Model output discussion pm 13/01/2016

[Methuselah]

Just now, Chris1986 said:

What's that coming over the hill... Is it an easterly  pure FI but still

But I wouldn't rule it (or something like it) out. It has happened before!

[Daniel*]

28 minutes ago, Jason M said:

Yep, id agree with that. If it reaches Kent / Essex / EA it will be a mostly rain event! With these they either drop snow west of the line you indicate or if they make it to the east coast its pretty much rain all the way!!

Eurgh don't agree with that the least marginal parameters are to the E the West Country is where it is most precarious it would be snow, it counts for nothing if there's no precip. 

[Laurence Hill]

3 minutes ago, GUWeather said:

It's the total accumulations from start of snow on Monday until date and time on chart, covering about 24 hours.

Thanks for clarifying GUW 

[Cheshire Freeze]

5 minutes ago, offerman said:

 But the 850-5 line is over the continent so how can we get snow if we are in the green area ?

 

 Hello  Blue , yes but if surface temperatures with the flow coming in from the south which is relatively mild  compared to  an easterly  component then I just don't see how we can get snow ? 

You only need a slight continental influence. Any track over the landmass to our S&E has the effect of drying the air out and lowering the dew point (possibly the most important factor in determining precip type in this set up).

The more saturated the air the higher the dew points tend to be and the lower the upper temperatures need to be to support snow. This is the reason polar maritime air can produce rain with 850s of -7.

Edited January 15, 2016 by CreweCold

[bluearmy]

1 minute ago, offerman said:

 But the 850-5 line is over the continent so how can we get snow if we are in the green area ?

 

 Hello  Blue , yes but if surface temperatures with the flow coming in from the south which is relatively mild  compared to  an easterly  component then I just don't see how we can get snow ? 

if the isobars are south to north then the surface flow is se. anyway, it might be more prudent to look at that run with precip instead of accumulated precip. welsh mountains, chilterns, south downs and kent are the only places to see decent snowfall.  again, over analysing of precip 3 days away!

[perry011110]

Well the bbc forecasting is certainly in a bit of a pickle..i remember yesterday seeing a euro4 chart on this forum of varying rain/sleet/snow predictions for Ireland/nw england pushing se..according to there latest forecast there is some uncertainty as to how much rain/snow these places will get..so to me it seems that fi begins at t36 if that..

[johnholmes]

try the Net Wx Guide on will it snow, it does work

 

[offerman]

3 minutes ago, bluearmy said:

far more to snow than uppers, especially with a continental flow

 Yes but our flow is from France as opposed to the east where all the cold is .

 

1 minute ago, CreweCold said:

You only need a slight continental influence. Any track over the landmass to our S&E has the effect of drying the air out and lowering the dew point (possibly the most important factor in determining precip type in this set up)

 Okay that's great thank you very much I did not know that . 

[IDO]

2 minutes ago, offerman said:

 But the 850-5 line is over the continent so how can we get snow if we are in the green area ?

 

 Hello  Blue , yes but if surface temperatures with the flow coming in from the south which is relatively mild  compared to  an easterly  component then I just don't see how we can get snow ? 

That is an Arpege chart and you should look at the uppers for that time from Arpege rather than GFS:

http://www.meteociel.fr/modeles/arpege.php?ech=3&mode=16&map=330

That keeps the uppers below 0c so your point maybe mute, but as other posters say there are other factors. 

[offerman]

2 minutes ago, IDO said:

That is an Arpege chart and you should look at the uppers for that time from Arpege rather than GFS:

http://www.meteociel.fr/modeles/arpege.php?ech=3&mode=16&map=330

That keeps the uppers below 0c so your point maybe mute, but as other posters say there are other factors. 

Thank You for this.

[nick sussex]

Great GEM with the cold hanging on, the UKMO not so good as this mornings run but the placement of the jet might well change in future outputs, the GFS better early then goes downhill.

There are some big differences upstream between the GFS and UKMO over the USA. Hopefully NCEP will shed some light on the likelier solution.

[Jason M]

Just now, Earnest Easterly* said:

Eurgh don't agree with that the least marginal parameters are to the E the West Country is where it is most precarious it would be snow, it counts for nothing if there's no precip. 

In these set ups the extreme east rarely does well. If the front reaches east of London it is usually a mostly rain event. Its not unheard of for a front to stall out over the SE and EA but its unusual (there was an example about 3/4 years ago). Come the day, the set up will probably either correct west keeping the SE dry or the milder air will quickly turn any snow to rain. Its mostly conjecture at this point but its one thing where past performance is a good indicator of the future! I'm sure TEITS would say much the same. 

Be great to be proved wrong though 

 

[Eskimo]

As others have mentioned, when you are faced with an occlusion in 'slider' scenarios, the air is being dragged from the continent and that's typically cold and dry. That helps in making sure any precipitation that does fall, falls the ground. The dry and cold air also keeps dew points down which is also a fundamental in keeping snow...well....snow. 

[swilliam]

17 minutes ago, offerman said:

 But the 850-5 line is over the continent so how can we get snow if we are in the green area ?

Because of the angle of the front the winds in ppn area would from the SE and coming from the cold pool on the continent.  This would mean air with low DPs even the upper air temps are quite high  - could even be an inversion. For the Aperge at this time the 850s are about -3 at the time the snow falls anyway. V small changes in the model output give big changes in the weather in this situation

 

In fact a lot of the snow shown accumulating comes on Sunday Morning from the area of moisture to the NW which dives S

 

 

Be nice if that came off.

 

 

 

Edited January 15, 2016 by swilliam

[joggs]

7 minutes ago, Ed Stone said:

But I wouldn't rule it (or something like it) out. It has happened before!

But surely at that time frame the Vortex over Greenland would start backing away due to the amplification from the w Pacific screaming jet burst?

So would tge high retrogress?

Most background signals have Scandi trough?!?

[Eskimo]

1 minute ago, Jason M said:

In these set ups the extreme east rarely does well. If the front reaches east of London it is usually a mostly rain event. Its not unheard of for a front to stall out over the SE and EA but its unusual (there was an example about 3/4 years ago). Come the day, the set up will probably either correct west keeping the SE dry or the milder air will quickly turn any snow to rain. Its mostly conjecture at this point but its one thing where past performance is a good indicator of the future! I'm sure TEITS would say much the same. 

Be great to be proved wrong though 

 

Not true, it's more likely in these scenarios for snow to fall across the east and rain in the west. This is because the warm front has pushed through the west, raising the temperatures, but it's still cold in the east as the block has more influence. Your right though that the extreme east never does well, as mostly the precipitation dissipates or doesn't push any further across. 

[fergieweather]

2 minutes ago, perry011110 said:

Well the bbc forecasting is certainly in a bit of a pickle..i remember yesterday seeing a euro4 chart on this forum of varying rain/sleet/snow predictions for Ireland/nw england pushing se..according to there latest forecast there is some uncertainty as to how much rain/snow these places will get..so to me it seems that fi begins at t36 if that..

Key issues into (the nearer-term) medium range are compounded by mismatches between 00z/06z model solutions and imagery. The latter is already looking more amplified in the Atlantic versus output, favouring the slower solutions. This slower progression was always suspected and remains the main caveat set against ongoing deterministic modelling, which continues to show marked swings including run-to-run within the same suites (and even lately between UKMO-GM Operational and Parallel suites). No detailed analysis of current output is really trustworthy into the start of next week... 

[Cheshire Freeze]

2 minutes ago, joggs said:

But surely at that time frame the Vortex over Greenland would start backing away due to the amplification from the w Pacific screaming jet burst?

So would tge high retrogress?

Most background signals have Scandi trough?!?

The end game is the Scandi trough. Reading between the lines, GP expects a Greenland/N Atlantic block as we enter Feb and I fully concur. So does the GLOSEA seasonal....I'm sceptical of any output attempting to show an easterly in all honesty.

I've seen hints within recent ECM op runs of attempted amplification towards days 9&10 with an attempted pull back of Azores heights. These attempts haven't been shown as successful.....YET!

[northwestsnow]

2 minutes ago, fergieweather said:

Key issues into (the nearer-term) medium range are compounded by mismatches between 00z/06z model solutions and imagery. The latter is already looking more amplified in the Atlantic versus output, favouring the slower solutions. This slower progression was always suspected and remains the main caveat set against ongoing deterministic modelling, which continues to show marked swings including run-to-run within the same suites (and even lately between UKMO-GM Operational and Parallel suites). No detailed analysis of current output is really trustworthy into the start of next week... 

Thanks Ian for your valued input.

While there are some outstandingly clever folk on Net weather its always great to hear pro's views.

As you say, GFS a lot slower with the Atlantic on 12z then the 6z so still obviously a fluid situation.:)

[Liam J]

11 minutes ago, GUWeather said:

It's the total accumulations from start of snow on Monday until date and time on chart, covering about 24 hours.

The chart Perfect Storm posted are accumulations from 0h onwwards not a 24hr accumulation. 

The ppn charts Monday & Tuesday showing fairly light ppn. 

[feb1991blizzard]

3 minutes ago, CreweCold said:

The end game is the Scandi trough. Reading between the lines, GP expects a Greenland/N Atlantic block as we enter Feb and I fully concur. So does the GLOSEA seasonal....I'm sceptical of any output attempting to show an easterly in all honesty.

I've seen hints within recent ECM op runs of attempted amplification towards days 9&10 with an attempted pull back of Azores heights. These attempts haven't been shown as successful.....YET!

I agree but I suspect more like the 2nd week towards mid feb before this displacement Strat warming (shown on the 12z very nicely) effects will be felt, Potent Northerly Mid feb is my bet.

 

Anyones guess after that though.

Edited January 15, 2016 by feb1991blizzard

[nick sussex]

Overall NCEP prefer the ECM ensemble mean solution for the USA but that's more out of sufferance as all the outputs have issues. The GFS too fast and flat, the ECM perhaps too amplified and that theres other issues described below.

 THE FULL RANGE OF GUIDANCE INDICATES A SENSITIVE/LOWER THAN AVG CONFIDENCE FCST GIVEN POTENTIAL FOR FLOW ALOFT TO RANGE BTWN A PHASED UPR TROUGH OR TWO SEPARATE STREAMS THAT WOULD LEAD TO A COMPLETELY DIFFERENT SFC EVOLUTION.

Looks like NCEP and the UKMO are having similar problems with trying to put a forecast together!

Theres later updates in the State forecasts and that will include more of this evenings info.

[Eskimo]

1 minute ago, *Sub*Zero* said:

The chart Perfect Storm posted are accumulations from 0h onwwards not a 24hr accumulation. 

The ppn charts Monday & Tuesday showing fairly light ppn. 

A lot of the snow across the southeast is from Sunday onwards, still showing 10-15cm of that paRticular system according to the ARPEGE. Probably overcooking the totals, but the arm of that precipitation stalls and spins across the London area. One run though...

[Nouska]

19 minutes ago, IDO said:

That is an Arpege chart and you should look at the uppers for that time from Arpege rather than GFS:

http://www.meteociel.fr/modeles/arpege.php?ech=3&mode=16&map=330

That keeps the uppers below 0c so your point maybe mute, but as other posters say there are other factors. 

The ARPEGE does provide other helpful charts in snow forecasting.

Freezing level  ....  http://www.meteociel.fr/modeles/arpege.php?ech=3&mode=37&map=330

Dew points   ....    http://www.meteociel.fr/modeles/arpege.php?ech=3&mode=18&map=330

Caveat - it has a very different solution to other models at this time frame - treat with caution.

Edit for Nick L post - snow that has fallen, not necessarily accumulated on the ground.

 

Edited January 15, 2016 by Nouska

[Nick L]

33 minutes ago, PerfectStorm said:

The ARPEGE going for eye-watering amounts of snow (5-15cm) widely across the Wales, Midlands down to the southeast corner for Monday.

I'm pretty sure this is the total precipitation equivalent of falling snow, NOT snow accumulations! But French really is not my strong point...

Edited January 15, 2016 by Nick L