Model Output Discussion

[Jezzer]

I'd agree PTFD, it's not looking too bad for a weeks time on the 06Z GFS

although that low pressure flirts across the north, bringing a band of rain across the country on Saturday. Obviously could change as the week progresses. Just hope the high makes it's presence felt

Edited August 10, 2009 by Jezzer

[Thundery wintry showers]

This week is still looking, at the very least, like a mixed bag to me. However, it does look like for south-eastern areas the only dull wet day will be Wednesday, with tomorrow and Thursday looking sunny and dry- today and Friday probably cloudy and dry. Further north a reasonably dry sunny window on Wednesday/Thursday and otherwise cloudy with drizzle.

This is the kind of week where personal preference comes in as I find this sort of dry but often cloudy weather yawn-inducing whereas many others love it.

The GFS has indeed downgraded that vicious low for the weekend but ECMWF keeps it going strong. In addition the GFS has been rather prone to overdoing those Azores ridges, so for now I say "I'll believe it when I see it" I'm afraid. If come midweek I'm still seeing that high over us on Monday and the ECMWF moves towards that scenario then I will probably start to believe it- but for now I urge some caution over it.

Edited August 10, 2009 by Thundery wintry showers

[BLAST FROM THE PAST]

Sorry BFTP, I've run through the models out to T180 and, (for what little jet there is), it's generally pretty amplified and generally no further south than 60°, which I wouldn't have thought is that remarkable ? And WRT to the depression progged for the back end of this week, 6z already starting the normal GFS process of reducing intensity of depressions as they get nearer. As Mushy has said above, not a bad week coming up (for much of Southern/Eastern UK anyway) and beyond that, all rather messy at present, so difficult to draw any real conclusions (as likely to be settled as autumnal, at least in my humble opinion).

Hi PTFD

I was rushing sorry. No I have touted mid month 15th onwards to see LPs affect the UK and be quite deep and of autumnal appearance [caveat not a succession of LPs]. ECM has shown this and is now intensifying said low over last couple of days. The jet weak and Amplified it is but well low latitude as that LP comes at us from SW midmonth. I will post chart that I think typifies my view.

http://212.100.247.145/ecmimages/20090810/00/ecmslp.144.png

BFTP

Edited August 10, 2009 by BLAST FROM THE PAST

[Pennine Ten Foot Drifts]

Hi PTFD

I was rushing sorry. No I have touted mid month 15th onwards to see LPs affect the UK and be quite deep and of autumnal appearance [caveat not a succession of LPs]. ECM has shown this and is now intensifying said low over last couple of days. The jet weak and Amplified it is but well low latitude as that LP comes at us from SW midmonth. I will post chart that I think typifies my view.

http://212.100.247.145/ecmimages/20090810/00/ecmslp.144.png

BFTP

Ah OK, and yes, ECM certainly keen on a 'hair ruffler' (!) for the beginning of next week, although, similar to GFS, it also wants to settle things down after this.

[mushymanrob]

well FI is back up to its old tricks, suggesting 'summer' (as in sun/heat) may make a return next week... although i am expecting a settled spell, im not so sure itll come just yet and september will i think be the settled month.

[Tucco]

GFS 12z going for a very wet spell in parts of the UK for later in the week and into the weekend. Still up the air, regarding the weeks end at this stage.

http://www.wetterzentrale.de/pics/Rtavn964.png

http://www.wetterzentrale.de/pics/Rtavn1264.png

http://www.wetterzentrale.de/pics/Rtavn1444.png

Mark

Teesdale,Co Durham

Edited August 10, 2009 by Tucco

[Jezzer]

Hrrmpphh! The GFS 12Z brings that pesky low into play, now looking a tad dodgy for this weekend!

[ANYWEATHER]

ERRR, gfs keeps showing that low for the end of the week ,the 06z shows it quickly replaced by high pressure, 12z shows the very unsettled weather continuing!!

[Jezzer]

ERRR, gfs keeps showing that low for the end of the week ,the 06z shows it quickly replaced by high pressure, 12z shows the very unsettled weather continuing!!

Weather watching is so frustrating, but also strangely addictive!

I'd hoped for some good weather this weekend as I'm spending the majority of it outside, not a happy chappy!

Anyone able to bring some positivity back?

Edited August 10, 2009 by Jezzer

[Eugene]

http://www.wetterzentrale.de/pics/Rtavn1441.png

Unfortunately a stalling feature now, thats all we need stalling low pressure systems after all the rain in July/early August, two or three settled days at a time does not maketh a summer i`m afraid.

[Bristawl Si]

Just spiffing!!

My wife and i are at my nephew's wedding all day Saturday. I, for one, hope there's a big backtrack on what the models are predicting for the coming weekend.

[Frosty.]

Not a bad GFS 12z considering, high pressure looks dominant in FI to the south and east of the uk perhaps holding off the atlantic depressions and sending them on a more north westerly track. There are signs of ex tropical storms making their way across the atlantic later this month but that is par for the course at this time of year. Closer timeframe shows thursday clearly being by far the best day of the week for widespread sunny weather thanks to a ridge but the bad news is that low pressure will be hot on it's heels for fri/sat/sun before a big improvement takes place during next week especially in the south & east with potentially very warm fine conditions but the north west looks like being more unsettled and less warm overall.

[Gavin P]

Given this week was supposed to be largely anticyclonic I would take any FI runs showing high pressure in control with a pinch of salt.

[Tucco]

Very unsettled ECM, potentially very wet and windy for the time of the year. Another low system appears to be on the cards.

http://www.wetterzentrale.de/pics/Recm961.gif

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

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

http://www.wetterzentrale.de/pics/Recm1681.gif

Mark

Teesdale,Co Durham

[evil monkey]

Looks like the jet-stream once again wants to spoil the party according to the GFS 12z run,

with the jet left exit intensifying the low pressure system as it approaches us on Friday.

The ensembles mostly have the pressure higher at that time so I think the timing of this

interaction is going to be crucial.

[Shiny_Bottom_1]

Interesting watch for Friday/Saturday.

I booked the day (Friday) off about 5-7 days ago, when the high pressure domination started showing.

By no means do I think the low pressure position is fixed, and Countryfile seemed to go for a fairly dry start to the day followed by some light rain later on (for Central and Southern England).

Expect some changes on the runs to come, but will be interesting watching verification.

[Glacier Point]

Longer range forecast discussion revolves around the potential reastablishment of an upper low in the eastern North Atlantic or close to the UK.

Total and relative angular momentum is slightly above average c/o convective forcing across the tropics of both hemispheres:

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

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

Outgoing long wave radiation anomalies show tropical convection centred in the central Indian Ocean, across the western Pacific, across much of the tropical Pacific and, interestingly, convection starting to show up around the dateline (180W):

http://www.bom.gov.a...m/OLR/m.3d.html

This recent forcing is indicative of a shift in the ocean-atmospheric process towards El Nino. This has shifted the Global Wind Oscillation towards phase 4/5:

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

Given convection and the dynamical processes outside of the tropics (torques and eddies), an orbit of the GWO into phase 4/5 should continue into the next week. Composites for GWO phase 4 are pretty consistent with numerical weather prediction models for the period t120 - t240:

(this composite may be slightly over-egging the deepness of the upper low)

Beyond this, an orbit of the GWO towards phase 5 seems plausible. Composites for phase 5 suggest the upper low to pull a little west allowing a pressure build from the south:

This is consistent with ensemble means for GFS and GEM @ t216:

http://www.cdc.noaa....m_f216_nhbg.gif

http://raleighwx.eas...nomalyNH216.gif

Beyond this, the GFS and NCEP ensemble mean suggest the MJO to shift towards phase 1 indicative of a negative tendency developing once more in the atmosphere (contrary to El Nino).

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

The 8-14 CPC outlook is along the lines of a shift in the GWO back towards phase 3-4 with upper low centred to our NW giving unsettled conditions for much of the UK, warmer and drier in the south-east:

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

Whether this negative shift will occur uncertain. Should we continue to see the impacts of tropical forcing move poleward, and the developing area of convection around the dateline grow, we could see the modelling pick up a signal for pressure to build from the south and extend further north. This remains a monitoring issue over the next few days to see whether the GFS is correct in the longer range.

[William of Walworth]

Just caught up after a beautiful weekend away in Dorset.

Mistrust of any HP dominated scenario shown in FI (ie after this coming weekend) seems to be the dominant theme of several recent postings. But given that the intensity of the threatened low this weekend might as easily be downgraded as intensified the nearer to this coming Friday and Saturday we get, then predicting whether summer will or won't make a marked return next week is at this stage a mug's game ....

Definitely don't write off a return of HP next week is what I say at this point ....

[chionomaniac]

Thanks for the update GP and well done for going green!

I thought over the last week that tropical convection that was growing around the dateline and pushing across the Pacific may give some coherent signal but convection has just gone flat since then (if you exclude cyclones!). This has left the MJO floundering in no mans land with no convective signal whatsoever. I know it is forecast to enter phase 1 which seems at odds with the GWO and the MJO H500 anomaly at odds with the phase 5 GWO composite you have posted. Is the subtle increase of AAM indicative of El Nino conditions slowly taking over? And in your experience do you think it is a difficult time to make accurate forecasts for a couple of weeks ahead?

cheers

c

[Glacier Point]

Thanks for the update GP and well done for going green!

I thought over the last week that tropical convection that was growing around the dateline and pushing across the Pacific may give some coherent signal but convection has just gone flat since then (if you exclude cyclones!). This has left the MJO floundering in no mans land with no convective signal whatsoever. I know it is forecast to enter phase 1 which seems at odds with the GWO and the MJO H500 anomaly at odds with the phase 5 GWO composite you have posted. Is the subtle increase of AAM indicative of El Nino conditions slowly taking over? And in your experience do you think it is a difficult time to make accurate forecasts for a couple of weeks ahead?

cheers

c

Thanks C.

Yes the phase 1 MJO projection is at odds with model outputs at the extended range although as we know, these MJO forecasts are pretty unreliable. It does make sense though given the warm SSTAs in the western Indian Ocean.

http://weather.unisys.com/surface/sst_anom.html

The position of tropical forcing is a dead-giveaway as to the state of El Nino. The stronger the Nino, the further east the centre of convection in the Pacific. One of the key inter-seasonal issues is where the signal is developing. I have a strong idea that we will see twin convective centres in the Indian Ocean and around or to the east of the dateline this autumn. For the time being though, until a strong convective signal breaks the dateline, I think we will continue to see the models playing around with different long range solutions.

[Gavin P]

I have a strong idea that we will see twin convective centres in the Indian Ocean and around or to the east of the dateline this autumn.

Hi GP

Generally, what would that mean for us this autumn?

[chionomaniac]

Thanks C.

Yes the phase 1 MJO projection is at odds with model outputs at the extended range although as we know, these MJO forecasts are pretty unreliable. It does make sense though given the warm SSTAs in the western Indian Ocean.

http://weather.unisys.com/surface/sst_anom.html

The position of tropical forcing is a dead-giveaway as to the state of El Nino. The stronger the Nino, the further east the centre of convection in the Pacific. One of the key inter-seasonal issues is where the signal is developing. I have a strong idea that we will see twin convective centres in the Indian Ocean and around or to the east of the dateline this autumn. For the time being though, until a strong convective signal breaks the dateline, I think we will continue to see the models playing around with different long range solutions.

Thanks again.

It does seem like a case of watching the tropical OLR for the coming weeks and looking for that coherent signal. Until it arrives I fear that the current pattern we are in will persist for a while longer.

[Glacier Point]

Hi GP

Generally, what would that mean for us this autumn?

I have a forecast nearly ready for issue although Netweather clients would get first call on this. Perhaps after its release Paul would authorise a video forecast sometime this month.

[Gavin P]

Oh, looking forward to it.

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

It look like there is more rain to come at the end of the week after a brief respite.