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Paul

This is the focused model discussion - please only post about the model output. 

For a more laid back, bantery model discussion please use the Cold hunt - models and banter thread.

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17 minutes ago, bluearmy said:

Good analysis @IDO  -

i think the Canadian stays just strong enough to keep the euro trough fed out to the end of eeek 2 and the developing scandi ridging should mean the uk is in the battle ground area - by that time the wild card of downwelling is thrown into the mix 

Yes. Need to watch developments for early next week as it looks like being a bit of a forecaster's nightmare by Monday. Still a lot of detail to resolve. Excellent analysis as always Knocker.

MJO continues to show a push through phase 6 and trying to get into phase 7. At the very least you would be hopeful that the signals are not counteracting each other as they have been recently. If we can get to day 4 as modelled then perhaps with a little help from tropical forcing we make see the Canadian PV lobe start to relax its grip on our winter and enable pressure to build to NE?

Downwelling of SSW has to happen sometime (it can't just disappear into the ether), so as Catacol said yesterday, maybe we do just need a bit of luck!

 

 

 

IMG_20190124_094732.jpg

IMG_20190124_094711.jpg

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12 minutes ago, Singularity said:

It’s not a Pacific ridge we should look out for as such; rather a western USA/Alaska one as part of the PNA pattern. Some suggestion of this in the D8-D16 but not as much so as would be typical of the MJO behaviour depicted for that time. Makes me wonder if the upper divergence above the Maritimes is really being got rid off; that’s were a lot of interference with the Nino pattern has come from in recent weeks.

Models are often just too broad with troughs in the longer-range though, so I might be reading too much into it; the Pacific one just needs sharpening up.

1

Agree, the MJO forcing -v- NH flow (pre-downwelling) may, of course, flip more to our benefit as we get towards the reliable. The Asia/Pacific wedge may also be modelled differently.

Within the long wave pattern, micro changes could also favour a better cold/snowy flow, so not downbeat, and as others have said a favourable flatter flow may bring us more chances of snow now that we have embedded colder upper air?

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4 minutes ago, IDO said:

Agree, the MJO forcing -v- NH flow (pre-downwelling) may, of course, flip more to our benefit as we get towards the reliable. The Asia/Pacific wedge may also be modelled differently.

Within the long wave pattern, micro changes could also favour a better cold/snowy flow, so not downbeat, and as others have said a favourable flatter flow may bring us more chances of snow now that we have embedded colder upper air?

I think that is going to be key, the Canadian PV lobe isn't the worst thing in the world if we can keep the cold air either within a 12-24hrs fetch of the UK, or preferably over the UK.

Unfortunately seems like we are going to be very susceptible to what is quite small adjustments on a global scale, but for us that makes the difference between cold and snow, and mild and wet.

It is about time I feel this winter we had a stroke of luck work in our direction, given there has been very little of it so far this winter with how the pattern has evolved.

Whitefox, I seem to recall there are some SSW that don't have any impact on the troposphere, especially with where we are in the QBO cycle, I think they more often than not don't impact (though this is a more severe SSW than normal which may balance that out.) I think that figures were something like 2 out of 11 had an impact?

Edited by kold weather

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True what you both say - some of the most snow-laden sequences of weather can result from a chain of lows that are disrupted and 'strung-out' on a NW-SE axis across the UK with the jet pattern featuring many small-scale fluctuations rather than broad ones and so appearing quite flat on the wide view. How far northeast the lows track is of course critical, and how much higher pressure there is to the NE and E to provide a greater wrap-in of continental cold is also a big deal for low ground locations.

The MJO developments should encourage a further SW track and possibly a weaker flow too, as much as that brings the risk of bothersome LP stall locations (but also severe winter-bringing ones!).

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Right ecm ensemble clusters just out - first, I'm wondering if there is continuity with the D15 height rise to the NE? This was last night :

ec-ens_nat_z500scenarios_2019012312_360.

and good news - not only is it maintained this morning but also increased with more runs going for a NE block of some kind:

ec-ens_nat_z500scenarios_2019012400_348.

 

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Worth noting perhaps that there is some very cold air to the NE

A quote from Mika Rantanen

The North Atlantic Oscillation (NAO) is currently in a positive phase. Usually positive NAO-index means mild weather in Fennoscandia, but not always. There's only ten January days in 1950-2018 when it has been colder than now in Helsinki with more positive NAO-index.

 

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21 minutes ago, Nick F said:

Just looking at the GOES and GFS NAM plots for the reversal downwelling and it still looks like its going ahead in the first few days of February

geos_nh-namindex_20190123.thumb.png.6365aa4d65077b91e9815a8813ca0f2b.pnggfs_nh-namindex_20190123.thumb.png.1d2d26232aad049f53a8feee6bac5eef.png

However, I'm starting to question whether this forecast impact on the trop circulation is actually going do anything anywhere near us to the north, as have yet to see any HLB appearing in NWP, however HLB is showing over central and eastern arctic Siberia as indicated by 00z and 06z GFS around the 2nd when the trop is forecast to reverse

 

Without the SSWE reversal downwell directly impacting the trop circulation to bring HLB to our N, the Canadian vortex will continue to prevent a -NAO, as indicated by the current NAO forecasts, so need to hope this vortex relaxes or retreats and wave alteration/amplification from more favourable MJO start impacting the flow over the Atlantic too.

nao.sprd2.thumb.gif.cc35d047f418ec954d100a6c3caaec4c.gif

Just our luck too to have -AO but still a +NAO, this why we aren't seeing the HLB this side of the pole for now and low heights dominate around Greenland and Iceland.

ao.sprd2.thumb.gif.39f592826390cf775f65da7cf8005518.gif

Still, the Euro trough is a godsend, because without it, our prospects could be much worse (milder).

Which brings up a further question I think: If the AO does move strongly negative, that obviously implies considerably higher heights over the Arctic than at the mid-latitudes right? Firstly, the AO is a measure of the differential between the heights over the Arctic (I can't find the exact definition of the Latitude used for the Arctic measurement) and the average heights at around 37-45N; clearly that can mask areas of significantly below average heights in some parts of the mid-latitudes with above average heights in other parts. Perfectly possible to have below average heights over a large area of Siberia/East Asia say and above average towards the mid-Atlantic.

The question is that if the AO moves down to around -3 or -4, does that imply that you could see the lower heights pushed that bit further south, leading to what we see forecast with a large trough across Western Europe? So although heights near the Azores may be at or even above average, we see a steep gradient appear on a NW/SE axis from Canada towards Southern Europe? The more negative the AO, the steeper the gradient, therefore keeping the UK on the colder side of the jet?

And then, of course, you have the trough digging more deeply over Central North America, and the returning wave pushing further North thus strengthening the higher anomaly towards the mid-Atlantic?

Again, all musings!

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2 hours ago, knocker said:

Worth noting perhaps that there is some very cold air to the NE

A quote from Mika Rantanen

The North Atlantic Oscillation (NAO) is currently in a positive phase. Usually positive NAO-index means mild weather in Fennoscandia, but not always. There's only ten January days in 1950-2018 when it has been colder than now in Helsinki with more positive NAO-index.

 

It’s hardly been a strongly positive phase though .... closer to neutral this past week 

B621704D-C41D-4F6A-A0F6-D3D9B296A9AB.thumb.jpeg.bb195f60d397b46985895537d1072f04.jpeg

 

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The warmer air creeping east today with the font

PPVA89.thumb.gif.e09f648e27928e0ac77e4a83433006e9.gifw12.thumb.png.68185895e59581603676b98c2329e9ce.pngw15.thumb.png.cb70e41195a81693a68113eae80f831b.pngw18.thumb.png.2fa9c5a7c3078e8548b02dd4a0d3bc58.pngw21.thumb.png.6c8c5bc2109df2e4c3b891a906bc3290.pngw00.thumb.png.234167d860bec29915d2757874d6ed7e.png

And to digress for a moment.

I was in a taxi just now and the driver started wittering on about how he loved cold weather. I thought, 'the bloody nutters are every where', as i deleted the taxi firm from my contacts.

Edited by knocker

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3 hours ago, knocker said:

The warmer air creeping east today with the font

PPVA89.thumb.gif.e09f648e27928e0ac77e4a83433006e9.gifw12.thumb.png.68185895e59581603676b98c2329e9ce.pngw15.thumb.png.cb70e41195a81693a68113eae80f831b.pngw18.thumb.png.2fa9c5a7c3078e8548b02dd4a0d3bc58.pngw21.thumb.png.6c8c5bc2109df2e4c3b891a906bc3290.pngw00.thumb.png.234167d860bec29915d2757874d6ed7e.png

And to digress for a moment.

I was in a taxi just now and the driver started wittering on about how he loved cold weather. I thought, 'the bloody nutters are every where', as i deleted the taxi firm from my contacts.

Hey... that's being 'coldist' Knocker!

😂

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What do people always say "Let's get the cold in place and the snow will follow"

Days 3 to 5 look good for cold (yes not day 10), no point fretting about snow just yet but the signal is there for just about anywhere!

Day 3

gens-21-0-72.thumb.png.a1ad460f98e9a0f951a49be7da054e61.png

Day 4

gens-21-0-96.thumb.png.d80bc76c976cd2f9487dbf26d97fd5de.png

Day 5

gens-21-0-120.thumb.png.0a26224b8f02d20163b5df5192091b95.png

Plenty going on next week, could be good for many.

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The gfs is quite close to Exeter with the low centre midday Saturday and then over the next 24 hours tracks it south east to be close to the Dutch coast

PPVI89.thumb.gif.1e4da5e1325e542f9f6f154ad4bdb09e.gifgfs_ptype_slp_eur3_9.thumb.png.fc3546cad47b919203d5f69b82414839.pnggfs_ptype_slp_eur2_11.thumb.png.64200a2e8b882768a582ac7aef7872b9.pnggfs_ptype_slp_eur2_13.thumb.png.a14d3c6a95abf0daa3868fcbbf8cf641.pnggfs_t850a_eur_13.thumb.png.72b046d58f1ea685c92b08b6138b5ae5.png

Edited by knocker

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At t132 the gfs has an Omega block in reverse and that little low south east of Greenland becomes something of interest as it tracks south east and merges with the main trough and runs up the Channel. Could there be snow in the northern quadrant?

gfs_z500a_natl_22.thumb.png.061e1c7e305e5d72606844f16e43f852.pnggfs_z500_vort_natl_27.thumb.png.3b8d086d25b6e5a10221b939996dcff5.pnggfs_ptype_slp_eur2_27.thumb.png.a190cf3bb48b3da695288ce30d931c0f.png

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20 minutes ago, knocker said:

At t132 the gfs has an Omega block in reverse and that little low south east of Greenland becomes something of interest as it tracks south east and merges with the main trough and runs up the Channel. Could there be snow in the northern quadrant?

gfs_z500a_natl_22.thumb.png.061e1c7e305e5d72606844f16e43f852.pnggfs_z500_vort_natl_27.thumb.png.3b8d086d25b6e5a10221b939996dcff5.pnggfs_ptype_slp_eur2_27.thumb.png.a190cf3bb48b3da695288ce30d931c0f.png

Some decent vorticity there too; fair bit of PPN on that I would suspect? Just goes to show that there are some good chances of some snow coming up. Dare I utter the horrible cliche about it being reminiscent of eighties winters? I think I just have... Still a lot of vorticity to spin out before we reach that point though; let's not make ourselves dizzy obsessing over it (sorry for the dodgy puns)!

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My thoughts on EC 240h

Canadian Vortex to be attacked, continental high streching from Russia twrds Fennoscandia replacing LP with HP there, could end in some easterly cold options in start of Feb

 

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The ecm and gfs both trending the same way during the run with the major trough hitting the buffers of the ridge to the east and slipping south as the Atlantic high  continues it's alternate phasing with the east bound energy. Thus the upstream cold feed continues

index.thumb.png.258f1aa28a42fe4047197c51f298fb28.png

 

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Looking at the ext EPS over two days for the same time frame this evening reveals a few subtle changes. Everything has shifted a tad east in the Pacific whilst the high cell over Siberia relaxing somewhat as the vortex over northern Canada becomes more diffuse but still a strong upper flow exiting the eastern seaboard, diverging in mid Atlantic courtesy the east European ridge and west European trough. These two are now a tad more orientated into Scandinavia and negatively tilted. Thus still portending unsettled with temps below average and a tricky surface analysis to sort.

10-15.thumb.png.2ce498990d79899836822eaea0401e44.png8-13.png

 

Edited by knocker

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Thought I would have a look at the trend on eps mean anomoly over past two days

day 12 to current day 10 shows fairly consistent in depth of trough into the med but with some movement day by day on the axis - note the updated run now has a feed in from the Canadian trough - maintaining the euro trough is important- presumably we stay in slider territory which will ebb and  flow with each run 

C742F049-EDF3-4470-8697-4FBA153C3E83.thumb.jpeg.a39ef07db9c3377a8aa4e7bab61245f9.jpeg 29FA52C9-0162-4BAC-8A6F-72B78E8EC2F9.thumb.jpeg.17a41c8367430a17c04737366e95d438.jpeg D8FE9AC6-B65E-4D3D-B7C0-D81A9E262D53.thumb.jpeg.6f5cfe416545288fd4f59be39455a2b7.jpeg

 

day 10 to current day 8 -  just edging the mean upper trough west but not much 

1E0F52A2-B685-4AC9-AABD-8344C548C784.thumb.jpeg.8fa0ac3cba49e146db83aab1bd84e410.jpeg B213A08A-822A-4F3B-896A-30C06106B653.thumb.jpeg.2f74a5d400751164d2953417fa4017c0.jpeg 5C573892-5528-4CCA-BB47-1233C6E8BF43.thumb.jpeg.9213c7cbc75ade52e7f33fd82ded93a6.jpeg

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1 hour ago, stodge said:

Evening all 🙂

After days (it seems) of conflicting and widely shifting model output, perhaps some signs of stability if not certainty this evening. 

As always, it will be the ECM 12Z which will set the tone for the conversation for the 8 year olds in the banter thread but here in the civilised world, some more objective thinking may be required:

Let's look at some 12Z output with some progression:

First, ECM T+144:                                     T+240:

ECM1-144.thumb.gif.72cc632de2eadbcc650874195d1acac6.gifECM1-240.thumb.gif.fecfac1f7a0f023a692fa3219fdc8019.gif

GFS Parallel in the same timeframe:

144:                                                           240:

gfs-0-144.thumb.png.3099393f24ec33c36c22f0bf2aa4b560.pnggfs-0-240.thumb.png.97b4f01813f64eb3fdd8076805258c6c.png

GFS OP:

144:                                                          240:

gfs-0-144.thumb.png.e7f6164d46424ffc1ed3f0ea9104e7c5.pnggfs-0-240.thumb.png.367509ba19aa6d2872c96200d67e7865.png

As a contrast, GEM 12Z:

144:                                                           240:

gem-0-144.thumb.png.8b40c31f75eeea47226984fbf816ac4f.pnggem-0-240.thumb.png.6ac7095d40b47599366de979710e1b2d.png

It's encouraging to see strong cross-model agreement and the ECM 12Z at T+144 is very close to the UKMO at the same time so that's helpful. GFS Parallel isn't far away but makes much more of LP to the NE of Scotland and up to the Norwegian Sea. Under a slack flow, stagnant cold air will get very cold so plenty of frost and perhaps freezing fog. I've also noticed how quick GFS does everything - it's an extraordinarily mobile model and that may work well on occasions but not all the time. The Parallel seems to be taking a more leisurely approach than the OP which is by T+240 already gearing up for the next slider from the NW. The GFS OP goes its own way and rushes everything through as you'd expect while GEM sort of gets there in the end.

The problem for me remains the lack of heights to the north and north-east and the NH profiles don't fill me with unabashed glee at this time. The Parallel is the most "hopeful" in terms of washing out the Canadian lobe but it still looks to have plenty of fight on the ECM and GFS OP.

I was musing on this today and trying to get my head round it. It occurred to me that we had less of a split than a strong displacement and that left a lobe on the Canadian side (always likely given the warming came from the Eurasian side). I just wonder if the downwelling actually re-enforces the PV at lower levels as it works down and does so until it reaches right down into the troposphere. The downwelling struggles to make headway and it's like trying to run up an increasingly steep hill. My conclusion is we will have a window of opportunity between the time the downwelling reaches the troposphere and the re-enforced zonal winds arrive (mid February maybe). We take the tanking AO which is fine but the NAO (thanks to the PV) continues at best neutral. We really need to see that NAO turn negative (though not too much in my experience) but that will be dependent on signals showing the PV is shifting off base. 

With the PV, if you can't weaken it, move it. Any displacement west or south west gives us a chance to get the Arctic HP more favourably placed toward the European side rather than over Siberia. As I mused last night, the westward shift of the Siberian HP into Scandinavia is something we see after mid winter as the Atlantic slows and amplifies and if Scandinavia has some seriously cold air (and you're looking at something like P19 on the 12Z GEFS) you can get some cold heights.

Oddly enough, the current scenario may play well for fans of snow rather than fans of cold. Most snow events are marginal especially in the south as others have pointed out so I worry less about -4 to -8 uppers at this time of year if we can get the thicknesses and DPs right. I simply don't see (and never have this winter in all honesty) a 10-14 day period of severe weather with ice days and frequent snow. Even if we get the pattern right (as we didn't this week but may next week) I don't see how the cold is sustained but in a scenario with a negatively-aligned trough and getting enough cold or very cold PM air it may not matter too much. A northerly is still a northerly even if it isn't being supported by a 1070MB Greenland HP. A NE still works even if it is reliant on an active LP over Europe. Getting the trough down into Europe gives some of us a sniff and I'd be quite optimistic if I lived on high ground in the north of England and Scotland - the prospects for occasional snowfall look very good. 

As for southern areas, well, the ECM offers -3 to -4 uppers at T+240 and interestingly while the current milder sector gets to +3 or +4 850s, the mild sectors next week are progressively shorter, weaker and smaller while both the GFS OP and Parallel have plenty of cold air about next week with 850s widely down to -8 which is all good stuff.

So, where are we? Utopia eludes but doesn't it always? In truth, we could use the precipitation be it rain or snow and there seems to be plenty of that on offer. It may be a "miss" for south western areas but high ground to the north and east looks favoured if you are after snow but as the air gets colder next week more areas come into the game, 

 

Very good analysis, although its worth noting that low lying areas of the Midlands and SE have seen more snow than higher parts of northern England this week.

The airbase was a lot colder than that modelled which bodes well for the next 10 days which could be very snowy almost anywhere across the UK depending on wind direction and depression track.

People crave northern blocking and Scandy highs but in reality both can bring dry,dull weather rather than snow, the current set up could be more interesting, more for filling if risky. 

What it most definitely is is a forecasters nightmare!

Andy

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The NH 500mb and surface analysis for midnight

gfs_z500a_nh_1.thumb.png.f7f0ab6e94eb9004a525a79aafcd63e1.pngPPVA89.thumb.gif.0c5f04b1d1b7d4f977cfd2cf914d07f4.gif

A cloudy and mild start to the day in the moist westerly airstream with some rain from the warm front still around in the south east and bits and bobs of patchy rain/drizzle elsewhere. The rain in the south east will clear but it will remain cloudy over much of the country through today, with some patchy drizzle around NW and W regions although the cloud may well break in some regions to the east. But by mid afternoon the cold front has encroached a little down northern Scotland with some heavy rain effecting the west coast

PPVE89.thumb.gif.afaeb4daab9c2fdd4b7f52d01ba5ec31.gif1982076446_maxf.thumb.png.9adfefed7189580f9e994a6deb91eb1f.pngp18.thumb.png.800dbd14c9c4731bf3c2764af6f49699.png

Through this evening and tonight the cold/warm front doesn't move very far as the wave that has formed on it to the west gets organized. Thus the persistent and heavy rain will continue over Scotland whilst further south cloud, mild and patchy rain/drizzle in the west remains the order of the day.

PPVG89.thumb.gif.641676451ff6421c3bbff0e4d665c05d.gifr22.thumb.png.fefea81a42fdce0c8ab8e0e0fdb8cffc.pngr06.thumb.png.3fcb0e65c010f2ddf1ab67e3f669ea66.png

The rain in Scotland will persist through Saturday but now the low is west of Ireland and the associated cold front with a band of heavy rain is down the Irish Sea at midday. This will track east through the rest of the day, followed by squally showers, with rain effecting all of the country with snow on the high ground in Scotland and accompanied by strong winds. Another mild day but colder air creeping into northern Scotland.

PPVI89.thumb.gif.fd1bffc606fc88ac1a0941afdbeff6ce.gif989083137_maxs.thumb.png.9f27cff290d697d54a6fa5ec8e90bcd5.pngrs12.thumb.png.dcb3380f1ca3c50eae07f84bf273880f.png1456601891_rs15.thumb.png.8d11a575968be7a218e23242831a3adb.pngrs18.thumb.png.14f73d663bea59b9522ead838839d8aa.png

Overnight Saturday and through Sunday the low tracks into the North Sea with high pressure ridging to the west resulting in a fresh northerly wind over the country with wintry showers and a much cooler day

gfs_z500_vort_natl_11.thumb.png.484493eab3273b5dbfb41d47cd8d9af0.pngPPVJ89.thumb.gif.923088e86bd95fb5069b4d22de8afd35.gifPPVK89.thumb.gif.b5236f85c0d0fa6b853e0d4a7bfe78c0.gif

gfs_t2max_c_uk2_12.thumb.png.c596f21827a29a9eeed982b3db54ad96.png

Still quite breezy on Monday with the wind backing a tad so the showers tending to be concentrated more in the north and west with snow on the higher ground

gfs_z500_vort_natl_15.thumb.png.dca8c02ebf49b93148d36a833f413e6c.pngPPVM89.thumb.gif.b3cafcea92125ac324dd937e20ca6079.gifgfs_t2max_c_uk2_16.thumb.png.685e2230996b615d2690ea9dc63f2d35.png

On Tuesday the upper trough dominates proceedings with a myriad of surface lows and fronts dotted around but essentially the UK remains cold with frequent showers in western regions with eastern and central areas predominately dry

gfs_z500_vort_natl_19.thumb.png.385154598eee5f23cb0d0b7c0a12e9de.pngPPVO89.thumb.gif.813e1d5c360dea08cba4bdbad56d84e3.gifgfs_t2max_c_uk2_20.thumb.png.b54088c2a93b242a136ae4afa44912a5.png

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Following on from the above with the gfs and by mid week an intense upper trough has tracked east across the Atlantic and is south of Iceland by Thursday midnight. It then deepens and tracks across the UK and the intense surface low brings strong winds and rain on Friday with snow on the northern flank of the front. Well that's the theory

gfs_z500_vort_natl_25.thumb.png.9faad9533f90daf0cadc1ec8fd58e469.pnggfs_z500_vort_natl_31.thumb.png.7ddffe694ff969f2a526ff3f62712a62.pnggfs_ptype_slp_eur2_31.thumb.png.9115b8837150a5a60896b81224b8e6c6.png

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As the cold front moves through S/E Sunday some pretty high winds to be expected especially for West S/W coastal regions. Snow showers for some especially over high ground continuing into the new week with some hard frosts especially under any clearing sky's and cold days under a brisk wind.

832409004_viewimage(8).thumb.png.4152f56cc0a41c99f10b558de9cd5723.png1265839044_viewimage(9).thumb.png.f31b6322632052d8f983685cd03c311e.png931737368_viewimage(10).thumb.png.5c25076b505c2e8baf9aae98bf0df6e0.png2008976973_viewimage(11).thumb.png.da34451bbfad1dc57422e10ee58bb8cb.png593547665_viewimage(12).thumb.png.8566716c8a52b9774b7076cec65efe5c.png1370080590_viewimage(13).thumb.png.192d8f140998413a37a0981e07e02dce.png

 

 

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