BrickFielder

Chance of heavy showers although there is some question about how high cloud tops will be. This would limit the severity of any convection with thunder and lightning likely to be rare. Models suggest low level wind convergence being the focus of heavy showers especially in the East of the UK. Eumetsat satellite images suggest to me the upper trough might be an hour or so late moving across the UK which might put central areas at more of a risk of heavy showers. With lowish temperatures then updrafts are likely to weak which would also limit convective storm potential.

Software and Modelling but not related to meteorology.

Slight chance of weak low topped storms today. The risk is highest in the west especially in Ireland. A long wave trough approaches from the west steeping upper level lapse rates. Winds will be generally weak with low level convergence zones being a focus of convection. Upper cloudiness will tend to limit the instability as temperatures are kept low. A short wave vorticity lobe current south of Ireland is forecast to stretch but I am not totally convinced that it will not push a trough across the UK. Worth keeping an eye on even though at the moment things look marginal.

Some models are suggesting the long wave trough to the west of the UK is not going to move as far east as was forecast yesterday in the time frame. This might move things a little bit more westward. Forecast SkewTs (based on GFS modelling) for the UK are not particularly convective looking. There is marginal surface based convection across the midlands and wales perhaps late afternoon. There is marginal elevated convection for the south east during the late evening. What the SkewTs do show is moisture coming in at low mid levels. Satellite imagery does not really show much in the way of short waves and the most pronounced is still to the west of Portugal and probably will not arrive in the UK till the early hours of the morning. Weak mid level lapse rates also do not suggest strong convection across the UK. It looks like not all precipitation forecast is storm based and the areas of highest wind shear do not coincide well with storms. Severe storms generally need strong up draughts and steep lapse rates so anything home grown probably will not be severe. Conditions over France are different but it is worth noting the highest areas of instability would not tend to create storms that would be steered towards the UK. Pointing out some of the issues will hopefully temper expectations a little. My best guess is that the South East will see some elevated storms during this evening and overnight with a good lightning display. There is still a question mark in my mind about the midlands and wales or even a late flurry of storms in the early hours of tomorrow. It is also still possible that there will be no storms at all just some outflow rain from the imported remains of storms from elsewhere.

Probably a good idea. The general idea is that storms develop towards France in a destabilizing plume and then get exported across the channel into the south east. This chart shows the elevated plume crossing the UK but notice the time on the chart (6pm) and also the steerage winds for storms which is more from Normandy than the red hot interior of France. Destabilisation of a plume can occur into the evening due to cooling aloft and across Normandy. So the next question is where does it start and what is the trigger. Precipitation starts out late afternoon in the south west which trundles north east. Further and more significant destabilisation is suggested towards Southampton and Normandy which looks like spreading across the south east. This looks like precipitation is linked to surface humidity. Spanish plumes tend to give elevated storms so why would surface conditions affect things ? UKV modelling is linking precipitation to low level wind convergence. Looking at the source of low level air ,it looks like it is being sourced from central France. So we have hot humid air from the continent under cutting a destabilising plume moving north eastward. Very complicated for forecast models to get right and I am not even sure I am reading things correctly. There are so many things that could be wrong and it is best to wait till tomorrow.

Tricky to forecast storms again today. Some early storms in East Anglia and broad band of cloud moving North is likely to become reinvigorated from midday onwards. Low level wind convergence is forecast and this could be a further spark for storm development, with the Liverpool and Manchester area being of particular interest. Looking at the Eumetsat satellite images then I see the suggestion of a split upper trough. This would give us clearing skies with storms forming in a line shortly afterwards. These would be surface based and with highish tops although with limited wind shear. This split could disappear or the trough angle change so that no storms develop but it does mean the forecast modelling will be slightly wrong since there has already been a slight deviation at upper levels. Back to radar watching.

Just an outside chance that low level wind convergence and outflow boundary convection can root into the boundary layer between 7am and 9am tomorrow morning. Instability is weak and driving factors for storms are drying up at that time , but you could in theory get a weak tornado from such a scenario. Worth mentioning but I am not convinced (low probability) and some where like Evesham or mid wales might be places to watch. Satellite suggest the biggest storms over the Bay of Biscay are likely to end up as more of a Kent clipper, but it may be worth watching closely developments now over Northern Portugal which would possibly create a storm threat for the early hours of the morning for the UK. I am not seeing developments in the areas you work like for a convincing storm risk for tonight. Channel Islands might be the best place to see lightning.

Still a tricky forecast to make but it looks an elevated warm sector wedge rides up over the cool surface layer. Forecast SkewT suggests a limited amount of instability in the south west before that wanes as the cooler upper vortex air moves away. Looks as if it could go either way and if it happened during daylight then I would be a touch concerned. Forecast cloud patterns almost suggest an upper low overriding the high pressure surface conditions with a trough in the warm sector. It could just be I am struggling to figure this one out. I feel Mondays potential will be a lot easier to understand.

Forecast SkewTs for the UK Saturday night do not look convective, there is however moisture at all levels suggesting deep cloud. Looking at the precipitation forecasts it looks like we have destabilisation towards Spain and out in the Bay of Biscay possibly from the remains of some upper level troughing. How electrically active the suggested imports will be is open to question. We still have the disconnect between upper and very low level winds along with lowish dewpoints which means we are not in a classic storm scenario. Neither does this look like a typical Spanish plume destabilizing in the upper levels (upper lapse rates look limited) even though it has similarities. Elevated moisture advection and an upper trigger look key.

I don't think I would like to forecast Saturday at this point as it looks like the models are not really stabilised for that time frame. Looking at the Satellite pictures and Jetstream forecast for now then I can see evidence of a cut of low out to the west of Spain. This puts the High pressure between this low and the Jetstream running over the UK. Models then suggest this low pressure will lift out towards the UK. What you would expect is that thunderstorm potential will be concentrated at Jetstream left exit regions where winds diverge aloft. The suggested idea is that thunderstorms develop over France even though we are probably looking at upper anticyclonic (High) conditions there. Divergence aloft might arrive earlier than thunderstorm predictions. Looking at the Jetstream forecast and low level winds forecast we have low pressure circulation aloft with cooler air aloft whilst high pressure conditions are suggested at the surface. When transitions happen upper and lower air conditions can disconnect, but the suggested disconnect feels more like models are playing catch up and the catch up is happening at upper levels quicker than lower ones. There is a thunderstorm risk for Saturday in my opinion with possibly at least a week of thunderstorm potential next week. I would be concerned about forecasting detail much more than a day ahead until I am happy models are handling the situation correctly. It is possible the modelling is correct so make up your own minds.

Instability looks fairly weak (skinny cape) so not a widespread outbreak of severe storms. There is some directional shear through mid levels which might be suggest potential for turning cells (not supercell characteristics because you need a strong updraft/high instability) which may help in cell longevity. Generally low level wind speed shear looks poor although we should expect some convergence zones and gfs/lightning wizard suggest some stronger low level winds (Not likely inflow winds as updraft strength is not high). This macro level detail will not show up on a lot of forecasting model data so it is possible low level shear could be locally higher than generally suggested. One limiting factor is that the vorticity lobe expected is not really showing up clearly on Eumetsat satellite imagery yet. Storm forecasting with temperatures below 20C is always a bit tricky at the best of times, so best of watching the Netweather radar and satellite images.

Not a bad call Ben and as ever models can chop and change. Forecast SkewTs now suggest about 18C and dewpoints of 10C might be enough. The difference is down to upper air being forecast to be a. touch cooler. I am not sure the wind shear helps in the way you suggest. I think it will push tops out ahead of convection southwards which might result in pulse storms along low level wind convergence lines. High level cloud might be a risk to convection as dewpoints might match temperatures just below the jetstream. I expect charts will change over night so the risk might change and risk in the north east should not be ruled out.

Not really impressed with the storm potential for today and tomorrow and I think cloud tops are likely to be limited. Wind from a north west direction does not often generate the surface temperatures to let convection really bubble up. Some models will under estimate temperatures at this time of year but even so we have had an unusually blocked pattern with winds from the North, East, North West and North East. Maybe a slight chance for storms later in the week although the timing at the moment looks wrong for the UK and better for the Dutch and Irish. Upper level wind divergence combined with a moister and slightly warmer air flow at the surface. Surface winds are not long feeds from the south and early morning is wrong. Further chances maybe Friday before we get winds from the North and East. With the forecast being a few days out then things can speed up or slow down. Often models under estimate speed at this time of year, but after heavy blocking models try to pick up speed to quickly. Worth keeping an eye on.

CPC Blocking forecasts suggests blocking high over the UK will migrate to Greenland while a blocking low develops over Scandinavia before it fills and lifts out northwards. From this I would expect an artic feed of air starting Thursday making its way southwards which steadily makes its way towards the UK before we get a breakdown next week as Atlantic mild weather returns. Leaving out the beast from the east snow scenarios then two synoptic situations are known to give significant snow to the UK. The first of these is the occluded warm front and the second the polar low. https://www.rmets.org/metmatters/snowmakers-uk-part-1 https://www.rmets.org/metmatters/snowmakers-uk-part-2 Fax charts hint at possibilities for both of these. The first hint may come on christmas eve as a possible disturbance crosses the UK. Models suggest the cold air flow from the north will not really have reached the UK by then. Christmas day afternoon does currently look like a possibility of snow although moisture looks a bit meagre. Fax charts followed by wind patterns suggest that small low pressure systems could develop in the eddies to the south of Norway and later from Iceland. Low pressure positioning over Scandinavia would suggest steerage winds for Norwegian polar lows would take them into the Netherlands and France. Possible Icelandic polar lows look a little late and may get shut out by the returning Atlantic flow. It is hard to predict at this range but it could just be a few light flurries on Christmas day with sleet turning to rain as Atlantic mild weather returns. On the other hand the ingredients are there for some snow and anybody travelling needs to keep a close eye on forecasts. My gut feeling is the high pressure ridging across the UK breaks down quicker than models suggest and the artic air flow reaches the UK a bit late favouring snow more in the North of the UK.

Maybe an opportunity for some lively showers Bristol and Cardiff areas late afternoon today which will trundle north east. Weak upper level band of cooler air aloft drives the risk, but cannot really see storm development. Tomorrow late afternoon looks like storms could be possible for Ireland ,West Wales and Cornwall as cool air aloft arrives. Whether storms develop and where is very much down to timing of the movement of the fronts. Still not impressed with the. storm potential but mid level lapse rates are better than todays. Weak winds will tend to limit storm severity and heavy showers seem more likely than storms from current weather modelling. UKV model is noted as showing a slightly different evolution of precipitation.

Storm threat mainly concentrated in the East today, but it is worth mentioning the Highlands of Scotland. There are some possible low level wind convergence zones which could be triggers for convection. Instability is not that great, winds are light and cloud cover will limit things so severe storms unlikely. Steering winds likely to move from coming from the South West to coming from the West and appear stronger than I expected. Pulse storms most likely.

MCS developing over Central France with Orange (Moderately Severe) Storm warnings for that part of France. Best guess is that this trundles North through parts of England late evening and into the early hours. Likely to give a deluge of rain and lightning show in some places. Since this is an MCS (Big blob of Storms) then storm like conditions might persist for some time. Somewhere between Exeter and Kent is likely to be the landing point although I should point out some models kill the storms over the channel. We have to wait and see.

CDC GFS blocking forecast keeps shifting and I guess this down to Hurricane Larry. GFS Jetstream forecast looks extremely implausible to me at the moment. At this point I usually take a step back and think about what the key air flows are that are affecting the outlook and what the likely consequences on weather are. Hurricane Larry as been a bit of an odd ball, through having a lot of eyewall replacement cycles, at times a very large eye and speeds which should give upwelling to kill it. These factors have confused the models. What we have is not a particularly strong hurricane but with a significant warm core which is likely to cause significant expansion as it goes extra tropical and give a deep low pressure system. The hurricane although moving north slowly is forecast in the near future to accelerate North such that it has barely turned ex tropical before it slams into Greenland and onwards into the artic. This will cause warm air to be spread into the artic and alter artic wind patterns. Mountain torque from the wave breaking caused by the storm crashing over Greenland is likely to create an upward propagating wave. This type of wave during winter can cause the polar vortex to shift or split in the stratosphere giving a blocked winter pattern. During autumn the most it can do is shift stormy weather towards Russia or Canada. A blocking low in Northern Russia might be a reasonable response in my view. That gives Scandinavian or continental high and still a blocked pattern for the UK. It all depends on the timing and course of ex hurricane Larry which has already had some oddball characteristics so all bets are off.

Wind flow Changes For much of Wednesday the low level air flow towards the UK looks like being sourced from the Meditteranean rather than across Spain. Air from this direction tends to be very dry in contrast to the mid level elevated warmth sourced from across Spain. So we have a Spanish plume undercut by dry North African air which will limit storm development over France until later when more Atlantic maritime Air gets mixed in at the lower level. Key to what happens overnight will be the low level wind convergence zone over France or not. Wednesday Day Time Storm Outlook. Satellite imagery shows MCS developed over Northern France is being Steered towards the southwest of the UK. This is likely to affect the South West for the next 3 hours and poses a risk of localized flooding. Estofex forecast warns of excessive rain fall with forecast moisture profiles showing very moist air aloft. I think i would go along with that as a prime risk along with lightning. Wednesday Night Thursday Early Morning Storm Outlook. Modelling suggests that Storms will develop over Northern France and move towards the UK overnight. The exact timing and positioning is a bit mixed in the models. Lightning wizard modelling suggests SuperCells and Tornadoes might be possible across France this afternoon, yet Estofex forecasters are not convinced. Having looked at the Satellite both visible and Infra Red then I think I would side with the Estofex Forecasters. Estofex The risk is very heavy rain and a significant lightning show over night for the southern half of the UK. Timing is key and storms could be surface based up to around midnight although I have a suspicion MCS conditions might cool things to change that. Tricky to forecast and we need to watch France this afternoon. Modelling output is likely to swap and change. Thursday afternoon Storm Outlook. Generally speaking the storm threat moves North to cover North Wales, North Midlands and Northern England. There is however some suggestion of a low level wind convergence over the south west which could spark showers which build and develop as they move North East. At this point I don't think we can rule out Storms just about anywhere but what does catch my eye is a possible upper level feature crossing which might bring slightly drier air aloft. Temperatures will mean that some moderately severe storms are possible but the greatest risk appears to be hail and localized flooding with a possibly a lightning show for some overnight. Confidence is pretty low on exact evolution of things but still worth pointing out possible features.

Multiple opportunities for Storms Wednesday and Thursday. Perhaps for the first time this year we have a storm threat where temperatures are above 25C with stronger updrafts possible as a result. Since this potential for storms is from a fairly sloppy low with individual features tricky to predict it is hard at this point to identify exactly where. Models at the moment suggest that the South West on Wednesday afternoon could see some Storms. Indications are that these might be a bit elevated and surface instability is very marginal. There is also a hint of elevated imports from the south for the South East and East Anglia in the early hours of Thursday. Then on Thursday afternoon there is a chance of home grown storms for Wales and the Northern part of England. Models are likely to get details wrong at this point and what we have is a Spanish plume like environment being slowly undercut by a moist maritime environment. This is the type of environment where localized low level wind inflow from the south can create moderately severe Thunderstorms. Too early at the moment to give any real details .

The exact Category will not matter and I suspect that effects will be significant. There are reported winds gusting over 100mph in remote slightly elevated outer areas. There are some reports from remote areas of sea levels rising 2 feet in hours even before full proper landfall. These may be extremes but but give an ominous outlook. Whenever I see a forecaster say this is unusual I tend to take notice. I am not an expert but vertically deep might suggest robust and keeping strength longer after landfall. When hard core storm chasers start taking precautions you know things could get tricky. Flash flooding across multiple states looks a possibility as well.

Looks like Ida is beginning to develop a new eye. Despite the developing towers around and the speed of wrap, time is beginning to get short for intensification. It does have a better symmetrical look and lightning detected in the eye wall does mean it is picking up. Some recent comments picked up on twitter. What better time could there be for issues with drainage and pumps in New Orleans. If true then somebody will not be popular if this is still the case when the Ida passes over. If I remember correctly Hurricane Katrina had about 5 hot towers develop just before the intensity increased significantly, might be worth watching out for more of these as it looks like Ida might developing them.

Blocking High over or near the UK looks set to be stubbornly in place giving a cool northerly air feed for next week. High then modelled to shift West which would tend to give an even more direct cold air feed although with less cloud. Hurricane Ida about to clobber New Orleans might scupper this as it leaves the US and goes extra tropical. Modelling then has high moving South over the UK whilst Greenland High recedes North. This suggests we might get a week or so of late summer warmth. Further out then Pacific blocking is forecast and this tends to give the UK a warmth wet mobile pattern. Given the amount of blocked weather patterns this year I would have very low confidence on this suggestion. Ensembles show that confidence is pretty low in any of this being true beyond the next few days. So looks all a bit fantasy island (FI) .

Probably a bit tricky to forecast the intensity at the moment. Latest discussion suggests the eye survived intake crossing Cuba. Latest Satellite loops suggest that deep rapid convection has disrupted the eye as Matty comments above. Regardless of the state of the Eye the hurricane has a fast spin on it which I think will cause intensification. It also looks likely to make landfall slightly West of New Orleans which due to the circular pattern of the winds will tend to drive waves into Lake Borgne. Seven to eleven feet surge could be a conservative estimate for New Orleans. We must not forget the flooding impact from this Storm especially since Tennessee is only just beginning to recover from earlier flooding (Just West of Nashville)

Looks like some enhanced convection in the South East quadrant. NHC Hurricane Henri Discussion Number 23