Short range model discussion - into 2018

knocker · September 25, 2018

Outlook – Although it’s fair to say high pressure will be the main influence over the next few days there is a major caveat. There is still a lot of energy exiting upstream south of the vortex putting it under pressure, and which drives systems north east towards another major trough area adversely effecting the north west of the UK with cloud and rain. Thus a tendency to a NW/SE split. Quite well illustrated with the rainfall chart.

A fairly clear night in most places, particularly England and Wales, leading to some quite low temps as noted on the 0300 chart

and also a bright and sunny day But a frontal system poised to the west of Ireland at midnight. evidence of this quite noticeable on the Valentia sounding,

will bring cloud and rain along with strengthening wind, perhaps reaching gale force, into N. Ireland and western Scotland by midday as it tracks north east, with the rain spreading east and south to northern England during the rest of the day.

Overnight and through Wednesday rain and strong winds will continue to effect Scotland, N. Ireland and the far north of England, with most of the rain concentrated over the former as fronts straddle across it. Worth noting here that these fronts run a long way to the south west to a cut off low created by the Atlantic trough being split by the Bermuda high amplifying. South of all of this activity sunny and quite warm.

No huge change on Thursday with the fronts still bringing cloud, rain and a fresh wind in the north whist continuing sunny and quite warm further south.

Over Friday and Saturday the front(s) will track south but fizzle out courtesy of the high pressure so essentially we are looking at cool nights with a touch of frost and fog patches with sunny days. Although not overly warm, feeling pleasant enough in the sunshine and light winds.

And the NH profile at T120

Edited September 25, 2018 by knocker

Interitus · September 25, 2018

13 minutes ago, knocker said:

2% RH at 850mb with the anticyclone.

knocker · September 25, 2018

Chart for Thursday 1200 illustrating the intense cut off low to the south west with the front connecting to low pressure over southern Norway via Scotland.

knocker · September 25, 2018

The 0900 sat. image

And

knocker · September 25, 2018

An attempt to clarify the cut off low situation. It would appear to be TS Leslie getting a boost from the upper trough exiting N. America as it just wanders around.

Edited September 25, 2018 by knocker

Interitus · September 25, 2018

1 hour ago, knocker said:

An attempt to clarify the cut off low situation. It would appear to be TS Leslie getting a boost from the upper trough exiting N. America as it just wanders around.

Yes fascinating little beast. In just 3 days since the first NHC advisories, after initially forming from an extratropical cut-off, it was a subtropical storm, was going to be absorbed by a larger low, become post/extratropical, merge with frontal low to the north, remain as the dominant system, strengthen by baroclinic forcing, become a cut-off extratropical low again and finally regain tropical characteristics - https://www.nhc.noaa.gov/archive/2018/LESLIE.shtml?

Despite calling for a period of extratropical transition with the approaching front, the phase diagrams have kept it as warm cored from shortly after forming with merely a period of asymmetry - http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/18092500/9.html

The 00z GFS used in the phase charts above keeps it out in roughly the same area til the end of the run, withstanding a couple of other trailing fronts but the 06z has it transitioning into a powerful extratropical low over the Labrador sea.

Edited September 25, 2018 by Interitus

knocker · September 25, 2018

50 minutes ago, Interitus said:

The 00z GFS used in the phase charts above keeps it out in roughly the same area til the end of the run, withstanding a couple of other trailing fronts but the 06z has it transitioning into a powerful extratropical low over the Labrador sea.

Does it ever!

knocker · September 25, 2018

The 1200 analysis and 1400 chart

knocker · September 25, 2018

The weather through this evening and overnight will remain wet and windy over northern Scotland in particular,, but stretching down to N. Ireland and England England as a complex area of low pressure amalgamates as it tracks north east to the Norwegian coast to be 973mb by 1200 tomorrow.leaving the associated fronts straddling Scotland. Elsewhere a clear and chilly night with maybe a touch of frost and fog.

knocker · September 25, 2018

A transition to a colder high cell around TS Joseph in 36 hours.

Edited September 25, 2018 by knocker

knocker · September 25, 2018

Quite a warm day south of the weakening cold front on Thursday as it tracks slowly south but by Friday it's in the Channel with the cooler air over all of the UK

And a chilly start to Saturday

Rocheydub · September 25, 2018

16 hours ago, knocker said:

Thanks for your concern Rocheydub. As t happens I've been lousy over the weekend with another flare up of psoriatic arthritis but now back on the steroids so feeling much better relatively speaking. Hopefully a hospital consult today. Meanwhile I'll cobble something together today as it's a quiet period.

Speedy recovery to you knocker. 3 cheers for steroids!

knocker · September 26, 2018

Outlook – Although high pressure is a dominating feature of the forthcoming evolution, it is in fact quite a fluid feature, mainly because it continually comes under pressure from the energy exiting upstream south of the Canadian vortex/trough complex which stretches east to eastern Europe. All of which complicates the regional detail of the UK regarding the temp, cloud, etc and tends to a N/S split

The rain and strong winds have persisted overnight in northern areas, particularly Scotland. whilst further south clearer skies and light winds have led to much cooler conditions with the odd mist and fog patch. These will clear quickly giving wall to wall sunshine in many areas but it will remain cloudy and windy in the north but with the rain mainly over northern Scotland as the main low pressure area clears to the north east leaving just the residual front. In general it's quite warm day.

With another little wave forming on the front, which stretches from Scandinavia to TS Leslie away to the west. the rain will continue over northern Scotland through the evening and into Thursday and track south with the front but dissipating as the front weakens, courtesy of the high pressure, by early Thursday afternoon. But remaining cloudy in the north of England and Wales. The passage of the front does introduce cooler air as high pressure once more builds to the west. Over the rest of England and Wales south of the front a warm and sunny day once more.

The front will continue to track south through Friday and by the end of the day, with the high now centred to the west, all of the UK is in the cooler air, albeit not unpleasant with sunny spells and light winds.

A not dissimilar day on Saturday further south but the pressure mentioned at the beginning of the post has brought a cold front into the proximity of the north west with some patchy rain and the freshening wind has introduced a much cooler feel to the proceedings.

The front will track south during Sunday but again tending to fizzle out as it hits the high pressure although it will bring some patchy rain and cloud to some areas on it's travels.

The NH profile at T120 indicating a very transient insurgence of the high cell into the Iceland area as major trough tracks to the north east of the UK

Edited September 26, 2018 by knocker

knocker · September 26, 2018

The ecm with a couple of cold mornings for England and Wales over the weekend,

More to the point a cracking clear morning here this morning

Edited September 26, 2018 by knocker

knocker · September 26, 2018

Interesting cloud in the 'tongue' of he ridge with the frontal cloud sweeping by to the north and over the northern half of the UK on the 0900 sat. image

knocker · September 26, 2018

The high res MODIS at midday and the chart. A touch of the Foehn in the north east

knocker · September 26, 2018

With the front(s) lying in close proximity the strong winds will continue this evening and overnight over N. Ireland, N. England and Scotland as well as the patchy rain although this will probably become confined to the far north of Scotland. Further south clearer skies and lighter winds leading to another much cooler night with the odd fog patch

knocker · September 26, 2018

Chart showing the weakening cold front across Scotland linked to Leslie flanked by warmer/cooler drier air midday tomorrow

And briefly in the northerly and much cooler air by Monday

Edited September 26, 2018 by knocker

knocker · September 27, 2018

No significant change from yesterday’s outlook so will just repeat and add maybe a little more influence from the sub tropical high that veers the upper flow a tad. Using the EPS this morning and a couple of other charts for further interest

Outlook – Although high pressure is a dominating feature of the forthcoming evolution, it is in fact quite a fluid feature, mainly because it continually comes under pressure from the energy exiting upstream south of the Canadian vortex/trough complex which stretches east to eastern Europe. All of which complicates the regional detail of the UK regarding the temp, cloud, etc and tends to a N/S split

The detail

The rain and cloud currently currently over northern Scotland will move slowly south during the day with the rain tending to fizzle out by early afternoon leaving cooler air in it's wake with some showers in the north. Further south over England and Wales, preceding the front and once any early morning fog has cleared, another warm and sunny day.

Overnight and through Friday the front continues to track south with perhaps some patchy light rain still on it, clearing the south coast by midday, leaving the whole of the UK in a drier, cooler northerly as the ridge becomes more influential. But in the light winds and sunshine by no means an unpleasant day.

But keeping in mind the opening comments by Saturday the high pressure is coming under a fair bit of pressure from the north west

Which on the surface translates into increasing wind in the north with some patchy rain into Scotland as a cold front approaches but still plenty of sunshine and light winds further south.

Overnight and through Sunday the front tracks south east with the surface wind veering north westerly, accompanied by showers, as the ridge once more builds to the west. A generally cool day.

By Monday the front is over France leaving the UK in some very cool air with temps way below average but surprise, surprise, the ridge is under pressure again with rain into the north west from an approaching frontal system.