Nick F
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Posts posted by Nick F
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Plenty of wintry interest for our Scottish contingent Boxing Day onwards from 18z GFS, with cold polar air bringing snow showers packing in behind that deepening low clearing out into the North Sea early Tuesday - though could be blizzards over the hills with the northwesterly gale. Then next low pressure system moving in from the west on Wednesday could bring further snow to Scotland as frontal system bumps into cold air here. However, differences quickly increase between GFS and EC on timing, depth and track of these lows Boxing Day onwards, so too early to make any worthwhile predictions of where and when it may snow let alone snow depth charts from EC!
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55 minutes ago, Seasonality said:
I was thinking the same thing this morning. Has certainly been an interesting week of model watching. Quite fascinating differences at t+144 as you've pointed out
Not a great fan of the meteociel 500mb/slp charts that a lot use and post on hereTBH, think it's the colour scales, but also the Mercator projection for Europe, prefer Netweather or wetterzentrale colour scale for 500mb and the projections. With regards to the effects of the -EPO ridge on the arctic and Greenland height fields, loop of the EC 500mb timeframes can clearly be seen ion the loop below (need to click in to it):
Be interesting to see if subsequent GFS runs pick up on the Greenland height rises and if the 12z EC has more sustained +ve heights over Greenland, as past t+168 the +ve heights over the arctic relax their influence with low heights taking over to our north.
Think we really need to rely on the high res runs to lead the way on the effects of the -EPO ridge over the arctic as the ensembles may be missing the changes in the early stages of initialization of the runs. But even the high res runs are just starting to catch up on the effects of EPO / MJO.
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Quite seismic differences between EC and GFS at only t+144: with EC making a lot more of the -EPO ridge across the arctic into Greenland by raising heights here.
EC seems to be the first model to perhaps start to truly grasp the effects of the highly anomalous -EPO ridge and wave breaking on the height fields over the arctic, but will it be sustainable height rises over Greenland? Perhaps we really can’t trust models past t+144. Interesting times ahead if this is a start of a new trend to see cross polar ridging effecting the height fields over Greenland, but not totally unexpected by some of us on here.
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25 minutes ago, comet said:
I was of the thinking that by showing the anomaly charts you could see where any forcing is taking place rather than the broad brush of the mean. The wave breaking several days back at the 10mb level is without doubt the reason behind the Alaskan ridge and cold surge that we engulf a number of states in America over the coming days rather than MJO, Glaam , GWO etc.
Certainly there looks to be downwelling through the strat, wave breaking like you say over Alaska, though yet to be convinced that the negative amomalies on our side of the northern hemisphere will work through to the trop. Would like to see a SSW rather than displacement to guarantee a cold pattern in January, but alas no signs yet. We've seen SPV displacements in recent winters but the cold patterns / HLB has failed to materialise.
11 minutes ago, Tim Bland said:It’s been a good evening for coldies! ECM & GFS have most parts of the Uk under a blanket of snow in just over a weeks time
It would be better if they were likely to verify though! Long way off to think about snow, but certainly looks like there will be some cold air following these lows moving west to east, but how cold and wintry will depend on the spacing between each of a succession of lows likely to roll in on the strong jet stream. A little amplification between systems will certainly help ...
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Sneaky strong northerly veering northwesterly developing next Wednesday on the back of those dumbbell lows affecting the UK Christmas and Boxing Day. Could be some wintriness for northern and western areas, especially hills.
Certainly a signal for some cold zonal polar flow after Boxing Day.
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9 minutes ago, comet said:
Way to much emphasis in here on EPS, GEFS, GloSea, Met etc etc they have all proven to be wrong many times in the past including the not to distant past and they will be again. The trend in the operational runs of the nwp models look quite positive and so does the progression of downwelling in the strat. I would expect to see further increases in northern blocking and a much colder pattern developing post Christmas. below are 30mb composite charts from the 14th and 16th this forcing downwelling from 10mb. This forcing started from wave breaking around the 8th and another slightly weaker one around the 16th.
But is that of evidence of downwelling though? They are anomaly charts you posted rather than geopotential height structure of the polar vortex at different heights in the stratosphere.
Certainly the strat forecasts from GEFS and EPS to day 10 suggest the SPV will stay displaced off the pole and centred towards the Barents and Kara Sea areas north of Russia by New Year, though extended forecasts from GEFS take it back to the pole.
My concern would be if the SPV becomes elongated and aligned with the tropospheric PV close to our NW, as if they become coupled, it would keep low heights intact to our NW for a protracted period in January. Though no evidence of this yet ... with signs of the -EPO ridge building heights toward Greenland, which will help drive the jet stream south. The question is, will the cross polar heights be sustainable into the New Year?
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Pretty impressive arctic high on the 00z ECM
I do think the models are underestimating the effects of the –EPO (which is tanking through the floor) + the effects from the MJO wave through phases 7/8 which combined will enact big poleward warming on arctic at 500mb and above into the lower stratosphere.
Mid-upper tropospheric and stratospheric forecasts have consistently signalled for major warming over Canada /Alaska side of the arctic which eventually warms the whole of the arctic above the boundary layer. The stratospheric PV is already displaced off the pole from recent warming on Canadian side and although shows signs of seasonal cooling/strengthening on forecasts, still looks in a more weakened state than is usual for the time of year.
But onto the model guidance, I do sense that they could be programmed with an overriding ‘La Nina’ code that seems to be trying to default the runs into producing patterns typical of Nina climatology towards/into low res – i.e. –EPO ridge, SW-NE aligned trough over N America above as SE U.S. ridge then downstream a zonal flow across the Atlantic and Europe as Canadian tropospheric PV extends east over far N Atlantic and Greenland.
However, do the models factor in the nuances of a MJO wave stuttering and stalling before heading through phases 7 and 8, which they are now only recently beginning to pick up on – along with the background of –QBO, downwelling / coupling between stratosphere and troposphere? Sometimes I think there are limitations to model guidance in that they are only as good as how they are programmed and the data that’s put into them and given they are not, as far as I’m aware, run with analogue data, exposes them to increasing margin of error when there is conflicting signals, such as La Nina against –QBO and coherent and amplified MJO, increased strat-trop coupling.
I’m not saying for one moment that we should ignore model guidance and that they will suddenly change from the strong +NAO look to bring as HLB and winter nirvana for coldies, but it maybe worth considering, given the background signal of –QBO, fall of solar activity toward 3 year minimum and the current forecast major warming aloft of the arctic driven by highly anomalous –EPO ridging to the pole and MJO divergence aloft, that the models may start showing some effects from the arctic warming on the mid-latitudes – by forcing the cold pools and vortices out into the mid-latitudes. ECM/EPS has indicated expanding polar high pushing low heights south, which in turn, pushes the jet and storm track over N Atlantic on a more southerly track, which may eventually open up the door for HLB over Greeland, Svalbard and Norway.
But it maybe a slow process, so we may not expect to see the fruits of the arctic warming until the New Year. We could see a spell of quite stormy weather between Xmas and New Year, if the jet starts to track more south as indicated by extended EPS/GEFS.
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Good to see the ensemble mean pull cold air down across eastern Europe and NW Russia in the medium to extended range, there is a lack of deep cold to the east right now, so to develop a cold pool to our E and NE will set up nicely if an easterly does transpire to end the year or early New Year.
In the meantime, we are likely to be stuck with a protracted spell of flow off the Atlantic from the W or SW, perhaps lasting through Xmas, given the colder operationals from GFS (yesterday's 06z & 12z and this morning 00z) were at the cold end or cold outliers of the ensemble spread. But the strong signal for the -EPO ridging to the pole with help of MJO, should in theory, eventually shift the tropospheric PV over Canada and Baffin S and SE, as per extended EPS H500 mean, which may mean a more southerly jet and storm track after Xmas, but perhaps encouraging height rises to the NE which could be aided by cross polar +heights / developing -AO.
But a lot of water to flow under the bridge before we may see concrete evidence from the model guidance for a pattern change to bring cold back after it turns milder from the west from Sunday. GFS operationals maybe too eager to change the pattern around Xmas, we could be looking at the period between then and New Year. A fairly reliable indicator of the braodscale 500mb pattern into the extended period is the CPC prognostic H500 charts - which suggest little indication of amplification over the Atlantic:
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18z GFS op perhaps a reality check, given the 12z operational was at the colder end of its own ensemble spread and also against the EC ensembles for London
Still think we will see changes for the better as we approach New Year, but 06z and 12z GFS ops perhaps a tad too quick with the pattern change.
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16 minutes ago, winterof79 said:
Yes I did need to put a chart up from Dec 86 same vortex intensity though
The difference back then was a deep cold pool over NW Russia, don't have that at the moment or probably next week or more. Need that cold vortex to develop to the NE to get anything like a Jan '87 or other deep cold easterlies.
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8 minutes ago, Dafydd Tomos said:
GFS 6z continues this theme too, could be more snow over S & SW England as well as the far South of Wales than Sunday if this verifies.
Just a quick word re: the snowy looking GFS projections for tonight / Thursday morning ...
IMO GFS always progs dew points too low in a NWly regime, so any snow likely only settling over the hills in the north and west. There could be some wet snow mixed in with the heavier bursts / showers at low levels, even in the south and east, but unlikely to settle unless with height.
Could be treacherous over the higher routes of Wales and N England in the morning though.
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More amplification on the 06z operational over eastern N America, which in turn amplifies the 500mb flow over the N Atlantic. This appears to be due to more of a +PNA ridge (over western N America) which allows the deep cold downstream to dig deeper over eastern NAM, as opposed to a -EPO ridge further west - which keeps the upper trough axis over N America aligned further west.
What we need to see is this amplification over the Atlantic but also at the same time upper cold pooling /low heights to drop SE and S across NE Europe to have any success at ridging NE and decently cold air to undercut from the E. Unfortunately only one operational run and the interest in Fi, but not without merit given the evolving poleward ridging upstream over NE Pacific / Wern N America.
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7 minutes ago, offerman said:
That Azores high is the culprit. Need that to migrate westward or northward then the fun would begin. It just seems too stationary . I wonder why it barely seems to move run after run week after week month after month?
Well, the Azores high is a semi-permanent ridge, part of a belt of sub-tropical high pressure systems around the northern hemisphere, Californian high and Bermuda High to name but a few. So probably why it doesn't move much and often we see it extend into Europe when the trop PV is strong to our NW.
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4 minutes ago, northwestsnow said:
SE hangs on to the colder air at the surface through next week- pretty much coming up to the shortest day so i would imagine temps will fall quite low esp overnight in this setup-
9-10C by mid-afternoon across the SE next Tuesday, day of that chart, and the following night won't be cold given the flow is progged from the WSW
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29 minutes ago, johnholmes said:
Having looked in more detail at the anomaly charts and other data covering the 6-15 days or so I think the unsettled spell will be fairly short, certainly possible to be rather windy for NW'ern areas then settling down. Indications seem to show that an upper ridge is going to develop from the SW moving over the UK and NW Europe?
Yes, strong agreement from EPS/GEFS means and the operationals at day 10 of a strong ridge being extended NE from the Azores across NW/W Europe. GEFS/GFS op more bullish with northern extent of the ridge.
The forcing of the Azores ridge NE initially appears to be driven by a lobe of the trop PV over northern Canada / Davis Strait dropping into the NW Atlantic - which eventually lifts out and flattens the flow.
But notice the -EPO ridge building poleward, the extended EPS out to day 15 appears to me to edge the trop PV to our NW further SE toward the Atlantic, a result of the ridge over Alaska, thus lowering heights over the Atlantic and driving a more southerly track in the polar front jet. This would indicate a more southerly storm track over the Atlantic after Xmas Day, perhaps some cold zonality. While the GEFS mean keeps the SW to NE orientation of the 500mb flow deep into the extended range
So a strong high pressure signal for next week and maybe into Christmas week too, the south looking rather dry post Friday, though Scotland and N. Ireland prone to Atlantic fronts. Those hoping for dry and frosty weather maybe disappointed, as it could be rather cloudy, given the flow will be off the Atlantic and rather moist. Boring as hell weather in my eyes, but I guess it will please some.
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16 minutes ago, bluearmy said:
Joe b argues that those troughs are too tilted and will be more north/south with less ridging in the east. He argues that the models don't deal well with Arctic outbreaks headed n/s into the east side of the rockies (which are nw/se ) as they lift the air and warm it too much. I assume that more troughing into se USA will help our chances of Atlantic re-amplification
Yep, read his musings, he is and has always been a big cold ramper - so will always look for cold patterns in the east of the U.S., even if tentative. But he may have a valid point with regards to the orientation of the trough over N America - given strong -EPO signal. He also points out the increasing amplitude of the MJO in phase 7 and 8 on the EC and GFS RMM plots compared to yesterday ... showing the models are only starting to latch on to the true movement of the tropical wave and may start reflecting this in the medium to extended range with some more amplification as the MJO and -EPO combine.
Though no signs of anything positive from the above occurring from the 18z GFS operational though!
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46 minutes ago, Bullseye said:
Is this the first signs of the major pattern change? Alaskian/Aleutian ridge returning this side of Christmas. How often do we see such agreement between ensembles at that range, may not lead to anything and could be gone tomorrow but signs are at least being sniffed out although not surprising based on thoughts on here and Twitter.
That has a classic La Nina look to the 500mb wave pattern, such a pattern change upstream over N America and N Pacific would not necessarily be good for the UK straight away, the day 12.5 (T300) EPS mean shows a strong zonal flow over the UK with low heights to the N and NW and ridging to the south.
However, the -EPO ridge anomaly will certainly help in the long term to warm the 500mb over the arctic with -AO signature.
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Away from the hunt for the return of cold in the long term, keeping my eye on tomorrow evening on the frontal system / low pressure trough moving SE bringing rain, sleet and snow.
IMO GFS, as usual, looks like overdoing the snow in southern extent, ECMWF snow charts showing N. Ireland, parts of Wales, NW England and parts of the Midlands seeing snowfall from this system. Though no snow to the south of this unlike GFS.
The issue with GFS, I think, is that it has dew points too low for a NWly flow, given long seatrack, so the model assumes all snow inland right to the south coasts as the system and it's precipitation moves SE.
The 2 charts below highlight the precip and dew point in 5C increments together in one and just the dew point in 1C increments in the other, these DPs too low IMO ...
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1 hour ago, johnholmes said:Not good news for coldies re the overall winter patterns, looking at the latest computer output from UK Met. What the discussions will be in their Ops room trying to marry this output with what we have had and the possibilities according to some on the longer range models we see would be interesting to be able to eavesdrop!
https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/glob-seas-prob
Oh John, don't make coldies reach for the Prozac. If it wasn't for the MJO heading into 'colder' phases, as Nick Sussex has kindly reminded us through the CPC update, I think I would be waving the white flag for a return of cold the rest of this month after the expected bout of milder more mobile weather indicated to take over next week.
With the MJO already in phase 7 and expected to move through into phase 8, with the associated area of upper divergence moving east across the tropical Pacific will likely induce further poleward wave propagation over the N Pacific and a return of a strongly +PNA / -EPO ridge later this month, as is being highlighted by the 00z EPS.
Couple this with an east Asian mountain torque event, working with the trop ridging to induce wave breaking over the N Pacific, which will continue to keep the strat PV displaced from the pole to other side over toward N Russia.
For now, we are probably seeing the lagged effects of the MJO movement of phase 6 as we see the models extend the influence east of the Canadian trop PV and enhance the Azores high toward western Europe as the Euro trough declines eastward, a composite of mean monthly 500mb heights for December in phase 6 produces this:
similar look to what's shown by GEFS mean next week:
However, move on to a phase 7 and 8, remember there's a lag of 10-15 days, we could be looking at a pattern change to more blocked look for later this month.
Ridging signal building to the N and NE with 7 and 8, with troughing over eastern N America and the polar front jet extending east on a more southerly track (-NAO) as a result. This could be the way forward, but, in reality the actual patterns often don't play out like these composites, which at the end of the day, are means over several years when the MJO is in certain phases.
So although the model guidance is all pointing to a more mobile, milder and maybe even zonal outlook as we count the days to Christmas, there is room for optimism given the MJO signal for a pattern change upstream. However, there is the caveat that a pattern change away from the likely increasing influence of the trop PV over Greenland and Iceland may not transpire until after Xmas.
As with all longer range predictions using drivers such as the MJO and ENSO, they aren't an exact science, with their influence perhaps more muted this side of the northern hemisphere than over N America, so there is the possibility that we may stick with a more mobile and milder pattern to the end of the year if the trop PV to our NW proves resilient to expected re-amplification upstream from the wave propagation over the N Pacific.
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3 minutes ago, john mac said:
What direction is it travelling?
From the NE to the SW. Though the surface wind appears to be more NLy now, probably why it's becoming the right side of marginal for snow, I am at 40m ASL and it's snowing, as a drier flow comes from inland off the snowfields to the north.
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2 minutes ago, john mac said:
can Anyone post the latest radar please?
Heavier bursts running through London atm, just starting to get heavier snow here on the southern edge of it now, nice big fat flakes.
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Getting some heavier bursts of snow now in the south London lowlands, but can't see it settling unless it gets much heavier.
Model output discussion - winter proper underway
in Forecast Model Discussion
Posted · Edited by Nick F
I think the problem is that without some meaningful amplification in the polar front jet across the N Atlantic to join the cross polar ridging moving south into Greenland, the strong zonal 200mph jet stream will carry on regardless, albeit in a more supressed southerly track into Europe. That's until the Greenland height rises fade, which brings me on the other issue that the ensembles eventually dampen and shrink back the anomalous -EPO ridging building into the arctic. This could be because the ridge has built so far north that it has allowed troughing to undercut over the EPO region and the N PAC jet to extend into Wern U.S./W Canada cutting off the WAA north across Alaska which maintains the -EPO ridge. But it may return to full strength after temporary relaxation.
Still, the southerly tracking jet will at least mean we will be increasingly on the cold polar side of the jet through next week, with snow likely for the usual suspects of cold zonality up north, but maybe a few snow surprises thrown in elsewhere. But we can't get any sustained wintry weather out of such a pattern in our maritime climate without blocking lending a hand.