18z Model discussion - snow but how much and where?

[Paul]

Please continue discussion on the latest model runs here. General cold spell discussion is available in this thread:

http://www.netweather.tv/forum/index.php?showtopic=36157

In depth/techie model discussion is here:

http://www.netweather.tv/forum/index.php?showtopic=34546

The latest GFS models can be seen here:

http://www.netweather.tv/index.cgi?action=nwdc;sess=

And the ensembles here:

http://www.netweather.tv/index.cgi?action=ensviewer;sess=

[guitarnutter]

Hows it looking???

[PB22]

18Z off, and already the Greenland High is a tad stronger with the ridge a tad further west at T+00!

[nick sussex]

I have posted this link a few times this evening but the discussions here are very important for our cold spell. See paragraph 2 where it talks about

CORE OF NEGATIVE ANOMALIES

TRACKING ACROSS THE NRN ATLC APPEARS TOO PROGRESSIVE...

This suggests that the models are being too quick to push low pressure across the atlantic towards the uk. Also paragraph 3 highlighting uncertainty.

AFTER DAY 3... MODELS SHOW

MEANINGFUL DIFFS WITH INDIVIDUAL SHRTWVS WITHIN THE NERN CONUS AND

ERN PAC MEAN TROFS. HIGH UNCERTAINTY WITH THESE FEATURES...

LIKELY NOT TO BE RESOLVED SATISFACTORILY UNTIL THE SHORT RANGE

TIME FRAME...

These shortwave features forming off the PV are important in relation to us, if the models are being too progressive then the scandi high is likely to get a better chance to build.

The full discussions are available here.

http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

[Cloud 10]

-->

QUOTE(Paul B @ 4 Feb 2007, 09:30 PM) <{POST_SNAPBACK}>

18Z off, and already the Greenland High is a tad stronger with the ridge a tad further west at T+00!

I await the 18z with hope,optimism and just a touch of trepidation.

[johnholmes]

a very interesting exercise is to key in, for the 850mb temps say, for different locations.

If the ensembles are showing tight agreement, then its usually, not always, the case that the forecast is about right. Once they start to scatter it is, again that word, usually correct not to trust the forecast in that period.

Do it for the 850mb temps and see how the scatter increases earlier in the south west than the east or north east.

I think its a quick way for someone with not much understanding of will it wont it, assuming the ppn is shown as occurring, and using a temperature of about -7C then it will snow.

try it its a quicker way than my full' will it snow' method that is available in the Guides section.

John

just to post some results re above

Cornwall=7/8th

N Ireland=8/9th

Northumbria=10/11

Surrey/Bucks area=10th

and so on

j

[Paul]

All gone wrong

(this chart is fake)

[johnholmes]

naughty man, you almost had me fooled until I looked at my watch!

[AlexL]

If the trend means anything at all, then the Wednesday/Thursday feature is going to end up missing the UK all together, and only bring the precipitation to the Southern fringes of the UK. I can't decide whether this is a good thing, as although we will be exposed to the cold easterly air quicker, and for a longer duration, bringing the odd snow shower for eastern parts, I fear that when the next system rolls in off the Atlantic with a more Northerly track, it will just smash through the cold air, and give rain to lower levels.

Of course I shall wait for the run before drawing any conclusions.

[shuggee]

You are such a tease Paul

[Evo]

AFTER DAY 3... MODELS SHOW

MEANINGFUL DIFFS WITH INDIVIDUAL SHRTWVS WITHIN THE NERN CONUS AND

ERN PAC MEAN TROFS. HIGH UNCERTAINTY WITH THESE FEATURES...

LIKELY NOT TO BE RESOLVED SATISFACTORILY UNTIL THE SHORT RANGE

TIME FRAME...

Translated into English this is:

Models show meaningful differences with individual shortwaves within the Northern Continental United States and Eastern Pacific mean-toughs. High uncertainty with these features, not likely to be resolved satisfactorily until the short range time frame.

Not sure this bit really applies to us yet, though their thoughts about the Atlantic definitely do, confirming the 12z to be too quick to develop the shortwaves.

[PB22]

Translated into English this is:

Models show meaningful differences with individual shortwaves within the Northern Continental United States and Eastern Pacific mean-toughs. High uncertainty with these features, not likely to be resolved satisfactorily until the short range time frame.

Not sure this bit really applies to us yet, though their thoughts about the Atlantic definitely do, confirming the 12z to be too quick to develop the shortwaves.

Translated into basic English: The models haven't got a clue?

[AlexL]

All gone wrong

(this chart is fake)

You had me fooled for a minute there.

[yamkin]

I have posted this link a few times this evening but the discussions here are very important for our cold spell. See paragraph 2 where it talks about

CORE OF NEGATIVE ANOMALIES

TRACKING ACROSS THE NRN ATLC APPEARS TOO PROGRESSIVE...

This suggests that the models are being too quick to push low pressure across the atlantic towards the uk. Also paragraph 3 highlighting uncertainty.

AFTER DAY 3... MODELS SHOW

MEANINGFUL DIFFS WITH INDIVIDUAL SHRTWVS WITHIN THE NERN CONUS AND

ERN PAC MEAN TROFS. HIGH UNCERTAINTY WITH THESE FEATURES...

LIKELY NOT TO BE RESOLVED SATISFACTORILY UNTIL THE SHORT RANGE

TIME FRAME...

These shortwave features forming off the PV are important in relation to us, if the models are being too progressive then the scandi high is likely to get a better chance to build.

The full discussions are available here.

http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

NS, A very good observation. This is precisely what the MetO have been observing for some time now. It does look like the Scandi High will build with stronger resistance. Exciting times with upgrades to come. By the way, I'm expecting even colder temps than forecast.

[Nick F]

Interesting info there Mr Sussex.

Not sure how we can really improve on prospects upto Friday with the 18z, maybe those wintry showers over the North Sea over the next few days affecting more inland areas of Scotland, the East and SE of England.

Wrt to the channel low shown for Thursday on the 12z GFS, faultless for here in the SE at slight elevation, though I'm sure those North of the M4 want the low to shift that bit further North at the expense of some disgruntled people along the south coast counties under milder air and rain! Less likely, the low may shift further South on it's track East over Northern France leaving the UK dry and cold. The 18z may be the answer to some peeople's prayers or cause some non-plussed reactions from some for the end of the week.

[PB22]

Possibly noteable, but maybe not, but at T+30 on 18Z GFS, there is a stronger ridge of high pressure (circa 1010mb) across Scandinavia towards Siberia.

[snowray]

If the trend means anything at all, then the Wednesday/Thursday feature is going to end up missing the UK all together, and only bring the precipitation to the Southern fringes of the UK. I can't decide whether this is a good thing, as although we will be exposed to the cold easterly air quicker, and for a longer duration, bringing the odd snow shower for eastern parts, I fear that when the next system rolls in off the Atlantic with a more Northerly track, it will just smash through the cold air, and give rain to lower levels.

Of course I shall wait for the run before drawing any conclusions.

This is my worry as well Alex, channel lows are of course notorious for missing most of the country, giving Northern France all the good stuff...

I must say I almost panicked thogh when I saw that chart come up, cant be I thought, the runs only out to t12!

[devon lad]

Translated into English this is:

Models show meaningful differences with individual shortwaves within the Northern Continental United States and Eastern Pacific mean-toughs. High uncertainty with these features, not likely to be resolved satisfactorily until the short range time frame.

Not sure this bit really applies to us yet, though their thoughts about the Atlantic definitely do, confirming the 12z to be too quick to develop the shortwaves.

The 12z is a computor model that attempts to translate all the masses of info it recieves. It's not bad, in fact pretty good ..... but it's not as good as Homo sapiens.

dl

[shuggee]

Interesting snow risk chart for midday Tueday. Snow level to sea level in eastern England:

[johnholmes]

its that trough i talked about Shugs

[Mammatus]

All gone wrong

(this chart is fake)

:lol: Nearly fooled me there Paul! :lol:

Mammatus

[PB22]

Maybe my first snowfall of the winter then?! Northern blocking that slightly stronger on 18Z GFS up to T+60 so far.

[AlexL]

Well what do you know, the low is marginally further north at T+60.

[Nick F]

Interesting snow risk chart for midday Tueday. Snow level to sea level in eastern England:

The updated t+60 FAX shows a cyclonic circulation just off the East coast with an occlusion circulatin around it, so some snow showers poss. for E coast and E Anglia on Tuesday:

http://www.wetterzentrale.de/pics/brack1a.gif

Still there at t+72, 12 hours later: http://www.wetterzentrale.de/pics/brack2.gif

[Thundery wintry showers]

Seems to me that the GFS 18Z is backing up the GFS and UKMO 12Z runs, and continuing to go against the ECM.