Thermohaline Conveyor

Sounds about right to me

Agree. Another model adds to the confusion. The only way of resolving this is to run regular verification tests over a long period of time to assess the variances in bias and reliability. So far I am not convinced. Too many cooks spoil the broth.

You make a pretty good point. If the spread of solutions within the ensemble suite is so deviant it makes the mean almost pointless in such a chaotic situation. T+120 850mb wind ensemble mean and OP 30m/s 850mb wind signal remains aligned over much of England and Wales with previous ECM runs favouring SE/E/NE England for most pronounced wind signal tied in with 27/28 Dec low. SD between 4.0 and 6.0 still indicates quite a spread in synoptic evolutions but interestingly the mean spread 25m/s signal with an SD of 1.8 overlaps with the 30/ms OP across N England and NE England down toward N Norfolk. The mean track of the low due S of Iceland, N of N Scotland toward Scandinavia. GFS06Z tracking further S as a weaker/delayed feature with explosive cyclogenisis occurring N Sea/Norway. So much uncertainty still but a consistent signal with N, NE England and East Anglia for wind signal.

It will be interesting to see how the GFS compares to the GFSP in verification of accuracy with some wild deviation in the operational beyond T+180. ECM spread is still significant for 27th-29th cyclogenisis with many possibilities in tracking, complex baroclinic secondary development, cylcone phasing and attendant cold pooling. The last two GFS runs have been similar with a less intense cyclogenisis across the United Kingdom, peak cyclogenisis occurring North Sea/Norway. Note very significant pressure gradient increasing upwelling in the North Sea around 27th - 29th with the risk of coastal flooding across East Anglia and Eastern England during the period.

I know Weather History, but I can't leave you guys out. That would be unfair.

Here we go again, another Bank Holiday weekend has creeped up on us and many people will want to know what days they can get out and about and what days they need to assign the “Duvet Dayâ€. Bank Holiday Saturday 23rd August We start with Saturday. Generally it won’t be too bad. The West will be best, the East – well not so great. It certainly won’t be a washout with low pressure exiting out across the North Sea and allowing high pressure to temporarily build into the South West. Mainly dry with variable amounts of fair-weather cloud across South West England and Wales. Elsewhere sunny spells and enough energy in the atmosphere to spark off one or two showers, these mainly isolated further South and West, but more frequent and heavier towards the North and East. The highest risk of a heavy shower will be across Yorkshire and North East England. Temperatures will continue below average for the time of the year with a range of 12ºC to 15ºC in the North and 15ºC to 18ºC in the South. Cool under the cloud and pleasant enough in any sunny breaks. Bank Holiday Sunday 24th August Sunday is perhaps the best day of the lot if you wish to get out and about or do some early washing. A mainly dry day across many parts of England, Scotland and Wales with variable amounts of fair-weather cloud and some sunny spells. The best of the brightness will be across Scotland with a little less cloud and a little more sun. Despite the mainly dry and pleasant start to the day an area of low pressure will begin to bring weather fronts into South West England, Western Wales and North West England by late afternoon/evening with increasing cloud and eventually some patchy rain moving in. The rain eventually becoming heavy and more persistent later in the evening and overnight before spreading across many parts of England and Wales during Monday. Turning breezy too. Generally temperatures will not be too bad with a range of 16ºC to 20ºC in the South and a cooler 12ºC to 15ºC under a cooler aimass across Scotland. Bank Holiday Monday 25th August Lets start with the good news. Scotland will experience a mainly dry, fine and pleasant day with variable amounts of fair-weather cloud, quite breezy with some nice sunny spells. Just a slight chance of the odd isolated shower. As for the rest of England and Wales bands of rain will move in from the Atlantic as an area of low pressure becomes slow moving. A mixture of patchy rain which could become persistent at times will clear through some areas to make way for heavy scattered showers which could be locally thundery in nature. Generally a very unsettled day is expected with further rain likely to spread in across Southern areas later in the day. Temperatures academic in the South across much of England and Wales with a range of 15ºC to 18ºC and pleasant enough under the brighter and drier skies further North across Scotland with a range of 13ºC to 16ºC. That’s all for now, have a great weekend.

Christobal will be born I feel. ECM keen on developing this wave into a hurricane before taking a sharp turn left and tracking around the sub-tropical ridge and keeping her a fish. GFS is a lot less aggressive keeping our wave a very weak feature before gradual intensification and tracking across the Caribbean towards FL approx. Massive deviance at the mo.

I'm a bit of a sucker for strong/intense zonal and Atlantic storms bombing out toward our shores. Hoping for an active season.

The disappearance of CAPE is down to the development of the low and the models trying to get to grips with where the low will track, what phasing the low will be in and how it will evolve ie. whether it will be a flabby low with a centre tracking through much of England and a slack pressure gradient running through W France or whether it will be a more intense feature with a stronger pressure gradient or another option is the development of a secondary low within the complex parent low which is what the GFS06Z dataset was teasing us with. It is simply too far out for any real resolution of this low feature at present but we may begin to see more consistency in the next few runs. ECM-mean takes the centre of the low through Northern England a little further North than latest ECM and GFS operational guidance so plenty will chop and change. Nevertheless no matter where the low tracks the environmental conditions will be favourable for some thundery activity some-where across England and Wales due to the simple fact that air will cool aloft and warm air will be passing through at the surface. Ideally for more "severe convective" chances we would like to see the more Northerly track taking the centre across Scotland or N England with a stronger pressure gradient to the South of the low centre across England and Wales (stronger) jet streak and an increase in windshear. Fingers crossed we get lucky.

If the secondary wave evolves it would be a potentially more severe feature with a stronger theta-e gradient and greater temperature differential. May take a day or two to resolve if it is going to be something - otherwise it will be the flabby low (possibly half decent pressure gradient).

NHC have an early advisory on a tropical wave several hundred miles East of the Windward Islands at present. It is likely that this wave will develop into a tropical depression in the next 48 hours and does look like it will become tropical storm "Cristobal" shortly after. The latest GFS FI T+300 shows possibly (Cristobal) becoming absorbed into the Atlantic flow through this period. ECM absorbs what would be "Hurricane Cristobal" as earlier as T+216 primarily because ECM is much more aggressive and considerably left of the guidance compared to the GFS. It's unclear how Cristobal will form, where she will track and whether she will have an influence on our weather in weeks to come, but it is certainly one to keep an eye on. Even if the current insignificant tropical wave does not affect our weather it is likely that this feature will develop into Cristobal. Once she becomes named as an Invest we will be able to dig a little deeper by assessing the higher resolution and more specialist tropogenisis models GFDL and HWRF.

Monday's area of low pressure is proving troublesome not only in the phasing, evolution and tracking but also the severe weather potential it could bring ie. wind, rain and again the potential of a few thunderstorms. It needs close monitoring. ECM-mean takes the centre of the low through Northern England with the strongest pressure gradient to the South across England and Wales, GFS operational offers up numerous solutions on the intensity of the system, the tracking and the exact evolution ie. A single primary low or the vigorous development of a secondary low within the parent low. Quite complex but one thing is for sure Monday is looking rather Autumnal.

Would be lovely. In reality the Westerly zonal flow may well deviate slightly. Something more along the lines of the AzH ridge building into South/South West England and across much of England and Wales leaving Scotland in a marginally more unsettled flow. Shift the baroclinic region on the above chart 150 miles South and the high pressure South East and that will be more realistic.

During the last week low pressure has remained stubborn across Scandinavia with high pressure strong and assertive to the West & North West across the North Atlantic ridging into the Arctic. This set-up ensures that cold air usually locked up across Northern latitudes (the Arctic region) is unlocked and given permission to flood South. Friday: Sunshine & Showers – Most Frequent In The East/Driest In The West The ECM mean above continues to forecast low pressure anomalies to the East and North East of England, Scotland and Wales across Scandinavia and high pressure anomalies to the West and North West across the North Atlantic. Friday 22nd August will remain on the showery side of the low with a continuation of the variable cloud cover, sunny spells and enough heat from the sun to spark off a few heavy showers, possibly heavy and thundery. Temperatures will remain on the cool side everywhere, although there is a possibility of 20ºC in the South which is close to average. Saturday: Drier & Brighter Across West England, Scotland and Wales, A Few Scattered Showers In the North & East The ECM data above shows higher pressure anomalies beginning to tentatively nudge into much of Western England, Scotland and Wales during Saturday 23rd August with drier, brighter and marginally warmer weather expected. Low pressure is still present across East Anglia, Eastern England, North East England and much of Eastern and Northern Scotland with the risk of a few isolated showers. What is noticeable is that the air will begin to be sourced from a milder South West direction across Southern and Western parts with temperatures ranging approximately 17ºC to 20ºC, just below average. Cooler across the East/North East. Sunday: Generally Dry to Start With Variable Cloud & Sunny Spells – Cloud Thickening From The West Later With Showery Rain by Evening The ECM data for Sunday looks encouraging as a temporary ridge of high pressure continues to build across much of England, Scotland and Wales. It will be a day of variable amounts of cloud, some good sunny spells and staying mostly dry. A feature that is particularly noticeable and is being monitored for the potential of severe weather is the area of very low pressure to the West and South West of Ireland; which will edge closer to South West/West England, Scotland and Wales during Sunday Evening. This area of low pressure will bring thickening cloud into Western areas toward late afternoon and evening with patchy rain beginning to spread East later on through the period. Monday: Potential for Wet & Windy Weather, Unsettled With Spells of Rain Clearing To Sunshine & Heavy Blustery Showers – Risk of Thunderstorms. That brings us onto a sneaky glimpse at Monday. ECM data consistently models the deep area of low pressure to the South West of Ireland on Sunday to begin to make inroads across all of England, Scotland and Wales on Monday. An unseasonably unsettled day can be expected with bands of rain sweeping East, winds unseasonably strong with coastal gales and the added risk of scattered thundery showers following on from the passing of the warm sector. In general the weekend is an improving one for much of South West, West and North West England, Scotland and Wales with drier weather, sunny spells and a more limited risk of the odd isolated shower. Further North and East across England and Scotland there will be more in the way of cloud, some occasional sunny spells and a higher risk of scattered showers – improving by Sunday. Sunday generally looks rather pleasant through the morning and afternoon before cloud thickens from the West and South West and patchy rain begins to move in by early evening. Temperatures remaining marginally below average and not feeling at all bad in the South. Cooler in the North. Wet and windy by Monday with much milder air spreading in.

I'm not a fan of looking much beyond that either. Picking out very generic trends is possible but it becomes more and more guess work beyond T+240

It has been a pretty active year for thunderstorms here in Herefordshire. Quite impressive really. Looking at the trees and nature at the moment it looks as if Autumn is very much just around the corner

Chilly start to the morning here in Herefordshire 11ºC Brrrrr

I've done a graphic to illustrate today's storm risk.

It's almost categorically because they simply haven't issued one yet. Expect expansive higher risk lightning and a level 1 expanding across Wales, a The Midlands into Northern England - perhaps SW Scotland. I would say a massive YES, very high risk today for Leeds.

There will be thunderstorms today, and these will be incredibly lively across North West England, Yorkshire & Lincs etc. Note a similar area of convergence across West/North Wales again too - fireworks for sure!

Some nice Cumulus Congestus developing to my North here in Hereford

The dynamics for snowfall on Friday were not even marginal, with the exception of the upper level temperature support, the BL and surface was too mild.

Developments to our NW are absolutely key. Ironically the largest deviation in the ensembles spread is immediately around Greenland and into US/Canada territory. A large-scale amplified long-wave trough dominates conditions across Canada, this likely fuelling the vortex and sending energy toppling over the sub-tropical ridge which is fairly flat at the moment. Better confidence in heights building across Scandi beyond T+168. Long-wave trough extends from UK into much of South Western Europe/Iberia and W Europe, but the problem we have at the moment is the energy propelling East from Newfoundland across the North Atlantic/South of Iceland and into the United Kingdom, low pressure systems will continue to topple the high, spin into the United Kingdom, won't be able to go anywhere but either oscillate and fill across the United Kingdom or make slight indentations into Iberia and the W Med. Short-waves that form within this long-wave trough across W Europe will likely draw in warmer air and may spin back in from the East to affect the United Kingdom, the cold locked away across Scandi.

This is set to change, unfortunately. Strongest PPN signals consistently occupying NW England, Western Wales etc. 50mm+, this excludes any convective elements associated with Pm airmass and the passing of cold/occlusion frontal passages.

Note, unlike recent convection ie. last few weeks, Monday will be less intense and severe due to weaker kinematic environment and general lower wind-shear. The jet isn't ideally placed to offer assistance in organisation. Nevertheless, a combination of rapid cooling aloft, lowering geo-potential thickness, a warmer BL and warm surrounding SST(s) around coastline, will be ideal to promote steepening mid-level lapse rates and heavy shower formation.