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In Depth Model Discussion, Analysis and Summaries


Paul

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Posted
  • Location: Addlestone, Surrey
  • Weather Preferences: Warm sunny Summer days and deep snow in Winter with everything in between
  • Location: Addlestone, Surrey

Easiest way to explain this, is if you imagine a low over Iceland, and a high over the Azores, the high pressure is essentially being pushed eastward by the Jet Streak between them, whereas because we have a low further west, in the Central Atlantic, what we see is the low pressure acting as a vaccum to pull the high pressure system back, over the top so that the low can undercut it.

That makes perfect sense, thanks summer blizzard, I wasn't taking the low in the Atlantic into account rolleyes.gif

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Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

That makes perfect sense, thanks summer blizzard, I wasn't taking the low in the Atlantic into account rolleyes.gif

Glad i could be of assistance.

Low pressure will always try to get in front of the high pressure downstream from it, the only way it can do that is to get underneath (undercut), because if it is above it, the high just moves east.

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  • 2 weeks later...
Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

It’s a long time since I did a LRF and where I used to post them seems to have gone off the site so I’ll drop it in the technical discussion but fear not its written and explained in reasonably simple detail.

see the pdf file below

lrf on friday 28 may 2010 for june 2010.pdf

Edited by johnholmes
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It’s a long time since I did a LRF and where I used to post them seems to

have gone off the site so I’ll drop it in the technical discussion but fear not

its written and explained in reasonably simple detail.

see the pdf file below

lrf on friday 28 may 2010 for june 2010.pdf

Excellent as ever John, I have started doing my Glasto forecast, what would be your current take on the likely weather for around the 23-27 June, as the current CFS models tends be rather on the unsettled side, would you go along with this or stick the average theme for June as pinpointed in your summary.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

mm, that is hard to call really Julian.

I suspect the further west one is then the more likely you are to have some thundery bursts but even the east is likely to have that at times.

Trying to be specific this far out is not possible I don't think.

Overall its looking like having temperatures above the late June average, muggy perhaps, and no sign of persistent weather systems rattling in.

Predicting just when rain will fall is probably not possible until about 10 days away?

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Posted
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield
  • Weather Preferences: Any Extreme
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield

mm, that is hard to call really Julian.

I suspect the further west one is then the more likely you are to have some thundery bursts but even the east is likely to have that at times.

Trying to be specific this far out is not possible I don't think.

Overall its looking like having temperatures above the late June average, muggy perhaps, and no sign of persistent weather systems rattling in.

Predicting just when rain will fall is probably not possible until about 10 days away?

So John we maybe continuing our settled unsettled spell then. looks like I may have to revise my cet guess for June though ....

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Posted
  • Location: Longden, Shropshire
  • Location: Longden, Shropshire

It’s a long time since I did a LRF and where I used to post them seems to have gone off the site so I’ll drop it in the technical discussion but fear not its written and explained in reasonably simple detail.

see the pdf file below

lrf on friday 28 may 2010 for june 2010.pdf

Thanks John. An interesting read as always.

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Posted
  • Location: Worcestershire
  • Weather Preferences: Forecaster Centaurea Weather
  • Location: Worcestershire

Really nice example of how tropical influences are impacting the hemispheric weather pattern.

Look at the storm track (cloud) in the western Pacific extending north-west from the tropics. Outgoing longwave radiation anomalies depict this nicely. Note also there is a similar flow in the Atlantic.

Now look at the weather satellite imagery which shows a large slab of the tropical atmosphere in the central / western Pacific moving eastwards tied into a renewed trade wind surge.

http://wxweb.meteost.../WV/&NUMBLOOP=9

What this is doing is increasing poleward fluxing and driving a strong negative frictional torque along 20N - 30N which is interacting with the westerly flow on the poleward side. You can clearly see how the fluxing of energy is causing the Pacific Jet to become amplified with a series of large wavelength disturbances working their way across North America.

Should this process continue, the Pacific Jet will become increasingly amplified as a negative (easterly) wind tendency becomes dominant and a large anticyclone develops in the Pacific above 30N. The downstream ramifications of this would largely be a mid-Atlantic ridge.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

No major reason to update what I issued last Friday I feel. There could be a more NW-SE split with a consequent lowering of temperatures for the NW’ern half later in the month but no major synoptic changes beyond that. There is no indication to me of rainfall being much different to normal in any part, no sign of any major Atlantic low with consequent strong winds. Temperatures as suggested in the second sentence. Otherwise the issue on 28 May or thereabouts seems okay.

see post 279 above for the original post

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Posted
  • Location: Formerly Walworth, SE17 ; Swansea SA1 since Dec 2008
  • Location: Formerly Walworth, SE17 ; Swansea SA1 since Dec 2008

Thanks John. An interesting read as always.

Yes,very interesting and reasonably? hopeful too for CHANCES of a not too bad late June in the South at least .... but we remain in the completely uncertain zone for now as JACKONE's latest Glastonbuty blog with its range of possibilities including wet, can only confirm ...

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Posted
  • Location: Exeter, Devon, UK. alt 10m asl
  • Location: Exeter, Devon, UK. alt 10m asl

It will be interesting to see a wind rose diagram based on data since mid December. I suspect the quadrant from west to south will be pretty small.

Not really for central uk and a couple of months behind but it does seem to confirm your suspicion.

http://www.northisles-weather.co.uk/weather/windrose.html

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Posted
  • Location: Worcestershire
  • Weather Preferences: Forecaster Centaurea Weather
  • Location: Worcestershire

Global models are showing exactly what we would expect given the atmospheric setup and we can have reasonable confidence in the extended range forecast.

Surface wind data in the Pacific shows a wall of easterly winds extending across large parts of the central and eastern tropics. Tropical convection (cloudiness) is firmly centred in the Indian Ocean:

http://cimss.ssec.wi...s/wavetrkP.html

Forecasts for the MJO are to be expected - showing the tropical wave to hit the easterly trades and becoming 'stuck':

http://www.cpc.ncep...._CFSOP_GEFS.gif

This will have important implications for the global circulation, effectively preventing any large scale and sustained westerly wind increase and holding angular momentum down.

The Global Wind Oscillation (which measures the tropical and extratropical component) is centred in phase 2/3:

http://www.esrl.noaa...gcm/gwo_40d.gif

Frictional and mountian torques are trying to add westerly winds to the system outside of the tropics. This augers for a strong phase 4 projection in the next 7-10 days. Composites for June and July are consistent in advetising a notable ridge in the north-east Pacific and mid Atlantic ridge.

Now looking at the GFS and ECM ensemble mean height anomaly at t240:

http://raleighwx.eas...nomalyNH240.gif

http://raleighwx.eas...nomalyNH240.gif

Excellent cross model agreement and agreement with the Global Wind Oscillation composites.

Edited by Glacier Point
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Posted
  • Location: York
  • Weather Preferences: Long warm summer evenings. Cold frosty sunny winter days.
  • Location: York

Global models are showing exactly what we would expect given the atmospheric setup and we can have reasonable confidence in the extended range forecast.

Surface wind data in the Pacific shows a wall of easterly winds extending across large parts of the central and eastern tropics. Tropical convection (cloudiness) is firmly centred in the Indian Ocean:

http://cimss.ssec.wi...s/wavetrkP.html

Forecasts for the MJO are to be expected - showing the tropical wave to hit the easterly trades and becoming 'stuck':

http://www.cpc.ncep...._CFSOP_GEFS.gif

This will have important implications for the global circulation, effectively preventing any large scale and sustained westerly wind increase and holding angular momentum down.

The Global Wind Oscillation (which measures the tropical and extratropical component) is centred in phase 2/3:

http://www.esrl.noaa...gcm/gwo_40d.gif

Frictional and mountian torques are trying to add westerly winds to the system outside of the tropics. This augers for a strong phase 4 projection in the next 7-10 days. Composites for June and July are consistent in advetising a notable ridge in the north-east Pacific and mid Atlantic ridge.

Now looking at the GFS and ECM ensemble mean height anomaly at t240:

http://raleighwx.eas...nomalyNH240.gif

GP does this mean that going forward over the rest of June and into july we can expectmuch of the same ie spells of pleasant sun (not hot) with cooler interludes of showery weather typical of my youth in the 60's

http://raleighwx.eas...nomalyNH240.gif

Excellent cross model agreement and agreement with the Global Wind Oscillation composites.

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Posted
  • Location: Orleton, 6 miles south of Ludlow
  • Location: Orleton, 6 miles south of Ludlow

GP thanks for all of your hard work that goes into your updates — I appreciate it. Does your analysis above mean that we can expect more Atlantic ridging through to the end of June and possibly, beyond, and therefore coolish, dry weather?

Edited by picog
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

Jonboy?

can you explain why you simply repeated the excellent GP summary with no comment please?

Edited by johnholmes
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Posted
  • Location: W. Northants
  • Location: W. Northants

Jonboy?

can you explain why you simply repeated the excellent GP summary with no comment please?

I can see whats happened.

This was "Jonboy's" post

GP does this mean that going forward over the rest of June and into july we can expectmuch of the same ie spells of pleasant sun (not hot) with cooler interludes of showery weather typical of my youth in the 60's

Which got mixed when up he quoted GP's post.

Edited by Gavin P
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

thanks for that Gavin-I did not look close enough-slap on wrist

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thanks for that Gavin-I did not look close enough-slap on wrist

lol john.

Beautiful sunny day here on the WYorks border.Looking nice for the rest of the week.At face value May and the first half of June have been lovely this year.With a strengthening La Nina on the horizon would it be fair to say the 2nd half of summer might not hold as

much promise as the 1st half?

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Jonboy's post now amended to read how it should have.

With Glastonbury now starting to get into the reliable weather time frame, what chances of the High Pressure managing to last through next week, and my summations that SW areas may escape the worst of the Western if winds do come from the NE are suggested by some models over the past couple of days.

Thoughts welcome here and in the Glastonbury thread.

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Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

lol john.

Beautiful sunny day here on the WYorks border.Looking nice for the rest of the week.At face value May and the first half of June have been lovely this year.With a strengthening La Nina on the horizon would it be fair to say the 2nd half of summer might not hold as

much promise as the 1st half?

La Nina won't take hold until at least Autumn, we are barely out of weak El Nino territory.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

I'll drop my ideas in here for late June into July later this week.

In the meantime in the pdf is the first of 6 checks with GFS and ECMWF on how good either of them are at providing forecast guidance for 10 days ahead.

comment into Net Wx so far 16 June 2010.pdf

Edited by johnholmes
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