Model Output Discussion - Spring Has Sprung

[DaveF]

No output from UKMO 0Z yet, and UKV (normally every 3 hours) hasn’t updated since the 18Z run. Anyone have any insight?

[CoventryWeather]

 Penrith Snow I know what you mean, but you have to start somewhere! 

Must admit, think it will turn drier this month, mid month seems a decent bet at the moment..

[BlueHedgehog074]

Does seem to be some kind of attempt from a number of the operational models to shift the string of UK Low Pressure this week somewhat further to the West and North into the weekend and beyond, along with some of the blocking around the Greenland area losing its power. So kinda allowing more from the European and/or Azores ridging to try take some visits to the UK.

After all the Spring months November so far seems to have gobbled up, even including April this morning (cloudy and damp), you would imagine a change to a less wet/more settled spell to take over at some point. So I’m sorry November, you can’t have April in your stomach forever. And even if April does stay remaining trapped in November’s stomach, I’d like to see it try and swallow up May.

[Addicks Fan 1981]

 damianslaw was 2006-07 in that bracket too? 

[LetItSnow!]

Peep a pocket of 20C air not that far away from us on the 6z by the 6th. It does actually bring the 15C line flirting with the south-east coastal regions in the early hours. However it moves through extremely quickly on this run so by daylight hours the air becomes cooler. 

[sundog]

The ssts in the North Atlantic seem to be cooling down. Certainly look cooler compared to less then 2 weeks ago. 

[DaveF]

Some info on the Met Office models not updating:

 

[SunnyG]

 BlueHedgehog074See May 2021...

[Jordan S]

Quite extraordinary model outputs atm, for example an ensemble model that I'll show below as a gif from last night of many models together, shows the UK being a low pressure magnet for its entire 16 day run, it's a typical synoptic that has taken place for a long time now. In these set of charts, barely a ridge of high pressure over the UK for the majority of the times with no high pressure cells setting up over the UK even for several hours, never seen that on this chart before, it's clear that unsettled or even at times very unsettled weather is likely to feature upto 10th April at least, for the majority, with confidence rating of 90+% of this occurring, less unsettled possibly at times after 11th-12th April particularly the south with increased temps for southern UK, but by and large higher pressure although closer to the UK to our south/southeast, not having much or any influence in the UK weather in terms of drying us out for any length of time before and over mid April and that hasn't changed from previous thoughts when I did my previous post.

Part of the reason this unsettled weather has continued so long is partly due to a slightly self feeding mechanism this wetter period we are stuck in and have been stuck in for several months has produced. 

Saturated soils and landmass generally promote more instability/lower pressure, whilst bone dry ground will generally have the opposite effect without the presence and influence of wind direction shifts/water sources/significant background synoptical changes further afield. Works a similar way to heat domes/ frozen landmass under snow cover.

It's uncommon to see sudden flips from long lasting extremely wet conditions such as the one we are in currently, to fairly or very dry sadly, though certainly not impossible, and what tends to happen if a drier spell is likely to develop for a more significant period of time (from natural variability of weather inevitably at our latitude and changes from further a field that are very pronounced) is more and more ridges of high pressure are "thrown" over a landmass particularly wet more and more frequently over a period of several days or weeks, this largely applies to areas such as the UK where synoptics can move along very quickly.

In theory you'd say the longer this wet spell continues then bigger and bigger shifts in weather patterns further afield would be required to shift the pattern enough to change the weather conditions to dry but many smaller scale things changing at once would of course help produce a similar outcome, of course the pattern will definitely change to something dry and that's why as never ending as these lows are, there will be a shift to a more typical UK weather pattern or sustained high pressure, but perhaps not for a while yet..

If I am to really take an educated guess as to when this relentless barrage of low pressure systems may begin to change to a more significant and longer term degree and move more to our northwest and produce less intense weather fronts and higher pressure have a more significant frequent, larger influence over the UK, then I'd be inclined to think last week of April onwards, BUT like I said above from the 13th-14th April increasing incidences of drier conditions perhaps presenting themselves especially for southern and eastern areas, with unsettled weather more likely for the west/northwest of the UK by this time, for a short time, and that does link to my previous two updates suggesting the possibility of this outlook for this time.. BUT I mean less unsettled overall, with a few more drier days, not likely to overall be settled and dry nationwide for any more than a day or 2 I'm afraid given the lows continued proximity to the west of the UK, but perhaps somewhat better than we've had and will have in the next few days to 10th April if that plays out for mid month onwards.

The latter part of April and especially into much of May, (may) generally be more likely to have more frequent occurrences of dry or drier days than we've been use to for some considerable time, partly given the time of year and warmer temps (higher evaporation rates) but I wouldn't be surprised to see frequent quick breakdowns to thundery/wet conditions particularly from our south/southeast, with the potential for these to cause further flooding problems where they do occur and that does seem more likely before it clears up for a few days at a time with warmer temps, indeed this thundery and overall less unsettled synoptic pressure pattern over Northwest Europe and UK is more realistic and in fact could easily remain for the Summer period in its entirety, but if this where to take place as per what I'm suggesting, then we would be more likely to have a thundery/ fairly, though not very or exceptionally unsettled first few weeks to meteorological summer, certainly less unsettled than what we've had upto now, with a shift to a much drier pattern later in the summer with higher pressure being the dominant player. As for temperatures more uncertain, could be much cooler than average or warmer than average tbh, I'd favour a cooler first part to summer in the south especially, then warming up later in summer to above average, perhaps significantly so.

 

Whatever happens this unsettled spell will break at some point obviously, small chance we see a sudden flip to high pressure dominated dry and warm conditions late April onwards but I don't think so, looks like we will have to wait for a few weeks yet for any sustained long lasting high pressure systems over the United Kingdom.

For the next 4-7 days though, very wet and that has flagged for a long time on my posts so not worth going into too much detail on this but 30-50mm is likely to accumulate widely, especially parts of England and Wales at first, locally a bit more, and upto 150mm on mountains.

Take care.

[Had Worse]

Sorry wrong tab

Edited April 1 by Had Worse

[CoventryWeather]

Trend continues to show us drying up - waiting for the latest ECM, but GEM, ICON and UKMO all interested in a drier pattern by mid next week. 

GFS is alone in keeping a much wetter pattern although moved slightly towards the others on its latest run. 

Let's hope it sticks.. and it lasts for a while too! 

[sebastiaan1973]

Hi guys, you miss for the a big part, a portion of extreme warm air. Anomaly 850 hPa is 20c in some places! 

[LetItSnow!]

This 20C line keeps popping up earlier and earlier! Fascinating from a meteorological perspective but also very concerning that it's feasible for the 20C line to be able to reach us so early in the season. Makes me think that 30C in April is achievable some year soon.

Edited April 1 by LetItSnow!

[raz.org.rain]

 sebastiaan1973 my lord, wouldn't a 20°c 850hPa be exceptional even in midsummer?

[LetItSnow!]

 raz.org.rain Considering it was virtually unseen in the UK except on extremely rare events until 2015, absolutely! Sadly, it's become less exceptional since, but for April I dare say it's not been seen in the reliable records. I'm sure someone will post a random chart from like 1982 proving me wrong, but basically yes, the 20C being in our vicinity in April is absolutely unthinkable, remarkable and extreme. Dare I say the equivalent would be the 27-28C line wafting to our south-east in mid-summer?

[WYorksWeather]

 LetItSnow! The 20C isotherm would absolutely smash it I think in terms of reaching 30C, but probably not so early in the month - it'd need to be at least mid-April. Plumes below 15C at 850hPa have produced temperatures in the mid to high twenties in the past at any point from mid-April onwards.

My bet would be that with ideal surface conditions, a 20C isotherm could produce 30-31C at the start of April, up to 33-34C or so at the end, because it's such a rapidly warming month.

In practice though, I don't think it's plausible to actually get the 20C over the UK for a 24 hour period in April - the Channel would cool it too much. Doubly so for very early April.

More realistically, if we got something like a 17-18C isotherm for a 24 hour average, I'd bet on something like 28-29C in early April or 31-32C at the end. That sort of temperature is definitely plausible for April these days if surface conditions allow.

The difficulty as always is getting the surface conditions - that sort of temperature contrast between land and ocean tends to promote absolutely vicious coastal breezes that take several degrees off the theoretical maximum. I've noticed that most of the warmest April temperatures tend to come from more sustained heat dome type patterns, with a high centred slightly to our east or north-east. Brief plumes tend to be less likely to do the job, with the notable exception being 2018.

See these charts below from 2007, 2011 and 2018 for some fairly recent examples for mid to late April warmth.

[WYorksWeather]

 raz.org.rain Looking through the archives for my post, I struggled to find any with even the 15C isotherm in! In practice though I don't think we could get the 20C isotherm over the UK in April (at least not yet), though 17-18C clipping the SE is definitely a realistic possibility.

[Methuselah]

 WYorksWeather: Well, we had 27C, up in the Highlands, in April 2003. . . and a load of forest fires to go with it.

[damianslaw]

Commenting on high temp likelihood in April.. given we have extremely wet soil content and surfaces this year, will be hard pushed to achieve max temp on record, but who knows. All conjecture I guess.

Back to the models, very unsettled in a word and not what many want given quite a few people are wanting to enjoy the outdoors this week thanks to easter school holidays. 

[LetItSnow!]

 WYorksWeather I respect that, but in a warming world and with a somewhat plausible chart, I do actually think it is indeed possible and I'd be surprised to not see an attempt at it in the next 5-15 years. All it takes is the right set up. Think back to pre-December 2015 times and pre-February 2019 times when those records seemed unlikely. I do think we're playing with variables we've not encountered in the technological forecasting world. 

Anyway, back to the forecast and ironically it seems the 6z is less feverish about the scale of the warmth though still manages to get the 10C over the extreme south-east but during the nighttime hours.

Despite the southerly influence, it's possible that due to all the cloud and rain associated with these moisture laden southerlies we may not see overly high temperatures. I know you can usually add on a couple degrees but unless there's any sunny spells, probably temperatures pegged into the mid-teens. The C.E.T. will be bolstered by mild, cloudy nights.

Further down the line (the 9th) it shows that some really wet weather (and perhaps stormy too) could come from low pressures grinding to a halt due to high pressure to our east. Ironically though on this chart any early spring warmth gets shunted west.

I wonder if this will be one of those "C.E.T. disguises the fact it felt poor" kind of months. Wouldn't rule out later cold spells though. Despite the exceptional surge of warmth I'm not sold 100% it's a nailed on super warm April yet.

 damianslaw  @WYorksWeatherJust to add, my thoughts on 30C in April are NOT about the coming April, I meant Aprils in the next 10-20 years or so. No further addition to this in this thread though, just clarifying.

[DaveF]

 CoventryWeather Indeed the MSLP ECM ensembles from the 00Z run are very encouraging with lots of members going anticyclonic. Waiting with interest for the 12Z output. Somewhat supported by GEM (especially the OP). But GFS is having none of it. Really marked contrast between the GFS and ECM ensembles.

[WYorksWeather]

Yep, on the models, key period seems to be around day 8 currently. Here's GFS and ECM 12z. Both unsettled at this point for the UK, but the ECM is a bit stronger with the tropical forcing.

Pretty much night and day by day 10.

Beyond that, the GFS FI extends a mid-Atlantic ridge northwards from the Azores, and we actually end up pulling down an cold northerly airflow. Of course far too late in the day for a -4C isotherm to produce anything wintry away from prone spots, so probably just wet and miserable under the low.

In terms of rainfall accumulations, this is where the GFS is still showing these ridiculous totals. Again, as you'd expect, the focus of the rainfall is changing from run to run, but tonight GFS is going well over 100mm for western Scotland by the middle of the month. Again though, nowhere really escapes it, some central and eastern areas maybe close to average but nowhere looks dry on the GFS solution.

The key really is trying to get something more settled in, and at the moment the GFS is leaving the option on the table for a bigger rise in pressure, but it's only a few ensemble members that are buying into it.

[WYorksWeather]

 LetItSnow! Again not to derail the thread but last comment on this in here - I was saying that if you take the ECM chart which shows the 16C isotherm over the UK, and shunt the pattern a couple of hundred miles west, you'd have the 17C or 18C isotherm in to parts of the south. But the 20C isotherm is hundreds of miles to our south, so I doubt that could happen even if you take the existing pattern and move it around a bit.

Agree with you though that further discussion of this should probably happen elsewhere, so happy to chat further on another thread if you tag me in.

[damianslaw]

 WYorksWeather There is a first 20 and 25 degree thread, it would be appropriate to use that thread to discuss likelihood of 20 degree isotherm etc in conjunction with predicting high temperatures. 

[WYorksWeather]

 damianslaw Already done - discussion is continuing in here actually. Normal model output discussion can resume