Model Output Discussion

[Eugene]

Looks like tonights fax will have fronts already moving in from the west at T+120 hrs, don't think many people will mention ECM tonight, GFS 12Z ensembles have excellent agreement on a one or two day plume before a rapid drop in 850`s with the atlantic rolling back in.

http://www.wetterzentrale.de/pics/Recm1201.gif

http://www.wetterzentrale.de/pics/Recm1441.gif

[PB22]

Still a fair degree of uncertainty about developments for next week, but it does look like the southeast will again become hot for a time as a southerly plume drifts north.

Certainly the week starts on a promising note with high pressure over or close to the country (note the differences at this stage though!)

http://www.wzkarten.de/pics/Rtavn961.html

http://www.wzkarten.de/pics/Rukm961.html

http://www.wzkarten.de/pics/Recm961.html

The warm/hot air really begins to move north by the midweek period:

http://www.wzkarten.de/pics/Rtavn1201.html

http://www.wzkarten.de/pics/Rukm1201.html

http://www.wzkarten.de/pics/Recm1201.html

And then there is the potential for thundery weather to move up from France by next Thursday:

http://www.wzkarten.de/pics/Rtavn1441.html

http://www.wzkarten.de/pics/Rukm1441.html

http://www.wzkarten.de/pics/Recm1441.html

Obviously, with the subtle differences between the models we do have to be careful, but certainly the trend is there for some hot weather in the southeast followed by thunder, before it turns unsettled again from the west across most parts. Of course, the north and west look set to remain cooler and more unsettled for much of the time, but even here Monday could be a half decent day depending on which model you believe. Time is running out now for Summer 2009 so expectations should be kept realistic for next week, but I see no reason at this stage why a potentially notable thundery outbreak can't occur later in the week.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

It's only an east-west split if you ignore Scotland

Technically, most of Scotland is west of the divide.

Edited August 14, 2009 by RAIN RAIN RAIN

[Frosty.]

well the 12z does support the 06z, largely settled throughout but never hot. the main thing is it should be mostly dry, suits me! .

early days yet, but tentetive signes of pattern change are looking slightly stronger.

Yes it looks like there are changes afoot, maybe even for the north of britain who have had a raw deal weatherwise since early July, we don't all live in the micro climate bubble of southern england. High Pressure for the last 10-12 days of August would salvage something from the poor july and first half of august in the north and north west.

[ANYWEATHER]

My thoughts on the next seven days is probably similar to the last seven days in terms of temps, warmest in the southeast, both ecm and gfs have got "something" of a thundery plume for next week, but as always it probably wont happen! Unsettled sums it up really , southeast best/northwest uk most unsettled..the "SeeSaw Summer" continues!

[damianslaw]

This rather tedious though admittedly very typical spell of weather and synoptics i.e. the NW - SE text book split goes on.. its a pattern us in the NW get preety quickly hacked off with but also know all too well..

Can't see high pressure building to influence the whole country just yet, signs of one of those southerly plumes developing next week, so for those in the SE the relatively good spell of summer weather continues, for us in the NW its a case of bracing ourselves for more of the mild mucky cloudy dismal stuff courtesy of the atlantic and that damned W/SW airflow..

[Bottesford]

Sure it may be dull & unexciting but at least it isn't raining. After July I think many of us will appreciate more benign weather. Bar the tomatoes I know my plants will - chilli plants don't like being waterlogged! I'm not a fan of dry, cloudy weather either but I'm more of a fan of it than wet & cloudy!

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

East - West split Mk II

[Thundery wintry showers]

Sure it may be dull & unexciting but at least it isn't raining.

Therein lies Damienslaw's problem - for him, it is raining, and will be doing so quite a bit in the near future! From the dry but fairly cloudy SE, I can say that I might well be the only member of the forum from the drier south who found July's weather more enjoyable than that of the last two weeks, but on the other hand, the last two weeks haven't been terrible by any means- just average.

For central southern and eastern areas, next week is looking increasingly likely to provide rather more interest than we've seen for a while. Tuesday and Wednesday both now look like being dry, sunny and increasingly hot- it could reach 30C locally unless there is a substantial downgrade (which is possible, but the models are definitely moving in the "plume" direction at the moment). I don't see there being much in the way of cloud about away from northern and western Britain. It will indeed be short-lived, but what follows afterwards is anyone's guess, and high pressure is one of the possible outcomes, depending on whether the slow down of the jet is only temporary or the lead up to a more blocked spell of weather.

[mushymanrob]

The last 10 days has been pretty good, mainly dry with a lot of bright or sunny weather, not boiling but decent temps. So I totally agree with you.

As for the summer as a whole Late May and much of June was decent, July was atrocious and August has been good.

'pretty good'?... not here in derby it hasnt! true we have enjoyed a few nice days this week but so far august has been plagued yet again by rain, often heavy (remember that troublesome cold front straggling the country last week? ) so far id rate august as slightly better then july but still atm below average.

Looks like tonights fax will have fronts already moving in from the west at T+120 hrs, don't think many people will mention ECM tonight, GFS 12Z ensembles have excellent agreement on a one or two day plume before a rapid drop in 850`s with the atlantic rolling back in.

...but that was always the case, the high pressure was always progged as transitory with a breakdown late wed/early thurs.

the big question is what happens next? ridging high (as per gfs) or flatter atlantic (suggested by the ecm)

Sure it may be dull & unexciting but at least it isn't raining. After July I think many of us will appreciate more benign weather. Bar the tomatoes I know my plants will - chilli plants don't like being waterlogged! I'm not a fan of dry, cloudy weather either but I'm more of a fan of it than wet & cloudy!

couldnt agree with you more!

[Frosty.]

All the main 00z models show a weak high building northwards early next week and then moving east, with low pressure to the west we will see a very warm & increasingly humid southerly airflow pumping northwards across the south and east of england mostly. Midweek will be best with hot sunshine for SE Britain but it won't last, northern and western areas will see very little or nothing of this good weather and will be generally more unsettled throughout (much as the last six weeks). a thundery breakdown then follows with slightly cooler and fresher air arriving but then pressure once again starts to build from the south with perhaps a repeat performance the following week, the only real difference being that more of the uk might share the high temps and sunshine during w/c 24th August. The GFS 00z then ends the month with a much stronger and better orientated Anticyclone.

[Glacier Point]

As we head into the end of August, the weather-climate system looks to be getting very dynamic. This is not an endorsement of a sustained blocked period however and I would favour an unsettled picture beyond next weekend, possibly a little after this into the following week.

Satellite imagery suggests a large slab of the equatorial atmosphere being shifted westwards across the western Pacific. This is indicative of tendency in earth angular momentum becoming negative.

http://www.cdc.noaa....teaam.90day.gif

This is also a strong signal for deep tropical convection to be initiated over the western Indian Ocean as strong westerly winds over Africa and west Indian Ocean converge over warm seas. MJO forecasts depict this convection programming a high amplitude wave to develop in octant 1:

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

Up until now, the northern hemisphere pattern has been driven by the global wind oscillation in the absence of any coherent tropical steer and a still deeply engrained -PDO pattern. Changes are afoot though as dynamical processes in the tropics and extratropics are starting to remove westerly winds from the system bringing the MJO and GWO closer together - although perhaps the GWO likely to be lagging behind the MJO a little.

http://www.cdc.noaa....ltaum.90day.gif

http://www.cdc.noaa....ltauf.90day.gif

This is resulting in a downward tendency in angular momentum, most evident over the tropics and across 40N:

http://www.cdc.noaa....d.sig.90day.gif

.... which is now starting to show up in total and relative angular momentum:

http://www.cdc.noaa....m.sig.90day.gif

http://www.cdc.noaa....g1-21.90day.gif

If as anticipated the GWO responds by shifting downwards, I think we are heading towards a spell within phase 8.

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

Composites for this phase are a little unclear although the MJO composite (phase 8 rather than 1 due to the GWO) looks to be the best indicator here:

This suggests something of a negatively tilted jet and trough extending across the UK from the NW. Last nights CPC 8-14 day looks about right:

http://www.cpc.ncep....y/814day.03.gif

Looking ahead, these changes in the atmosphere are significant as they will begin to initiate the next phase of tropical convection which could have seasonal ramifications with a strong MJO wave helping to drive an interesting September.

Edited August 15, 2009 by Glacier Point

[ANYWEATHER]

Of course, to add into the equation we now have extropical storms to contend with, ecm picks this one out and quite a bit of activity in the tropical Atlantic at the moment,which makes the models turn into a frenzy, so a lot more in the way of hiccupps perhaps as we move into the next few weeks with big changes in small timeframes from the models :excl: :lol:

[Gavin P]

Looking ahead, these changes in the atmosphere are significant as they will begin to initiate the next phase of tropical convection which could have seasonal ramifications with a strong MJO wave helping to drive an interesting September.

Interesting as in....?

[Terminal Moraine]

Interesting as in....?

Just what I was thinking. My 'interesting' tends not to be the same as most other people on here.

[Terminal Moraine]

Just had a scan through the GFS 06z and seen charts to make me weep tears of pure joy around August 29th.

If only it wasn't so far away.

Overall a more unsettled look than the 00z once the warm spell in mid week has passed and even this offers up the potential for some heavy thundery rain as it is displaced eastward later on Thursday and into Friday morning.

[The PIT]

Looking like our weather with the odd light shower here will continue into next week although it'll become dry altogtehr. Should get rather hot as well which is bad news. Screaming kids and having to keep the windows open isn't very good. Looking at the GFS it suggests we may get an above average month temp wise and a outside chance of a dry one as well. Very unlikely that we'll see a record wet summer. 100mm needed from here on in to get that.

As for the tropical storms expect some bizzare runs from the Models.

[Frosty.]

Just another possible scenario from the GFS 06z with deepish low pressure steaming in by the 24th when the 00z showed high pressure building north in the same timeframe. Which will be correct is another question, it's a bit of a lottery really although I would probably still favour another pressure rise similar to the coming week.

Edited August 15, 2009 by Frosty039

[chionomaniac]

As we head into the end of August, the weather-climate system looks to be getting very dynamic. This is not an endorsement of a sustained blocked period however and I would favour an unsettled picture beyond next weekend, possibly a little after this into the following week.

Satellite imagery suggests a large slab of the equatorial atmosphere being shifted westwards across the western Pacific. This is indicative of tendency in earth angular momentum becoming negative.

Looking ahead, these changes in the atmosphere are significant as they will begin to initiate the next phase of tropical convection which could have seasonal ramifications with a strong MJO wave helping to drive an interesting September.

I too wonder what the interesting September will bring. Certainly one can see the recent increase in NH westerlies at the jet stream level from the latest average wind troposphere/strat profile

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_UGRD_MEAN_JAS_NH_2009.gif

Now, if these westerly wind anomalies are removed leading to a reduced westerly flow and the GWO becomes negative, will there be more chance of a blocking type pattern for September or am I reading the signals wrong, GP? Certainly the 500hPa anomaly composites lean this way.

c

[Glacier Point]

I too wonder what the interesting September will bring. Certainly one can see the recent increase in NH westerlies at the jet stream level from the latest average wind troposphere/strat profile

http://www.cpc.ncep....JAS_NH_2009.gif

Now, if these westerly wind anomalies are removed leading to a reduced westerly flow and the GWO becomes negative, will there be more chance of a blocking type pattern for September or am I reading the signals wrong, GP? Certainly the 500hPa anomaly composites lean this way.

c

Those westerlies over the polar field should help to mitigate any massive fall in the GWO keeping total angular momentum close to average - it's worth noting though that a lot of the MJO composites for phases 1,2,3, 7, 8 have a negative height anomaly over Greenland, as do the seasonal composites I'm working with. The ongoing solar minima should see the polar atmosphere cool quite readily under this regime which will prohibit any high latitude blocking for some time - probably until November now.

In essence, I'm thinking very unsettled for early part of September into mid month, followed by a notable anticyclone forming over NW Europe towards the final third of the month tied into an active MJO wave. So from a weather point of view maybe not that excitig but very involved if you're into tropical forcing and the ocean-atmosphere dynamic.

Current OLR plots do suggest multiple areas of convection starting to show up axcross the equator and tropics.

http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/m.3d.html

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

This would be interesting...

[ANYWEATHER]

This would be interesting...

It would be, some nice thundery activity in that setup I would expect....but the chances of that happening ...... :lol:

[SteveB]

That is slap bang over my area, It would be nice but unlikely.

[William of Walworth]

So many possibilities!

All I selfishly care about is how the weather in Devon will look Friday 21st to Sunday 23rd ....

Monitoring, but daren't commit myself to any firm prediction ....

[Shiny_Bottom_1]

This would be interesting...

...it would, if it wasn't the worlds largest outlier