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Paul

Mid-winter - models, teleconnections and nowcasting

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The gfs has a nasty looking low forming on the front over the weekend. Could bring some very strong winds to Scotland if it's correct

gfs-deterministic-natl_wide-z300_speed-5763200.thumb.png.ef8723d2023e7a98fda0a22acc358b4b.pnggfs-deterministic-natl_wide-t850_anom_stream-5763200.thumb.png.6b560ab139768829ab7ad82b1133ecd0.png

64.thumb.png.12df7a3f44fde4a7c7fe84db47dfb2ba.png102.thumb.png.8ffea510cf6f5b3aa826fc519bf1cc8b.png

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According to the gfs intense amplification of the Alaskan ridge displaces the vortex south which sets in motion explosive cyclogenisis to the NW of the UK To be viewed with extreme caution

gfs-deterministic-nhemi-z500_anom-5979200.thumb.png.98e6440279ffccc526eab3fe74697237.pnggfs-deterministic-nhemi-z300_speed-6022400.thumb.png.c29038c85b0b877dc5657583bd0c8fa9.png138.thumb.png.6e3e179ec0d130591a03d2ca7d3aa4fc.png156.thumb.png.125377d968295abadd654dc41e96dcdb.png

 

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Of all the 12Z runs that have come out so far (such as the GFS, UKMO and ICON and GEM), they’re all showing quite a devilish Low for that Tuesday next week.

12Z GFS

09989AA9-903C-4347-BFAB-C895BE6FC9CF.thumb.png.8271925cd8401faced55ce9b0c4338a3.png

12Z UKMO

1A4C926B-DE28-4CD9-BDE7-056DE892100E.thumb.png.953809807ff7ed5180a0d2ed8b94520f.png

12Z ICON

C42610AC-CECF-4E09-9AAC-0CD1531ABFBF.thumb.png.e8cbd9bf7c2b4c6a177ea9b6df11cca1.png
 

12Z GEM

1873ACE9-0185-410F-9BAD-CC3E628682DE.thumb.png.c06f7011d28c55a69f7c2de7b2ab971d.png

Out of all the four runs above, would say the 12Z GEM just about shows the Low being the least intense. Still fairly menacing, though. 

Some models I think were originally showing a more shallower, disrupted, feature for early to mid next week. While the intense Low is a plausible outcome, especially considering the amount of operational models going for it, maybe a possibility that they are suddenly over-blowing that Low a bit? Some interesting weather if you like heavy rain and strong winds. (Personally hoping the Low Pressure system will become more relaxed and chilled out than what’s being currently modelled).

Edited by DiagonalRedLine

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The 24hr fax for noon Thursday confirms the change to more unsettled weather already in the north as the high finally releases it's grip slipping away to the south.

fax24s.thumb.gif.8ca26083db0cc8424f09f9fb1a090dbc.gif

The Atlantic fronts moving in with rain for much of the uk and this changeable pattern is the picture for the next week at least.A snapshot of the expected picture for Monday from the gfs is typical for the period.

j.thumb.png.300d7bee05a31316785babd022580729.png850.thumb.png.7c649e28753c2836b30d2c20984f688e.pngnh.thumb.png.9b97f462908d14064565247c4848bb4d.png
 

A flat and active jet flow headed for the UK so periods of wet and windy weather with changes in air masses from time to time. 

 

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Talking overall about the USA pattern but shows that the models do chop and change often and writing off patterns quickly often not a wise move.

 

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A few images from the 12z gefs illustrating the changeable outlook as the mean jet flow meanders across our latitude over the next 14 days.

Currently the near term looks a little milder as the flow picks up from mid-Atlantic but the trend is for this to turn more north westerly in week 2 with a increasing risk of snowfall further north especially over higher levels.

mean jet days 2-6                                      days 10-14

gfs-ens_uv250_nhem_1.thumb.png.17360d9da85372010bd5aec3d1cf6404.pngj2.thumb.png.d075a3f6aac07422817e6d1f49782904.png

850 hPa temps anomalies

    days 2-6                                                 10-14

 t1.thumb.png.b7ef4f693a43a7a1de12669acdc6be13.pngt2.thumb.png.212d4a5eec20d84f432dca2f40cd2961.png

Of course these spread over 5 day periods don't show any fine details day on day but give an overall picture and trends.

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The 3 main models at T120hrs

ECH1-120.thumb.gif.8ee8a18665ef1c64a65880780d2b1444.gifUN120-21.thumb.gif.c7c7f47c47f6c955ea5aeec795d9bfe5.gifgfsnh-0-120.thumb.png.6db3f4338aa8706ce9053469f99e786e.png

It's all been said really just to say pretty good agreement on the NH pattern at this range.

 

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I posted the Lerwick midday sounding earlier showing a temp of -85C at 30mb

ecmwf-deterministic-nhemi-t30_anom-5460800.thumb.png.e0814f74882e947662c89be456ba7fab.png

And at t240 with the 500mb profile

ecmwf-deterministic-nhemi-t30_anom-6324800.thumb.png.9dc6e578db37d464fac1e4899f4d3f28.pngecmwf-ensemble-avg-nhemi-z500_anom_5day-6324800.thumb.png.90b79dfb44d5985e3493ba03e2504aec.png

Edited by knocker

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Dropping the latest 500 mb anomaly charts in along with my comments on them

Wednesday 4 December

A while since I made any comment, this morning both ec and gfs showed a similar pattern with very –ve heights and deep troughing in much the same place=nw of Norway-uk-down to n Africa, slightly different angle though

Noaa shows a not dissimilar pattern, some ridging in w atlantic and the fairly –ve heights troughing the other 2 have.

Overall the 3, over several days seem to have been moving to this pattern, rather more mobile than recently but with a tendency perhaps still for features developing e of n America to run s of e rather than the more usual n of e? Also surface temps probably around or even below at times. The 540 dm line runs just s of uk and originates from fairly high latitudes!

Time will tell I suppose.

Wednesday 4 December

A while since I made any comment, this morning both ec and gfs showed a similar pattern with very –ve heights and deep troughing in much the same place=nw of Norway-uk-down to n Africa, slightly different angle though

Noaa shows a not dissimilar pattern, some ridging in w atlantic and the fairly –ve heights troughing the other 2 have.

Overall the 3, over several days seem to have been moving to this pattern, rather more mobile than recently but with a tendency perhaps still for features developing e of n America to run s of e rather than the more usual n of e? Also surface temps probably around or even below at times. The 540 dm line runs just s of uk and originates from fairly high latitudes!

Time will tell I suppose.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

 

 

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The North Atlantic 300mb wind field and surface analysis for midnight

gfs-deterministic-natl_wide-z300_speed-5504000.thumb.png.6edfe2b929e873e10c4ed6c585e2c997.pngPPVA89.thumb.gif.6e961a857765ea852963eb728ea8d984.gif

The weakening front has brought more cloud to central and southern areas but in the clearer patches still some fog around but once this clears not a bad day with sunny intervals. But further north the frequent heavy showers will soon give way to more persistent rain as the next complex frontal system sweeps in from the west accompanied by an increasingly strong surface wind

PPVE89.thumb.gif.1003f6f821faa5bb1ff55eb3039ef3e1.gifsfcgust_d02_21.thumb.png.f3bb2295a465cd0866ffd3e8d7263860.png2mtemp_d02_20.thumb.png.0364310521ecf95fe706dc6b50383e4a.png

meanreflec_d02_15.thumb.png.3904667528df77b3e8b8dbfd8d748118.pngmeanreflec_d02_19.thumb.png.bfaac08e2acd50563f3edd5cb85d7506.pngmeanreflec_d02_24.thumb.png.23606ea0bc1ec3c45bb38b0597a08ede.png

Tonight the rain, with heavy pulses, will persist over western Scotland and move further south over north west England whilst cloudy with the odd spot of drizzle further south. Generally windy but milder than of late

PPVG89.thumb.gif.d8014557914d70306a1b5ed2416bd01f.gifprecip_d02_28.thumb.png.a8100d859bd36c7f85d8ff94119ea724.png

The system will clear to the east and merge with the trough to the north on Friday so a day of sunshine and heavy showers, particularly in the west, where they may coalesce courtesy of a trough embedded in the flow. Could turn a tad colder in the far north behind the trailing occlusion, Still quite windy

PPVI89.thumb.gif.2fcb5cd2bbec7ab5756b58c1d6435273.gif2mtemp_d02_44.thumb.png.c71e2e4649bd71f04ba7cbb2ea6d2183.pngprecip_d02_41.thumb.png.b94868d60466886bf8f4e286d97bf836.png

The showers fizzle out to a great extent over Friday night and Saturday will be not a bad day thanks to a transient ridge. But out to the west some explosive cyclogenisis has taken place near the left exit of the jet and rain from fronts associated with this will encroach during Saturday evening

gfs-deterministic-natl_wide-z300_speed-5720000.thumb.png.5b7b325ad7a44d66d65ee8ea0cd4ba8d.pngPPVJ89.thumb.gif.35df52b8638e636dcff8e2bfb56b4f93.gifPPVK89.thumb.gif.862c914c574cac3d3d3cf0c134ac3b9d.gif

gfs-deterministic-uk-precip_1hr_inch-5752400.thumb.png.8fc7d88f4c53c155ceab85d8e8d3463d.pnggfs-deterministic-uk-t2m_c_max6-5741600.thumb.png.1818ee298129435cd384b21dba7b754d.png

The rain soon clears to the east resulting in Sunday being a very windy day with frequent heavy showers but the analysis has become quite complex as the latest trough merges with the one to the north (again) and a ridge starts to build to the north west

gfs-deterministic-natl_wide-vort500_z500-5806400.thumb.png.fbbf9e481ce701b1f2e39ed90e8b2636.pngPPVM89.thumb.gif.e2d06d42e3f0d54cb09b15660120fbe7.gif

gfs-deterministic-uk-precip_1hr_inch-5813600.thumb.png.ad20f45ccb5e8527998cd4536b94255b.pnggfs-deterministic-uk-t2m_c_max6-5828000.thumb.png.ddb840af809decf6013772db55018be6.png

The new trough re-orientates and moves east over Sunday night and by Monday the surface wind has veered northerly initiating some wintry showers in the north but in particular some heavy showers down the North Sea coasts where it will be quite windy

gfs-deterministic-natl_wide-vort500_z500-5903600.thumb.png.76bcaa16eb8a97ac7422bf48d8bdc897.pngPPVO89.thumb.gif.9ba2a35e0cb6e256e6803354d6b18b88.gifgfs-deterministic-uk-t2m_c_max6-5914400.thumb.png.3147c3e7b198c1aa67c63314ac41aaa2.png

 

 

Edited by knocker

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According to the gfs (and the detail over this period is a long way from being nailed down) the next low has arrived by Tuesday morning with the UK in a very windy warm sector whilst upstream the amplifying Alaskan ridge has displaced the Canadian vortex 

gfs-deterministic-nhemi-z500_anom-5957600.thumb.png.659bafeeb6a41f0306be49c458ba4ee1.pnggfs-deterministic-nhemi-t850_anom_stream-5957600.thumb.png.e3bd88fca24c9758769d885b104ea430.png126.thumb.png.eac40490f837f3da6fc3270320024580.png

Not a lot of point in being too concerned vis the detail from this point but over the next couple of days the main trough moves east which once again initiates a transient northerly with perhaps some wintry precipitation in the north

156.thumb.png.5c73998b417d6c05d0f2bb8c5f0ff28e.pnggfs-deterministic-uk-t2m_c_max6-6087200.thumb.png.7b9902f3baff7500fd6dd4c9857867c5.png180.thumb.png.83005809c482abd7c3ea0144816fe5cf.png

Edited by knocker

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The ecm take on the middle of next week

ecmwf-deterministic-nhemi-z500_anom-6022400.thumb.png.2a7203538890ad3f6e8f9d0b66a59635.pngecmwf-deterministic-nhemi-z300_speed-6022400.thumb.png.0673527415d2ad5914343dde1bfa3383.png

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Edited by knocker

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ECM 0Z just shows mild zonality and not those short northerly cold snaps like last days. Only positive thing is that the azores high is getting further west at 240h+. 

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The EPS mean anomalies this morning merely indicate slight adjustments to the NH pattern which essentially is as has been described previously. Thus the outlook continues to indicate unsettled with temps varying around the average but with the usual caveats regarding the impact of eastward movement of systems on the day to day detail

ecmwf-ensemble-avg-nhemi-z500_anom_5day-6368000.thumb.png.202838e0c7a02bdbc19bcbca3ea314f7.pngecmwf-ensemble-avg-nhemi-z500_anom_5day-6713600.thumb.png.97d823c33d68d28dd5997730721174e5.pngecmwf-ensemble-avg-eur-t2m_c_anom_5day-6713600.thumb.png.c0067359264098e7f6eaf5ea650e1bfc.png

Whether the eastward shift of the cold vortex is down to Alaskan ridge wave activity is a tad above my pay grade I'm afraid

ecmwf-deterministic-nhemi-t50_anom-5504000.thumb.png.d94d271cc2507bf655f6ca08a0cfc1f9.pngecmwf-deterministic-nhemi-t50_anom-6368000.thumb.png.a19d5332dd9d0dd5c9a900e435beda83.pngecmwf-deterministic-nhemi-z50_anom-6368000.thumb.png.37cf0ba2ad9ad4961170aacb3e6bdf11.png

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Any ideas on why the jet stream appears to be so strong? there seems to be a lot of energy , possibly more then usual?

 

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An excellent example of a warm front approaching from the west on the Camborne midday sounding and the same front, which is part of a complex low pressure area to the NW of the UK, has already brought some heavy rain into N. Ireland, western Scotland and down the coast to west wales. The warm and cold fronts will track south east down the UK through this evening and tonight, with frequent squally showers in their wake, and by morning the whole of the complex low pressure area wilt have merged with the trough to the north. The rain and increasing cloud and wind results in a much milder night than of late and will generally be fog free in the morning

PPVA89.thumb.gif.bc564bc2ab99ab9f6413cca07a112514.gifPPVE89.thumb.gif.cd5a6b8ba4d1fc39aa92fd27e9661935.gif2019120512.03808.skewt_parc.thumb.gif.ceec2391295d605d672c08cbe9e592b6.gif

meanreflec_d02_10.thumb.png.8d0fbe3118386bab10c216fd4c86d18e.pngmeanreflec_d02_13.thumb.png.550b33b427c4a147b8561fb130ce8f40.pngmeanreflec_d02_16.thumb.png.b4a5b6757b9cc70e4e77448107ae9eb2.pngmeanreflec_d02_20.thumb.png.845c2515b8f7802097f8c9fb42d36920.pngmeanreflec_d02_24.thumb.png.cf7230544c8837020995843fe37a791d.png

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Looking a little further on and focusing on Sunday and we see the UK back into a colder polar maritime flow and a stiff westerly.Rain or showers quite widely with some snowfall quite likely further north over higher levels.

The T84hrs fax and gfs images

fax84s.thumb.gif.54d8ca6c23df9d1161d4b026c42c1fae.gif11.thumb.png.830185a0eedbc537b38c9b96c5f20c65.png10.thumb.png.ce2dfc4febea0294099f7fbfa49b3d75.png

The Atlantic jet by then quite active-note the sharp temperature boundary on the 850 hPa chart- with more systems waiting to come in.

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A closer look at ecmwf earlier output for Sunday. 

Qpo3nij5sy.thumb.gif.a206860f85b77988772f4fd51a6dd16d.gif

Very windy especially for the West with very strong gusts. Subject to changes ofcourse. 👍

EzrkoVfR5G.thumb.gif.2c1b00552bc12e6b76dd73780f25b957.gif

Edited by jordan smith

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