Model Discussion - 10th March Onwards

[skifreak]

I'd take a repeat of April 2008! GFS 18z is quite encouraging in that regard, a couple of weeks of steadily topping up the snow on CairnGorm would suit me and my season pass nicely!

[Polar Maritime]

The GFS this morning is still showing an unsettled outlook throughout, With PM air from the N/W bringing heavy rain, strong winds and snow for the Scottish Highlands, sinking South over the whole of the UK from Monday. With Frost where cloud breaks in the North.

Befor turning into a colder Northerly flow, bringing -8 uppers into Scotland and -4 uppers into the Middlands. Pushing bands of showers or longer spells of rain South, with Snow over high ground from the Middlands North and Scotland, and rain for the South. With frosts at night, and daytime Temps into single digits on a Northerly flow it will feel rather cold. A very seasonal picture on the cards for April for once.

Edited April 6, 2012 by Polar Maritime

[Weather Wizard]

The GFS this morning is still showing an unsettled outlook throughout, With PM air from the N/W bringing heavy rain, strong winds and snow for the Scottish Highlands, sinking South over the whole of the UK from Monday. With Frost where cloud breaks in the North.

Befor turning into a colder Northerly flow, bringing -8 uppers into Scotland and -4 uppers into the Middlands. Pushing bands of showers or longer spells of rain South, with Snow over high ground from the Middlands North and Scotland, and rain for the South. With frosts at night, and daytime Temps into single digits on a Northerly flow it will feel rather cold. A very seasonal picture on the cards for April for once.

Those GFS precip charts are rubbish at predicting coonvective rainfull any more than 24h in advance, so i wouldn't take the continous rainfull shown to seriously.

[Polar Maritime]

Those GFS precip charts are rubbish at predicting coonvective rainfull any more than 24h in advance, so i wouldn't take the continous rainfull shown to seriously.

I have always used them as a guide, as with any other model.

But as the other models show, with big lows sweeping S/E it's almost inevitable we are in for some good prolonged rainfall amount's.

And with the cold air aloft with strong N/W winds, Snow on high ground for the Middlands North and Scotland is certainly not out of the question in these type set up's.

Edited April 6, 2012 by Polar Maritime

[Weather Wizard]

I have always used them as a guide, as with any other model.

But as the other models show, with big lows sweeping S/E it's almost inevitable we are in for some good prolonged rainfall amount's.

And with the cold air aloft with strong N/W winds, Snow on high ground for the Middlands North and Scotland is certainly not out of the question in these type set up's.

I disagree after monday there is very little frontal rainfull and most of the rain will be from convection which will not be "prolonged"

[TonyH]

I would also cast doubt on the coolness of next week, even with coldish uppers, the strong April sunshine between showers will cause temperatures not far off the average of 12-14c at least until the end of the week.

Edited April 6, 2012 by TonyH

[TonyH]

We managed 12c yesterday even with -5c uppers.

[Cloud 10]

You done with being misleading, PM?

I advise you to not look at the surface pressure and precipitation charts in isolation. What's going on aloft- i.e. at the 500hPa height? Have another look at the output for next week and get back to us.

Doesn't look misleading to me,just a reasonable assessment of what the model is showing.

[Polar Maritime]

So the models are misleading people......

You done with being misleading, PM?

I advise you to not look at the surface pressure and precipitation charts in isolation. What's going on aloft- i.e. at the 500hPa height? Have another look at the output for next week and get back to us.

Im just showing what the models are showing.

Not what im wishing for.

Please do not misslead people on here, to think that im being missleading.

[johnholmes]

How about less of the bickering and more of the objective viewing of model outputs? Its not difficult, just show the chart(s) you are referring to, make your comment as to how you see it and leave folk to make their own minds up. How several of you can have differing views from apparently looking at the same model is a bit beyond me.

for instance the link below shows the GFS predicted rainfall for the period out to T+144 for most of England and Wales, unfortunately this particular output does not show Scotland or N Ireland, otehrs do, but, however reliable/unreliable it is its showing 10-30+ mm for pretty much all parts shown so even the drought areas are predicted to get some meaningful rainfall.

http://www.wetterzen.../fsgfsmeur.html

Amounts/when/where beyond T+24 have always been subject to considerable variation from what actually falls so I think most folk are aware of this.

As to how UK Met, fine mesh output out to T+48 along with Net Wx NMM out to T+36 compare I've not looked. Even at these time scales its not unusual for the outputs to be quite wide of the mark, sometimes they are very accurate.

The NMM out to T+36 shows as below

http://www.netweathe...449f444b9e5ba9d

GFS output, courtesy of Wx Online shows this for T+48

http://www.weatheron...M=0&PERIOD==

NAE ( UK Met)

for the same and from the same issue shows as below

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=ukuk&MODELL=nae&MODELLTYP=1&BASE=-&VAR=rsum&HH=48&ZOOM=0&ARCHIV=0&RES=0&WMO=&PERIOD=

so you takes your pick and hangs your hat on whichever you believe but at least everyone can see what you are saying and probably why-no bickering?!

Edited April 6, 2012 by johnholmes

[TonyH]

A coolish outlook, Wednesdays charts seem typical with April showers, although GFS tends to undercook it's maxima so nearer average where decent sunny spells occur:

Convective precipitation suggested by the above with most of the modelled rainfall amounts in the afternoon and inland.

Snow highly unlikely except above 500 masl and in the far north.

ECM seems showery too with a shallow low nearby much of the week, uppers showing no sign of especially cool or snowy weather even by Friday:

Edited April 6, 2012 by TonyH

[J10]

Latest Skiing blog now out, and the colder air set to push across the UK, is also set to push into the Alps, with chance of decent snowfalls for the mid part of next week, but uncertainty as to how cold it will turn over the Alps.

[johnholmes]

the latest update by the 'experts' is out=ta Stewart and tends to support the idea of showers or longer spells of!

UK Outlook for Wednesday 11 Apr 2012 to Friday 20 Apr 2012:

Remaining generally unsettled, with a mixture of bright or sunny spells and showers. Some of the showers will be heavy with hail and thunder, and, at times, merge into longer spells of rain.

[Polar Maritime]

the latest update by the 'experts' is out=ta Stewart and tends to support the idea of showers or longer spells of!

UK Outlook for Wednesday 11 Apr 2012 to Friday 20 Apr 2012:

Remaining generally unsettled, with a mixture of bright or sunny spells and showers. Some of the showers will be heavy with hail and thunder, and, at times, merge into longer spells of rain.

Correct John.

And also supports the GFS idea for snow over high ground from the Midlands North, even down to low levels for some.

"Meanwhile, over high ground there will be some sleet and snow showers, especially in the North where showers may turn wintry to some lower levels at times later next week".

Edited April 6, 2012 by Polar Maritime

[johnholmes]

Of course we are all entitled to make our own judgements but to suggest some are 'struggling' as you put it is a touch unkind in my view.

I tend to agree with the Met O suggestion that there are likely to be a fair number of showers about, due to cold air aloft, reasonable sunshine heat available by day, and that they may be prolonged in places at times, even extending into longer periods of rain.

With relatively deep cold air at 500mb, colder than -20C showing on GFS over the UK much of the time, even colder on Wednnesday, reasonable sunshine amounts probable, the two=heavy showers in places next week and this 'could' lead to more prolonged type showery rain?

Perhaps you can explain why you feel this to be unlikely?

[Polar Maritime]

Er, that's exactly what I'm doing, John. Other than from the frontal system on Monday/ early Tuesday, can you point me to where on the model output next week's "prolonged" rainfall is being modelled? It's not about "takes your pick and hangs your hat", it's about intepreting model output correctly.

The reason for such differing views when looking at the same output is down to one's ability to intepret the output. Clearly some struggle with this.

GFS showing persistant rain and prolonged showers for all but the S/E from the 11th.

[Weather Wizard]

Of course we are all entitled to make our own judgements but to suggest some are 'struggling' as you put it is a touch unkind in my view.

I tend to agree with the Met O suggestion that there are likely to be a fair number of showers about, due to cold air aloft, reasonable sunshine heat available by day, and that they may be prolonged in places at times, even extending into longer periods of rain.

With relatively deep cold air at 500mb, colder than -20C showing on GFS over the UK much of the time, even colder on Wednnesday, reasonable sunshine amounts probable, the two=heavy showers in places next week and this 'could' lead to more prolonged type showery rain?

Perhaps you can explain why you feel this to be unlikely?

I don't think the showers will be so prolonged as

1. There is not such deep cold at 850 (-1 to -4)

2. any convection that gets going will move along rather quickly on a strong breeze

[JP1972]

I think we could do with a bickering thread to be honest.

Mainly because I'm ace at bickering but frankly rubbish at reading weather charts

[Weather Wizard]

GFS showing persistant rain and prolonged showers for all but the S/E from the 11th.

Those GFS precip charts as mentioned by john h are terribly innacurate especially for convection and at +132h

[johnholmes]

I don't think the showers will be so prolonged as

1. There is not such deep cold at 850 (-1 to -4)

2. any convection that gets going will move along rather quickly on a strong breeze

I will try and show why I think the showers COULD be heavy possibly prolonged regardless of the wind strength but it will have to be using a pdf format as I need several charts to try and illustrate my view. Back shortly.

No arguments we are just having different views-it all helps us to understand the weather rather better hopefully or rather what the models are showing us.

[Thundery wintry showers]

Some rather over-sensitive posts and bickering here, but the core issue appears to be the automatic association of low pressure with cloudy skies and belts of prolonged frontal rain. There is a correlation of course, but some slack slow-moving lows instead give day after day of sunshine, sharp showers, hail and scattered thunderstorms, as happened over the southern half of England in particular during the 6th-15th April 2008. The latter is dependent on lack of frontal activity, so it's not unusual for projections for a spell of "sunshine and showers" to be wiped out by unexpected frontal activity at the last moment, but the less strong the jet, the more likely it is that we'll see a fair amount of sun as well as showers under a slack are of low pressure.

Meteociel's versions of the GFS precipitation outputs do not differentiate "convective" from "large scale/frontal" precipitation, whereas Netweather and Wetterzentrale's versions do offer such a distinction. This is important because convection generally implies sunshine and showers whereas large-scale/frontal generally implies dull and wet. It's worth noting though that convective precipitation can be prolonged under some circumstances, especially when the individual cumulus/cumulonimbus cells are slow-moving and/or merge together (the latter is common in association with troughs). However slow-moving showers also imply that some areas will be getting prolonged slow-moving sunny intervals.

It's an area where people can easily get confused- if the distinction between convective and large-scale precipitation is poorly understood, or poorly labelled on the model outputs, it's very easy to see a mass of "rain" and think "dull and wet".

[johnholmes]

Those GFS precip charts as mentioned by john h are terribly innacurate especially for convection and at +132h

but what else would you suggest is used to TRY and predict the weather.

If they are so inaccurate how come you seem to be using them to predict less in the way of showers?

We all know they are not accurate in terms of specifics but I am using them to try and illustrtate how the weather MAY turn out. I always make comment on just how much precipitaion charts change as we near T+00 even though neither the upper air pattern nor to a lesser extent the surface pattern may not.

[Polar Maritime]

Those GFS precip charts as mentioned by john h are terribly innacurate especially for convection and at +132h

They are the only percipitation chart's to use to show whats in stall for next week. Whether it be right or wrong, this is what the models are showing.

Like any model prediction, time will tell.

[Weather Wizard]

but what else would you suggest is used to TRY and predict the weather.

If they are so inaccurate how come you seem to be using them to predict less in the way of showers?

We all know they are not accurate in terms of specifics but I am using them to try and illustrtate how the weather MAY turn out. I always make comment on just how much precipitaion charts change as we near T+00 even though neither the upper air pattern nor to a lesser extent the surface pattern may not.

They are the only percipitation chart's to use to show whats in stall for next week. Whether it be right or wrong, this is what the models are showing.

No they are not!!!

As TWS just said dont use the charts on meteociel use the ones on netweather as the charts on meteoceil make it look like a lot of frontal rainfull which clearly there won't be.

compared to exactly the same chart on net weather at the same time (meteociel is french time)

shows more convective weather (i still don't think it will be anything like shown on netweather as I think it will be more scattered than one big blob of convection)

It's an area where people can easily get confused- if the distinction between convective and large-scale precipitation is poorly understood, or poorly labelled on the model outputs, it's very easy to see a mass of "rain" and think "dull and wet".

That is exactly my point

Edited April 6, 2012 by Weather wizard

[Weather Wizard]

It's an area where people can easily get confused- if the distinction between convective and large-scale precipitation is poorly understood, or poorly labelled on the model outputs, it's very easy to see a mass of "rain" and think "dull and wet".

That is exactly my point