Thermohaline Conveyor

Hi folks! How're we all doing? Well I hope Snow .... I hear you say? Sunday is looking quite good at the moment

Original thoughts of some snow or wintry precipitation to lower levels for North West England seem to be supported more now by the GFS. Not much change in my thoughts. Although the presence of a strong unstable NW Pm airflow could promote a few surprises mainly in the form of moisture streamers extending from NW England into the N Midlands area. At the moment though the streamer potential is just a theory based on moisture content, instability and the strength of the upper flow. A cold weekend for may! Brrrrr

Wintry PPN signal for Pennines, Scottish Highlands, and higher ground of N Wales toward the end of this week and into the weekend period. Any signal for snow to lower levels below 400m is inconsistent, with mainly any appreciate snow signal related to an area of rapid cyclogenesis modelled by the GFS. As a few have alluded to already ECM guidance diverges from the GFS in the rigorous cyclogenesis solution but does maintain a cyclonically dominated regime with wintry signals for NW England, perhaps to lower elevation in places. 12Z ECM and GFS will be interesting viewing. The probability of snow falling and accumulating is greatest across higher elevation 300-400m (hills and mountains) of England, Scotland and Wales - more especially at the end of this week into the weekend. Elsewhere, the probability of snow falling to lower elevations is around 30-40% in the North, lower still in the South. North West England is the exception with some generic signals from the Euro of the 0oC isotherm lowering below 200m in places, supporting a wintry mix of sleet and snow - again though this is one to watch and remains inconsistently modelled.

DANGEROUS SITUATION STATEMENT for EIRE - EXTRA TROPICAL OPHELIA EXPECTED LANDFALL MON AM There is now a high risk of severe disruption for Southern Ireland with Co Cork, Kerry, Limerick and Clare thought to be the worst affected by a powerful extra-tropical storm with hurricane force conditions expected across exposed Southern and Western coastlines on landfall. Extra tropical storm conditions will begin to affect Southern Ireland from Monday AM peaking in intensity through Monday afternoon before transferring North to affect Northern Ireland later in the afternoon and evening on Monday. Damaging winds of 70-80mph are expected with gusts in excess of 100mph possible across the highest ground. Severe disruption to transport networks, power utilities and damage to trees and buildings is expected. Advice would be to take immediate action to protect property and avoid venturing out on Monday. Additional threats will be storm surge inundation with Co Kerry, Waterford, Cork and Wexford most likely to be worst affected by storm surge related coastal flooding. Marine conditions will be extremely dangerous and the coast should be avoided. Elsewhere further North across remaining Co of Ireland severe conditions are expected with severe gales gusting 50-60mph quite widely, locally 70mph to lower ground. Storm force winds are likely across higher ground with gusts of 70-80mph possible. Some damage to trees and buildings is possible and some disruption to transport and power is anticipated. Extra tropical Ophelia will be weakening rapidly as her wind-field extends into parts of Scotland, England and Wales during Monday evening and into Tuesday AM. Widespread gales are expected inland across Scotland, N England, locally severe or storm force to higher ground across North Wales. Gusts to 50-60mph are expected widely with isolated gusts to 70mph across Cumbria and higher ground across Scotland. Gusts in excess of 90mph are not ruled out across Capel Curig in N Wales and well renown exposed locations and higher terrain across Scotland. Some minor disruption to transport and interruption to power is possible across worst affected parts of England, Scotland and Wales. Please stay safe and refer to your local authorities for further advice on how to stay safe.

A beautiful but scary sight!

So far my original thoughts seem to be coming to fruition with a track generally just off the West coast of West Ireland. A shift could still happen. We will actually know more by Sunday PM as Ophelia officially undergoes tropical transitioning around 15:00 on Sunday according to GFS. Likely to be slight variations in this interaction between the Euro and Global suite.

Current most probable solution. Obviously subject to change. Those residing in S Ireland and in the red zone should be taking appropriate action as advised by Met Eireann.

Trailing fronts were responsible for the recent flooding in Cumbria, i think that is what he means.

Sounds about right. Potentially around 100mph across N Wales too especially in your typical spots such as Capel Curig. Also gusting close to hurricane force across Cumbria. Ireland inland widespread gusts to 60mph, wouldn't be surprised to see localised 70mph especially inland to higher ground and in exposed locations to lower levels. Theses wind speeds will cause issues usually but especially so considering the foliage abundance on the tree this early in autumn, coupled with saturated soil weakening tree roots - impact due to fallen trees is relatively high. Timing looks to be from Monday afternoon into the Evening across Ireland and through the early hours and into Tuesday morning for the rest of England, Scotland and Wales (mainly Western and Northern parts).

That's one for the bedroom wall that! Fantastic.

Yes it does look that way. I had a feeling the trending would be marginally more to the West and it seems to have panned out that way. Well lets just say that it seems to be panning out this way thus far, we still have a few more runs until the wobbles firm up. A slight shift left or right would still not be unusual given the set-up. Ophelia still needs to interact with the upper trough and undergo extra tropical transitioning and this will largely determine the track on approach to Ireland. Interesting though because if you analyse the potential temperature at 850hpa you will notice that Ophelia still has a warm core on approach and during the early passage across W Ireland, largely suggesting she maintains quite a strong tropical dynamic. I think by the stage she makes landfall she will be entering a warm seclusion process but nevertheless a rare and exciting sight indeed. You over there in Dublin will certainly feel the effect of Ophelia with inland gales gusting 50-60mph, perhaps edging 70mph in exposed coastal locales and across higher terrain.

The main cluster sits around the OFCL issued by NOAA NHC so that will be where Ophelia will sit. Consider the three deviating toward the major category status to be significant outliers, especially when you consider the models involved.

I think considering the inherent uncertainties in the model forecasts at the moment due to the tropical interaction with the mid westerlies anything beyond T+120 should be taken with a pinch of salt. Interesting feature though for sure and the ECMWF also picks up on it but bombs it out to the North of Scotland.

True. No doubt considering the context of the talk and the ironic similarities with the current weather set-up a short synoptic analysis on Ophelia will also be discussed. Fascinating meteorology right now. I get to tick meeting another famous BBC weather presenter off of my tick list too 6 down and many more to go.

I'm surprised Michael Fish isn't participating in the Royal Meteorological Society talk on the Great Storm of 87 with Peter Gibbs at University of Leeds on Monday. Either way I'm sure it will fantastic! I'm counting down the days until Monday.

What is absolutely key to impact will be the timing Ophelia makes landfall and the tracking she takes with regards to population density. I.e. a rush hour landfall across S Ireland will have a much greater impact than one much earlier or much later than the rush hour. It will be interesting to see if OFCL guidance issued by NHC is adjusted more to the East or whether it sticks with the more W track that a lot of ECMWF ensembles deviate toward. I think also the HWRF (a tropical model) well respected too is well to the West in its forecast but I suppose question marks should be raised about the HWRF ability to resolve post tropical processes when it specialises in tropical genisis. A averaged (mean) blend between the global model GFS and ECMWF would be the best bet right now. Probably a 4 run multi-model operational GFS with ECM operational forming the mean basis and perhaps taking into account the EPS suite. What do you think PIT, I still think it'll be slightly further West.

So ECMWF tracks Ophelia across Dublin and then ENE into Southern Scotland with severe wind gusts of 60-70mph possible for Cumbria on the latest model run. One thing to note also is that ECM12Z fills Ophelia out quite rapidly with the example being she is projected to have a central pressure of 974hpa just W of Waterford in the S of Ireland at around 18:00 on 16th October then 9 hours later at 03:00 on 17th October pressure increases to 990hpa (16hpa +/9hour) 1.7hpa +/ph. Seems the Euro is struggling to handle the tropical nature of Ophelia's interaction with terrain. Incidentally the track is S Ireland, Dublin, Southern Scotland and out into the N Sea with rapid cyclolysis. I still think this solution is too far East but we'll see. Worst affected areas for wind gusts on this run would be a line from Cork, Waterford to Dublin extending across the Irish Sea into Cumbria. 60-80mph gusts, mainly lower end of this range inland away from mountainous terrain.

Guidance issued a few days ago

I have a feeling it will trend more West

Hurricane strength but post-tropical or extra-tropical in transition. As you know the dynamics are different. Note the black dots with white H when Ophelia is a true hurricane (latent heat fuelled through oceanic processes) where Ophelia has a white dot with black H meaning post tropical/extra tropical transitioning and some interaction with the jet-stream. Although you could argue that judging by the latest models namely the ECMWF the concentric banding with the strongest winds around the inner centre the physical characteristics are not too dissimilar to a hurricane. However convective processes usually fuelling the spiral bands associated with stronger coriolis will have been sheared by the jet and largely dissipated. Fascinating to watch unfold, and to see just how close Ophelia will be to a true hurricane. Analysis of the PPN distribution on radar will be worth noting as well as the modelling of the pressure gradient around the centre circulation. I feel those in Ireland should be watching this one closely. Sadly for us in Leeds it largely looks like a no show unless some dramatic turn in the ensembles takes place.

I think the most likely track takes Ophelia just to the West of the West coast of Ireland although wobbles that take the centre circulation across inland Ireland are entirely feasible. A majority of the ensembles would suggest a more Westerly bias though. ECMWF operational is further East with the core circulation crossing much of inland Ireland however EPS generally back the westward trend along with NCEP and HWRF. The CONUS issued by the official guidance of the NHC is a blended mean and is reasonable. Still some minor shifts plausible in the next 48 hours. Is there anyone on the S coast of Ireland on this forum?

Following on from my thoughts a few days ago I now believe the eventual synoptic we will experience will be closer to the EC solution. The overall trend is for poor EC ens performance beyond 29th with HRES often running outside the spread. GFS ensemble performance has also been poor, although the signal for dramatically lower MSLP toward the end of the month has strengthened with a majority of the perturbations running with this lowering MSLP solution. Of course, a lowering of MSLP does not necessarily correspond with cold temperatures. GFS T850 ensembles have deviated hugely with vastly large deviation in spread across a suite of variables, again indicative of the jumpiness nature of the model at the minute. Beginning of December W1 I have noticed the EC EM trending toward an anticyclonic regime across S England with lower height builds across the North. On this basis, right now, with the guidance the way it is, I would have to go with a slight modification of the EC, closer to the EC EM with a W/NW flow and increasingly cool/cold showery regime (especially for N areas early in the period) and perhaps drier further South. The vigorous Northerly of the GFS does not seem like the most likely option at present despite massive spread across both EC and GFS suites.

It is very much a battle between the ECM and GFS tonight. ECM is pumping much more energy into the higher latitudes beyond T+144 whereas GFS resists the higher energy and favours stronger height builds in crucial areas in and around Greenland. The Greenland to Newfoundland region is the area that holds the key. To be honest the differences are minimal and only very slight changes will alter the outcome thus slight sensitivities to the starting data in each model may be the cause for discrepancies between ECM and GFS at lead times beyond T+144. ECM has been more consistent and bullish in building the extended ridging into the UK around the 1st week of December whereas the GFS has had a tendency to add increased incidences of jumpiness in the possible outcomes. Despite one models apparent consistency on modelling a particular synoptic over another it remains impossible to favour one solution over the other at this stage.

I will be keeping a close tab on the SFC wind and the undercutting. A very marginal set-up and the complexities in the forecasting of this event clear to see when analysing the latest GFS06Z ensemble suite with many of the perturbations in the pack deviating away from the mean. The spread is loosely -4.35°C to -1.15°C with the operational sitting around the mean approximately half way. Considering we are merely 6 hours prior to the onset of this event the large deviance in T850 spread shows the uncertainty in the precise evolution and tracking of the lows warm sector. We are relying on the colder undercutting (the Easterly component) as you alluded too and of course precipitation intensity and longevity to help lower the 0°C isotherm closer to SFC.

White Christmas anyone? Now wouldn't that be lovely! The extent of the Eurasian snowfields is certainly encouraging.