Spring Model Discussion 18Z 6/3/13 onwards....

[Cheshire Freeze]

The gfs is so frustrating when it does this in fi , completely forgets the major negative NAO and whisks up a strong autumn like low pressure and shoots it up the uk toward northern most countries , so annoying because it gives us some implausible outcome that's not even worth looking at.

And NO this isn't because it isn't showing what I want , it's because it's doing its usual trick it does every time , you can see as soon as it get its into low res it just goes wild. The 06 recently have been performing well Iv noticed , picking out trends before the rest

It's perfectly plausible with a WB -NAO. It's a very real risk, to mitigate this risk we need heights to remain more solid and centrally across Greenland rather than heading off west. When the high retreats further west it lets the jet loop N around the UK. The upshot of this is pressure rises on the continent and the energy from the Atlantic heads NE rather than into the continent. It's undone many a cold spell.

[Captain Shortwave]

The gfs is so frustrating when it does this in fi , completely forgets the major negative NAO and whisks up a strong autumn like low pressure and shoots it up the uk toward northern most countries , so annoying because it gives us some implausible outcome that's not even worth looking at.

And NO this isn't because it isn't showing what I want , it's because it's doing its usual trick it does every time , you can see as soon as it get its into low res it just goes wild. The 06 recently have been performing well Iv noticed , picking out trends before the rest

Yep, from what I saw greenland high to greenland polar vortex in just 96 hours. It took 2 months to get that damn thing to move .

Either way beyond T120 is fi now if not earlier. There seems to be some energy moving south East from Greenland UKMO and GEM really blow this up. The differences between the 00z GEM and the 12z is completely laughable.

[Methuselah]

The gfs is so frustrating when it does this in fi , completely forgets the major negative NAO and whisks up a strong autumn like low pressure and shoots it up the uk toward northern most countries , so annoying because it gives us some implausible outcome that's not even worth looking at.

And NO this isn't because it isn't showing what I want , it's because it's doing its usual trick it does every time , you can see as soon as it get its into low res it just goes wild. The 06 recently have been performing well Iv noticed , picking out trends before the rest

But the NAO is only arithmetical index, derived from the synoptic pattern anyway, SSIB...

[Dave Kightley]

GEM is also further North like the GFS for snow in the South. The Low pressure moving down from the north next week is the next thing to keep a eye on. If it clears South or South east we will be back in an Easterly again maybe (colder uppers moving back west). The models will take a few days to sort this out.

Edited March 8, 2013 by Dave Kightley

[Cheshire Freeze]

Yep, from what I saw greenland high to greenland polar vortex in just 96 hours. It took 2 months to get that damn thing to move .

Either way beyond T120 is fi now if not earlier. There seems to be some energy moving south East from Greenland UKMO and GEM really blow this up. The differences between the 00z GEM and the 12z is completely laughable.

The issue with the UKMO is it drops that low due S with only a very slight E movement. at 168 it's certain to have phased with that low to the SW and we'd be in the same situation as the GFS come low res. Really need more of a SE or ESE movement of that low and keep it well clear of engaing with that jet at the worst possible moment that it could,.

[mushymanrob]

But the NAO is only arithmetical index, derived from the synoptic pattern anyway, SSIB...

does it drive the synoptic pattern or does the synoptic pattern create the nao?

[weather eater]

Potential for a proper channel low, we haven’t seen this sort of scenario for a good few years, a lot will depend on how much precipitation but with gale force winds we would see genuine blizzard conditions so drifting snow will be a real hazard if the precipitation is high.

[CWT2012]

Mixed feelings about that channel low

If it hits us then there could well be record breaking snow for the time of year but if it sinks south and misses us we are kept in the freezer for longer and more chance of reloads from the north and east

12"+ on Tuesday or a few more snow events, hard choice

[Thundery wintry showers]

does it drive the synoptic pattern or does the synoptic pattern create the nao?

A common question- I think the short answer is that the synoptic pattern creates the NAO, since the NAO is just a measure of the mean pressure difference between two places (for example Iceland and the Azores).

[chris55]

The northward extent of the Low pressure and the associated fronts Sunday/Monday certainly could produce a noteworthy snow event for some. The question is where?

At present I'd say southern counties south of the M4 are looking pretty good, however GEFS 12z shows the uncertainty. Some members takes the ppn to the south whereas some have it as far north as Northern England, and some in-between. From an IMBY perspective a nudge north would be nice, but regardless of IMBYism this could certainly produce the goods for some!

The two extremes

Misses to the south,

Up Towards Scotland,

Edited March 8, 2013 by chris55

[weather eater]

does it drive the synoptic pattern or does the synoptic pattern create the nao?

The synoptic pattern creates the NAO, positive or natural or negative, if negative it really just means pressure is high over Greenland and low in the Azores unless its a west based NAO, of course what state the NAO is in has a knock on effect for weather over northern Europe so in that regard it effects our synoptics.

Here is a good description

http://www.nc-climat...tterns/NAO.html

Edited March 8, 2013 by weather eater

[BLAST FROM THE PAST]

So as recently as this morning Carol Kirkwood said 'snowfall not anticipated to be problematic 'anywhere'. Lets see how or if the forecast changes. Many on here have suggested [for days] it would produce more than unproblematic snow. This is dynamically developing situation...however, due to the depth of cold and set up it always looked a possibilty. Great call if the system shunts south and there's no streamers/ almagamted bands of showers, but we are close to this happening now.

I mentioned freeze frame of the day re ECM, well another has popped up and its the UKMO at T144. That LP is diving SSE but to the west side bumping into embedded very cold air. That could be a very interesting 'second' scenario.

and 00z ECM at same timeframe

BFTP

Edited March 8, 2013 by BLAST FROM THE PAST

[Thundery wintry showers]

Looking over the potential for snowfall this weekend, it looks like the main frontal system moving southwards on late Saturday and into Sunday will produce mostly rain and sleet at low levels, with snow on high ground. Into Sunday, the easterly flow to the north of it will be associated with a dry stable layer starting at around the 750-800hPa level but vigorous convection below it, so we can expect fairly shallow convection and a fair amount of cloud, with a mix of scattered snow showers and some sunny intervals. Most of the showers are likely to be concentrated near North Sea coasts but a few well-scattered showers may also break out inland on Sunday afternoon thanks to solar heating.

As we head into Monday, a low pressure system to the south of the English Channel may throw up another frontal zone and this may well produce significant snowfalls on its northern flank as it engages the cold air, but at the moment its positioning is still prone to revision. Further north, the dry stable layer associated with the easterly is forecast to strengthen and penetrate to lower altitudes and thus the weather is likely to turn increasingly dry and cloudy. I think many places to the east of high ground will have up to a few centimetres of snow on Monday morning, but larger 5-10cm falls will only be localised.

The skew-t forecasts for Hull show this up quite well, with a dry stable sector above the 750hPa level at 2100 on Sunday, but by Monday night it extends below the 850hPa level and the implication is dry cloudy conditions:

http://nwstatic.co.uk/gfsimages/tempskew/skew0.762959337866963.png

http://nwstatic.co.uk/gfsimages/tempskew/skew0.0596456528446687.png

On Tuesday and Wednesday as the winds swing around to the north the weather is set to turn somewhat brighter with a scattering of wintry showers and temperatures of 5-8C by day, before it turns colder and more unsettled again at the end of the week.

[Ian Brown]

The issue with the UKMO is it drops that low due S with only a very slight E movement. at 168 it's certain to have phased with that low to the SW and we'd be in the same situation as the GFS come low res. Really need more of a SE or ESE movement of that low and keep it well clear of engaing with that jet at the worst possible moment that it could,.

If UKMO went to T168 and T192 we wouldn't be looking at mild, the low would be a slider and we would be on the cold side of the PFJ.

[Captain Shortwave]

The issue with the UKMO is it drops that low due S with only a very slight E movement. at 168 it's certain to have phased with that low to the SW and we'd be in the same situation as the GFS come low res. Really need more of a SE or ESE movement of that low and keep it well clear of engaing with that jet at the worst possible moment that it could,.

Yep, the GEFs have some real stinkers in there from a cold point of view. greenland energy drops straight south on quite a few which builds the Azores high right over the UK.Lets just say there are a lot of ensembles that Gavin would be happy with and this is only at day 7. Whatever shortwaves develop over southern Greenland/Iceland, we need these to go east. The more east they go the better as they engage troughing over Scandinavia instead of the low in the Atlantic.

[chris55]

So as recently as this morning Carol Kirkwood said 'snowfall not anticipated to be problematic 'anywhere'. Lets see how or if the forecast changes. Many on here have suggested [for days] it would produce more than unproblematic snow. This is dynamically developing situation...however, due to the depth of cold and set up it always looked a possibilty. Great call if the system shunts south and there's no streamers/ almagamted bands of showers, but we are close to this happening now.

I mentioned freeze frame of the day re ECM, well another has popped up and its the UKMO at T144. That LP is diving SSE but to the west side bumping into embedded very cold air. That could be a very interesting 'second' scenario.

and 00z ECM at same timeframe

BFTP

GFS showing a similar evolution, though a little earlier,

[bobbydog]

Looking over the potential for snowfall this weekend, it looks like the main frontal system moving southwards on late Saturday and into Sunday will produce mostly rain and sleet at low levels, with snow on high ground. Into Sunday, the easterly flow to the north of it will be associated with a dry stable layer starting at around the 750-800hPa level but vigorous convection below it, so we can expect fairly shallow convection and a fair amount of cloud, with a mix of scattered snow showers and some sunny intervals. Most of the showers are likely to be concentrated near North Sea coasts but a few well-scattered showers may also break out inland on Sunday afternoon thanks to solar heating.

As we head into Monday, a low pressure system to the south of the English Channel may throw up another frontal zone and this may well produce significant snowfalls on its northern flank as it engages the cold air, but at the moment its positioning is still prone to revision. Further north, the dry stable layer associated with the easterly is forecast to strengthen and penetrate to lower altitudes and thus the weather is likely to turn increasingly dry and cloudy. I think many places to the east of high ground will have up to a few centimetres of snow on Monday morning, but larger 5-10cm falls will only be localised.

The skew-t forecasts for Hull show this up quite well, with a dry stable sector above the 750hPa level at 2100 on Sunday, but by Monday night it extends below the 850hPa level and the implication is dry cloudy conditions:

http://nwstatic.co.u...59337866963.png

http://nwstatic.co.u...56528446687.png

On Tuesday and Wednesday as the winds swing around to the north the weather is set to turn somewhat brighter with a scattering of wintry showers and temperatures of 5-8C by day, before it turns colder and more unsettled again at the end of the week.

ahh shut yer face ian, we're getting 3 feet!!

[Cheshire Freeze]

Yep, the GEFs have some real stinkers in there from a cold point of view. greenland energy drops straight south on quite a few which builds the Azores high right over the UK.Lets just say there are a lot of ensembles that Gavin would be happy with and this is only at day 7. Whatever shortwaves develop over southern Greenland/Iceland, we need these to go east. The more east they go the better as they engage troughing over Scandinavia instead of the low in the Atlantic.

Yep, stinker of an ensemble mean, which I feel is well supported now

You see the importance of that shortwave/low. It promotes a pressure rise around the UK and Atlnatic energy heads NE instead of heading into the continent. Poor really from a cold perspective and quite a flip from previous suites.

If UKMO went to T168 and T192 we wouldn't be looking at mild, the low would be a slider and we would be on the cold side of the PFJ.

Ian, you only have to look at the GEFS to see what would happen. A not insignificant number of perturbations have us in a S'ly flow at 192.

Control run at 216...

These little shortwaves/LPs around Iceland, once picked up, tend to not be dropped from the ouput IMO and have a tendency to erode the cold/chances of cold quicker and quicker. Not good going forward so far this evening. The 18z last night was as good as it could have got.

Edited March 8, 2013 by CreweCold

[Ian Brown]

Yep, stinker of an ensemble mean, which I feel is well supported now

You see the importance of that shortwave/low. It promotes a pressure rise around the UK and Atlnatic energy heads NE instead of heading into the continent. Poor really from a cold perspective and quite a flip from previous suites.

Ian, you only have to look at the GEFS to see what would happen. A not insignificant number of perturbations have us in a S'ly flow at 192.

Control run at 216...

Yes i see what you mean, though it is far from certain that it will develop in that way. Anyway it will be the second half of March by then and I don't think too may will be bothered if thats what plays out !

[BLAST FROM THE PAST]

Aaron

The UKMO though still has two ways to go I reckon. The development looks like it could follow the ECM, which is the best position. At t144 we are certain to see adjustments but one to watch for sure. Its interesting as there is an anticipated 'wild' swing from very cold to quite mild/warm anticipated last 3rd of March.

BFTP

Edited March 8, 2013 by BLAST FROM THE PAST

[Cheshire Freeze]

Yes i see what you mean, though it is far from certain that it will develop in that way. Anyway it will be the second half of March by then and I don't think too may will be bothered if thats what plays out !

It limits the chance of us seeing snow though Ian as realistically I think the south is likely to be the place to see the snow judging by the output. We're reliant on showers and as TWS has pointed out, convection looks to be capped (which I initially wouldn't have thought). Our chances were probably higher later in the week.

[mushymanrob]

The synoptic pattern creates the NAO, positive or natural or negative, if negative it really just means pressure is high over Greenland and low in the Azores unless its a west based NAO, of course what state the NAO is in has a knock on effect for weather over northern Europe so in that regard it effects our synoptics.

Here is a good description

http://www.nc-climat...tterns/NAO.html

thanks.

[Purga]

Potential for a proper channel low, we haven’t seen this sort of scenario for a good few years, a lot will depend on how much precipitation but with gale force winds we would see genuine blizzard conditions so drifting snow will be a real hazard if the precipitation is high.

METO are very mediocre about any snow impact for the SE

Outlook for Sunday to Tuesday:

Cold with brisk northeasterly winds giving a marked chill. Sunday, cloudy with rain, sleet and snow becoming mostly light. Clearing early on Monday, then brighter with a few snow showers.

Updated: 1535 on Fri 8 Mar 2013

I'll go back to sleep..

[Summer Sun]

12z ensembles

Looking like Monday will see the peak of the cold

[Cheshire Freeze]

12z ensembles

Looking like Monday will see the peak of the cold

Yes but we have to be careful when using ensembles in this scenario. The situation portrayed is one where very small differences in that SW behaviour will have huge rammifications on our weather....this being tied in to the behaviour of the GH. At present the pendulum has swung in favour of milder next weekend but it's one of those situations where individual ensemble suites can change at the drop of a hat.

I've said before, the GFS ensembles can be about as useful as a catflap on a submarine. This may be one of those occassions.

If the next suite decides to follow the ideas of one of the colder members than the whole set will have a completely different complexion.

Edited March 8, 2013 by CreweCold