Model output discussion - August hot spell - how hot, how long?

[mushymanrob]

I dont share the optimism some of you are holding on to. Id be very surprised if this chart which yet again suggests troughing and a mean upper northwesterly will be inaccurate enough to allow much of a more summery feel by later next week. (True early next week is looking pleasant).
If you go on the GFS on Wetterzentrale and click North America, you can see this trough develop over Canada, as very warm/hot air drifts up from the American midwest and clashes with cool polar sourced air . That trough deepens and tracks rapidly Eastwards to take up residence in the north Atlantic, drifting slowly Eastwards.

 

[northwestsnow]

As ever mushy the proof will be in the eating..

Looks mainly dry locally after a blip today and tomorrow.

Next week looks nice to begin with but subtle hints the high pressure in the mid Atlantic may be dragged west opening the door to a north westerly.

 

[Scorcher]

1 hour ago, mushymanrob said:

I dont share the optimism some of you are holding on to. Id be very surprised if this chart which yet again suggests troughing and a mean upper northwesterly will be inaccurate enough to allow much of a more summery feel by later next week. (True early next week is looking pleasant).
If you go on the GFS on Wetterzentrale and click North America, you can see this trough develop over Canada, as very warm/hot air drifts up from the American midwest and clashes with cool polar sourced air . That trough deepens and tracks rapidly Eastwards to take up residence in the north Atlantic, drifting slowly Eastwards.

 

I don't think anyone has said that it's going to be outstanding. Of course these charts show a predominantly westerly regime, but you can still get the odd nice day here and there. These charts are a good summary of the overall pattern but they don't necessarily show the minutiae from day to day.

I think most people's expectations are low at the moment, but in the medium term there has been a small improvement from yesterday from the op charts.

[mushymanrob]

1 hour ago, Scorcher said:

I don't think anyone has said that it's going to be outstanding.

 

nope they havnt, just "optimistic" , but apart from a few days of pleasantness early next week, theres no real evidence (imho) of a shift to a lengthier settled warm spell (which i would certainly welcome) showing... of course the outputs are subject to change, im just commenting on what the current outputs are showing now.

[mb018538]

1 hour ago, Scorcher said:

I don't think anyone has said that it's going to be outstanding. Of course these charts show a predominantly westerly regime, but you can still get the odd nice day here and there. These charts are a good summary of the overall pattern but they don't necessarily show the minutiae from day to day.

I think most people's expectations are low at the moment, but in the medium term there has been a small improvement from yesterday from the op charts.

Definitely looks better than yesterday. The deep low in our neck of the woods in just over a weeks time isn't half as bad on today's output. The 6z extends the low but is a big outlier.

[Ice Day]

Not a bad ECM tonight.  Days 5-8 looking pretty warm and settled, certainly for the south of the UK.

 

By day 10, there's an attempt for another push of heights from the south west but far too out to worry at this stage (nice to see -18 uppers over Greenland as well, if that's your thing  )

  

Nothing spectacular on the cards, but overall quite positive for some 'usable' weather ahead.

 

[mb018538]

Looks pleasant enough - that ecm run isn’t overly hot, probably 23/24c maxes - but more than decent for mid September. We need a southerly now for some proper heat, the longer hours of darkness and decreasing sun angle really curbing daytime heating. That setup with a strong ridge and good 850s a couple of months back would probably be high 20s.

Edited September 2, 2020 by mb018538

[Mike Poole]

I think ‘useable’ is a good word in the upcoming spell.  It isn’t going to be hot, high pressure in all models in the wrong place for that.  GFS, GEM, ECM, JMA T192:

Admittedly the JMA does look more interesting, but yes high pressure, no favourable wind direction the message apart from JMA, as I said usable nice weather.  Where we go after we will see....

 

[damianslaw]

Quiet in here today, as said September the quiet month, always hard to get enthusiastic and excited by September weather.

[MP-R]

6 minutes ago, damianslaw said:

Quiet in here today, as said September the quiet month, always hard to get enthusiastic and excited by September weather.

Hardly surprising when it’s wet and windy for many. Little hope of August heat or the first October frost. Tentative signs though of some settled weather next week, especially across the south. May not be long lasting though...

[summer blizzard]

Tonight’s Euro was largely the same as the morning with a likely milder, drier and duller than average westerly outlook until day 9.

GFS more exciting but less likely to be the result.

[bluearmy]

No dramatic improvement generally in the pipeline as the Atlantic high ebbs and flows and the changing wavelengths make the troughing rather more notable than the ridging for n Europe 

Edited September 3, 2020 by bluearmy

[SMU]

Morning -

After a brief settled spell the ECM introduces the first -4c of the season to the UK

[Skullzrulerz]

45 minutes ago, Steve Murr said:

Morning -

After a brief settled spell the ECM introduces the first -4c of the season to the UK

Good to see you back! 

The cold hunt is on

[ICE COLD]

1 hour ago, Steve Murr said:

Morning -

After a brief settled spell the ECM introduces the first -4c of the season to the UK

I’ve noticed on the last few ECM op runs towards the end of some kind of Northerly flow with -4 uppers getting into Scotland. 

[Tamara]

10 hours ago, damianslaw said:

Quiet in here today, as said September the quiet month, always hard to get enthusiastic and excited by September weather.

This is not true for everybody.

What of the Septembers pattern for those who are still interested ?   A  lot of caution remains heading through this month with the upstream amplification pattern -  based on the progress of another high frequency MJO signal across the tropics and an associated fresh jump in angular momentum tendency that may well bring about further curveballs with time. Whilst it looks like yet another La Nina-esque influenced autumn - and these have been numerous over the last decade overall, that doesn't mean that the atmospheric circulation does not wax and wane within such a default parameter. The first half and middle of August was an excellent example of a wane period

The balancing act within the atmosphere, and how this impacts the jet stream, pivots around the substantial extent that AAM has fallen back once more, following the August rally and attendant downstream ridge and spectacular heatwave. 

 

 

NWP has been spooked by strong scrubbing of westerly wind inertia c/o of robust  -ve mountain torques across the extra tropics. It is this that has been sending an equally robustly strong upstream amplification signal (very La Nina-esque).

 

 

The Global Wind Oscillation, a phase plot depiction of global wind-flow inertia, represents this steep fall back in globally averaged angular momentum since the last 10 days of August, with a deep amplitude orbit return to La Nina phase 1 on its way to Phase 2.

 

 

This underpins the NE Pacific amplified wavelength configured to equally amplified sub tropical ridging in the central and Western Atlantic and troughs peeling off close to Iceland around the perimeter of the Atlantic ridging and sending phases of chilly polar maritime air south eastwards in between humid sub tropical frontal sectors which are mainly being seen further south.

The persisting issue, as discussed in previous summaries, is that the low frequency tropical signal that is driving this default pattern continues to blindside numerical modelling to this next further eastward propagation of the high frequency signal that has some hallmarks to what happened in late July and the first part of August..  Based on the steepness of the ongoing fall in momentum, an unstable wind-flow budget in the atmosphere is being created, which means any subsequent rebound and rally will likely trigger quite a further NWP shake-up as this month moves forward

Ultimate Pacific engagement of the high frequency tropical signal implies another interruption to the African Easterly Wave pattern c/o the low frequency feedbacks in the region (such as happened in the early part of August.)

 

 This leads to a rapid de-amplifying of the upstream pattern and hence the jet stream, downstream, switched right away from a NW-SE angle and as a consequence cutting off airflows sourced from the far Northern Atlantic and instead engaging airmasses from increasingly warmer vectors

 It will be interesting to see how the numerical modelling continues handling this over the coming 10 days or so and whether another mid stream change of fish shoaling is around the corner.by the time we are getting through the second week of September and looking mid month period onwards.  Much as happened looking ahead from the latter part of July into the first half of August.

Whilst the coming period certainly sees the continuation of the strongly amplified upstream pattern, it remains wise to watch for the models eventually becoming a cropper if they try to persist with this pattern too far through the month.

A further six weeks on from the August heatwave, as it will be by this stage of a very extended period, it certainly still doesn't preclude further reminders of summer to come. Plenty of time remains for that yet  and those who continue to appreciate warm days and warm evenings, irrespective of less daylength, will consider it worthwhile sticking around a bit longer while such an opportunity remains

 

[Frosty.]

Looking at the ECM 0z ensemble mean there’s certainly some settled and warmer weather indicated across the south at least during next week!..

[damianslaw]

Re post Tamara, perhaps I should have clarified, I don't believe we should avoid taking an interest in the weather in September, or that likely synoptics developments have no interest. It was more a personal statement on my perceptions of September, our most benign month, absolute extremes in condition and feel of things reaches its annual low. We can see temps in 30s still, significant wind storms as well, but they wont pack the same punch as they would in summer or other autumn and winter months generally in other words cant feel maximum effect in September.

[Man With Beard]

ECM clusters - after an above average week with temps back in the mid 20s for a while, next weekend needs keeping an eye on. A really deep low looks a strong possibility, and if cluster 2 holds the eventual outcome, then a very windy, even stormy weekend could materialise

Further out - still the chance that we could draw heat back up from the south but unlikely I would wager - note how many clusters have a trough anomaly over Europe - this usually prevents warm air circulating from the SW, though it could possibly introduce warm air from the east if the draw comes from the Mediterranean - touch and go because we are rapidly approaching the time of year when easterlies flip into colder solutions, and potentially much colder ones. 

Overall, though, I'm sensing a much more active Atlantic than usual for September - a slightly displaced jet to the north means most of the unsettled weather is staying north in the next week, and our chances of settled weather will continue to rely on a northerly tracking jet for the foreseeable - any southerly correction will put us in a wet/windy cycle.

 

[Zak M]

I've been going through some of the 06z GFS perturbations this afternoon and I found this on perturbation 6:

   

A plume scenario is being shown on this, with 18c uppers in the SE. This would deliver temperatures into the high-twenties quite widely with a 30c somewhere in London and the home counties. Into the more reliable timeframe, however, the models are showing signs of something settled and warm at the beginning of next week. 00z ECM has uppers of 14c in some spots on Tuesday, which would result in temperatures hovering around the mid-twenties at highest. The problem that lies here is how long this settled pattern lasts. The GFS, GEM, ICON and a few other models have the settled pattern lasting up until the end of next week, with the chance of some rain/showers in the north where the cold front is present but then heads SE and decays. The ECM though is a bit different from the rest as it shows the settled pattern lasting for only a few days and then shows a northerly, along with the Azores High ridging to the west. I would also think that there could be some cold and frosty nights up north if the 00z ECM comes off. In my opinion, we may have to wait for a few more days so that we can have a clearer picture on how long this settled weather will last, and where abouts it will be confined to.

This is just for fun, but this was shown on yesterdays 12z JMA run:

         

Obviously this is pure FI, but there would certainly be some spectacular weather if this was to verify, and it just shows that the chance of getting summer-like weather in Autumn is far from over yet.

Edited September 3, 2020 by Zak M

[Mike Poole]

I think there’s an awful lot of uncertainty after the settled but probably not particularly warm spell for the south up to day 6.  T240 has these massively different offerings from ECM and GFS 12z:

My money is on ECM being closer to the mark.

[carinthian]

38 minutes ago, Mike Poole said:

I think there’s an awful lot of uncertainty after the settled but probably not particularly warm spell for the south up to day 6.  T240 has these massively different offerings from ECM and GFS 12z:

My money is on ECM being closer to the mark.

Hi Mike, yes difficult to be precise with low tracking that far out. Certainly, both models showing classic Rossby wave formations profile along the NH jet. Looks like a fluid period developing with fluctuations between cold and warmer. The positioning of the NW European trough being the main influence in the weather type likely to be experienced but no settled or unsettled period likely to dominate. Probably work out towards normal temps .

C

[mb018538]

Much of this uncertainty is down to Typhoon Maysak throwing a massive ripple into the Pacific jet - this then builds a huge ridge in the western USA, a big trough through the centre (hence Colorado going from 38c to 0c within 3 days), with the whole wave travelling further downstream and also effecting Atlantic patterns. It’s that time of year when anything can happen!

[MATTWOLVES 3]

Hi gang not been posting much lately but still having a catch up, and good to see the standard still remains very high. 

Quick one on tonights EC weeklies... Next week we have High Pressure bringing some decent conditions at times and especially further South, towards next weekend we need to keep an eye on a deep Low situated to the NE bringing some potentially much cooler and wetter conditions... Into the following week things look to improve again with High Pressure again building in from the SW.. so all in all some very usable conditions to look forward to over the next couple of weeks.. Enjoy your evenings.

[summer blizzard]

Some movement to a consensus this evening with the Euro and GFS having the trough move in at day 8 and removing the milder westerly flow in favour of polar maritime air.