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Model Output Discussion - 14th Jan 12z Onwards

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You talk of day 5 but post a chart at day 10

Small differences in how the slider low is modelled at D5 equals large differences at D10. That was my point. Looking at the ECM compared to the 0z run also highlights this. So expect lots of changes, for better or worse (cold wise).

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JMA 12Z shows the worst case scenario tonight of a quickly collapsing mid atlantic ridge and mild atlantic westerlies, looks plausible too i'm afraid.

 

http://www.wetterzentrale.de/pics/Rjma1681.gif

 

http://www.wetterzentrale.de/pics/Rjma1922.gif

Probably not a favoured option though. And it's at T168. Enough said.

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There are two choices here. If you're going to get the blown up low like the ECM then you don't want it to head south too far west, this will drive too much milder air into mainland Europe.

 

If its a shallow feature that moves se then that's less of a concern, so I'm afraid its a case of perhaps suffering a short less cold interlude before the low has tracked into the Continent.

 

Preferably I'd prefer to see the shallower feature because theres always that concern that the ECM low might fill and becoming slow moving too close to the UK.

Surely shallow calm features are the main possibility .

Strong winds into next week are not even being mentioned by met office .

Suppose the set up of any low is key even after a full undercut

Thanks nick as ever

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Im very happy with tonights runs, the main 3 do all point to cold, just varying ideas. It will be fun over the next few days watching it evolve and discussing which model may have a better handle on it and watching them adjust as we count down.

 

We could even be back to wintryness tomorrow afteroon/evening as a trough works its way down from the North, especialy on the hills. We then have Sunday to watch and then hopefully a big snow event with a slider low next week!

 

Its all going on and its fascinating to watch it unfold and a pure joy to be on here with you all talking out our love of weather :)

 

Maybe the chart of the winter for me below. ECM 850s for 23rd (just for fun I know). All the country covered in at least -7 uppers and a big chunk of it under -8/-9! We even see the -10 approaching. Shades of 1st December 2010 here with that strong north easterly bringing in big snow showers :D

 

ECU0-216.GIF?14-0

 

Its looking like our cold spell should last at least all next week! HOPEFULLY!

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A very cold outlook, from ecm and gfs. We need to be careful with regard  reading to much into detail, the fine tuning of who will get snow will go down to the wire, the cold is in ,that's the main thing. Charts look like  late esque  2010 to me ,so a very, very interesting outlook for winter weather, but by no means read models to literally five days ahead, things will change, but I think we can at least say for a while, we are at last boarding the Winter Roller coaster,,,Enjoy the Ride.... :D

post-6830-0-76273400-1421264567_thumb.gi

post-6830-0-41826200-1421264597_thumb.pn

post-6830-0-00710700-1421264629_thumb.pn

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Does anyone know if the EC32 and Mogreps are showing the cold spell lasting towards next weekend? As mentioned above , a little tweak from from the ECM could lengthen it a bit, Azores high may ridge up over scandy!!

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Wow the hunt for the breakdown is on I see even before the starter let alone the main course.

 

No - this is a model chat thread, the breakdown is just as relevant in the model chat as any cold synoptics that are showing.   

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No - this is a model chat thread, the breakdown is just as relevant in the model chat as any cold synoptics that are showing.   

 

Not really considering we don't even know if this coldspell is going to happen or not.

 

FI is really close so there is no point getting caught up with anything T144+

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A quick illustration, as per IanF's allusion to other parameters besides 850 temps being more important. Exhibit 1, suggested weather type, look at the swathe of heavy snow down through England down to the south coast.

 

1

15012006_2_1412.gif

 

Now, look at the 850 temps for that time -5? -4? Surely not cold enough?

 

2

15012006_2_1412.gif

 

Now look at the Wet Bulb Freezing Level, snow suggested for anywhere from 300 and below (the sort of figure you are looking for, although this appears to have Wales up to 400-ish and still snowy). In Northern Ireland you have very similar 850 temps but rain where the WBFL level is over 400. Other parameters are in play such as intensity of precipitation but you can see how it might be affected. The WBFL charts are available for GFS on Weather Online.

 

3

15012006_2_1412.gif

Edited by ukpaul

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So then, we arrive somewhat disjointed at a potent cold snap.- which has the potential to last 8 days ( day 1 is T48)  - possibly longer.

 

Since March 2013 there haven't been ANY HLB synoptics, with just very short NW transitional Pm flows last winter. - so of course we can all understand the desire for our own 'imby' to come up trumps in next weeks scrum of low pressure drifting / sliding SE.

 

My thoughts thus far is that as we home in on the slider low the track & intensity probability wise do NOT favour snow for the following areas.

 

SW - South of M4, southern England- again along the south coast & the shires more so & also the SE corner like Kent & Essex / sussex. ( if the PPN makes it at all)

 

Why? If we look at the information available from UKMO & ECM we see the tracks:

 

ECM-

 

120-

http://www.meteociel.fr/modeles/ecmwf/runs/2015011412/ECU1-120.GIF?14-0

144-

http://www.meteociel.fr/modeles/ecmwf/runs/2015011412/ECU1-144.GIF?14-0

 

The ECM tracks the low across Ireland towards wales & then into the channel & deepens it to 976MB, which is far to deep for a slider.

 

This sort of depth - creates turbulence & forces milder TM saturated air ahead of the system, because of the turbulence the slightly milder uppers & indeed a increased 'melt layer' in the column of air from cloud base to ground mix ahead of thee frontal zone NE wards- so your surface cold is all gone by the time the PPN arrives.

 

remember 'Deeper the low = further NE milder penetration', so along the lows track you would need to get into the midlands to find the snow line.

 

UKMO is better because the intensity is shallow- which is likely to be the form horse- However the track is flatter & less acute.

 

120-

http://www.meteociel.fr/ukmo/run/U120-21UK.GIF?14-18

 

144

http://www.meteociel.fr/ukmo/run/U144-21UK.GIF?14-18

 

Track is through Ireland across the central belt, meaning again you can forget snow for the south, its reserved for the North along the line where those tight easterly isobars are.

 

So of the Euros overall neither paint a great signal for the UK, however the ECM does look good for snow further North.

 

Whats going to change? well the optimum for retaining snow prospects was the NAVGEM

http://modeles.meteociel.fr/modeles/navgem/runs/2015011412/navgem-0-132.png?14-17

 

low mixing from the warmer air & a very shallow system.

 

So as it stands based on a blend of ALL tracks & intensity + the fact there's no HLB directly to the east enforcing a deep SE flow out of the continent theres is MINIMAL slider snow prospects for the SE / SW / South- but please reflect on the high uncertainty allowing for some adjustments that could suit these areas ( the most likely adjustment is the PPN doesn't even reach these SE / E areas. )

 

Once again areas in the firing line seem to be the central / North midlands & areas possibly further North which if you catch the slider right, will see continuous snowfall as PPN arrives then slides east & stalls before pulling away south.

 

Prior to the slider, A potent storm- followed by Squally Wintry showers in the NW when eventually becomes Northerly -

 

As the wind swings closer & closer to the North so this flow becomes very cold  & associated dew-points will drop out sub zero. I have highlighted an embedded trough swinging SSE through the UK on Sunday, however again the south & SE may not have sufficient depth to the cold ahead of it at that point to support snow. - so what appears as snow in the midlands may end up a sleety mess in the E/SE corner.

Post the slider event may well be the chance the NE/E & SE have been looking for with a backing west of continental cold, this all depends on the ridging NE of the altantic high cutting off the trough feeding the sliders from SE Greenland.

The immediate upper air profiles to the east wont be 'that' cold so 24 hours of flow at least will be required before any deep cold may arrive. ( triggering convection )

 

What's not been mentioned to much thus far is the potential for a very low CET period spanning 7 days for Scotland & the North. The central belt of Scotland could see overnight lows approaching the magical -15c & with that depth of cold the recovery across the snowfields may only see maxima -5cs returned. - so low single digits of negative CET could be the order of the day.

Frozen rivers & lakes etc could be common place by next weekend.

 

In summary then a bit of a messy pattern, - Messy usually means lots of snow & if I was located in the central / northern belt as it stands I would be satisfied that I have the highest probability of frontal snow.

 

For the snow starved elsewheres in the south its a case of wait & see with baiting breath but as it stands the initial set up & prognosis doesn't look 'that great'

 

regards

S

 

 

Steve I know this is all academic at this range and predictions are just built on experience rather than genuine certainty in the model output, but what do you think of Cambs and the western portion of East Anglia? TBH this is more of a regional question I recognise, but seems heavily model related given current synoptics. Whatever the answer to this and indeed any other IMBY posts, worth bearing in mind that even the pros don't  know the exact location of the rain/sleet/snow boundary for Saturday, let alone into next week so we should all focus on the inroad of cold as a first and foremost (he says, blushing).

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No - this is a model chat thread, the breakdown is just as relevant in the model chat as any cold synoptics that are showing.   

 

 

happens every time, ridiculous!

 

How different is it to looking for a change from zonality

Edited by Weather Wonder

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Aww for once Mr Murr's comments are very sobering for us snow aholics South of the Midlands

Hope these lows that can be very frequently over cooked are once again toned down allowing a colder fetch of air to reach us below the magical midland snow line

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Let's think back to yesterday, some of the models were showing milder air pushing in by next midweek..not anymore they ain't. Let's get the deep cold in and see what develops, it looks to me as though this weekend will bring organised bands of sleet and snow southward with the arctic air digging in behind, and next week could bring several big snowfalls as lows slide SE into the very cold air..I'm delighted with this turnaround in fortunes, this winter was in dire need of revival but it's soon going to look very healthy indeed

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Steve I know this is all academic at this range and predictions are just built on experience rather than genuine certainty in the model output, but what do you think of Cambs and the western portion of East Anglia? TBH this is more of a regional question I recognise, but seems heavily model related given current synoptics. Whatever the answer to this and indeed any other IMBY posts, worth bearing in mind that even the pros don't  know the exact location of the rain/sleet/snow boundary for Saturday, let alone into next week so we should all focus on the inroad of cold as a first and foremost (he says, blushing).

 

I would phrase it 'on the cusp' - poss could stay dry though....

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So yday and even this morning it was game on for ALL.

This evening because of a few runs it's only game on for the usual suspects.

What's happened to the fluid situation that basically said you cant really call the specifics at this range?

It is fluid. People are just commenting on the current charts and posters are trying to show what that means for different areas. That sounds very reasonable and helpful to learners viewing the output. This is more than likely to change tomorrow and then maybe different areas will be favoured or maybe not.

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