Model Output Discussion

[Buzzit]

I must admit I am somewhat surprised the NAE is suggesting rain, sleet.

My personal preference is the NMM but I need to renew my subscription. Currently waiting because I don't want to put a jinx on the cold spell.

Hello TEITS

The 6Z NMM shows the chance of a brief flurry for Peterborough around midnight tonight

(is better then the 0Z for your area) However when considering 12am Monday to

12pm Monday Line is definitely more Norwich / Cambridge than Kings Lynn / Peterborough

Which i find consistant with some of the recent model output

Edited February 7, 2010 by Buzzit

[Lewis]

For those of you wondering why the models are showing rain and sleet, and then snow etc.

It's not that hard to look at conditions.

1. Is the dew point ok? "0c below"

2. Is your temperature ok? "2c-3c is still fine"

3. What are the 850's like "-8 + to avoid any marginal situation especially for coastal areas" -5 to -6 sufficient enough for areas inland.

4. Is there any modification off the North Sea? Is the flow slack? and coming off the North Sea, if it is expect some mixing.

5. Is the 500-100 thickness (DAM) at least 530 or sub 528

6. Last but not least the most important, the 0C isotherm. (0(being pefect)-200M is ok if you have pretty cold uppers and heavy precipitation, anything above a little marginal to support snow down to the surface so it would be more likely to give a wintry mix) Of course the 0C height will drop in heavier precipitation, this is why on the NAE precip charts it shows it turning to snow, as it's during the heavier precipitation.

If you look at the charts for tomorrow and at the time the precipitation falls, the 0c isotherm is around 200-300m.

Of course the above chart is at a lower resolution, so at a higher resolution and for better accuracy I recommend NW extra for the Custom Skew-t charts, and also the higher resolution NMM model. As we are coming into NMM range, i'll keep an eye on how things develop, and i'll do a post later after the 12z and 18z with regards what areas should expect to see snow.

In the mean time if you stick to all the above points, and your local conditions at the time, then you'll have a good idea of what will fall from the sky.

Hope this helps

Edited February 7, 2010 by Storm Force Lewis

[TEITS]

Hello TEITS

The 6Z NMM shows the chance of a brief flurry for Peterborough around midnight tonight

(is better then the 0Z for your area) However when considering 12am Monday to

12pm Monday Line is definitely more Norwich / Cambridge than Kings Lynn / Peterborough

Which i find consistant with some of the recent model output

Thanks ever so much for letting me know.

GEFS mean at +192 is frankly stunning and you can't ask for more.

http://91.121.94.83/modeles/gens/run/gens-21-1-192.png?6

[Bobby]

It's going to be very marginal at times with any precipitation.

Dew points above freezing here, rain/sleet especially for the coasts I'd imagine.

Doubt there will be much precipitation about anyway looking at the charts away from the SE. Probably will have to wait until that pesky high migrates to greenland and opens the Arctic floodgates which looks like being towards next weekend. In the West where a lot of people live it's going to be almost entirely dry and frost til next weekend at least.

Does look interesting after then though with the risk of widespread snow and potent cold.

[BLAST FROM THE PAST]

Nick

Sussex said

I think this has been one of the most dramatic weeks in terms of the models that many of us have ever seen. Earlier in the week it was impossible to think that we would be seeing this kind of output. All the global models this evening have finally arrived at similar patterns with easterly and the high edging nw towards Greenland later on. [/quote

Both agree and disagree with the above. IMO It wasn't impossible to think we'd be seeing this output, indeed I thought it was impossible that we would see mild SW'lies. I agree though that it has been dramatic model watching.

What i'll say is for folk not to worry to much about signs of the HP sinking as this is going to happen a little but it won't affect the cold spell or the evolution. Like I have said for a while, drier the further NW you go and SE is the favoured snow area....no doubt. Like I say 10 days but a chance of it going to 2 weeks....but don't be suprised to see the block break between 17-20 Feb and less cold air win out. But that is a long way away and plenty of cold to very cold to enjoy.

BFTP

[Nick L]

It's going to be very marginal at times with any precipitation.

Dew points above freezing here, rain/sleet especially for the coasts I'd imagine.

Doubt there will be much precipitation about anyway looking at the charts away from the SE. Probably will have to wait until that pesky high migrates to greenland and opens the Arctic floodgates which looks like being towards next weekend. In the West where a lot of people live it's going to be almost entirely dry and frost til next weekend at least.

Does look interesting after then though with the risk of widespread snow and potent cold.

That chart doesn't look marginal in the slightest to me, don't know where you are getting the "dew points above freezing" from? -3c--4c across Wales.

[Backtrack]

It's going to be very marginal at times with any precipitation.

Dew points above freezing here, rain/sleet especially for the coasts I'd imagine.

Doubt there will be much precipitation about anyway looking at the charts away from the SE. Probably will have to wait until that pesky high migrates to greenland and opens the Arctic floodgates which looks like being towards next weekend. In the West where a lot of people live it's going to be almost entirely dry and frost til next weekend at least.

Does look interesting after then though with the risk of widespread snow and potent cold.

How is that the least bit marginal?

Away from the 0c dewpoints on the East coast (Which are still sufficent enough to support snow), the dewpoints are well into negative numbers.

[SP1986]

It's easy to forget in a situation like this when the cold is portrayed on the charts that past 144 hours some big changes have the potential to happen. Even with the outlook pointing to a northerly in most we all known this can change and I imagine because the outlook is now pointing to cold the wide assumption is that it has to evolve as shown.

Unfortunately as with any evolution it's a constantly changing scenario, so we can't guarantee it will be showing cold in say 2 days at 120 hours.

How is that the least bit marginal?

Away from the 0c dewpoints on the East coast (Which are still sufficent enough to support snow), the dewpoints are well into negative numbers.

These negative dewpoints are indicative of a lack of precipitation

[Bobby]

That chart doesn't look marginal in the slightest to me, don't know where you are getting the "dew points above freezing" from? -3c--4c across Wales.

The dew points are 0 or so where the precipitation is, there is no precip over Wales. The fact precipitation will mainly be light makes it more marginal as you don't get the evaporitve cooling effect. The NAE, NMM, GFS precip charts show this rainy/sleety/snowy mix well.

[Backtrack]

It's easy to forget in a situation like this when the cold is portrayed on the charts that past 144 hours some big changes have the potential to happen. Even with the outlook pointing to a northerly in most we all known this can change and I imagine because the outlook is now pointing to cold the wide assumption is that it has to evolve as shown.

Unfortunately as with any evolution it's a constantly changing scenario, so we can't guarantee it will be showing cold in say 2 days at 120 hours.

These negative dewpoints are indicative of a lack of precipitation

Yes, although the GFS this morning is showing show showers on and off tomorrow.

I was just wondering where Barb- got this from? 'Dew points above freezing here, rain/sleet especially for the coasts I'd imagine.'

[SussexmarkyMark]

Doubt there will be much precipitation about anyway looking at the charts away from the SE. Probably will have to wait until that pesky high migrates to greenland and opens the Arctic floodgates which looks like being towards next weekend. In the West where a lot of people live it's going to be almost entirely dry and frost til next weekend at least.

Does look interesting after then though with the risk of widespread snow and potent cold.

Which charts are you looking at that suggest widespread snow and potent cold, I wonder? I've had a look through the output for the main three models this morning and they all seem to keep the very cold air to the south and east of us, with the 528 DAM line barely reaching the UK before +144, whereas a couple of days ago the 512 DAM line was making an appearance over SE England. The HP seems to be much more centred over the UK through the next four or five days, keeping the colder air over mainland Europe. Only once we get towards next weekend and beyond does any potent cold arrive in the UK which, as we all know from the last week, is well beyond the reliable time-frame.

[Bobby]

I was just wondering where Barb- got this from? 'Dew points above freezing here, rain/sleet especially for the coasts I'd imagine.'

Well look at the chart, the 0s in the East (where the precip is). That's above freezing.

Here is the GFS precip chart for the same time:

As you can see, mainly rain/sleet.

Which charts are you looking at that suggest widespread snow and potent cold, I wonder? I've had a look through the output for the main three models this morning and they all seem to keep the very cold air to the south and east of us, with the 528 DAM line barely reaching the UK before +144, whereas a couple of days ago the 512 DAM line was making an appearance over SE England. The HP seems to be much more centred over the UK through the next four or five days, keeping the colder air over mainland Europe. Only once we get towards next weekend and beyond does any potent cold arrive in the UK which, as we all know from the last week, is well beyond the reliable time-frame.

I'm talking about FI, next weekend and after. This ECM chart for example:

Edited February 7, 2010 by Barb-

[cooling climate]

It's easy to forget in a situation like this when the cold is portrayed on the charts that past 144 hours some big changes have the potential to happen. Even with the outlook pointing to a northerly in most we all known this can change and I imagine because the outlook is now pointing to cold the wide assumption is that it has to evolve as shown.

Unfortunately as with any evolution it's a constantly changing scenario, so we can't guarantee it will be showing cold in say 2 days at 120 hours.

These negative dewpoints are indicative of a lack of precipitation

The pattern that is setting up is a very stable one with massive blocking over the Arctic, ridging over western America,

troughing over east,northeast US southerly tracking jet combined with strong STJ and the UK on the northern side of

the block. I would lay money on Sunday the 14th to Saturday the 20th being very cold and wintry and infact quite

possibly much further than this.

[TEITS]

Which charts are you looking at that suggest widespread snow and potent cold, I wonder? I've had a look through the output for the main three models this morning and they all seem to keep the very cold air to the south and east of us, with the 528 DAM line barely reaching the UK before +144, whereas a couple of days ago the 512 DAM line was making an appearance over SE England. The HP seems to be much more centred over the UK through the next four or five days, keeping the colder air over mainland Europe. Only once we get towards next weekend and beyond does any potent cold arrive in the UK which, as we all know from the last week, is well beyond the reliable time-frame.

I have to ask what charts are you looking at?

528 dam line across the UK at +48 which is supported by the fax charts.

http://www.wetterzentrale.de/pics/Rtavn483.png

http://www.wetterzentrale.de/pics/brack1.gif

ECM upper temps for Thurs/Fri.

GEFS mean for Cambs.

http://cirrus.netweather.tv/ensimages/ens.20100207/06/t850Cambridgeshire.png

The forecast at the moment for next week is simple. The risk of snow showers moving into E areas from midweek onwards. This is what the Met O also suggest!

I really wish some would make the effort of actually looking at the charts!!

Edited February 7, 2010 by THE EYE IN THE SKY

[FENDER.]

Sems the really cold air keps getting put back. Now its next wekend before the fun starts

In the meantime for central and western regions, nothing too much to get excited about

[SP1986]

The pattern that is setting up is a very stable one with massive blocking over the Arctic, ridging over western America,

troughing over east,northeast US southerly tracking jet combined with strong STJ and the UK on the northern side of

the block. I would lay money on Sunday the 14th to Saturday the 20th being very cold and wintry and infact quite

possibly much further than this.

Yep just warning though that I have actually been in more stable patterns than this (apparently), in the past few years on the MO discussion which have broken down quicker than expected.

At the moment it looks good, but if it can break down (which it has to eventually sometime in the future), then it could break down at any time, as signals can change at the snap of a finger.

It does look stable at the moment though, agreed.

[Jayces]

Sems the really cold air keps getting put back. Now its next wekend before the fun starts

In the meantime for central and western regions, nothing too much to get excited about

I've been following this latest development since it was first hinted at 2 weeks ago and to be honest the knowledgeable people here have never said there would be really cold air this coming week, the forecast was for cold to slowly start and the following week to get colder and also the risk of snow really only in the NE, E, SE.

[Osbourne One-Nil]

Why is there such a prevalence of charts showing the southern UK and all of France? Are there not similar charts available showing the northern half?

[Iceberg]

We have to admit that these synoptics are pretty darn good, the 0 isotherm needs to be at around 150m for snow at ground level unless it's very light drizzle, so I think it will be cold enough.

Meto certainly seem to think so as well from their latest update.

"Friday will be cold with brisk northeasterly winds and wintry showers, these more persistent across eastern areas with the risk of significant snow accumulations, mainly in the southeast and East Anglia, possibly central and southern areas as well. Some snow showers likely across Scotland."

[TEITS]

Why is there such a prevalence of charts showing the southern UK and all of France? Are there not similar charts available showing the northern half?

Do you mean these mate?

if so then its because they are coming from the Meteociel website and to get a more detailed look at the UKMO precip charts you have to select France.

[Iceberg]

Why is there such a prevalence of charts showing the southern UK and all of France? Are there not similar charts available showing the northern half?

No the free ones don't tend to cover northern england, ( northern UK have to pay).

[SussexmarkyMark]

I have to ask what charts are you looking at?

528 dam line across the UK at +48 which is supported by the fax charts.

http://www.wetterzen...cs/Rtavn483.png

The forecast at the moment for next week is simple. The risk of snow showers moving into E areas from midweek onwards. This is what the Met O also suggest!

I really wish some would make the effort of actually looking at the charts!!

FYI I have spent quite a bit of time looking at the charts this morning. I have looked again at the same time scale as the chart that you have produced (ie the GFS +48 chart) and the one I am looking at does not show the 528 DAM over the UK. If the chart is wrong, then so-be-it, but I can only look at the charts that are being shown. So perhaps it would have been politer to ask which charts I was looking at without the rude comment to finish your post ?

http://www.weatheron...=0&ARCHIV=0&WMO=

As for my original post, I was asking where the widespread snow and potent cold was showing, which the original contributor has now clarified by explaing he was talking about FI, which is fine, but I was just wondering what he was referring to. As for your comments about the Met O, this maybe the case, but as it is a model discussion forum, it doesn't seem unreasonable that I discuss the model output this morning.

Edited February 7, 2010 by SussexmarkyMark

[Hammer]

For the week ahead, whilst not country wide, the models suggest growing cold, with an increasing risk of snow from midweek onwards. With between 9th Feb - and 14th Feb, significant snowfall in some areas quite possible, at first in SE & EA, but growing risk in more Northern and Eastern areas. Met Office themselves in their latest website updates suggest this also.

Later, any breakdown from the south west probably allowing for some snow for a time in some of the west also. Possibly significant depending on the success or failure of such a breakdown attempt.

Ok so we won't be buried in Washington style snow, but this clearly has the potential of being a fairly decent spell to start with for SE & EA but with no doubt many other areas benefiting and no doubt as can often be the case seeing more snow than what we might be considering the favoured areas at the moment.

[michail]

With this high pressure to the north of the uk (which i think originated in scandinavia?), will there be some very low minimums this week?

[Rob]

Looking good in SE and EA for some significant snow Thursday/Friday, models seem consistant in this and Meto going for it now. Should be good, as to whether the west get a blast of wintry weather later is still yet unknown.