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Short range model discussion - into 2018

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Latest HIRLAM for snowfall by Wednesday 12Z. Disruptive snowfall to the east of the Pennines and down the east coast, perhaps North Downs too. Also localised falls for S Devon and S Cornwall, and places in the south that virtually never see snow are covered (Isle of Portland, Ventnor, etc). Snow falling out of the sky at some point for everyone?

hirlamuk-45-48-0.png?26-17

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13 minutes ago, Man With Beard said:

Latest HIRLAM for snowfall by Wednesday 12Z. Disruptive snowfall to the east of the Pennines and down the east coast, perhaps North Downs too. Also localised falls for S Devon and S Cornwall, and places in the south that virtually never see snow are covered (Isle of Portland, Ventnor, etc). Snow falling out of the sky at some point for everyone?

hirlamuk-45-48-0.png?26-17

Thats going to be carnage for the Scottish Central belt ...

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Still tricky at the end of the week and looking like possibly a quick snow to rain event in Cornwall but more concentrated snow the east and north east ahead of the front

gfs_ptype_thick_eur2_17.thumb.png.5509d2278a1282801c465d5b40ec7e64.pnggfs_t850a_eur_17.thumb.png.6b3df0a0127772b98433145bc3864e7b.png

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With regard to the front tonight aka the polar low, just been looking on the latest satellite images from Norway and to my eye it seems to be tracking slightly south of where the models have been showing it. Any thoughts?

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19 minutes ago, Matthew Gill said:

With regard to the front tonight aka the polar low, just been looking on the latest satellite images from Norway and to my eye it seems to be tracking slightly south of where the models have been showing it. Any thoughts?

Keeping an eye on it. Looks like it's moving sw landing Lincs?

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2 minutes ago, Sweatyman said:

Keeping an eye on it. Looks like it's moving sw landing Lincs?

Was my thinking as well. Maybe a little surprise later for some 

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The updated fax charts for midday Tuesday-1200 Weds showing the wave over Wales and the convergence zone through the channel. Thus the snow showers may impinge more along the south coast.

PPVE89.thumb.gif.313250f23d03a4c38f7e173bdc54c02a.gifPPVG89.thumb.gif.26a47d55f0fd7b22258ac982d052e07b.gifPPVI89.thumb.gif.d3f87760114f8d5d7c5860f828920d7e.gif

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49 minutes ago, Sweatyman said:

Keeping an eye on it. Looks like it's moving sw landing Lincs?

yes it does look to be taking a track further south ,time will tell , but a very interesting feature ,cheers all .

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Some nice convergence zones at 1800 and the upper front in the Channel 1200 Thursday with warm front northern France

PPVA89.thumb.gif.87a4e87094ebb090b5ca91e5c6426448.gifPPVK89.thumb.gif.03b3ab5d8349d6ca61550ed689e3ca6d.gif

Edited by knocker

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9 minutes ago, knocker said:

Some nice convergence zones at 1800 and the upper front in the Channel 1200 Thursday with warm front northern France

PPVA89.thumb.gif.87a4e87094ebb090b5ca91e5c6426448.gifPPVK89.thumb.gif.03b3ab5d8349d6ca61550ed689e3ca6d.gif

Two questions:

1. Will showers forming over those convergence zones continue to track in a line moving in a south-eastward direction?

2. What is the difference in relation to snowfall between the upper front and the warm front?

Cheers,

TE

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11 minutes ago, The Enforcer said:

Two questions:

1. Will showers forming over those convergence zones continue to track in a line moving in a south-eastward direction?

2. What is the difference in relation to snowfall between the upper front and the warm front?

Cheers,

TE

1.Sorry not following the south-eastward direction bit. More south west tending towards the west depending on the low level flow more likely.

2. A lot less, if any, if any on the upper front assuming of course that everything else is conducive to snow which looks likely. But I'm open to correction on this by JH who is much more knowledgeable than I on the subject. :)

EDIT

But thinking about it it may modify the upper air a tad which may impact on snowfall from the following warm front. On the other hand that might just be waffle.

Edited by knocker

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4 hours ago, knocker said:

As for accuracy i've no idea but as they are official sites I doubt you will get better. If you change the filters you get a much bigger coverage,

A bit late to the party on this conversation but I can confirm anyone with a station can upload to this site. I know because I connected my station last week!

But most amateurs who have added their sites (just like Wunderground I suppose) tend to state what equipment they have and where it is located so you can make a judgement.

I guess from a Met Office perspective they get access to ‘big data’ akin to crowd sourcing and can make use of that.

keep up the good work on this thread guys. I’m just starting an Open University course on the weather so I hope to be able to contribute soon!

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42 minutes ago, knocker said:

1.Sorry not following the south-eastward direction bit. More south west tending towards the west depending on the low level flow more likely.

Apologies, I don't know my east from west either. So, it's reasonable to assume a south-westwards to westwards extrapolation of showers out from the line of the convergence zone.

Ok, so the upper front is bad news for snowfall and ideally it should go away.

Edited by The Enforcer

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1 minute ago, The Enforcer said:

Apologies, I don't know my east from west either. So, it's reasonable to assume a south-westwards to westwards extrapolation of showers out from the line of the convergence zone.

Ok, so the upper front is bad news for snowfall and ideally it should go away.

Yes I would think so. And a sat. image from 10 minutes ago

ch4.thumb.jpg.a8de46c838a70e4e5ce2dbc48d956bdf.jpg

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No huge change in this evening’s anomalies so will keep this brief. The high pressure/ridge still over NE North America into southern Greenland and signs of the second coming of an old friend over Banks Island, The main vortex lobe still N. Russia with the associated trough running all the way west through Scandinavia/UK and across the Atlantic ending south of the ridge.

This gives a pretty slack gradient over much of the UK, more particularly the north with a moderate westerly jet running into France and Iberia and just about impacting southern Britain and it’s along this path that any systems will travel. Precisely how and if they impact the UK is for the det runs to sort and this will also dictate the temps but probably a reasonable call the they will remain below average.

ecm_eps_z500a_5d_nh_11.thumb.png.8beb26d4aea4771059577f5e2f00d2d5.pnggefs_z500a_5d_nh_41.thumb.png.d2057525822281c755751288d8868579.png610day_03.thumb.gif.bd0dd82d275ea8ee222f5556881f361e.gif

gefs_t2ma_5d_nh_41.thumb.png.0f8c275aaa03124db90ba71bf166d3b9.png

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My own synoptic analysis for the next few days, won't bother with Thursday/Friday's low until nearer the time, but will concentrate on tonight, tomorrow and Wednesday.

Current synoptic overview

A large blocking anticyclone is in place over Scandinavia, with a surface high around 1051mb centred over northern Norway Monday evening and a strong upper ridge over the Norwegian Sea extending from Iceland NE toward Svalbard. A slow-moving low pressure system affects central and eastern Mediterranean. Below 500mb/MSLP and T+00 fax from Exeter for 18z this evening

GFSOPEU12_6_1.thumb.png.ccdd64265b90b46d2dd049e098626849.pngfax18z_260218.thumb.gif.a3187b97594a5ab432ca6597b5551253.gif

 

The jet stream loops around the Scandinavian ridge going northeast over eastern Greenland before dropping south over Svalbard then southwest across Scandinavia and then on across the British Isles, south into Iberia before joining the southern arm of the jet extending from the Azores eastward across the Mediterranean.

GFSOPEU12_6_21.thumb.png.474c8bb778c57ded4b2765ba1da82611.png

Between Mediterranean low and the high over Scandinavia, a very cold easterly flow covers much of Europe, bringing snow as far south as Rome today, while the deep cold air (-13 to -14C 1500m above) crossing the relatively warmer North Sea (between 5-6C) is causing a classic ‘lake effect’ snow shower machine.

GFSOPUK12_6_2.thumb.png.410c894987e3d89a70fca364550e5040.png

Tonight

Wind convergence zones this evening and overnight will enhance snow showers activity across eastern and southeastern England – particularly areas southwest of the Wash as far as the Southeast Midlands, also from areas around the Thames Estuary/North Kent coast and southwest across Kent and East Sussex. We could see up to 10-15cm in some spots that receive frequent heavy falls through the night, but not far away may see only a few centimetres at best.

03z.thumb.png.038d1ccb2500aef25a890f6e1e8bb889.png

Tuesday

Scattered snow showers overnight elsewhere along eastern coasts overnight giving a dusting in places. Then as we head into Tuesday morning and already appearing on the radar this evening is a mass of heavy snowfall over the North Sea off eastern Scotland and northern England – which marks an area of enhanced ascent ahead and along a surface trough and associated back-to-front frontal system over the North Sea moving toward NE Britain. This will bring an area of heavy snow showers or more persistent heavy snow in across parts of eastern Scotland and NE England overnight, before spreading southwest across northern England and north Wales during Tuesday morning. Further scattered snow showers for eastern areas through Tuesday, some flurries getting further inland towards the west too.

2155.thumb.JPG.e77d24c95f09fe9c87de82fa83fc9ead.JPG loop.thumb.gif.ee91e1107ebe3b8b053de4d1ff33f0d5.giffax24.thumb.gif.3f679764fc75936a3d6d1b0ad7d7cdcc.gif

 

A unusually deep pool of cold air or upper low, coming out of NW Russia tonight, moves southwest  on Tuesday and over the British Isles Tuesday night into Wednesday morning. This deep upper cold pool is forecast to have 500mb temperatures of below -40C and will create steep lapse rates allowing vigorous convection, with increase of thunder and lightning, over the north North Sea and into eastern Scotland and NE England. It may also enhance snow shower activity further south along North Sea coasts of England Tuesday night.

500mb_loop.thumb.gif.2b21b080fe2efd5faab5c68d6108632b.gif

Wednesday

Into Wednesday, and it looks like the wind will veer more easterly or southeasterly while strengthening – which will mean snow shower activity will ease across SE England, with shorter sea track to near continent and concentrate showers along eastern coastal areas from East Anglia northwards with longer sea track but showers also getting well inland across central and northern Britain. The strong easterly wind, which may touch gale force towards eastern coasts, may cause drifting of snow, given its powdery nature.

loop_weds.thumb.gif.d419b532378efab2bff186a8cdaff63a.gifwinds.thumb.png.df322204e668042826771c65e2d556de.png

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Here's how the faxes have developed Friday's conditions so far:

T+120:

20180225_2132.PPVO89.thumb.png.56519ddb542b8a593cbe60653b479287.png

T+96:

20180226_2205.PPVM89.thumb.png.1c93114a9c6dc5da1b7996521828df3d.png

Summary: Low further south-east and flatter. Frontal boundary further south in the south-west and further north in the south-east, occlusion slower. 528DAM line further north.

Edited by The Enforcer

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Thanks both for the fax updates. Can you please elaborate on what the Low is doing in them? Thanks 

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24 minutes ago, knocker said:

And the latest for Friday/Saturday - problem solved :)

PPVM89.thumb.gif.1c77fd5477ea0efa369b597c3185ad2b.gifPPVO89.thumb.gif.e308202efb6ed3c970b43f6095bbc91a.gif

Still liable to small changes in frontal positioning having a significant influence on surface conditions.  Do you think that upper warm front will increase the risk of freezing rain on Friday?

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5 hours ago, chrisbell-nottheweatherman said:

Still liable to small changes in frontal positioning having a significant influence on surface conditions.  Do you think that upper warm front will increase the risk of freezing rain on Friday?

I've no idea to be honest Chris but it may well help forming a 'warm nose' Does this ring a bell?

A freezing rain event

Quote

The map below shows the area which was affected in this particular event. High pressure over Northern and Eastern Europe had been controlling the weather with cold easterly winds affecting the UK. On the evening of the 23 January an area of low pressure moved slowly northwards across the south of England and gave outbreaks of rain. In some areas the rain turned to snow but in the areas marked on the map the snow turned to freezing rain with outbreaks through the night and intermittently through the 24 January.

https://www.metoffice.gov.uk/learning/learn-about-the-weather/weather-phenomena/case-studies/freezing-rain

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After the excellent summation by Nick above it's really a question of attempting to dot the eyes and crossing the Ts a bit.

Out little wave feature has been busy tracking south west overnight bringing more consolidated snow showers to many areas and by 00 it is SW of Ireland.There have been some hefty snowfalls in many areas in the east, north the Midlands and north Kent. Behind a rather perturbed low level flow with some hefty convection going on as the UK comes under the influence of even colder air.

PPVA89.thumb.gif.a36fa76675f69aa7a2bc9fb1fc787e42.gifPPVE89.thumb.gif.5213195f5e5e657c0086873215bb14ac.gif5a94e7eebe167_shower1.thumb.JPG.b49e8677250bdcf9fe12108a86084764.JPG

5a94e7f85ce23_shower2.thumb.JPG.ec0a7f2d6f28350fd2b9ff7228f16c74.JPG

And talking about colder air the UK is now entering what is likely to be the coldest two or three days of this cold spell so worth a quick glance at the forecast wind chill over the next 36 hours according to the GFS-WRF

5a94e8cfe2ea1_chill1.thumb.JPG.3d21b888ff1992f164f7c062cc3bd695.JPG5a94e8d6be10a_chill2.thumb.JPG.00fac5b0603600b9af2088f4983f072c.JPG5a94e8de67c76_chill3.thumb.JPG.6fc3bc05c12a30bb6d3b6e56d0050739.JPG

As the depth and intensity of cold increases it serves to boost convection and perhaps it's no coincidence that tomorrow there are likely to be some steep 850mb-500mb lapse rates in the north and much showery activity in the same area, according to the GFS-WRF anyway The showers will continue through the day with strong winds along the north east coast, and later in the south, perhaps reaching gale force, thus feeling bitterly cold.

lapse.thumb.JPG.cf5b7df4335f357807ddc2c0aba28a7b.JPG5a94e9fc367d9_showerschill.thumb.JPG.d14d41d5ce512c05be5354d4ac491d96.JPG

Thursday starts with a severe frost in many areas and feeling bitterly cold in the strengthening E/ESE wind touching gale force but changes are afoot to the south.

gfs_t2min_c_uk2_10.thumb.png.624a97d419f99c7b04f38527e6cb7dea.pnggfs_ptype_slp_eur2_10.thumb.png.9b745413b4990603e6ccd7e68e0e2e23.png

So the key question remains how will the breakdown in the south materialize and will it produce copious amounts of snow in southern and western areas? It remains unanswered but as to the latter looking leas likely but the best way to illustrate the problem is to post a few charts from this morning's gfs.following on from the one above.

gfs_ptype_slp_eur2_11.thumb.png.ac19f3616e0aa91d68697f537b2e7915.pnggfs_ptype_slp_eur2_12.thumb.png.0613429eab1f2e2e4736941341c11a42.pnggfs_ptype_slp_eur2_13.thumb.png.45964fb107355cef658411a7a7b19af8.png

And then on Friday the warm front does push north but there does not appear to that much snow on it and freezing rain is still being bandied about (keep an eye out for the warm nose) so as mentioned previously the detail of this is still not sorted and it is certainly questionable as to how far north the 'warmer air will reach without 'mixing out' as for most areas, apart from God's Little Acre, Friday remains a bitterly cold day.

gfs_ptype_slp_eur2_15.thumb.png.1ff40b7cc3e9f0b430f3fe2029c0ca80.pnggfs_ptype_slp_eur2_16.thumb.png.e96ff4854ebb76b868cc4ad0bc5347b0.pnggfs_t850a_eur_16.thumb.png.19edb328c62991808638c6f012bb32f6.png

gfs_t2max_c_uk2_16.thumb.png.778224fea814c890fc1f403b1961d462.png

Edited by knocker

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Since going to press the fax charts have updated. Interest one for Weds showing convergence zones and a trough over the north east coast, Might support my waffle above of increased shower activity in that region.:)

PPVG89.thumb.gif.cc58e7fc1e3af0867a37f1bbc7832105.gifPPVI89.thumb.gif.e256d646cab60969a2fd38917f9c7982.gifPPVJ89.thumb.gif.a9d4781426327d7bb3001a0f692d7003.gif

PPVK89.thumb.gif.5e8dc99a679634ee1825c347ce522d46.gif

Edited by knocker

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Many are wondering, including myself, why given the upcoming scenario of warm air approaching very cold air we aren't getting the snow ploughs on standby. I did some very simplistic musing about this whilst perusing this morning's ecm, And simplistically it appears me down to the position of the deep upper low to the south west and the formation and track of the surface lows and fronts associated with it. Because moving within the former's circulation does not facilitate a direct confrontation between the warmer and colder air, rather a sliding and much slower approach which has within it a SE-NW component as well as northerly, which allows a certain amount of upper air mixing. I can't post the most relevant charts but these will do.

ecm_z500_anom_natl_5.thumb.png.21fc9fbf3abd0b0847698afd880bc60b.pngecm_t850_anom_natl_4.thumb.png.58f18cac52f9c61170e5a31e1ba7e7c3.pngecm_t850_anom_natl_5.thumb.png.8d7df41ccde45bfdd2668297e420d420.png

ecm_mslp_uv850_eur_3.thumb.png.e60e0548c2accd90e282434ec74bfaf9.pngecm_mslp_uv850_eur_4.thumb.png.a45cf6ad13872890c09f498a1f824cda.pngecm_mslp_uv850_eur_5.thumb.png.0b89236dd16a2bf865193b6a41abed32.png

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