chionomaniac
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Posts posted by chionomaniac
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For coastal areas in our region, it with be important to see what is happening in the south coast thread early tomorrow. If Isle of Wight sees snow, then relax. If it doesn’t, then start looking at Southampton and Portsmouth. If they don’t, then the marginal risk is great further east. ( obviously further east has better chances with more continental flow and probably lower dps
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3 hours ago, Tamara said:Attempts to fit the MJO to idealistic blocking scenarios is fraught with error risk because it is just one part of the global wind-flow inertia weighting used to calculate ALL probabilistic outcomes in respect of pattern evolution and change.
One has to look at total global wind-flow inertia which encompasses not just the tropics but also within the extra tropics at different latitudes. That is where the GSDM (modelling) gives diagnostic clues as to where switches in the speed and path of the jet stream are most likely to occur. Simply taking an MJO composite that reflects a tropical phase space element (i.e pinpointing the MJO within one part of the tropics) and without looking at the whole atmospheric circulation - is not a ticket to automatically finding blocking (where it is most desired) Looking at the broad-scale might not provide only the outcomes that are being sought but will be give a more accurate and objective overview.
Lets briefly look at the here and now and put an overview into practice of latest consolidated data we have of the atmospheric circulation, and which compartmentalises the latest position within the upper atmosphere reflecting a period where the polar vortex remains relatively weak, but is nevertheless undergoing some re-organisation before potential further instability.
Relative global atmospheric angular momentum has sustained its New Year slump and is now wholly reflective of the overall Nina base state. The distinct banding of easterly inertia at 30N c/o enhanced trade winds (shaded blue) is overlaid by compensating westerly inertia driving the extra tropical circulation (shaded deeper orange/red). Good support for the NWP advertised downstream jet pattern driving successive troughs eastward vs the disjointed and relatively weak polar field pressure profile
This distinctly Nina-esque wind-flow pattern, following the much more a-typical relationship maintained during late autumn and the first part of the winter. So, since the turn of the year, it is incorrect to try to maintain any position that says that the atmosphere is behaving in any Nino-esque manner. Indices such as the SOI as well as the GWO firmly point to pressure and wind-flow diagnostics well within La Nina territory. the GWO rooted within the low angular momentum La Nina attractor phases, mostly centred around Phase 2.
With this in mind, considerable amounts of -ve wind-flow (easterly) inertia remains present across the Equatorial Pacific, at the same time as the high frequency tropical signal (MJO) propagate into the Western Pacific and add westerlies (forward momentum). Convergence strength of westerlies, as added by tropical convection, has being mitigated by easterly trades ahead of it .
Potential pitfalls lie ahead.
NWP will be somewhat blindsided by the immediate signal from the tropics to ignite active tropical convection phasing in the Pacific - and context of the maximum bandwidth capacity of any westerly wind additions has to be taken from the existing position of low angular momentum inertia within the extra tropics. There is a distinct risk that a rise in angular momentum tendency, as created by (attempted) eastward propagation of high frequency tropical forcing, grinds to a halt - as trade wind inertia resumes after a pause. The effect of this would be for the high frequency tropical signal to beat a retreat and any programmed blocking signals advertised at distance within NWP be prone to correction in both amplitude and duration - and/or more energy switched to the polar jet as a result of angular momentum tendency being over-egged. Or any such rally programmed to be sustained for too long a time.
Break in trade winds indicated here (ringed in red) :
If the upstream Pacific pattern quickly returns to increased amplification c/o trade winds buffering increased momentum in association with MJO thunderstorm development (and weakening it due to wind shear) , then sufficient polar jet flow soon returns on a temperature gradient out of the US and Canada to negotiate the weakly disjointed tropopause. Much as discussed as the default in recent summaries.
Putting all this together, if the numerical models get the modelling wrong, and there is shortfall in suggested upturn of wind-flow inertia, this will be registered by the MJO beating a retreat in Phase 7. This will signpost extended ensembles to trend away from some of the coldest downstream solutions . Any element of retained Pacific ridge is likely to continue to assist some polar jet flow in the Atlantic sector and it is not enough, on its own, to just assume, through bias tendencies, that there will be enough weakness within the polar field to stump up a large blocking high.
Extended ensemble suites which might include scenarios of Scandinavian/Arctic high combinations should ideally be viewed objectively within a wider probabilistic field which may tend to create something of a NE/SW split. Colder and drier to the NE and milder and wetter to the W and S. Without a concerted push, not just from the high frequency MJO signal eastward into the Pacific (that question mark over trade winds sapping its strength) but also with some deficit of momentum to recover within the extra tropics - then the chances of some retrograding high pressure out of the arctic are reduced and while forecasts of further warmings of the stratosphere will no doubt keep the partisan on their toes, it could equally maintain an average to rather cold type of default winter pattern - and as stated, the coldest conditions further north east and with milder conditions continuing to push into southern and western parts.
Meanwhile, my own eyes remain on fortunes across S and SW Europe, where the unprecedented cold weather of early January has been relaxing to something more familiar for the time of year - with warmer temperatures, albeit attendant with some wet weather. Later this coming week there are signs of some lovely Spring-like temperatures into the high teens Celsius. Its a case of remaining patient until it finally becomes very much safer & possible to leave and enjoy such conditions
Just reading through your post, and the one thing that I notice is that despite the drop in GLAAM, and a reduction of the more Nino-ish December response, we have yet to see a traditional Nina H500 pattern to develop. I suspect that we have to grateful for the SSW for that - not only for well recognised polar and mid latitude responses, but also the feedback indirectly to tropical regions. I know that there are those who are far more qualified to put more meat on the bones regarding this than me and there have been a number of papers on this in the last few years, but it is another wild card thrown into the equation.
And, if you had to, and your life depended on it, what would your punt for February be? After all, you have spent years on research of mid latitude responses to tropical forcing, it would be great to see the end product of what you consider more likely. One of the reasons, that I suspect you don’t or can’t ( you are not alone) is the lack of forecast data in this field. This would help a lot. When looking at the data, it is recording what has already occurred and the MJO forecasts are reliably unreliable. This makes commentary on what has happened far easier than being able to predict in the mid range.
I think that the sooner that we can get more pieces in this jigsaw, the better.
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6 minutes ago, Tim Bland said:
Latest GFS good for the whole region late tomorrow’
I reckon that shows a mixture of rain, sleet and a wet snow slush fest for all southern coastal counties
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23 minutes ago, kold weather said:
Also should be noted most models keep the snow restricted to that western area of precip.
It's not here yet. As evidenced further west it's turning to snow
So very premature to assume it's a bust. As long as it holds together I'm pretty confident of snow for some areas of EA tonight. Won't be huge amounts but it should fall.
Sunday is firming up well now. Still some southern outliers which only give snow to more southern counties, but the setup is firming up far better than they did last time we had this setup earlier in the month.
I was talking about south of the M4. Any winter night that reaches freezing, one can expect ice - but is that worthy of a warning? Freezing rain is, but general frost and ice on a expected cold winters night. Nope not for me. Save the warning for more severe conditions.
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5 minutes ago, Polaris said:
Yes. But it should have been for Ice only
Just to add, my main issue here is with the dreadful metoffice warning. Jeez, I wish I was in control of that department, I would really shake it up and completely overhaul the met office warning system.
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2 minutes ago, Polaris said:
Yes. But it should have been for Ice only
It was a poor warning but the narrative suggested rain and sleet for southern areas. So no it didn’t.
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2 minutes ago, Polaris said:
Amen
I am currently under a warning of snow and ice and it’s raining outside.
Feels like we are pulling teeth this winterWas the warning for snow tonight?
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With these variable forecasts and marginal scenarios, as far as I am concerned- it doesn’t snow until it snows. The models suggesting it won’t here have been far more accurate than those that suggest it will.
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11 hours ago, Weather-history said:
Pretty remarkable day, yesterday. 11C at 2pm to 0.3C about 9pm with very heavy snow after a soaking during the day.
It’s a pity that you can’t link your outside temp to your webcam.would have been very interesting with yesterday’s dramatic drop.
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So many river levels in the north west are at their highest eve levels. Too many to mention. Many around Warrington. Hopefully rain will ease over the next few hours, but still moderate currently.
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This is not what the North west wants to see atm
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From this
to this
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The channel low runner is a shortwave west of Ireland at T+48 on the ECM
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03z ukv has the system clipping the south coast. Doesn’t get as far as north of the Thames.
Be interesting to see next extended run 1500z
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Latest readings and warnings from the upstream Mersey
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River Mersey close to flooding
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8 minutes ago, georgiedre said:
Wonder how many mm has fallen in my area in nw wales. Surely this is the hot spot
Here is the last 24 hours totals according to NW beta radar
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28 minutes ago, Typhoon John said:
Do you think we could get close to any rainfall records?
405mm in 48 hours
456mm in 72 hours
Probably some areas.
looking at the Severn tributaries and some forecast record river levels
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Latest radar shows the train of persistent moderate rain hitting north wales before heading eastwards
Looking at that, perhaps north wales should be included in the amber warning?
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River Ouse in York forecast levels
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1 minute ago, Cymro said:
You are correct Chionomaniac. It’s NRW who have responsibility in Wales and of course they collaborate with border catchment areas as well, it really isn’t difficult to understand!
What does need to be emphasised again is the absolute and sheer negligence of the METO that there is no all-Wales amber warning at the moment! The Met repeatedly underplays extreme weather in Wales when it comes to warnings and this affects authorities' response and their ability to deal with any problems! We need a lot better!
I agree. The met office warning system has left a lot to be desired. But that is another thread.
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10 minutes ago, matty40s said:
Youve had a hard day, sorry, so have I. But regardless a river flows from the top to the sea. The top is the catchment area.
My expertise is rivers and waterways.
A dry gulch or canyon in Arizona can have a catastrophic to those caught in it flash flood from rain in a state 50 or 100 miles away. That is a catchment area.
Lol. I am aware of catchment areas, Matty. But thanks for the clarification
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Just now, matty40s said:
I should bloomin well hope so as that's the next wave coming in.
I suspect the EA only mention England in their report solely because that is the area they are responsible for. No more no less. Perhaps you should contact them for clarification
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1 minute ago, matty40s said:
Youve had a hard day, sorry, so have I. But regardless a river flows from the top to the sea. The top is the catchment area.
The catchment area is any tributary that flows into the river regardless of country. I am sure that the EA aren’t pedantic over whether it is Wales or England. They have a responsibility to the area they have to cover. And will also be looking at this
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South East and East Anglia Weather Discussion January 2021 onwards
in Regional
Posted
Just worked out that I am 69m asl and 16 miles from the coast. I’d give myself 0.5°c for altitude and 1°C for sea modification. Small margins