General Model Output Discussion

[TEITS]

The Leicestershire Snow drought continues , we now need to look towards Saturday night , with that little shortwave trying to bring a trough down from the North , looks as though it might die out as it moves south currently but it needs to be watched.

Im not so sure you will have to wait till Saturday.

I hope Paul forgives me for posting this from the NMM model but this is for tonight.

I believe conditions are very favourable for this to occur based on my local knowledge. Im not expecting huge amounts but I shall be glued to the radar this evening.

[Paul]

Anyone ever seen the signs in car parks - "So far this week xx cars have been clamped for not paying and displaying".

Well here's the netweather version:

So far in the last 48 hours 4 people have been stopped from posting for continuously posting off topic in the model threads (despite direct and indirect requests not to)

Based on this morning's posts we could easily double that as some posters aren't just posting the odd off topic or wandering post (which is fair enough), but they're posting off topic time after time in here. There's no valid reason to do it, there are plenty of other threads available (including a model chat thread for the shorter, more light hearted model related comments), so it's just laziness and a lack of respect for the other members of the forum, and with that in mind we have no qualms whatsoever in stopping the worst offenders from posting...

[andy_leics22]

Im not so sure you will have to wait till Saturday.

I hope Paul forgives me for posting this from the NMM model but this is for tonight.

I believe conditions are very favourable for this to occur based on my local knowledge. Im not expecting huge amounts but I shall be glued to the radar this evening.

TEITS correct me if i'm wrong but I have seen the wind directions that the models give for tonight and they are NE, NE wind will push those showers through the Wash and down towards Northants, Leicester will most likely not get a flake, I have seen this happen before in NE'erlys.

Edited December 31, 2009 by andy_leics22

[snowmadchrisuk]

Im not so sure you will have to wait till Saturday.

I hope Paul forgives me for posting this from the NMM model but this is for tonight.

I believe conditions are very favourable for this to occur based on my local knowledge. Im not expecting huge amounts but I shall be glued to the radar this evening.

I can see there is a 12 hour window as the winds swing round. What are the current SST's like in the North sea, I expect they may have cooled a bit with all this cold air about.

[karyo]

Is it me, or does there appear to be a mild sector entrenched within that.

Hard to say on the precipitation chart. The bbc forecast talked only about snow showers (no rain) and the gfs is showing uppers lower than -5 so we should be ok.

I'll be flying back from Amsterdam tomorrow morning, so hope to see the snow clouds from above!

Karyo

[Bolton67]

CMC Precipitation accumulations +144

Show NE scotland and the NE of England getting the brunt.

[Lewis]

I can see there is a 12 hour window as the winds swing round. What are the current SST's like in the North sea, I expect they may have cooled a bit with all this cold air about.

Hi Chris,

They have cooled down a fair bit since the last cold snap, but they are still considerably warm enough to be a convective machine.

Here is the latest chart showing the North Sea's SST'S;

[Southender]

Im not so sure you will have to wait till Saturday.

I hope Paul forgives me for posting this from the NMM model but this is for tonight.

I believe conditions are very favourable for this to occur based on my local knowledge. Im not expecting huge amounts but I shall be glued to the radar this evening.

Hi TEITS. That PPN distribution looks very similar to what happened on 17/18th of this month?

2 lines of snow again. One affecting the Wash and areas to the SSW and the other affecting the coastal areas of Norfolk, Suffolk, Essex and more Central/West parts of Kent/Sussex. With that horrible dry slot in the middle.

Or am I way off the mark?

Edited December 31, 2009 by LeighShrimper

[weather eater]

Yes, at least. The severe warning I issued which RRR initially had on his sig was for real. This is a humdinger of a cold spell coming AND WILL STAND UP TO ANY OF THE GREATS IN 70s and 80s......wtach this space and watch for snowfall upgrades. Not everywhere will get it at the same time but each fall 3-5, 7-10, 15-20 will be very notable for those that have it.

Just got to love the post from JH above, that one is what NW community need to take note of.

BFTP

It certainly looks a classic 80s style cold spell, though I doubt it will come close to the great spells, if only because I see no mega falls of snow for much of the country, especially in the west, plenty of time for that to change. As for Blizzards, they need strong winds and although the 06z has a spell from the mid range it does look rather dry to my eyes, this may also change. I think we need to hold back on the hyperbole until events are in the can, we have seen over the last few days the weeping, wailing and gnashing of teeth that occurs when sections of the NW community gets their hopes up, often influenced by posts short on detail, low on specifics, but high on hyperbole. We do have a window this month for something special, but mainly dry and cold is not what most members want, reading GP post on the technical thread he hints at the possibility of a blowtorch February if this turns out to be correct, given that he has been on the ball so far this autumn and winter, then we need it to happen this month. Don't get me wrong, this has been a great start to winter, but I like my money in the bank, not on a promise of the lottery win that is the UK climate.

[Alex95]

CMC Precipitation accumulations +144

Show NE scotland and the NE of England getting the brunt.

I find those charts a little misleading, it shows 43mm of precipitation (over 40cm of snow) just off the coast of NE England, but that figure would probably apply to anywhere within about 10 miles of the coast and the showers sometimes actually intensify as they hit land before dying out.

All in all though that is a fantastic chart for this area, some people are predicting 5cm for this area, I think 10-20cm at least would be safer bet.

[Paul]

Im not so sure you will have to wait till Saturday.

I hope Paul forgives me for posting this from the NMM model but this is for tonight.

I believe conditions are very favourable for this to occur based on my local knowledge. Im not expecting huge amounts but I shall be glued to the radar this evening.

No problem TEITS, although the 6z has backed away from that a touch, with a lot less precip getting inland (look for a new version of that precip type chart in the new year btw)

[johnholmes]

Looking at the latest set of Fax charts from Exeter they look more coherent and to me, more sensible, in that they have dropped the idea they ran last evening of an actual low with warm and cold fronts tracking south over the country. In its place are a succession of troughs/minor lows, tracking south down the North Sea with some suggestion on their T+120 of an actual front.

This gives a better pattern it seems to me with the trough enhancing wintry shower activity on each one. Their effect will be to move a spell of showers further inland than would otherwise occur in a straight northerly without troughs. This brings most areas over and east of the main mountain chains into the areas under threat, of at least a covering of snow. Even western areas as the winds back ahead of each trough are likely to find at least some wintry showers working inland over the next 3 days or so.

[Bolton67]

I find those charts a little misleading, it shows 43mm of precipitation (over 40cm of snow) just off the coast of NE England, but that figure would probably apply to anywhere within about 10 miles of the coast and the showers sometimes actually intensify as they hit land before dying out.

All in all though that is a fantastic chart for this area, some people are predicting 5cm for this area, I think 10-20cm at least would be safer bet.

NAE +48

SHowing the same areas

[Iceberg]

ECM 00Z ensembles have updated for London and show that the ops run was very dry, however the ensembles do spell two possible periods of snow the 3rd and 4th still and the 6th of Jan.

Temps are bang on average for the run pretty much. With maximum day temps throughout the run at around 0 maybe +1 for London, so certainty very cold, but nothing severe.

Night time temps around -5 ish seem to be pretty average again for London.

No real sign of a breakdown in the prolonged below average weather though even in the extended 10+ day time range.

[Guest North Sea Snow Convection]

ECM 00Z ensembles have updated for London and show that the ops run was very dry, however the ensembles do spell two possible periods of snow the 3rd and 4th still and the 6th of Jan.

Temps are bang on average for the run pretty much. With maximum day temps throughout the run at around 0 maybe +1 for London, so certainty very cold, but nothing severe.

Night time temps around -5 ish seem to be pretty average again for London.

No real sign of a breakdown in the prolonged below average weather though even in the extended 10+ day time range.

The ensembles for Reading from ECM that someone produced earlier were also very interesting. The median of max temps indicated on there were if anything below zero, which would tie in I guess with inner London temps hovering around zero. I would say though that any min of -5C for the heart of London is very low, and only spells like 1987 and 1991 have beaten that. I still wouldn't be surprised if the city has at least one or two sub zero ice days in the upcoming cold spell. Especially if snowfall comes into the equation, as it looks like it will do.

Edited December 31, 2009 by North Sea Snow Convection

[TEITS]

No problem TEITS, although the 6z has backed away from that a touch, with a lot less precip getting inland (look for a new version of that precip type chart in the new year btw)

May I ask Paul and other members who have used the NMM model how reliable the precip charts have been during this recent cold spell, including before xmas. I did use this model during last winter but I can't remember the accuracy.

[West is Best]

Good grief. I nearly fell off my chair when I saw that the 6z operational was actually one of the mildest members up to half way. They are astonishingly cold ensembles.

This really is a throwback to 20-30 years ago now. A phenomenal run with considerable snow potential for the south.

Edited December 31, 2009 by West is Best

[Paul]

May I ask Paul and other members who have used the NMM model how reliable the precip charts have been during this recent cold spell, including before xmas. I did use this model during last winter but I can't remember the accuracy.

It's not been bad at all actually, as with any mesoscale model it's never going to validate 100%, but it's been there or thereabouts much of the time so far this winter.

After a lot of testing last year, we switch to a different convective system on there during the winter as it's a better fit for cold weather convective showers than the one we use in the summer which is more suited to warm weather convection.

[TEITS]

It's not been bad at all actually, as with any mesoscale model it's never going to validate 100%, but it's been there or thereabouts much of the time so far this winter.

After a lot of testing last year, we switch to a different convective system on there during the winter as it's a better fit for cold weather convective showers than the one we use in the summer which is more suited to warm weather convection.

Thanks for the reply.

I suppose the best way of using the NMM isn't to take it literally but more as a guide to where convection is likely to occur. Looking at the 06Z NMM and the pattern pretty much fits with what I would expect to happen. As the colder air begins to push S the convection will gradually transfer S also. The main convection appears to be around NE Scotland/NE England but come this evening I would expect to see some scattered snow showers into Humberside and then finally into E Anglia around midnight.

[kold weather]

ECM 00Z ensembles have updated for London and show that the ops run was very dry, however the ensembles do spell two possible periods of snow the 3rd and 4th still and the 6th of Jan.

Temps are bang on average for the run pretty much. With maximum day temps throughout the run at around 0 maybe +1 for London, so certainty very cold, but nothing severe.

Night time temps around -5 ish seem to be pretty average again for London.

No real sign of a breakdown in the prolonged below average weather though even in the extended 10+ day time range.

Yep this is looking very prolonged, the difference is I don't think we've seen too many spells that long with temps so surpressed, Dec/Jan 2009 gave a good stab at it and this is going to have a good go as well.

Anyway looks like the first 10 days are nailed on cold, then utterly huge disagreements once the high pressure topples towards the UK and this is because the models cannot agree on the PV's placement. The southerly jet looks like keeping in place, the thing we don't want is a mid Atlantic high, because that would probably the quickest route to less cold and possibly even milder conditions...

[cooling climate]

I notice quite a big descrepancy between the GFS run this morning and the 0z ECM at t168

where by the ECM shows the US east coast low moving north along with NOAA's thoughts where

as the GFS ejects it eastwards which has the knock on effect of lowering heights quicker over

Greenland.

It will be interesting to see what the 12z has to say.

[john w]

Agree Tamara.

Heat Island effects of London etc means that a sub zero day for London actually is an extreme. sub zero for places outside of London...not such an extreme.

Just wondering, do models model the heat island effect?

I cant see the South getting huge amounts of snow from any troughs, but as always, some falls are likely.

Still I await the blessed streamer.... some potential for this showing on Monday.

Have to say these are some of the weirdest and interesting synoptics ever seen and it is causing some rather interesting work as well.

Breakdowns if anything are well out in FI and again appear at the moment to be the oddest looking breakdowns ever seen. GFS is probably veryover progressive building the high south and particularly with the monster low developing by T240.

Also of interest is the number of minor shortwaves that try to develop over iceland, but just get popped or absorbed by the Greeny High (I think).

[NorthantsSnow]

Confidence now increasing on a cold but very dry spell of weather for the UK. Largely unremarkable really with no ice days likely in the south for the next 5 days at least. Possibly some low minima for central and northern areas but again nothing too remarkable here.

Overall the phrase "at least it won't be mild!" come to mind, but I'm finding it increasingly difficult to find anything worth getting excited about in the model output at the moment.

Cheers & all the best for New Year.

[TEITS]

TEITS

Could you please give me (a novice by comparison!) an idea of whether Kent will see any snowfall over the next few days? It is very difficult for me to tell by just looking at the GFS. Or post a chart for the benefit of less informed members such as myself?

Thanks!

Very diffcult to say.

Look at the precip chart from the 06Z GFS.

http://charts.netweather.tv/gfsimages/gfs.20091231/06/21/ukprec.png

Now I have seen 10cm of snowfall via showers from similiar precip predictions and other times only a flurry.

Looking at the upper temps for tonight and we have -9C into E Anglia/Lincs but around -7C in the SE. Now for coastal counties of SE I would expect temps to remain just above freezing due to the warming effects of the N Sea.

http://www.wetterzentrale.de/pics/Rmgfs212.gif

At this moment in time I would say chance of a few scattered snow showers which might give a dusting. However later tonight the radar could say the opposite!

[kold weather]

Confidence now increasing on a cold but very dry spell of weather for the UK. Largely unremarkable really with no ice days likely in the south for the next 5 days at least. Possibly some low minima for central and northern areas but again nothing too remarkable here.

Overall the phrase "at least it won't be mild!" come to mind, but I'm finding it increasingly difficult to find anything worth getting excited about in the model output at the moment.

Cheers & all the best for New Year.

Does the fact that we could finally be within grasp of a severe winter month (sub 1.5C) help bring out the excitment a little more, given we've not had one now since Feb 91?

Also whilst we may not get no ice days at first, I'm willing to bet by the 5-7th we will see ice days, indeed the 0z ECM is rather suggestive of many ice days at Reading, some occuring in the next 5 days as well...