Interitus
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Posts posted by Interitus
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29 minutes ago, I remember Atlantic 252 said:
Just shows that when members say 'models underestimate the cold block' is normally untrue, the Atlantic will find a way in, often quicker than NW members predict
Breakdowns can sometimes show a tendency to be delayed with cold hanging on, but what's amusing is that when these charts appear is the common insistence is that they are wrong and the colder output is more likely, rather than the writing's on the wall.
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24 minutes ago, iand61 said:
Some in the town obviously have a thing for inviting a couple of friendly sheep to illegal lock ins but I think a camel might be pushing it a bit
just think how much it would drink
Illegal flock ins.
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On 28/01/2021 at 15:59, h2005__uk__ said:
Unfortunately that doesn't seem to have all stations - at least it doesn't have my two local ones (Andrewsfield 03684 and Writtle 99127).
I can't believe the MetOffice is still so bad at providing this basic info free of charge.
Andrewsfield data is available quite widely as it is a SYNOP site so is carried by Ogimet for example - enter the WMO number in this form -
Form to get daily summaries from synop reports
WWW.OGIMET.COMHourly data can be found by clicking on the dates.
Skylink offers a wider range of sites, some that weren't available on weathercast. Not convinced by the accuracy of all the stations but a potentially useful and interesting resource -
SkyLinkWeather Aviation - Latest Weather for London Stansted
SKYLINKWEATHER.COMCurrent weather for the UK, Europe, Australia and New ZealandAlas no Writtle...... but for that try weatherobs, fantastic site, possibly better than weathercast for viewing observations, which includes the additional Met Office sites as well as the standard WMO SYNOP and METAR locations -
Weatherobs
WWW.WEATHEROBS.COMGlobal weather observations (METAR, SYNOP, BUOY, SHIP, TAF, CWOP) decoded to enable display of latest temperatures, weather, snow depths, precipitation, wind and wave conditions and more -
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12 hours ago, SP1986 said:
That's interesting, everything further south looks incredible marginal on that FAX chart. Even the 528 DAM zone is north of most of the NW at that point. I would have thought the cold air would be thoroughly entrenched everywhere by that point (12pm Sunday).
The thing is the 528 DAM is deceptive, it is representative of the temperature between 1000-500 mb but despite mention of 'deep cold', it is actually concentrated in the lower levels of the atmosphere. Temperatures up towards 500mb are not especially cold relatively speaking - indeed it soon becomes a westerly flow above the easterly lower down.
The repercussions of this means it's cold near the surface, which is want you want for snow, however with regards to shower activity it is largely developing below the 800mb level generated by surface forcing, there is limited deep convection.
Taking this precipitation chart for Monday as an example -
The black line in the middle from roughly Liverpool out into the North Sea is represented in the cross section below -
This shows vertical velocity - vertical air movement. Following the direction of wind flow from the east on the right hand side and comparing to the precipitation chart, there is gentle convection (max at about 700mb) over the North Sea producing showers, shown by the upwards arrows on the chart. Moving leftwards (towards the west) the showers are enhanced on meeting the Lincolnshire Wolds but the uplift is only up to about 800mb, the air is quite stable and the topographic wave forms a descending air at 750mb reducing shower activity inland.
Moving further westwards, upon approaching the Pennines, there is strong uplift below 850mb, producing heavier showers, but the topographic wave and strong descent caps development to below 800mb and effectively kills showers to the west of the Pennines, on the left hand side of the chart.
One way this flow pattern may breakdown is suggested by this run on Tuesday evening is a convergence zone (sometimes misleadingly described as a streamer).
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Just now, Wardlegacy said:
Id have to check my records but on the slopes of the Pennines we had already got a covering of snow at that point from showery snow. You do seem to want to argue rather a lot, are you OK?
It's a discussion forum, disagreement should be permitted (unless in the MOD thread, obvs.)
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18 minutes ago, Wardlegacy said:
Depends where you were in the region
The notable March 2013 snowfall chiefly between 22-24th, a report from the Met Office -
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40 minutes ago, chris78 said:
That is what you are inferring, it is not what people are saying. Christ mate its a weather forum, the models are showing snow, and you are making out we cant be interested. Plus if I get a 2cm of snow (I wont) or if someone in Blackburn gets 8cm (they might) Why should either of us give a lemon that someone else has 2 foot. That is a very mean spirited way to look at it. If I win a million on the lottery should I not be happy because someone else won 10?
It's not what has been inferred at all, in the same way that it's not been made out the people can't be interested.
It has been regularly posted to ignore the precipitation and snow depth charts. Of course showers are parameterised in NWP output, and it isn't always precise, but equally they won't be a million miles out, that's just wishful thinking, unless some trough or other feature etc. materialised.
Think your analogy was wrong, you're winning the tenner
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23 minutes ago, iand61 said:
I can’t speak for the rest of the region but the March 2013 easterly certainly floated a few boats around these parts as did the 2018 one although I’d gladly miss out on the heavy disruptive snow part of the next few days if it means that my 85 year old Mother in Law can get her COVID vaccination and we can start to get some normality back into our lives.
However, March 2013 was a frontal system.
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1 minute ago, Dexter said:
Simply not true I'm afraid. I can't speak for Western parts of the region having not lived here that long, but I can assure you from personal experience that Eastern parts of the region can and have seen significant amount of snow from an Easterly, several inches on occasions.
Ok, lol, and on these occasions what were depths like in other parts of the country? It's almost like people are insinuating that this area is a match for other areas for snow showers in an easterly, it beggars belief!
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59 minutes ago, chris78 said:
For some in the region easterlies are great. Now for me out on the West a big fall is incredibly unlikely, so for anyone living in those areas your get real comment would apply to every single snow forecast ever made/ i think lots of us here look at others in the N.West predicting ONLY 8cm of snow with disappointment and think...you dojnt your born!
People are bigging it up, it's *possible* that there could be widespread notable depths, but the balance of probability is that it is unlikely and it will pale in to insignificance compared to other regions which will be worse affected. Without some frontal activity, that is the reality of the situation for most parts of this region away from the Pennines.
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3 hours ago, cheshire snow said:
Indeed
And on the basis of 40 years local knowledge of the area and a very unstable Easterly flow i would like to up my prediction but will stay within the rules of the game the myth of this area been bad for snow from the east was put to bed long before the Beast of 2018 people in this thread looking at PPN charts and taking as gospel then more fool you I am not ramping this up and if I am wrong then so be it I will hold my hands up and take it on the chin.
Transition day is Saturday then we are locked in to cold spell also breakdown is delayed again on this morning charts so could well be still in this cold spell into the next weekend as well.
Enjoy your snow its on its way.
C.S
Most of the North west typically gets naff all from an easterly, BFTE was no different. Sure, maybe a few cm here and there, and if that floats your boat then fair enough, but it's not the foot plus that some charts are touting for eg the eastern side of the Pennines or East Anglia.
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9 minutes ago, Chris.R said:
Because the inversion dropped lower in the atmosphere and became thinner probably due to evaporative cooling so freezing level fell. WRF was showing this could happen last night.
Indeed, thanks for saving me from explaining it
The deceptive thing is how far advanced the precipitation is from the front at the surface - so the milder air is not at the back edge of the snow/rain. There is quite a sharp temperature contrast at the surface eg. North Wales 8°C at Capel Curig, 1°C at Lake Vyrnwy 29 miles and 4°C at Rhyl 23 miles distant; in Herefordshire 9°C at Hereford, 4°C at Shobdon 15 miles away. But the rainfall has long cleared these areas.
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3 minutes ago, Interitus said:
Heavy dumping of NO in Warrington, expecting some more in the next week.
Actually, to be fair there was sleet for a couple of hours - though more rain than snow. And then at roughly around 5am there was about half an hour of heavy wet snow, oddly as the front mostly passed through and was more likely to expect rain. Left the merest patches on grass and at bottom of windscreens where it slid down and accumulated.
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Heavy dumping of NO in Warrington, expecting some more in the next week.
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Disappointing, could be the end of 9 years of data downloaded for hundreds of UK stations.
Weathercast was a decent site, been replaced by utter garbage at the moment.
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Rain and hail overnight left nothing on the ground in south Warrington, just started snowing now, got 20 mins to leave a covering for 9am, lol.
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On 16/01/2021 at 07:40, sebastiaan1973 said:
Why is it ironic? I try to understand/ learn
Sorry for late reply. You posted charts which take their inspiration from these classic images -
Tim Dunkerton was one of the authors of these, but sadly didn't respond to the Cohen tweet with anything as insightful regarding the current situation going forward.
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On 17/01/2021 at 17:54, Frostbite1980 said:
No disrespect to Marco but he has been saying about the SSW possibly causing cold air into the uk etc when it first started and it didnt work out like that so i will take this tweet as a pinch of salt....no idea comes to mind
Maybe not quite no idea, but little idea with regards to details - and this probably goes for all tweets and analyses by whomever.
17 hours ago, Bricriu said:Not me. I got stuck at WAF. Wave forcing??
Wave Activity Flux - which is essentially wave forcing, propagating up through the atmosphere.
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9 hours ago, sebastiaan1973 said:
Well. Some time ago, I posted the study by Domeisen et al. There are different types of effect of SSWs related to the regime five days before the SSW onset and five days after.
It is my guess, Cohen tweet points in that direction, we see a dipping effect of the 'European Blocking' type. If this is true, we can expect more 'dipping' in february.
The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events
WCD.COPERNICUS.ORG<p><strong class="journal-contentHeaderColor">Abstract.</strong> Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in...The use of 'dripping' paint charts in association with the Cohen tweet is ironic as one of the replies was from Tim Dunkerton (and characteristically slightly off the wall) -
Incidentally, the charts Cohen posted don't really show the expanded geopotential heights at the end of January that he was alluding to, oddly.
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8 hours ago, Catacol said:
But - I'd prefer this 100% over a year without a SSW which is much more predictable, largely because I'm not convinced in our modern climate that cold weather of any real depth can arrive in the UK without strat forcing and ideally a full on SSW.
December 2010.
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2 minutes ago, bluearmy said:
I get the context - but 2021 jan now has two dates with the lowest zonal flow at 10hpa 60N ..... as jan 21 progresses more of these clearly won’t happen!
Well, exactly - date records are interesting but not necessarily particularly significant.
Stratosphere and Polar Vortex Watch 2020
in Spring Weather Discussion
Posted
This "theory" first did the rounds a few years ago and unfortunately it is as wrong now as it was then.
To start with, the Taklamakan desert and Tamir basin are not a source of warm air in winter, it is typically bitterly cold with temperatures below freezing.
For sake of argument and assuming anomalous warmth, a bigger issue is that positive omega represents sinking air - negative omega is rising air.
But the biggest problem is that it fails to grasp the stratification and stability of the atmosphere. Ironically it is dismissive of moist processes which actually go a long way to overcome the stability, but also the tropopause which magnifies the scale of the problem, and also that adiabatic cooling would continue up to 10mb.
A convenient way to examine it is with consideration of potential temperature to compare the density of air at different altitudes. Theoretically, parcels of air with equal potential temperature are equally buoyant and interchangeable. Indeed for much of the atmosphere this holds true with isolines of potential temperature forming natural flow pathways - see isentropic analysis.
At the 10mb level in the stratosphere, potential temperature might be in excess of 850K - this would be the temperature an air parcel here would have if brought down to 1000mb. Conversely, an air parcel from near the surface would have to be much more than anomalously warm to remain buoyant at 10mb, rather hundreds of degrees C.
Studies of large forest fires have shown estimated surface temperature perturbations of 60C initiating large pyro-cumulonimbus clouds but the significance of latent heat release from adiabatic processes was 3 times that of the sensible heating (ie the fire). This is able to overshoot into the lower strat like regular storms but further uplift is capped by the tropopause. Examination of volcanic eruption plumes shows only the largest would be capable of reaching above the middle stratosphere. In any circumstance it must also be remembered that air parcels in reality are subject to substantial mixing and entrainment of the ambient air.
So there is no 'launch pad' producing a plume of warm air to 10mb (even the driest desert air would produce clouds as evidence), mountain uplift creates air parcels which rapidly become denser than the environment and negatively buoyant, returning to their initial level - or actually oscillating above and below this level ie orographic gravity waves.