Model Output Discussion - Spring Has Sprung

[feb1991blizzard]

 bluearmy

I would prefer a more conventional spilt, pacific to Atlantic - eg - Jan 09 & Feb 18

[daz_4]

I would prefer no split at all as everything is starting to bloom here. February will be warmest on record and is tracking to be warmer than many Aprils in recent years in Central Europe.

[Dennis]

GWO 

Global Wind Oscillation (GWO) and the Global Integrated Atmospheric Angular Momentum (GLAAM or AAM). What these terms refer to is the winds of the planet being weaker (less westerly than normal) in terms of a low or negative AAM, and the winds of the planet being stronger (more westerly than normal) in terms of a high or positive AAM. In general, the jetstreams of both hemispheres are more poleward and contracted in a low AAM, and more equatorward and expanded in a high AAM.

Edited February 18 by Dennis

[feb1991blizzard]

 Dennis

Not bad.

[bluearmy]

 feb1991blizzarddoesnt look to be on the agenda feb 

too early for analysis although the 00z run was very much an upper strat led split so should be more predictable if it becomes the way forward 

[feb1991blizzard]

A cracking storm on the 6z

[Cambrian]

6z GFS op shows how we just might have a bit of a surprise with this low pressure at the end of the week. 

At day 4, it’s landed in where it’s been modelled for several days now, to the north of the UK and Ireland, with its core of low heights over where Iceland used to be. 

It’s a complex low, with secondary centres continually forming around and becoming engulfed within the primary low, this process serving to drag the main core further south, dragging pockets of colder air south with it. Day 4-8 animation.

 

This sets up some heavy snow next Saturday night on the northern edge of one of these secondary lows. 

  

Just one model, so a low chance of it happening like this, but a timely reminder that once we get a complex low, developing and spinning features around in decently cold air, with heavy precipitation at night - the 6z GFS is a great run for showing that while the overall setup is perhaps just a bit too mild, events can crop up that demonstrate that marginality is a two-way street.

At the very least, worth keeping an eye on - it’ll be interesting to see if anything similar crops up in the next few runs and days.

[Neilsouth]

Can someone post the models for the 23rd and 24th please, as I have an archeological dig coming up on those dates and wondering if it needs moving . Thank you

[ANYWEATHER]

 Neilsouth There you go....

[knocker]

 Neilsouth There is a problem with pinning down the detail at this range as it the start of pattern change. All one can say at the moment is it is likely to be cool and breezy (depending on where the dig is)  and with a wave on the front crossing the south late on the 24th according to the gfs. Not very helpful I'm afraid

[Neilsouth]

Thank you both of  you! 

[Rain All Night]

On 17/02/2024 at 11:04, Rain All Night said:

0z deterministic runs, Sat 17th to Sat 24th (day 7)

0z ensemble means, Sat 17th to Sun 3rd (day 15)

0z/6z deterministic runs, Sun 18th to Sun 25th (day 7)

I am generally looking for the trough to either do something interesting or to naff off as soon as possible. Looks like there's some prospect of it chucking us a storm at some point during its tenure.

0z/6z ensemble means, Sun 18th to Mon 4th (day 15)

Not a lot has changed with the ensemble means in the last few days (so we can credit them with giving us some good and consistent guidance), with the UK under control of the imminent trough from 22nd to 26th Feb, and the ECM and GFS means then remaining more or less aligned showing a sinking upstream Atlantic ridge until around 1st March (day 12), after which point we diverge with ECM then bringing us under the influence of a further mean trough, whereas the GFS mean instead goes pretty flat.

Perhaps most notably, no supply of subtropical air to the UK shown by any model after 21st Feb. I personally would have preferred to have had the chillier air in mid-Feb and then the milder air for the start of March, but you know how it goes...

Edited February 18 by Rain All Night

[Jacob]

 Cambrian a little bit further south and then I’m happy!!

[Dennis]

LOW AMM forseen

[Dennis]

next sunday.....

[feb1991blizzard]

 Dennis

Love the optimism Dennis - love your posts, however, no evaporative cooling with those windspeeds, trough running into a past week of high temps.

[Kirkcaldy Weather]

 

Following on from this post and honing in on the 22nd - 23rd to begin with.

I've discussed in the past there are multiple pathways to cool - cold conditions in the UK and this will excellently fit into the cool - cold STORMY category, we've got the continuing influence of a strong positive North Atlantic Oscillation pairing with a strengthening positive Arctic Oscillation which will see the prior US snowstorm track into the UK as a very deep trough with means being indicative of the region of 960-970 hpa being reasonable estimates though lower pressure readings at the core of the trough cannot be discounted.

This will be a section of the Tropospheric Vortex.

With these setups it's a case of everything and the kitchen sink Thunder hail gales where the isobars are tighter and with increasingly Lowering thickness snow though being most prominent over high ground will mix in at lower levels

From the 24th current data shows this trough will gradually weaken as it moves south across Europe likely becoming a cut off low into Italy and the Mediterranean.

There then becomes a few discrepancies with how quickly we see a link with the increasingly strengthening high pressure into the Maritimes and Eastern US [strongly negative PNA] and the blocking to our East Northeast > MJO phase 6 / 7.

This is a combination of teleconnective feedback we haven't had at any point during winter 2023>24 with this being the strongest negative PNA since October

Focusing on developments in the stratosphere too, overall I'm really happy with how my post below has went with the precursors doing a great job again

 

• Reversal of zonal winds at 10hpa 
• Displacement event at 10hpa
• Split event at 50hpa
• Split event at 100hpa

With further precursor patterns there are already signals of new stratospheric warming heading into March

[Ali1977]

Icon has a similar set up as the 06z GFS, no snow but can’t be far off!! 

[Ali1977]

High ground wintery stuff on Thurs maybe , in the south and wales 

 

And saturday, could be a decent few falls for high ground in this flow. 

Edited February 18 by Ali1977

[Ali1977]

[phil nw.]

GFS showing a noticeable change from midweek as we see the jet strengthening and powering towards us.

Increasingly  unsettled and wet as bands of rain and blustery showers head in.As if we haven't seen enough this month.

Becoming colder too as polar maritime air sweeps in from the north west so as already mentioned snowfall likely to be seen at higher levels by the end of the week.

 A big difference to the feel of things after this prolonged mild period.  

[Snowyowl9]

Late february 2004 Nly..Not as cold as that but similar..

Edited February 18 by Snowyowl9

[phil nw.]

UKMO view t120

Similar outlook to GFS, as expected, very unsettled through next week with deep lows across the north and a displaced Azores high.Further systems look like heading in from the north Atlantic around the the high as we go further forward.

 

 

Edited February 18 by phil nw.

[CoventryWeather]

The GFS goes towards a cold outlook around day 10 again, with a cold northerly or NE wind. The GEM and GFS have been fairly interested at this in the mid range, and the latter certainly been the one recently that makes trends. 

Anyone (like me) looking towards more drier and spring like weather will be disappointed with the output tonight. Early march looking a lot like winter. 

[Dennis]

NOAA 17-2