Spring Model Discussion 17/3/13 6PM onwards....

[snowking]

I'm going to hazard a guess that this mornings Met Office update may have been based upon the EC det this morning (and to a certain extent the EPS mean) as opposed to the UKMO GM (which gives just a leading edge snow to rain event).

The det. keeps the 30F dewpoint line in a pretty similar position to that described last night, though the western flank of the line moves south from Anglesey to Aberystwyth, only moving north of the Midlands for a period of around 12 hours between midnight and midday Saturday.

At the moment, the best location to me looks to be N Ireland from this mornings output, especially looking at the location of the triple point on the FAX charts.

I can only assume that the MOGREPS-R is suggesting something similar to the EC det. this morning. I'm awaiting the control run data which should be through around 11am.

Very odd though that they produce a public facing forecasting suggesting mostly snow north of the M4 through to Saturday, then produce a FAX chart like this:

The only thing that you could say here is the initial slow movement of the warm front:

May cause sufficient uplift to create persistent snow ahead of the warm front as it heads into the colder air mass, but once that warm front passes your location, its pretty much game over for snowfall.

SK

Edited March 19, 2013 by snowking

[Tim Bland]

06Z NAe has Dew point temps ranging from 0c on the south coast to -6C in the north east, Precip is making inroads to the south west.

Met office forecaster on bbc 3 counties (Herts, Beds & bucks) has just said sleet turning to snow and becoming persistent on Fri / Sat, This is for the area just south of the midlands. If there is a an easterly flow ahead of the prcip and dep points remain 0c or below then the upper temps need only be -1c or lower for snow. Some are analysing the NWP and only looking at the upper temps and assuming anything aove -5c will be rain.

IMO the only areas likely to miss out on the snow is the south west, extreme south and coastal wales etc. Not saying it will be drifting and powdery but most areas will see sleet / snow for a while

[Summer Sun]

Just looked at the ECM ensemble midlands north (east Anglia is the exception at first for the south) remains cold for now the south never gets cold enough for snow

Less cold air spreads to all by the end

ECM looks like a cold outlier to me especially for those in the south

[snowking]

Latest ECM32 might gradually turn things less cold as we head towards April, but still well below the seasonal average:

Though the hope of things turning a little drier the further on we go:

SK

EDIT: Whilst we're looking at the Birmingham ensembles, might be worth taking a look at just how many members went with the cold swing on yesterdays 12z ensembles:

Edited March 19, 2013 by snowking

[cooling climate]

With the flip flopping the ECM has been showing in it previous runs post

t144 I must admit to being very surprised this morning to find the model

backing its 12z run from yesterday. In fact this is an even colder run

although it may be an extreme solution to what may eventually be a more

watered down version.

I certainly will not be so keen to discard it now that it has shown some

consistency over its last two runs.

[Harsh Climate]

Regarding the snow potential later this week I think the general rule is, the further north east you are your greatest risk of snow.

GFS is a pretty none event for most, maybe some preceding snow for a time quickly turning to rain in most areas. Perhaps a little wintryness remaining in north east scotland as they just hang on to the south easterly breeze.

ECM has some snow for the midlands but probably turning back to rain, but northern england looks prime for some heavy snowfall if these charts were to come to fruition. Scotland would probably get in the act later on two.

UKMO - Probably similar to the ECM but a bit more watered down.Still plenty of snow in northern england/scotland (probably a bit of alltitude required in northern england at first.)

So from looking at the models this morning I think things are swinging back in favour of prolonged cold/snow. I would discount the GFS operational at the moment as it is clearly one of the milder members of its esembles and there are a lot of good perpetrations at around -10 (850s) for this weekend.

I'm not sure why some sources have northern ireland at primary risk this weekend as they are closer to the centre of the low pushing in this week and therefore the warmer air wrapped around the southern flank of the low has less far to travel to reach that area. Also places in the west are further away from the keen easterly wind filtering colder air over the british isles.

[Harsh Climate]

GFS 6z already swinging more towards the UKMO/ECM

528 dam line a good 200 miles further south west than on the 00z

Edited March 19, 2013 by Harsh Climate

[SomeLikeItHot]

The 6z puts higher pressure over the UK, keeping it slightly colder over much of the UK on Friday, and forcing a more elongated low compared with the 12z. Will it keep correcting this direction in future runs?

And the 12z

[Matty M]

Yes the updated GFS 6z is ~50-100miles further southwest.

Just another 100/150mile shift southwest please

[cooling climate]

06Z NAe has Dew point temps ranging from 0c on the south coast to -6C in the north east, Precip is making inroads to the south west.

Met office forecaster on bbc 3 counties (Herts, Beds & bucks) has just said sleet turning to snow and becoming persistent on Fri / Sat, This is for the area just south of the midlands. If there is a an easterly flow ahead of the prcip and dep points remain 0c or below then the upper temps need only be -1c or lower for snow. Some are analysing the NWP and only looking at the upper temps and assuming anything aove -5c will be rain.

IMO the only areas likely to miss out on the snow is the south west, extreme south and coastal wales etc. Not saying it will be drifting and powdery but most areas will see sleet / snow for a while

Um that is an unexpected and interesting forecast along with hints from the 0z ECM and

the 06z GFS that with a better orientation and perhaps undercut the snow line may

very well be moving back further south as we head towards the weekend.

As Crew Cold pointed out I may well have been premature in calling it game

set and match yesterday as far as the weekend is concerned.

Edited March 19, 2013 by cooling climate

[snowking]

I'm not sure why some sources have northern ireland at primary risk this weekend as they are closer to the centre of the low pushing in this week and therefore the warmer air wrapped around the southern flank of the low has less far to travel to reach that area. Also places in the west are further away from the keen easterly wind filtering colder air over the british isles.

Perhaps because its not quite as simple as that HC.

Perhaps its because at no stage does the ECM bring that 0c 850 isotherm away from N Ireland:

Perhaps its because at the same time as this, the heaviest of the precipitation occurs across northern ireland:

And perhaps its because at the same time the ECM projects the heaviest totals across N Ireland:

Maybe I should have provided a footnote to suggest that this was based upon the 0z ECMWF det, but this is why 'some sources' suggest N Ireland could be a good spot based upon the latest data

SK

[shaky]

Well well gfs correctiing southwards again!!lets hope it continuous!!i still think the midlands and north of england are the places to be for snowfall continuously!!

[Harsh Climate]

Perhaps because its not quite as simple as that HC.

Perhaps its because at no stage does the ECM bring that 0c 850 isotherm away from N Ireland:

Perhaps its because at the same time as this, the heaviest of the precipitation occurs across northern ireland:

And perhaps its because at the same time the ECM projects the heaviest totals across N Ireland:

Maybe I should have provided a footnote to suggest that this was based upon the 0z ECMWF det, but this is why 'some sources' suggest N Ireland could be a good spot based upon the latest data

SK

Sorry but you have just totally contradicted yourself there SK,

You say northern ireland has the lowest 0C degree isotherm throughout but does it???

You will find that the further north east you are the lower these are. Probably because we have colder continental air undercutting the warmer air mass, this is why being close to that colder continental (easterly breeze) airmass is so important. It keeps the dew point down as well as lowering the effects of the much milder weather pushing up from the south.

You are completly mis-reading the charts SK,

If this chart was to come to fruition and lets say the warm front was to remain stationary (obviously it wont ; ) ) it would be the midlands at risk of snow, not northern ireland. The reason again because they have a feed of the colder airmass to the east, of which northern ireland doesn't.

[snowking]

Sorry but you have just totally contradicted yourself there SK,

You say northern ireland has the lowest 0C degree isotherm throughout but does it???

You will find that the further north east you are the lower these are. Probably because we have colder continental air undercutting the warmer air mass, this is why being close to that colder continental (easterly breeze) airmass is so important. It keeps the dew point down as well as lowering the effects of the much milder weather pushing up from the south.

You are completly mis-reading the charts SK,

If this chart was to come to fruition and lets say the warm front was to remain stationary (obviously it wont ; ) ) it would be the midlands at risk of snow, not northern ireland. The reason again because they have a feed of the colder airmass to the east, of which northern ireland doesn't.

Hmmm

First of all, the charts you have posted are from the GFS, when I quite clearly stated that these views were based upon the ECMWF

Never the less, ignoring this oversight, the next stage of your post is plain crazy. lets dissect it:

"You say northern ireland has the lowest 0C degree isotherm throughout but does it???"

No I didnt, at no stage did I say N Ireland has the lowest anything

Heres what I said:

"Perhaps its because at no stage does the ECM bring that 0c 850 isotherm away from N Ireland"

So please point out there where I said that Northern Ireland had the lowest 0c isotherm?

Secondly:

"You say northern ireland has the lowest 0C degree isotherm throughout but does it???"

Wrong again i'm afraid.

Lets look again at what I said should we:

"Perhaps its because at no stage does the ECM bring that 0c 850 isotherm away from N Ireland."

Which, as far as I can see from the 0z ECMWF, is completely factual. Heres the charts again to support it:

So when you suggest:

"You are completly mis-reading the charts SK"

I'm not entirely sure where you are coming from, as I have now posted countless charts to support what I have been suggesting this morning (based around the 0z ECMWF det.).

Its more a case of you appear to have been mis-reading my posts, which seems to have caused some confusion

SK

Edited March 19, 2013 by snowking

[Matty M]

Sorry but you have just totally contradicted yourself there SK,

You say northern ireland has the lowest 0C degree isotherm throughout but does it???

You will find that the further north east you are the lower these are. Probably because we have colder continental air undercutting the warmer air mass, this is why being close to that colder continental (easterly breeze) airmass is so important. It keeps the dew point down as well as lowering the effects of the much milder weather pushing up from the south.

You are completly mis-reading the charts SK,

If this chart was to come to fruition and lets say the warm front was to remain stationary (obviously it wont ; ) ) it would be the midlands at risk of snow, not northern ireland. The reason again because they have a feed of the colder airmass to the east, of which northern ireland doesn't.

I don't think he is mis-reading the charts HC.

Yes they are nearer the warm sector but its a combination of being in the heaviest precipitation and on the right side of the 0c isotherm.

SnowKing is just conveying what is the ECM Det output. ECM Det gives the heaviest snow in that region.

Of course areas north and east are more secure for snow actually falling rather than rain but SnowKing is just illustrating where the heaviest stuff MAY occur as per the ECM Det

Edited March 19, 2013 by Matty M

[Tamara]

06Z NAe has Dew point temps ranging from 0c on the south coast to -6C in the north east, Precip is making inroads to the south west.

Met office forecaster on bbc 3 counties (Herts, Beds & bucks) has just said sleet turning to snow and becoming persistent on Fri / Sat, This is for the area just south of the midlands. If there is a an easterly flow ahead of the prcip and dep points remain 0c or below then the upper temps need only be -1c or lower for snow. Some are analysing the NWP and only looking at the upper temps and assuming anything aove -5c will be rain.

IMO the only areas likely to miss out on the snow is the south west, extreme south and coastal wales etc. Not saying it will be drifting and powdery but most areas will see sleet / snow for a while

At the risk of sounding IMBY, but meant purely from an exclusive synoptic viewpoint of possibilities i wouldn't rule out snow anywhere in the UK within the 7 to 10 day period the way the models are trending. The ECM would produce snow for southern regions if its overnight output verified through the latter period with an undercutting low, very low dewpoints and very cold surface air off the continent. At the same time, the upper temperatures are fairly low anyway - plus the low disrupts into France. It isn't as severe of course, but there are similarities with what happened just over a week since..

Clearly the GFS is now also thinking along similar lines

Edited March 19, 2013 by Tamara Road

[Frosty.]

According to the Gfs 06z, there is no sustained mild weather until T+216 hours onwards which means the breakdown to the current pattern is now way off in FI, let's also remember the gfs eastward bias and it's default mode comfort zone, there is no clear signal for an end to the current pattern and judging by the ecm 00z, the cold is likely to become even more entrenched as time goes by. Some parts of the uk are going to get buried in snow later this week and through the weekend with strengthening SEly to Ely winds bringing drifting, we already have a taste of that today for eastern scotland and ne england with some of that disruptive snow spreading further south tonight into tomorrow, a taster of things to come later this week.

[Harsh Climate]

I don't think he is mis-reading the charts HC.

Yes they are nearer the warm sector but its a combination of being in the heaviest precipitation and on the right side of the 0c isotherm.

SnowKing is just conveying what is the ECM Det output. ECM Det gives the heaviest snow in that region.

Of course areas north and east are more secure for snow actually falling rather than rain but SnowKing is just illustrating where the heaviest stuff MAY occur as per the ECM Det

''Of course areas north and east are more secure for snow actually falling rather than rain''

Yep that's the point I was making and why I think the further north east you are this weekend the gretest the chance of good snowfall. The reason I dismissed northern ireland being the primary risk I just think any snowfall there would be transient unlike what the north east could get (thus why I have them at highest risk.)

But SK seemed to get angry because my ideas of what will happen this weekend are a little different to his

And he seems to be underplaying the importance of having that all important feed of cooler continental air to undercut anything milder approaching from the south west. Just look at any chart and you will see the winds circulating around the approaching low later this week has it coming directly around the low from the ATLANTIC ocean into northern ireland, whereas areas to the north east have a feed coming from the COLDER east!

You can look at all the charts you want but common sence and experience tells you that is why the north east is at current highest risk.

I would even put my neck on the line and say I think Northeastern most parts of england and south eastern scotland will get the most snow come the end of the week!

Edited March 19, 2013 by Harsh Climate

[bluearmy]

It might be worth looking at the surface wind flow charts on ukmo/gfs. se or east which will keep dp's supressed the further south you go wrt the uppers. as you head north, the uppers sutain snowfall chances anyway.

i'm sure ian will update later re exeter's 'hidden' modelling. safe to say that its too early for any forecast to have any confidence at all.

[Dancerwithwings]

John hammond on the bbc forecast for friday quote " blizzards for parts of the midlands northwards"

Edited March 19, 2013 by dancer with wings

[Thundery wintry showers]

A slow-moving front is currently keeping things pretty grey over parts of southern Scotland and northern England, with snow on the northern flank of the system and with brighter showery weather for the north and south of the country. Into tomorrow the front will still be there but it is set to weaken, so the brighter showery weather should establish more widely:

http://www.wetterzen...ics/brack0a.gif

The GFS is going for a mix of sunny intervals and scattered wintry showers away from that frontal system, though cloud may well remain quite stubborn along the frontal belt.

I think Thursday/Friday may well be an all rain event in parts of southern and south-western Britain, and the heavy rainfall may lead to renewed flooding problems:

http://cdn.nwstatic..../60/h500slp.png

http://cdn.nwstatic....0/ukmaxtemp.png

but once the belt gets to the Midlands it is likely to start turning to snow at low levels. There is currently fairly strong agreement on a significant frontal snow event over northern England, perhaps into southern Scotland, on Friday/Saturday before the front gradually fizzles out.

http://cdn.nwstatic..../84/h500slp.png

http://cdn.nwstatic....4/ukmaxtemp.png

UKMO, ECMWF and GFS are now all agreed on the return of a cold easterly flow after Saturday. Despite the cold 850hPa temperatures I have a feeling that if this verifies it will be a mainly dry, cloudy and cold type of easterly- the GFS precipitation outputs aren't suggesting much showery activity over the North Sea except in eastern Scotland, and with a straight airflow off the continent there is a high probability of a dry stable capping layer developing at around 700-850hPa. An east to north-easterly regime may be more likely to bring snow showers to eastern areas but it currently isn't what the models are showing.

Edited March 19, 2013 by Thundery wintry showers

[fergieweather]

It might be worth looking at the surface wind flow charts on ukmo/gfs. se or east which will keep dp's supressed the further south you go wrt the uppers. as you head north, the uppers sutain snowfall chances anyway.

i'm sure ian will update later re exeter's 'hidden' modelling. safe to say that its too early for any forecast to have any confidence at all.

As of last night they favoured a consensus between GFS and MOGREPS into trend period, given good agreement between them, but a 'nod' towards EC longer-term solution. Update on 00z suites due imminently.

[Matty M]

''Of course areas north and east are more secure for snow actually falling rather than rain''

Yep that's the point I was making and why I think the further north east you are this weekend the gretest the chance of good snowfall. The reason I dismissed northern ireland being the primary risk I just think any snowfall there would be transient unlike what the north east could get (thus why I have them at highest risk.)

But SK seemed to get angry because my ideas of what will happen this weekend are a little different to his

And he seems to be underplaying the importance of having that all important feed of cooler continental air to undercut anything milder approaching from the south west. Just look at any chart and you will see the winds circulating around the approaching low later this week has it coming directly around the low from the ATLANTIC ocean into northern ireland, whereas areas to the north east have a feed coming from the COLDER east!

You can look at all the charts you want but common sence and experience tells you that is why the north east is at current highest risk.

I would even put my neck on the line and say I think Northeastern most parts of england and south eastern scotland will get the most snow come the end of the week!

Unfortunately you are simplifying the matter too much. The flow is not as simple as just following the isobars. The surface flow can be quite different, with the angle of adjustment varying.

Let's just take a quick example from the 6z GFS.

Isobars over Ireland might indicate a southerly or southeasterly to a viewer but in reality the surface wind is easterly.

[Harsh Climate]

Unfortunately you are simplifying the matter too much. The flow is not as simple as just following the isobars. The surface flow can be quite different, with the angle of adjustment varying.

Let's just take a quick example from the 6z GFS.

Isobars over Ireland might indicate a southerly or southeasterly to a viewer but in reality the surface wind is easterly.

I see where your coming from but not when the isobars are tightly packed packed together with near gale force winds. The milder air would filter down into the lower atmosphere in no time at all.

[Frosty.]

As of last night they favoured a consensus between GFS and MOGREPS into trend period, given good agreement between them, but a 'nod' towards EC longer-term solution. Update on 00z suites due imminently.

That sounds like a progressively more unsettled spell developing during second half of this week and the weekend with snow to rain but perhaps staying as snow across the far north/ne of the uk, temps becoming less cold/milder in the south & west but feeling cold in the wind and rain, then colder uppers spreading south/sw to all areas after a less cold interlude, also a chance of major disruptive snow in the transition and more generally across more northern parts of the uk?

Edited March 19, 2013 by Frosty039