Model Output Discussion 26/08/2012

[Gavin P]

Hi all,

Here's todays model based video: Rapidly Alternating Airmasses Heralds The Arrival Of Autumn; http://www.gavsweathervids.com

I mention ex-hurricane Lee a couple of times, but I mean Hurricane Kirk - My little "helper" was distracting me.

Sorry about that.

Edited August 30, 2012 by Gavin P

[Summer Sun]

Well out in FI but if it came off it would be the first storm of Autumn

[Frosty.]

Yes summer sun that's one nasty looking depression and I think something similar to that is highly likely once the anticyclonic spell ends which will herald autumn's arrival. As for the latest weather, there is going to be a very chilly night ahead in rural areas where temps could dip to 4 or 5c so it will be a cold start tomorrow but then a fine day in most areas except for scotland where a spell of rain will move from west to east, light and patchy but heavier and more persistent across northern scotland, then more rain across the far north of the uk on saturday but fine further south, a weakening front pushing south on saturday night with patchy rain fizzling out then sunday a fairly sunny day once residual cloud breaks up, then more rain in the north on monday but fine further south.

Edited August 30, 2012 by Frosty039

[Summer Sun]

The storm showing for around the 11th september has been removed from the 12z

06z

12z

Edited August 30, 2012 by Summer Sun

[AWD]

The storm showing for around the 11th september has been removed from the 12z

06z

12z

The models will flip and flop like that for many days yet, undecided on which track any TD's from the States take. You'll probably find a selection of further model runs will put it back there.

As some knowledgable members have said, this time of year, with storms/hurricanes being ejected east from the Eastern Seaboard, model output from 7 days + will significantly chop and change!

What is more reliable, is a settled opening week to 10 days of Sept, over most of the UK, although a little more cloud and drizzle at times the further North you go!

[Polar Maritime]

Some cool 850s pushing South tonight. Most places hovering just above freezing in the North away from towns and citys, with frost's in the Glen's and valleys.

Edited August 30, 2012 by Polar Maritime

[Methuselah]

It looks like 'Scottish Glen' is in for a cold one tonight, then?

[Gibby]

Good evening. Here is tonight’s look at the 12zs of the big three.

All models continue to agree on the synoptic pattern between now and Tuesday. High pressure is developing down to the SW with a ridge moving into Western areas overnight and across other areas tomorrow. The weekend and start of next week sees the basic pattern of High pressure to the South and Low to the North remain with the caveats of a couple of weak fronts moving SE over all areas Sunday and again Tuesday. The North will see further rain at times over this period while Southern areas see a lot of cloud at times with Saturday and Monday the brightest days while cloudier conditions here on Sunday and Tuesday could prove to be thick enough to produce a little rain. Temperatures will rise steadily in the South over the period.

GFS then shows High pressure building over the UK following Tuesdays’ front to give the UK a couple of warm and potentially sunny days. By the end of next week the Status Quo of the North/South split returns with more unsettled conditions in the North while the South hangs on to dry and bright weather. Through FI which takes us into week 2 a more unsettled pattern develops for all as the Atlantic ramps up with Low pressures moving East into Northern Britain with rain and strong winds for all by then.

The GFS Ensembles keep the warm up to a period between the 1^st and 5^th before uppers fall back to near normal levels. Thereafter the ensembles are fairly uneventful with rainfall amounts unremarkable with a fair amount of dry weather for all at times. The Control run was a warm outlier at the end.

The Jet Stream Forecast shows the flow ridging North through the Atlantic currently to eventually settle in a position between Scotland and Iceland for most of next week.

UKMO at Noon next Wednesday shows High pressure close to SW Britain with a NW flow blowing down over the UK. Away from the far NE where a few showers could occur most areas will be dry and bright with temperatures near normal.

ECM at noon next Wednesday shows the High pressure centre slightly further North than UKMO centring it off Western Ireland. Over the following 48hrs it moves East across the UK so with light winds affecting all of Britain fine and increasingly warm and sunny conditions predominate by day with chilly nights leading to early morning mist and fog patches. Towards the end of the run the High is shown to relax slowly South while maintaining fine and warm conditions for Southern areas. The North sees the threat from Atlantic fronts return with a little rain.

In Summary tonight’s output is a much improved outlook on what we’ve become accustomed too. It’s a High pressure dominated set of runs in the reliable timeframe tonight with just the position of the High centre making fundamental differences on the day to day weather up and down the UK. All areas should see at least some pleasant warm and settled early Autumn weather and this looks like it could become prolonged in the South. GFS does show us collapsing into Autumn in FI but the closing FI charts of ECM don’t support this.

Edited August 30, 2012 by Gibby

[Summer Sun]

In Summary tonight’s output is a much improved outlook on what we’ve become accustomed too. It’s a High pressure dominated set of runs in the reliable timeframe tonight with just the position of the High centre making fundamental differences on the day to day weather up and down the UK. All areas should see at least some pleasant warm and settled early Autumn weather and this looks like it could become prolonged in the South. GFS does show us collapsing into Autumn in FI but the closing FI charts of ECM don’t support this.

Thanks GIBBY some lovely weather coming up then after the wettest summer in 100 years I wonder what the odds are on the driest Autumn in ... years

The one good thing is the days are more than long enough to enjoy the sun and warmth

[Gavin Hannah]

You have to go back to 2008 before you see the last time the first 10 days of September were colder than average. This will make it 4 in a row where the start of September has had a decent warm spell.

2008 was actually the coldest Autumn on record since 1993.

2011 was 2.1deg above the 71 - 2000 Average. All the recent Autumns though had close to 100% average precipitation or above.

http://www.metoffice....uk/climate/uk/

Edited August 30, 2012 by IBringTheHammer

[Glacier Point]

Four tropical systems on the go in the Northern Hemisphere (arguably the now dispersed super typhoons Tembin and Bolaven were more influential here) and angular momentum is responding.

Tendency in relative angular momentum is surging positive (increasing westerly influence) - note the increase in westerly winds across 30S and 30N:

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

CPC have noted tonight growing ensemble mean agreement in the 6-10 and 8-14 day timeframes and this follows the ECM's lead from this morning and 06z and 12z GFS ensemble means beyond day 10 begin to develop anomalously low heights over the Arctic. Net result, increasing trend for mid latitude highs as tropical depressions get hoovered up by longwave troughs migrating through the mid-west and eastern Canada.

Edited August 30, 2012 by Glacier Point

[Gavin Hannah]

Four tropical systems on the go and angular momentum is responding.

Tendency in relative angular momentum is surging positive (increasing westerly influence) - note the increase in westerly winds across 30S and 30N:

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

CPC have noted tonight growing ensemble mean agreement in the 6-10 and 8-14 day timeframes and this follows the ECM's lead from this morning and 06z and 12z GFS ensemble means beyond day 10 begin to develop anomalously low heights over the Arctic. Net result, increasing trend for mid latitude highs as tropical depressions get hoovered up by longwave troughs migrating through the mid-west and eastern Canada.

Trying to get an idea of what that means for us?? More settled weather?

[Glacier Point]

Correct

[ICETAB]

Four tropical systems on the go and angular momentum is responding.

Tendency in relative angular momentum is surging positive (increasing westerly influence) - note the increase in westerly winds across 30S and 30N:

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

CPC have noted tonight growing ensemble mean agreement in the 6-10 and 8-14 day timeframes and this follows the ECM's lead from this morning and 06z and 12z GFS ensemble means beyond day 10 begin to develop anomalously low heights over the Arctic. Net result, increasing trend for mid latitude highs as tropical depressions get hoovered up by longwave troughs migrating through the mid-west and eastern Canada.

Do you expect angular momentum to remain positive as we go into winter? Will you be publishing a forecast soon?

[Alex]

Four tropical systems on the go and angular momentum is responding.

Tendency in relative angular momentum is surging positive (increasing westerly influence) - note the increase in westerly winds across 30S and 30N:

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

CPC have noted tonight growing ensemble mean agreement in the 6-10 and 8-14 day timeframes and this follows the ECM's lead from this morning and 06z and 12z GFS ensemble means beyond day 10 begin to develop anomalously low heights over the Arctic. Net result, increasing trend for mid latitude highs as tropical depressions get hoovered up by longwave troughs migrating through the mid-west and eastern Canada.

Yes I have noticed this in the last few days, trying to establish why for another year running we have a surge in angular momentum in September, coincidence or something else? Just wish July could of incorporated the positive levels forcing larger shift in our summer patterns.

[phil nw.]

Certainly a more Anticyclonic and settled outlook as we enter the first week of September especially for England and Wales.

I don`t think it`s plain sailing for more northern areas further on though with uncertainty over how far north the core of the Azores heights will extend towards week 2.

ECM seems more inclined to push the heights further north both on the means and op runs than the GFS at this distance.

The CPC mean height anomol. still favour a flat looking AH

http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif

leaving northern areas under that Atlantic westerly flow.

Not cut and dried beyond week 1 with these subtle differences showing.

[damianslaw]

Models continue to suggest the azores high will be the major influence on our weather in the coming days, trying to muscle NE into the country but not quite making it, meaning northern regions will see much more cloud and windy weather and the country as a whole will remain exposed to atlantic albeit weak attacks. So a pleasant start to September looks on the cards, with plenty of dry fine weather with temperatures above average by day but possibly quite cool at night preventing a particularly warm start.

Longer term - difficult to call, ex tropical storms will be a key factor, if they move up the eastern seaboard of USA then this will help to build mid atlantic heights, but conversely this leaves us exposed to chilly northerly blasts and eventually the remnants of the storms as they track into Greenland, however, if these storms become sluggish affairs then we may well see heights building into the country more which would mean some decent sunny warm weather.

[bluearmy]

Certainly a more Anticyclonic and settled outlook as we enter the first week of September especially for England and Wales.

I don`t think it`s plain sailing for more northern areas further on though with uncertainty over how far north the core of the Azores heights will extend towards week 2.

ECM seems more inclined to push the heights further north both on the means and op runs than the GFS at this distance.

The CPC mean height anomol. still favour a flat looking AH

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

leaving northern areas under that Atlantic westerly flow.

Not cut and dried beyond week 1 with these subtle differences showing.

not greatly impressed with cpc this past week phil. too much variation day to day for my liking. i await 2 days with similar looking output before having any confidence in week 2 modelling.

[snowfluff]

Do you expect angular momentum to remain positive as we go into winter? Will you be publishing a forecast soon?

It has been the wettest summer on record,who got anywhere near forecasting that?

7 to 14 days is the max with what science we have at our disposal, next week looking settled further south according to the models,as we slip into autumn

[Jason T]

It has been the wettest summer on record,who got anywhere near forecasting that?

7 to 14 days is the max with what science we have at our disposal, next week looking settled further south according to the models,as we slip into autumn

No one i doubt,However whats to say this type of pattern evolved prior to records taken.? As you say science at our disposal to which only can go back as far as records recorded. The golden egg really...If only we knew.

[Glacier Point]

Yes I have noticed this in the last few days, trying to establish why for another year running we have a surge in angular momentum in September, coincidence or something else? Just wish July could of incorporated the positive levels forcing larger shift in our summer patterns.

The last few years have seen very cold stratospheric temperatures persist well into the summer, both over the Arctic and more particularly over theTropics, and the last few polar springs have seen sharp downwelling of easterly zonal wind anomalies / blocking at high latitudes (warmer air at the surface layers). It's no coincidence that period has also seen record low levels in sea ice. The stratospheric temperatures I think have been a major driver in effectively killing tropical activity until well into the summer, by which time we get going and make up ground hand over fist with the net result that tendency in relative angular momentum is largely positive as the equilibrium attempts to rebalance.

Will it last into the winter ? Technically with a weakish El Nino and an atmospheric profile that should be cooperative, potentially so, which can only be a good thing if your're loooking at the ingredients for high latitude blocking.

...and just to tag this on, NAEFS 12z just sniffing a reloading Atlantic trough into week 3..very plausible given where we're heading angular momentum wise in the next week (large scale shifting between sharp increase, decrease then increase)

Edited August 30, 2012 by Glacier Point

[Milhouse]

ECM looks very good throughout with settled conditions persisting out to day 10. Only downside is the close proximity of the low passing on Tuesday and the cooler northwesterly associated with it on Wednesday. Apart from that its looking pleasantly warm, perhaps very warm in the south at times.

[Thundery wintry showers]

Good to see Gibby's summaries come back- some really good ones over the last few days.

Tomorrow may well turn out to be unseasonably cool over most of Scotland with the rain band pushing in from the west. Most eastern and southern parts of England should get a dry sunny day, but cloud will thicken from the west, and some light drizzle is likely to move into NW England and north Wales as well as most of Scotland and Ireland.

The weekend is looking mostly dry and cloudy thanks to the westerly flow on the northern flank of the high pressure, but there will probably be some sunny intervals about in central and eastern England and where the sun does come out for a significant length of time, highs of 21-23C are probable.

It's looking like one of those occasions where the first attempt at high pressure ridging brings a relatively cloudy westerly on the first attempt but then the high builds right on top of us at the second attempt- the GFS and ECMWF are unanimous in showing a dry sunny regime following a brief polar maritime incursion on Wednesday and the UKMO looks like evolving the same way- but how long it will last is open to question.

[Geordiesnow]

Tomorrow may well turn out to be unseasonably cool over most of Scotland with the rain band pushing in from the west. Most eastern and southern parts of England should get a dry sunny day, but cloud will thicken from the west, and some light drizzle is likely to move into NW England and north Wales as well as most of Scotland and Ireland.

It will be interesting how cool it will be across Northern parts as I feel the Met Office are overcooking the temps and in the end we may see temps struggling to reach 10-12C as the cloud cover will be coming across cooler upper air and cool air at the surface and coupled with the rainfall bringing those cooler uppers down. Could be a case where the highest temperatures won't occur until the evening time as much milder air does make it way in.

No real signs of Autumnal weather, infact for those further south and east, its going to feel like summer especially in any sunshine where it could feel quite warm and humid. There has been a small trend for the Azores high to ridge in a bit more for Sunday in the last few runs which may encourage the weather front in the South to weaken quicker and for Sunday to be brighter across Southern areas. It may also limit even more any showers getting into the far NW.

Whilst its not a completely dry set up, its a weather pattern which is more normal for this time of year and especially in September, PV starting to form, heights and temperatures start to fall over the Arctic and for pressure to be generally high across out neck of the woods. Be interesting if this September continues that trend.

[Scorcher]

The GFS 18z is a really good one for those wanting dry, settled conditions. Monday is looking warmer now if this run is to be believed with 24-26C probably being reached quite widely across England and still a warm 18-22C across Scotland. High pressure is in control right into FI on this run which is something we haven't seen recently with the GFS. It also sets up to our east in the latter part of the week which would allow temperatures to rise again. Deep in FI it shows a Spanish plume with a rather nasty looking depression following on after this.