Model Discussion January 18th

[TEITS]

Delighted to see the Oslo SLP mean increase.

http://cdn.nwstatic.co.uk/ensimages/ens.20120119/06/prmslOslo.png

Whilst some of the ensembles do take us on a quick route to cold E,lys the underlying trend is for pressure to increase over Scandi. I think im right in saying that this is an increase of 15mb compared to a few days ago.

When you have a 50/50 forecast from the Met O its this rise in the SLP mean that you want to see. Using the SLP mean for Iceland/Scandi proved a valuable tool for me during Dec 2009/10.

[Jayces]

There was a post recently (From Nick I think) about someone in the States (NOA?) wanting to send out an aircraft to get atmospheric pressure readings as they weren't convinced with what the models were showing.

I also think somewhere along the line I read about how different data is fed into the model runs at the start so is it possible they have done the plane thing and fed that data into the GFS 06 run which is why the output is now so different?

It does seem like a radical change from 6 hours ago and if it's going to kep doing that then FI would seem to be 4 days away on Mon / Tue at the moment which sounds crazy.

[feb1991blizzard]

Good to see pressure dropping off in Europe on the GEFS as well, not massively but a trend, indicating the AH could be staying out of harms way and hopefully ultimately troughing digging south.

[Radiating Dendrite]

So what do we want to see on the 12z?

The most crucial time period is post +96, out to around +160.

It was this period which saw the greatest difference between the 00z and 06z.

On the 00z run the low that dropped off the PV still remaining around Greenland deepened and travelled in a NE direction. As can be seen on the image below, this is not good for our cold chances in the medium term.

We need to see the 12z pick up the development that the 6z had. The 6z did not deepen the low as much as the 00z did and had it moving in a SE direction, over the British Isles and not to the north of us. This lead to a pressure rise to the west of the low and allowed winds from the N/NE to develop over the UK as it cleared away, undercutting high pressure to the NE. This can be seen on the image below:

We therefore need to see this development continue on the 12z if we are to see colder weather in the next 7 days.

Edited January 19, 2012 by Radiating Dendrite

[Timmytour]

The way things are going, I wouldn't be surprised to find out that GFS modelled sunday at T384 a whole lot closer than it did in a lot of runs closer to the day!

[phil nw.]

The 00z and 06z operationals still show quite Zonal conditions in the early to mid term.

A slight tilt to the North west at times with some incursions of PM air but any wintry stuff seems destined for higher ground further north at the moment.

The 3 main runs show this well at T120(114 fro GFS06z)

http://www.wetterzen...s/Rtavn1141.png

http://www.wetterzen...cs/Rukm1201.gif

http://www.wetterzen...cs/Recm1201.gif

Still a colder outlook shown on both Ens graphs though

The GFS graph is now showing a good clustering of cold members beyond day 6-just as the OP run goes milder.

Certainly details on which way this will go are still to be resolved beyond around T120hrs.

[stewfox]

Who needs model output, just come in here and see how many pages the thread has extended to, I left to go out at page 8 and came back to see its upto page 13!

There is of course an amazing correlation between models showing colder solutions , particular ones that take you by surprise and number of pages posted within a certain time frame.

I'll come back after the 18z and expect 13 new pages, then i know its good before I start reading. if its 5 pages it will be bad.

[legritter]

looking at all of todays output so far i think that low pressure will move s/e across the uk at about 120/144 hrs from now ,. tonights 192 hrs ecm i am HOPING will be the start of the change , its also worth using the gfs 144hrs / 192hrs for trend setting ,been on a GFS HUNT IN NORTHERN HEMISPHERE ,and its been pretty good last couple of days predicting local ised weather events .i am sure that all professional met office personal have some very good model scenarios at the moment but are sworn to secrecy ,im going to give these postage stamp things a go soon , best of luck all ,

[Osbourne One-Nil]

New thread available - if anyone's interested.