Models, teleconnections and nowcasting

[knocker]

Of course Europe is the big loser over the weekend as cold air sweeps south behind the front whilst he UK becomes cooler in the more tranquil setting of the eastern flank of the high cell

[knocker]

Sat > Mon

Mainly sunny with a few showers down eastern coastal regions. Frosty mornings

I notice that unusually there was a full radiosonde program from the UK stations today

 

[knocker]

The ext anomalies this evening are all agreed on the direction of travel if not the detail.

The main lobe of the tpv now now more or less over the North Pole with a fair field of influence. With a trough in the NW Atlantic and most of the subtropical zone amplification gone a fairly innocuous westerly would appear to be the form horse and thus some changeable weather Temps around average

[knocker]

A quick glance at today's EC weeklies up date for April

9 - 16

A ridge NW North America alongside a fairly benign tpv northern Canada with associated trough into the NW Atlantic.This allows the subtropical high to exert some influence in the east in the vicinity of the UK and thus not unpleasant weather with temps perhaps a tad above averahe

17 - 24

No huge change but less influence from the subtropical high and thus a tad more changeable with temps around average

25 - 02

Not dissimilar to the first week albeit the main lobe of the tpv has moved to northern Russia. The usual caveat that patterns like this always favour the southern half of the UK

[knocker]

Although we are creeping into unreliable territory it's looking increasingly likely that a lobe of the tpv will develop over Greenland and track east through the latter part of next week, whist at the same time the high pressure migrates W/NW. Thus colder Pm air will be introduced across the UK. The ecm and gfs are broadly speaking in agreement over this but go there different ways quite quickly so best left at t168 with the ecm until the ens are available

Edited March 27, 2020 by knocker

[knocker]

The brief description above is accommodated pretty well by the medium tern mean anomalies

Edited March 27, 2020 by knocker

[knocker]

This evening's  version from the gfs of the movement of the tpv and the subtropical high sees a surface low track east via Iceland but as the high fails to migrate west sufficiently it ends up going via Scandinavia

[knocker]

The ecm has the trough, associated with the tpv, developing in the Denmark Straits at t120 as the high pressure ridges north west

Over the next 24 hours the trough tracks east but just you think it will merge with one over western Europe the residual ridge pokes it's nose in

Bu not to be thwarted it phases with the trough in the Atlantic instead

O, what a tangled web we weave when first we practise to deceive!

[knocker]

Taking an interim look at the EPS and this phasing of the troughs in mid Atlantic would appear to be paving the way for what has recently been indicated by the ext anomalies

[knocker]

The ext anomalies are still more or less in agreement on the direction of travel but not completely on the detail.mainly to do with tpv over the Pole and the phasing with the trough in the NW Atlantic. Anyway the upshot of all this is the removal of most of the Amplification from the subtropical highs and replacing it with a westerly upper flow. I say most but the Eps does keep some residual heights over Europe which is not unimportant when it comes down to the detail of the weather as can be seen

[knocker]

The ecm analysis at midday Weds is not a million miles from the fax

Over the next 24 hours it deepens the Iceland low as it tracks east whilst migrating the Atlantic high pressure NW. but leaving behind a residual ridge

And over the next 24 hours the troughs to the NW/SWphase and a quite intense surface low develops in the Atlantic and drifts north east

Edited March 28, 2020 by knocker

[knocker]

The essential difference between the GEFs and EPS in the medium term this morning is the alignment of the tpv

Edited March 28, 2020 by knocker

[knocker]

More moisture today in general, but particularly above the inversion/isotherm

[knocker]

The spv still very cold at 50mb but losing some symmetry

Edited March 28, 2020 by knocker

[knocker]

The sequence for the latter half of next week from this evening's gfs det run is, in simplistic terms, as follows

At t120 a lobe of the vortex is tracking east from Greenland as the high pressure migrates to the latter. But a subsidiary trough has tracked down the eastern flank of the high cell, now over Greenland, and is putting pressure on the residual ridge and by t168 the main troughs to the NE/SW have phased in mid Atlantic but still with a ridge over the UK

So very much a N/S split with the former getting some wet and windy weather whist the south remains dry

Edited March 28, 2020 by knocker

[knocker]

Between t120 and 144 the ecm is much bolder with the subsidiary trough and by t144 the troughs have merged in mid atlantic and thus major differences with the gfs already This trough then consolidates and moves east whist the subtropical high ridges north east into Europe

Surface weather wise this does not make a huge difference with the wet and windy mainly confined to the north but low pressre is west of Ireland by 168

Edited March 28, 2020 by knocker

[knocker]

The ext anomalies this evening are pretty much as previously discussed with the tpv over the Pole phasing with the trough in the NW Atlantic whist the subtropical high attempts to ridge north east into Europe. The precise position of the trough will dictate how much the latter will effect the UK and whether it will be generally unsettled or very much a N/S split A North Atlantic view to clarify

[knocker]

High pressure in charge at the moment,  centred south of Iceland, but over the next few days it will weaken rapidly as high pressure builds over northern Canada. Note the high cell of 1065mb. At the same time fronts associated with the deepening low, which by midday Thursday is north of Scotland. will move south east down the latter and N. Ireland. Thus becoming quite windy in the north with rain and then wintry showers in the colder air behind the fronts

We are now approaching the time that has previously been discussed as the lobe of the tpv to the north moves east but a subsidiary trough tracks south along the eastern flank of the high cell resulting in the main troughs merging in mid Atlantic But simultaneously the subtropical high ridges north across the UK and into Europe

All of which means that as low pressure develops in the Atlantic the south remains pretty dry with most of the inclement weather again concentrated in the north. This is according to the gfs

 

Edited March 29, 2020 by knocker

[knocker]

The ecm has a much more bullish approach to the merging of the troughs resulting in a deep surface low tracking north east bringing strong winds to most areas by next Sunday. Obviously much still to be resolved in this period

[knocker]

Looking at this morning's ext anomalies the orientation of the tpv, in conjunction with the trough in the NW Atlantic would appear to be dritical to the outlook for the UK. The GEFs version is obviously the favoured option

[knocker]

Cold and showery down eastern regions

[knocker]

I will skip the preamble with this evening's gfs and by t120 the subsidiary trough is on it's way south to merge with the trough in the NW Atlantic resulting in residual high pressure over France ridging NE into Europe. A position that is consolidated by t168

This pretty much continues to leave the UK under the influence of high pressure and staying dry, apart from the north which could see some rain and be quite windy. But this still at odds with the earlier ecm so leaving it there

Edited March 29, 2020 by knocker

[knocker]

The ecm is not quite so keen to merge the two major troughs this evening between t120 and 144, Consequently the tpv lobe has more influence in the northern regions of the UK and a shallow low tracks east over northern Scotland and cold air is introduced behind the associated front

 

 

[knocker]

And if ever an example is required to illustrate the dangers of looking too far ahead the ecm for midday Monday on the last two runs

[knocker]

Leaving aside the difference in intensity of the complex configuration of the tpv then the ext anomalies are on the same page and it still appears to boil down to how much influence the subtropical high will have in the east with a weakening of the westerly upper flow. But hopefully looking to warm up a tad