Model Output Discussion - Autumn 2018

[Man With Beard]

Interesting outlier on the clusters (bottom left, 13%) showing enough retrogression for a northerly plunge, but on the whole the settled picture set to continue, different temperature possibilities depending on the positioning of Atlantic trough - cluster 1 could still be warm if the flow originates in the Med

 

[mb018538]

1 hour ago, Interitus said:

The active spell of weather that has just passed and the upcoming quieter spell can be seen quite well in terms of zonal available potential energy (ZAPE). The build up in ZAPE is related to temperature contrasts and a fall occurs with its conversion to kinetic energy through baroclinic processes in favourable regions eg north Atlantic - it is suggested that the largest fall in ZAPE occurred during the 'superstorm' of March 1993. The chart below shows the recent anomalous rise in energy available for extratropical storms -

The forecast shows that this surplus energy has now largely been expended leading to a quieter spell of weather for the NH extratropics in general -

(charts courtesy Jason Cordeira http://jasoncordeira.weebly.com/atmospheric-energy.html)

Thanks for this post @Interitus , something new i've learned today on this great site!

I would assume ZAPE increases through autumn and winter due to the polar air mass growing and clashing in our latitudes, before obviously dropping off through the summer as the jet weakens as the N/hem warms up.

Edited September 24, 2018 by mb018538

[Sky Full]

2018 - will it be the year that delivered in every season?  Exciting Winter weather, spectacular Summer and now looking like a decent Autumn.  Now, can we hope to see some snow before Christmas?  The CFS is working hard on this one.  Bring it on!

.  . 

(Just for fun, obviously...)

[feb1991blizzard]

3 minutes ago, Sky Full said:

2018 - will it be the year that delivered in every season?  Exciting Winter weather, spectacular Summer and now looking like a decent Autumn.  Now, can we hope to see some snow before Christmas?  The CFS is working hard on this one.  Bring it on!

.  . 

(Just for fun, obviously...)

That's an awful pattern for xmas, there will soon be a miles better chart than that for xmas time.

[Frosty.]

Amazingly long lasting anticyclonic spell on the Gfs 6z operational and a pretty settled looking Ecm 00z ensemble mean even at day 10..it does look like a prolonged spell of mainly fine weather, at least for the southern half of the uk with pleasantly warm sunny spells and light winds but some further cold nights with mist / fog patches where skies clear and slight frosts at times, especially in rural areas.

[BlueHedgehog074]

While not the most exciting chart for snow and cold that Sky Full posted, and while it is dominated by very low heights to the North and West of the U.K (and over the U.K itself), would at least deliver some wintry showers over high ground with those widespread -4*C to -6*C 850 hPa temperatures (so still better than nothing I guess. True, however, there could be better charts ). Hopefully, though, some proper blocked and snowy express charts will indeed turn up as it approaches Christmas! (For those, including myself, who like the cold and snow).

As mentioned above, does look to be generally dry and bright with some good sunny spells at times this week. The best of the dry and bright weather though does, on the whole, look to be concentrated more towards Southern parts with the models showing the pressure generally the highest over Southern U.K. But even Northern areas of the U.K. seeing some drier, brighter, periods at times, especially as renewed ridges of High Pressure out West in the Atlantic try to move over the U.K. But there could still be a possibility that these ridges could get squeezed out further West, instead of being allowed to move over the U.K, from Lows trying to drop down to the East of the U.K allowing a Northerly to break through, but confidence of this happening seems fairly low currently. (Not saying it can’t happen at some point, though).

[Frosty.]

Looking at the Gfs 12z operational, the generally uk based anticyclone is under sustained attack and gets pushed and pulled around a lot more than the 6z..and then it turns colder and very unsettled with a Northerly blast which is set up for further reloads beyond the end of the run..even some snow for the hills / mountains of scotland and quite a wintry feel to early october on this run! ❄

Edited September 24, 2018 by Frosty.

[Mike Poole]

Anticyclonic. Settled.

Model consensus on this, most models have the high drifting west then back over UK, so cool mornings but respectable temperatures in the afternoon with plenty of sunshine.

Here's the latest two models out ECM and FV3 at T240:

FV3 has the strongest influence of the high, although that 960 low in the Atlantic looks suspect to me, the idea of pulling big warmth from south fades today in favour of generally settled benign conditions with daytime highs in the mid to high teens.  Can live with that.  

Edited September 24, 2018 by Mike Poole

[damianslaw]

A generally settled outlook away from the north which will be under the influence of an atlantic flow. Becoming warm for a time mid-week, before cooler air moves down from the north for the weekend.

A pleasant usable spell of weather for the south, but some rain or showers in the north Wednesday and possibly later in the week.

As we enter October - no major change, strong signal core of heights will ebb and wane over the UK, eventually advecting west and a quite likely northerly plunge could develop, but may take a bit of time. I can see why some of the models are suggesting a cool October.

[Frosty.]

Tonight's Ecm 12z ensemble mean again ends on a high note ..and there's plenty of anticyclonic weather through the run, especially for england and wales..looks predominantly pleasant but with some cold starts as many of us had this morning.

Edited September 24, 2018 by Frosty.

[feb1991blizzard]

Another cold CFS for October.

[Mike Poole]

8 minutes ago, feb1991blizzard said:

Another cold CFS for October.

I'm at a loss to understand why people are getting excited about a cold October (leaving aside that I actually think we're going to get a warm October until at least mid month).

My problem with charts like that is uncertainty.  The CFS is only useful if it is used probabilistically, one run tells us nothing, neither does cherry picked runs.

And October weather in the UK tells us nothing about the coming winter. 

[ICE COLD]

1 hour ago, Mike Poole said:

I'm at a loss to understand why people are getting excited about a cold October (leaving aside that I actually think we're going to get a warm October until at least mid month).

My problem with charts like that is uncertainty.  The CFS is only useful if it is used probabilistically, one run tells us nothing, neither does cherry picked runs.

And October weather in the UK tells us nothing about the coming winter. 

I get excited about a cold October . I would rather have a cold/cool October than a mild or warm one . Why can't we have a different October for once ? Why can't we have a below CET for once ? We've had sunny hot weather all summer , with every month being above average . But as you say Mike the CFS is not the most reliable . But it has showed a cool October in quite a few runs lately . 

[feb1991blizzard]

While we are on the subject of seasonal models, did anyone else watch Gavsweathervids ECM update on the weekend, the H500 +ve anomaly over Scandinavia was quite staggering.

 

[Cheshire Freeze]

17 minutes ago, feb1991blizzard said:

While we are on the subject of seasonal models, did anyone else watch Gavsweathervids ECM update on the weekend, the H500 +ve anomaly over Scandinavia was quite staggering.

 

That long range seasonal ECM run is about as good as it gets in terms of forecast anomalies for those of a cold persuasion. Quite staggering really. 

[James Gold]

17 minutes ago, feb1991blizzard said:

While we are on the subject of seasonal models, did anyone else watch Gavsweathervids ECM update on the weekend, the H500 +ve anomaly over Scandinavia was quite staggering.

 

Yep some very nice patterns being forecast, shame it’s so far off and will no doubt be changed somehow  — but I guess it’s better than it not showing up at all

[feb1991blizzard]

2 minutes ago, CreweCold said:

That long range seasonal ECM run is about as good as it gets in terms of forecast anomalies for those of a cold persuasion. Quite staggering really. 

 

2 minutes ago, James Gold said:

Yep some very nice patterns being forecast, shame it’s so far off and will no doubt be changed somehow  — but I guess it’s better than it not showing up at all

 

Yes my only reservations are that didn't the ECM do this a couple of years ago, and even the autumn patterns that looked promising between 2013 and 2017 end up just firing blanks early winter and then just going zonal at the wrong time, could Steve M's theory that analogues could be useless because of the changing climate be what caused so many failures in the aforementioned years, because I remember a lot of positivity in all the years early on in the season, could this also be manifesting in the models too.

[Cheshire Freeze]

7 minutes ago, feb1991blizzard said:

 

 

Yes my only reservations are that didn't the ECM do this a couple of years ago, and even the autumn patterns that looked promising between 2013 and 2017 end up just firing blanks early winter and then just going zonal at the wrong time, could Steve M's theory that analogues could be useless because of the changing climate be what caused so many failures in the aforementioned years, because I remember a lot of positivity in all the years early on in the season, could this also be manifesting in the models too.

I think in terms of the modelling shown by the ECM seasonal the other year, people were reading it wrong. The issue the other year was that at no point (I think) was there lower heights forecast anywhere to our S or E. EC46 was the only product that was suggesting lowering European heights as I recall. Infact the seasonal model showed a HP anomaly stretching down across E europe (indicative of more sinking HP scenarios). The absolute MUST HAVE is some form of below average heights to or S or E.

You can see from the EC seasonal this year, there is a conveyor belt of LP under the HP signal. That scenario is pretty much as good as you'd get in winter if it's snow and cold you like. 

Edited September 24, 2018 by CreweCold

[feb1991blizzard]

Meanwhile - here she comes.

 

[Mizzle]

48 minutes ago, feb1991blizzard said:

While we are on the subject of seasonal models, did anyone else watch Gavsweathervids ECM update on the weekend, the H500 +ve anomaly over Scandinavia was quite staggering.

 

I've watched it twice now - and try to contain my excitement at the cold potential . I know it's all months away but it does keep my meteorological education enthused.

[Interitus]

8 hours ago, feb1991blizzard said:

Another cold CFS for October.

Hmm it showed this beaut on one of the runs the previous day -

To be fair, the CFS trend has been for a cool October.... but then a mild winter.

 

6 hours ago, feb1991blizzard said:

While we are on the subject of seasonal models, did anyone else watch Gavsweathervids ECM update on the weekend, the H500 +ve anomaly over Scandinavia was quite staggering.

 

The chart in that video frame is sea level pressure but no matter, assuming that the video covers z500 geopotential later on, this was dealt with on the stratosphere thread recently. Regarding the slp, it shows a slight tendency towards a southerly displaced jet - the positive anomalies to the north are quite meagre between 1-2 mb peaking between 2-4 mb over a small area of Scandinavia in DJF. Hence the T2m charts are near average and show nothing out of the ordinary.

Allowing for the fact that these charts are diluted over an average of three months, they certainly aren't a Dec-Feb 2009/10 -

or a NDJ 2010-11 -

+14mb, those are anomalies.

[NO LONGER POSTING]

Anyone else find it really really suspect to have that low out in the Atlantic still there at the end of the run on the 00z?

Ive never ever come across something like that before.. It just doesn't look right considering how deep the low is it can't be stuck in limbo all that time.. 

 

[Scorcher]

Some nice developments from the GFS 00z this morning if it's settled weather you're after. The high remains slap bang over us for most of the run after slipping west for a time over the weekend.

I can't see anything particularly cold in the offing. 

If the GFS run comes off it would mean cool nights (probably not particularly cold) and warm afternoons in the high teens to low 20s for many.

Edited September 25, 2018 by Polar Maritime
To move discussion on..

[mb018538]

1 hour ago, Scorcher said:

Some nice developments from the GFS 00z this morning if it's settled weather you're after. The high remains slap bang over us for most of the run after slipping west for a time over the weekend.

I can't see anything particularly cold in the offing. 

If the GFS run comes off it would mean cool nights (probably not particularly cold) and warm afternoons in the high teens to low 20s for many.

Exactly, what's the point in posting charts from months ahead.....they are irrelevant at the moment, and clearly not going to verify. 10-14 days is about as reliable as you are going to get from the models, and even then the reliability is low at day 14. Early october is too soon for anything other than a cool night really.....we can start worrying about the white stuff in another month.

Edited September 25, 2018 by Polar Maritime
To move discussion on..

[Frosty.]

Looking a bit further ahead, the GEFS 00z mean indicates an anticyclonic first week of October with very pleasant surface conditions by day but some cold nights with a risk of mist / fog patches and slight frosts but then a change to colder and more unsettled from the NW / N in the run up to mid month..just checked the postage stamps and there are some cold Northerly shots and also a generally more fired up atlantic beyond week 2.