Model Output Discussion 29th December - Into mid-Winter.

[Ice Day]

3 minutes ago, kumquat said:

The Hooker is in place but there are no props.

That's a Rugby reference....right?

Deep FI, I don't even know how to describe this one.

What a ridiculous way to spend a Saturday night.

[johnholmes]

Turning to the realistic time scale, what more do folk want than this Fax for 120h. Yes it may change but it is probably more reliable than any of us on here trying to suggest waht the flow might be.

http://www.weathercharts.org/ukmomslp.htm#t120

Direct from santa land, time to start watching the weather reports from Jan Meyen then Thorshave to get an idea of the T and Td values. Any minor troughs will enhance shower activity giving the probability of it well inland from the coasts. Possible development of one or more actual lows (may be Polar Lows) which would enhance even more. So lots for the coldies to be upbeat about instead of worry yet again at the outer realms of GFS.

[Frosty.]

Very interesting charts for next Saturday with snow across Wales, the midlands and parts of the south. I'm really looking forward to this cold outbreak, I know we have had some cold quiet weather but this should be exciting with a good chance of snow for most of the uk for the FIRST time this winter!

Edited January 7, 2017 by Frosty.

[mountsbaysnow]

3 minutes ago, Frosty. said:

Very interesting charts for next Saturday with snow across Wales, the midlands and parts of the south. I'm really looking forward to this cold outbreak, I know we have had some cold quiet weather but this should be exciting with a good chance of snow for most of the uk for the FIRST time this winter!

Any chance we may get a smidging down west?

[kumquat]

6 minutes ago, johnholmes said:

Turning to the realistic time scale, what more do folk want than this Fax for 120h. Yes it may change but it is probably more reliable than any of us on here trying to suggest waht the flow might be.

http://www.weathercharts.org/ukmomslp.htm#t120

Direct from santa land, time to start watching the weather reports from Jan Meyen then Thorshave to get an idea of the T and Td values. Any minor troughs will enhance shower activity giving the probability of it well inland from the coasts. Possible development of one or more actual lows (may be Polar Lows) which would enhance even more. So lots for the coldies to be upbeat about instead of worry yet again at the outer realms of GFS.

That train of troughs following the 528 DAM line @120 could cause Knocker's mate to go into hibernation, at last.

Edited January 7, 2017 by kumquat

[johnholmes]

Possibly time to revise the snow indicators from the Guides area. Remember the most important is does ppn show for your location, if it does procedd with another 5, 6 maybe 8 parameters that will indicate the probability of snow. If not forget it.

[phil nw.]

 

Cold looking outlook confirmed on Weds. and Thurs.fax's with a direct Arctic flow reaching N.Scotland by Thursday

Anyone's guess at this range where snow would fall but there are plenty of small trough lines coming south towards the UK.

The fax's look like the raw charts earlier-a much sharper trough than the GFS runs with a more direct northerly once it sets up-the Azores high further west too.

Interesting looking generally further on with evidence of the increasing influence of the Russian heights.This could well extend the cold for us.Early days but a smooth transition to the Atlantic returning not looking so certain now.

[chris55]

 

@Frosty.

these are my favourite kind of snowfalls for the Cotswolds, can't do much better than an Atlantic low bumping into the cold air and pivoting east. They can be hard to nail down and have to be just right in positioning but when they land right they can produce a lot of snow.

[The Enforcer]

47 minutes ago, PerfectStorm said:

Snow for midlands next saturday 

For goodness sake another run with a warm sector = 'rain day' Saturday.

[Frosty.]

4 minutes ago, mountsbaysnow said:

Any chance we may get a smidging down west?

I think anywhere in the uk could see some wintry ppn later next week, even the woodshed in Cornwall is not to be ruled out. It looks like a cold snap / outbreak is on the way, duration and strength still unclear but it's the most interesting spell of the winter so far we are looking at.

[Ice Day]

According to the Control, a decent snow event for most of the country on Thursday night.  Further North and West you are the better, but details will change as we count down of course.

This is now down to 120 hours!

 

[kumquat]

16 minutes ago, johnholmes said:

Possibly time to revise the snow indicators from the Guides area. Remember the most important is does ppn show for your location, if it does procedd with another 5, 6 maybe 8 parameters that will indicate the probability of snow. If not forget it.

When JH pulls out the guns - it's time to take notice.

[SMU]

here are your parameters for snow over the UK @ T126 for central England 

* Upper air temps -8c Tick

* Dewpoint -4c Tick

* heights of WBPT 0M Tick

* 850-1000mb thickness 1280 Dam Tick

* 850 Theta charts 10c Tick

* surface Temp 0c Tick

chances of snow falling from any showers >95%

S

 

Edited January 7, 2017 by Steve Murr

[Frosty.]

Looking at the GEFS 18z mean...cold wintry spell later next week looks locked and loaded!

Some of us are likely to see a covering of snow soon

[Scandinavian High.]

So ecm tonight was not a cold outlier .

[Man With Beard]

ECM ensembles suggesting coldest days will be Sunday 15 to Tuesday 17

[The Enforcer]

13 minutes ago, abbie123 said:

So ecm tonight was not a cold outlier .

Was the op a warm outlier on Saturday?

[radiohead]

18Z GFS op was an off-the-scale outlier in terms of pressure south of Greenland on the 15th. 

Edited January 8, 2017 by radiohead

[Trom]

2 hours ago, Steve Murr said:

Well all I can say is yes it may not happen however if you look at the change in the last 24 hours from the 216 mean yest to the 192 mean today you will see that the clustering must have shifted towards cold ( hence why I posted it ) 

yest 216

 

today 192

 

also a very crude measure of why the scandi high means get muted

if we have 35 members with a 1040 MB high over scandi & just 15 rogue members that are flat & have a deep 980MB low over scandi at the same time them the mean pressure at day 10 will be 1022 MB -& the contour lines will look significantly flatter as a result...

Its all about clusters if you want to use the mean & the clusters have shifted more to cold tonight ....

 

Excellent post - the obsession with mean runs (which I haven't noticed in prior years) in FI seems very odd to me.  As an Economist looking at data distributions and describing them by mean without a dispersion measure seems pointless.  Even with a dispersion measure you would still want to see skew.  From my perspective all these charts give you is a very broad brush trend of all the ensembles.  When you look at the dispersion patterns in FI they are so vast. Median would be a better measure given how most people use them.  There are dispersion measures using standard deviation which give a good idea of how well the op is supported relative to ensemble mean.  Nick F posted one back on page 168.  I'd like to see much more of this data being posted on the model thread.  The charts he posted showed exactly where the models had the greatest variability in the northern hemisphere.  We have a lot of data produce by the models but this measure goes under reported on the forum.  Essentially it's telling us where the models are solid and where they are uncertain.  Nick F if you could post more (or let me know where they can be found) that would be great.

[ArHu3]

I don't think I have ever seen such narrow bandwidth for so far into the future before

[alexisj9]

59 minutes ago, radiohead said:

18Z GFS op was an off-the-scale outlier in terms of pressure south of Greenland on the 15th. 

Agreed, although it does look like the trend is for the pressure to drop, just not as far.

[Nouska]

22 minutes ago, ArHu3 said:

I don't think I have ever seen such narrow bandwidth for so far into the future before

Quite a bit colder in the SE of Holland too. I'm wondering how far south and west this can go - maybe all the way down here given the suggested longevity in the ensemble.

[Geordiesnow]

Fantastic ECM run upto 144 hours, low thicknesses, unstable clean flow with frequent blustery wintry(snow) showers and snow falling quite widely at lower levels in North Western areas although almost anywhere could see snow falling at some point.

I'm not sure where the talk of its only going to be a toppler with just snowfall confined to the hills is coming from tbh, low thicknesses tend to come with a lower DAM point and therefore lower dewpoints, low thicknesses also causes deeper convective potential and much to my surprise the flow is looking very 'clean' at least initially before shortwaves do start to come into play.

Hopefully there won't be any significant downgrades in terms of the initial cold NW'ly blast and what happens after that remains very much uncertain. Just hope the UKMO is right regarding the amplification in the short term as that gives us the best chance for this NW'ly to deliver the best potential.

[Ali1977]

This little system could give a proper snow event in the SW, shame it come through during the day as that could make the difference on settling etc...

[Mucka]

Fairly big differences with UKMO and GFS by 120 this morning, both in how deep and fast the trough is and in the upstream pattern. So UKMO colder initially at least.

By 144 UKMO quite amplified, very nice looking chart but very different to GFS next to it.

Edited January 8, 2017 by Mucka