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


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ECM mean looks interesting in backing up the op at T168:

2EB91762-7CBF-4ECB-8EB0-92B9B01DD606.thumb.gif.8418ff82994dc9752fc239b558d419f8.gif

Heights into Scandinavia always a good thing...let’s see, signals strengthening for a settled warm start to September. We haven’t looked at the FIM for ages, but looking nice for the south anyway at T240:

81C94DC9-B7A6-47E7-91F6-B28D54C19241.thumb.png.edaca1a69e94fa7ced3fac36fac74f87.png8EC41C25-954A-4145-941D-6D7FFD291DA8.thumb.png.4605d1420b0f0eba17755d1a40fa2a43.png

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Astonishing rebound in momentum transport that is behind the current spectacular synoptics and associated high impact weather. Both the heat, and also the powder keg potential for thunderstorms.

*** USING THE ECM TO FORECAST TEMPERATURES IN A HEATWAVE - A REVIEW *** I often make predictions based on models several days ahead, and then I find it useful to revisit these predictions after t

The reality is that NWP is wholly congregated on, but susceptible to be blindsided and over preoccupied by, the re-ignition of the low frequency tropical convective standing wave across Africa and the

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6 minutes ago, Mike Poole said:

ECM mean looks interesting in backing up the op at T168:

2EB91762-7CBF-4ECB-8EB0-92B9B01DD606.thumb.gif.8418ff82994dc9752fc239b558d419f8.gif

Heights into Scandinavia always a good thing...let’s see, signals strengthening for a settled warm start to September. We haven’t looked at the FIM for ages, but looking nice for the south anyway at T240:

81C94DC9-B7A6-47E7-91F6-B28D54C19241.thumb.png.edaca1a69e94fa7ced3fac36fac74f87.png8EC41C25-954A-4145-941D-6D7FFD291DA8.thumb.png.4605d1420b0f0eba17755d1a40fa2a43.png

Haven't had a warm September since 2016.  Would be nice to have some clear, blue skies without the ridiculous heat (something this summer has seriously been lacking in, with the exception of the first few days of June after the May warm spell).

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image.thumb.png.bf7e8fd3e8d096966005d38579e9e203.png

I'd still take any forecast  into next week with a large dose of salt. Ex-Hurricane Laura (over the USA still in this chart) will be heading out into the Atlantic and likely alter the ridge/trough set up. Models notoriously bad at handling these.

 

 

 

 

 

 

 

 

 

 

Edited by mb018538
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1 hour ago, JON SNOW said:

Looking at the GEFS 0z mean, let’s just say I’ve seen worse this summer ( most of July for example!!!! )...sure it’s far from perfect but let’s face it, the meteorological summer is almost over...BUT that doesn’t mean to say there won’t be any more summer-like weather!!!!...anyway, enough with the waffle already...the mean indicates some improvement at the weekend as a ridge of high pressure pushes across the u k from the west..and then, essentially thereafter it turns into a northwest / north - southeast / south split with the best of any fine & warmer spells further s / se and the coolest most unsettled conditions further north by northwest!.🙂

747F4E12-6B56-4EC2-B1C4-196D12396699.thumb.png.b1b85e809de97d9143d6b1ef347d961e.png708D58AC-7C42-4AF9-A46E-9B4C725665F0.thumb.png.1602e262379d2c41efbf1612c28a0eca.png990ADB46-1F06-4C2E-8AC2-218242451910.thumb.png.7eb0b37a175c2ca294fd9a18e7793f14.pngC5665E3B-D9EA-4187-A501-D320BBDDB7C2.thumb.png.95152cca947df06b20f6d94b099e5883.png10432C5F-F965-401B-AB63-A9D8581B8F4D.thumb.png.7c2484b64ce99fd1b26137d674ecc436.png

Yep you can often get temperatures well into the 70s even in October.  Good to see high pressure never far away on those charts.

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10 minutes ago, Tamara said:

...And so the "worst" of the pattern switch is duly very much focussed within this last week of August and with an underwhelmingly cool introduction to the Bank Holiday.

However,  the renewed stranglehold of the low frequency tropical signal across Africa and the Indian Ocean, which has re-set set this unwelcome pattern wavelength, faces a further interruption as September progresses. NWP is still a bit tentative with this, but then as stated in last weeks post this is to be expected based on how strongly they congregate around such a default signal - until the flag is really waved that something else is about to shake-up the wavelength.   As the MJO cycle progresses eastwards once more through the first part of September then this is the starting pistol for another AAM rally and re-booting of downstream ridging. We cannot guarantee record breaking late seasonal heat, but every reason for a warming trend to renew after an initially disappointingly cool start due to the incoming amplified Atlantic ridge trapping lower uppers as the next trough passes east of the UK at the end  of the week

The switch in the upstream pattern should, with time, start to send Atlantic lows further to the NW and allow warmer air to mix out the coolness.   Updating tropical convection forecasts will start to define the extent of the next rise in angular momentum as associated rossby wave-breaking propagates into the extra tropics - and on that basis the extent of a further downstream ridge will be defined accordingly.  But the theme of the final paragraph of the quoted post still very much applies 🙂

 

Thanks @Tamara

CFS seems to be strongly suggesting a rise in AAM as we hit September, with a turn to positive by around the 9th/10th. I've been keeping an eye on this as it has a known positive bias, but it has remained rock-steady on this date for a while now. ECM is also sniffing out this change too.

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No comments on the 12s?  I’ll kick off with GFS at T144, T192, T240, T300:

7A7506F9-7879-4B07-BEB2-C6DA16D8C1BE.thumb.png.c32608f3dbdc6113848db19368ca43af.png7E9CD951-E31A-43BB-8992-AD464B0A6BA6.thumb.png.0d1a4c05712c8263400fb897ccf533d1.pngB5101633-ADA6-4EE6-95C4-E98417C878D2.thumb.png.6d01ab679dbb10fb85cf4eb643f80fc2.png0C6E5192-F4F6-42D6-813B-0E6E0DE9ACA5.thumb.png.19d2e60cde767e4409b16eb3de7b0fa4.png

What’s not to like?  

GEM not quite as good, but decent for the south...

72DF6DE4-D0A2-4AED-9B0F-38AB26982134.thumb.png.be34c54b12a60443aa88bbefe540c539.png09452859-9A47-48BF-BD6C-9811635DECF3.thumb.png.02b8f40dc8ea9ed0512d8494841a51c8.png00E5D96D-F6C8-4143-B88E-AB4C55BCCA36.thumb.png.4f82b59de2d964e25012f7a19752496f.png

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12z GFS is pretty good for the south with 12c uppers on day 8

@192

gfseuw-0-192.thumb.png.fe4699ede0b1bda55ea37b882e56207f.png

But then, later in the run, it goes on and produces this @300. 🤯

gfseuw-0-300.thumb.png.881156b91999714a3741da3c2edf7bba.png   gfseuw-1-300.thumb.png.425e7523629c7df8c581aabe2753619b.png

And I'll throw in the uppers too for good measure @318 - look how far north that 16c isotherm gets!

gfseuw-1-318.thumb.png.5e63bb40c747f83a752b1cef8e1da231.png

Edited by Zak M
12z
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ECM T168 is showing the kind of pattern that I have been on about for some time:

9E7A70DC-393B-425E-AC3C-5FF06C5F1777.thumb.gif.4244aeba25e0ab529247e85ae37b9e43.gif

There have been signals for this Azores -> Scandi link now for a few days now giving broadly settled UK position...not guaranteed of course, but now seems to me more likely than not....we will see....

Edited by Mike Poole
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7 hours ago, Tamara said:

...And so the "worst" of the pattern switch is duly very much focussed within this last week of August and with an underwhelmingly cool introduction to the Bank Holiday.

However,  the renewed stranglehold of the low frequency tropical signal across Africa and the Indian Ocean, which has re-set set this unwelcome pattern wavelength, faces a further interruption as September progresses. NWP is still a bit tentative with this, but then as stated in last weeks post this is to be expected based on how strongly they congregate around such a default signal - until the flag is really waved that something else is about to shake-up the wavelength.   As the MJO cycle progresses eastwards once more through the first part of September then this is the starting pistol for another AAM rally and re-booting of downstream ridging. We cannot guarantee record breaking late seasonal heat, but every reason for a warming trend to renew after an initially disappointingly cool start due to the incoming amplified Atlantic ridge trapping lower uppers as the next trough passes east of the UK at the end  of the week

The switch in the upstream pattern should, with time, start to send Atlantic lows further to the NW and allow warmer air to mix out the coolness.   Updating tropical convection forecasts will start to define the extent of the next rise in angular momentum as associated rossby wave-breaking propagates into the extra tropics - and on that basis the extent of a further downstream ridge will be defined accordingly.  But the theme of the final paragraph of the quoted post still very much applies 🙂

 

Agreed, but the law of Chaos always seems to bugger things up for us.

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1 hour ago, NewEra21 said:

Think it's fair to say the GFS 12z was a bit of a warm outlier in terms of 850s

IhNP1z1.png

It was, but there are a fair few ensemble members going above 10c into September. Ridge and trough positioning hard to predict with the ex hurricane chucked into the mixer, hence the pretty wild ensembles.

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Remainder of the month looking decidedly cool, but hopefully alot of dry sunny weather over the Bank Holiday weekend, not exactly sunbathing weather, but bet it won't stop many from doing so. Pleased we are not about to see a washout weekend.

Into September, more mixed weather but signs perhaps azores high building and low pressure taking a more northerly trajectory, rather average conditions overall, nothing overly wet or especially warm.

Longer term - some stirrings may see something more longer lasting in terms of settled stakes, and warmer. All very normal, rare not to see a quiet warm settled spell at some stage during first two thirds of September, indeed I always expect one, summers last hurrah.

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3 hours ago, NewEra21 said:

Think it's fair to say the GFS 12z was a bit of a warm outlier in terms of 850s

IhNP1z1.png

At least it does seem to be more settled in the near term. First chart Suffolk for comparison then a snapshot down the spine; Berkshire, Leicestershire and Perth and Kinross. Very much as John said based on the 500mb anomaly charts:

13 hours ago, johnholmes said:

No signal for a late summer but a mix some days not unpleasant and a few not pleasant is a non meteorological summing up!

As it's peak hurricane season all subject to change. 

prcpSuffolk.png

prcpBerkshire.png

prcpLeicestershire.png

prcpPerth_and_Kinross.png

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Plenty of positive anomalies on the ECM ensembles by next weekend (4th September), though not conclusive yet

ec-ens_nat_z500scenarios_2020082700_192.

Back to unsettled by 11th September on the main clusters, but that's a very long way off

ec-ens_nat_z500scenarios_2020082700_360.

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9 minutes ago, Man With Beard said:

Plenty of positive anomalies on the ECM ensembles by next weekend (4th September), though not conclusive yet

ec-ens_nat_z500scenarios_2020082700_192.

Back to unsettled by 11th September on the main clusters, but that's a very long way off

ec-ens_nat_z500scenarios_2020082700_360.

Yes looking promising. From Windy.com and the ECM 00:00z for next Saturday, a very strong Scandi High Building next week and a link up with the Azores, so hopefully settling down as the week progresses 

image.thumb.png.6b37ee8ab92deca83d9e83dd468bc20d.png

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5 hours ago, Downburst said:

Yes looking promising. From Windy.com and the ECM 00:00z for next Saturday, a very strong Scandi High Building next week and a link up with the Azores, so hopefully settling down as the week progresses 

image.thumb.png.6b37ee8ab92deca83d9e83dd468bc20d.png

Entire North Atlantic filled with a huge trough in 8 days time.....

Enjoy the pleasant spell in between

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