes cross-polar air towards the western and central US and the re-retraction of the US zonal jet pushed rather far south. That could slowly recover momentum into the north Atlantic and depending on how much built up momentum was left (e.g. less if the upper Trop pushes down earlier and/or if the AAM recovers slower) and so the stress on upper Trop and lower Strat for upper Strat re-connection will increase and the Rossby wave momentum should transfer back up and that's where our next SSW potential comes from. However, taking a mean at face value is still rather risky, it's the best we can do at the moment and given the AAM cycle makes fairly good sense in terms of the connections between Trop-Strat especially. The problem w/AAM amplitude being lowest in the important trading area of Rossby waves and an area especially where the swap in regions of the EHF occurs, it needs a good tropical drive to force that exchange in energy. I suspect we'd have seen a lot more SSW's if it didn't do that.
So a mini-recover in the NAM feels unavoidable due to the Tropospheric connections. However, doesn't rule out the possibility of a transient cold-mild-cold scenario, w/an especially transient mild if the AAM can recover quickly. Wouldn't be surprised if we don't even get a proper AO recovery, given the quick AAM rise. The shorter the frictional response the better and the wavebreaking is the starter of the eventual re-rise in AAM that feels likely to me, just that, it would be preferable for the initial wave base of the north Pacific to be similar to that at the end of the run.
The GWO continues to favour what I was saying before about the loss of frictional torque into the earth, however the release of +VE EAMT looks to be overcompensating and we could well see a large response. I suspect the response will be quicker with this, generally, the CFS has felt a bit behind with these forecasts to me. So we should be circling towards a phase 5-6 where we gain momentum and there's southwards momentum transport mid-latitudes, forcing a more southern and weaker jet, building up a poleward jet and the general model is a flip of the pattern.
However, it's not as simple as there, there's generally as may southwards moving warm episodes due to the initial wave setup and the energy distribution. Along w/that, that's a top end +VE EAMT event w/large kinetic energy. These are generally weak events compared to what's theoretically possible. So the energy burst cannot really change the entire zonal pattern and is more renowned for re-distribution of momentum. Generally, the pattern is for redistribution of westerlies southwards into the equatorial jet with the flip of the zonal anomalies.
The transitional between tropical and extratropical momentum tends to be having the sinking jet exchange rebounded by a symmetrical response of a weakening jet which leads to a complete flip in the previous frictional torque momentum exchange. However that is not a flip of the pattern, as there has been time passes and the wave setup has differed, not only that but a complete flip would require a lot of time to occur and AAM is not the only input into the atmosphere that there is. So you always have to remember to think about how the initial setup will move based off the changes the rise in momentum makes into the atmosphere.
Generally, the northern response to the event is stronger and more variant over Eurasia which leads down the line the north American variance in patterns. That Pacific area in general is extremely important because there are a few different scenarios w/jets and waves that lead to vastly different patterns to a change in AAM. The main area of variance for future forecasting is the Eurasian area as it's the first area affected.
The Japanese signal is important to the evolution of the Pacific ocean as it's the transitional area between land and ocean and is also important for determining the distribution of energy between the Pacific and north America. Given a similar strength AAM to what we're likely to see, I'd rather an extended north Pacific jet and a retracted north American jet ripe for AWB just off the eastern seaboard which pushes the -VE NAO and Greenland high again. That's what's currently being modelled on the mean but it's low amplitude as expected and still a fairly weak winning signal.
When combining a potential rising MJO w/the AAM signal then it becomes a bit of a problem. As the MJO interactions affect both the tropical forcing and extratropical interactions, they can constructively or destructively interact sometimes w/the building of waves and that becomes important for the waves amplitude. That is likely to have less of an affect on the north Atlantic signal. However, as the Pacific leads most of the rest of the wave interactions, it's still very important the initial wave interactions. Generally, this is an amplitude issue and so using regimes for forecasting and general responses, isn't necessarily that bad nor is the teleconnection forecasting if you can imagine interacting signals.
Along w/that, the use of pacific jet modes to forecast with extreme composites can also be a help. So, navigating this site, can be of use.
North Pacific Jet Phase Diagram
WWW.ATMOS.ALBANY.EDU
Back to the Strat.
The driving long-term does look good. However, the disconnect from the upper Trop to the mid Trop stopping the influence on the Strat may undo quite a lot of work. W/ the loss of heat flux into the Strat, there's a good chance that the dynamical recovery can happen quickly due to it not being a major SSW and so we see a recovery to pre-minor SSW. That recovery is unfortunate but likely given the strength of the polar-night jet over Winter, that's why it's so hard to get a SSW.
The vortex finds it easy to return unless it's constantly connected up to when it's Winter.So, that mini-disconnection essentially loses our progress like it's a game but because of the AAM recovery we saved a few steps before we got there.
However, towards the end of the run, the AAM rises again and potentially that's enough to push into the Strat again. It could bring us wvebreaking into Greenland, a well known Strat driving wave that can do a lot of damage. It's something to keep an eye on but until the Ural Omega block can return (our best chance at another strong wave) then I don't think it's worth much. The problem is that I think the unstable inertia hides this well enough that people will be wondering why the upcoming wave (not the one past day 12 on the mean but the one between about day 7-10) isn't going to be able to connect up to the Strat.
However, thinking right at the end of the run, a weak Wave-3 rising has been supported and if a stronger Eurasian and Alaskan wave can materialise then yes it's possible. However, that's all it is for now.
Beyond modelling, we should push into an MJO phase 4 for early February. The general composite does suggest for a continuation of the -VE AO mode. This combining w/the AAM is another good sign away from the Stratospheric signal. However, you have to take these composites a month away w/a pinch of salt. It's just a general signal for a continuation of the Greenland high that mostly seems to just be an extension of the +VE EAMT signal so perhaps that phase doesn't have a particularly coherent signal though the specific week composite is a lot more zonal, I suspect the lowpass analogs will have more of the other signals taken in to account so as long as the MJO isn't the biggest signal we should be fine.
Reanalysing based off the 00Z EPS
There has been some cutback on the initial and secondary setup. The initial wave setup has become more UK based but it's still rather close on the mean. Could well become a big snow event w/a few changes and it only takes a few miles (relatively) of difference which won't be resolves till maybe a day or 2 before and almost certainly won't be resolved on the mean yet and a fair amount of the Isles could well get snow. Pretty much the same w/the next potential showing up. Like I've said before, we are surely unlikely to get through such a long time w/good driving factors w/out having a decent cold and hopefully snowy spell. The upcoming period is almost certainly going to be cold, however, the snow from the direction of flow and amount of moisture is clearly a potential issue.
There's not actually a big change in the overall idea of the pattern however, it's only localised changes.I wouldn't be surprised if we do see it delayed again but just because the main snow potential has technically been delayed, doesn't mean it actually has when you think about. The wave has just moved, the delay is not a result of a slow down but it's a different wave altogether that could cause the return to the potentially snowy pattern on the models. We're still in w/a chance of snow w/shortwaves but I'm not overly confident on this. Still, a repeating pattern over the next few weeks, wouldn't be that surprised to see snow turn up. Surely, we can't go that many chances w/out snow. Well, now that I've said that ha ha.
I'll stop there for now, not going to wait for the 12Z EPS's to add here.
Fantastic, happy new year
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7 minutes ago, That ECM said:
Sometimes jumping on every run"good or bad"isn't a good thing. A lot of the more experienced will sit back and analyse it. Its better because its a 12/24 window on the nhp. Its optional but give it a 7/10 days ie outcomes, happy new year from swfc. Blessings
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Just now, booferking said:
Yes i also sell kayaks for a living
Nice, not
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2 minutes ago, booferking said:
I kinda use to the rain & storms now lots of excitement and records been broken
And floods
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4 minutes ago, northwestsnow said:
That isn't strictly true though .
UK highs can absolutely be the first step to a cold spell.
Of course they can sink but to suggest the outcome is singular isn't accurate.
I saw them in 78/79-80/81.different times but synoptics wise
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Just now, sheikhy said:
Beware the deep purples over the pole clumping together again
!the uk high can banish aint got time for it !!once bitten twice shy!i shall continue to watch over like i have over the last month until/if the time comes to unleash!!1 month of winter gone already and the days continue to dissapear
!!!!!
Sheikhy relax dude. Its not January yet boss
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1 minute ago, northwestsnow said:
I suspect short term changes can have big knock on effects ..
I'm hopeful winter is coming ..
12z v 6z 102h
I agree. Hopefully things can change very quickly on the nhp
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1 minute ago, northwestsnow said:
ICON looks an upgrade
12 v 6z @ 102
Nws is this regard to drier cold weather within the next ten days. Tia
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3 minutes ago, prolongedSnowLover said:
Until the Met Office change the wording to widespread significant snowfall this winter will remain a non event.
Close but no cigar CURRENTLY.
It does happen a lot during winters in general. Obv they have greater info but the bottom line is it can be vague
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11 minutes ago, northwestsnow said:
Obviously we are all entitled to our opinions but I'm personally a firm believer in telecommunications- 9 times out of 10 from my POV,if telecommunications are not supportive of a UK cold spell it won't happen.
I freely admit a lot goes over my head but the above I believe to be true.
Me also esp the over the head bit. Ive picked up and learnt a lot over the years but via various health problems my memory isnt what it was. My main go to now is the ukmo and various control and mean outputs. The ops obviously cause much more interest but a broadscale look at things is better for me. The actual telecommunications are of interest but you need a long term understand imo, like guys on here
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Looking at the various nhps and shuffling of heighths it woudnt suprise me to see even more large scale changes. The 0z gfs mean looked a lot better than the op etc. Maybe today will bring a "snorter" of a run just to up the anti a bit, hopefully
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2 minutes ago, Lukesluckybunch said:
Might have too change that haha..ECM is gorgeous at 168!
Done
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6 minutes ago, Allseasons-Si said:
In the ext'd gefs mean i see renewed push of heights,...i don't think we a done after this initial cool/cold blast in the medium term and would tie in with the Met's thought's.
Funnily enough was just pondering that. Way in fi but a huge amount of very low 850s to the north of uk. Usual nuisance low needs to move ese and not fill
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Just now, TSNWK said:
Better than 12z heights into Greenland and more energy heading south coldies hope?
Yes control and mean look bangers
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18z looks pretty good imo. Where is it flat
Model Output Discussion - Into 2024
in Forecast Model Discussion
Posted
Thanks boss
