Model Discussion - 10th March Onwards

[PersianPaladin]

I think it's worth doing a brief comparison of how the GEM, ECM and GFS compare at mid-range.

GFS at T96

http://www.wetterzen...cs/Rtavn961.png

ECM at T96

http://www.wetterzen...ics/Recm961.gif

GEM at T96

http://www.wetterzen...ics/Rgem961.gif

Notice the GEM and the ECM model the upper trough over northern Canada and NE US/Canada in a different fashion to the GFS. The cold pool at 500hpa level is considerably more intense on the GFS and the orientation of the depression helps to result in a slightly less amplified pattern towards Greenland. The mid-Atlantic ridge is effectively stationery, with shortwaves and associated energy moving across southern Greenland.

GFS at T120

http://www.wetterzen...s/Rtavn1201.png

ECM at T120

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

GEM at T120

http://www.wetterzen...cs/Rgem1201.gif

Upper-level trough over NE Canada on the GFS is modelled differently to the GEM and ECM. The latter models continue to show a bifurcated pattern, with the orientation of the depression pulling warmer air slightly further north into southern Greenland, and thus resulting in a bit of a more amplified profile in the mid-Atlantic. The GFS continues to pull more energy westward albeit with a fairly strong northern arm bleeding shortwaves south of Greenland; that high certainly isn’t going to be eroded any time soon.

GFS at T144

http://www.wetterzen...s/Rtavn1441.png

ECM at T144

http://www.wetterzen...cs/Recm1441.gif

GEM at T144

http://www.wetterzen...cs/Rgem1441.gif

The cold pool over NE Canada on the GFS moves only slightly northward but is effectively in the same place and at the same intensity. Energy is moving westward and reducing the northward amplification of the mid-Atlantic high. The long-wave trough resultingly comes out of the Arctic and heads into Scandinavia with not much residual lower-heights entering the UK.

The GEM and the ECM, on the other hand continue to show a different and more amplified profile in the mid-Atlantic and also with the upper-trough towards the Canadian sub-arctic. The result is that a shortwave forms over the north of the UK and some instability and showery weather looks a possibility for central England northwards.

At T168 on the ECM, things look uncertain, with respect to what happens to the mid-Atlantic ridge. The orientation of the northern arm of the jet is obviously important. We could end up locked into a generally settled pattern –albeit an ECM\GEM evolution could result in more instability and showery rain for Scotland and the far north-west of England and Northern Ireland and continued settled dry weather for much of England. The ECM ensemble mean suggests such an evolution (http://www.wetterzen...s/eempanel1.gif). Clearly, small differences can have significant consequences further down the line. The ECM and GEM models suggest a possibility of a cold surface high resulting from the arrival of the longwave Arctic trough into Europe. It’s not a particularly strong scenario of upper-level convergence and thus a strengthening sun could yield some convective activity in some areas.

My hunch is that the Canadian model probably has the upper trough in their location, modelled more accurately than the GFS. The ECM after all, agrees with it. And we’re seeing a similar evolution on the UKMO. However, the GFS is being pretty persistent with its modelling of things upstream, and may end up trumping the other models come the end of the month. My own personal hunch is that an average from the current teleconnections and ensembles suggests a generally dry picture for the UK –give or take a few elements of showery rain for some coastal regions and Scotland. It may be into mid-April by the time we see a pattern change; but don’t expect strong zonality.

Edited March 28, 2012 by PersianPaladin

[IDO]

GFS 0z sticking to its guns this morning with regard to the cold pool coming from our north, and again this weekend avoids the cooler uppers. ECM have also come on board with the HP still maintaining its grip at the weekend:

http://policlimate.com/weather/ecmwf/2012032712/ec_gfs_z_panel.html

ECM now suggests this cooler outlook will hit us Monday for circa 72 hours. However bearing in mind their backtrack I would still favour the GFS, which has the HP just holding off the cooler PM shot early next week.

GFS has HP pretty much all the way through to the end of FI (13th April). The PM shot that showed up in yesterday's output for the Easter weekend has gone, as HP continues to be the dominant pattern. Temps. are however significantly below this weeks marks, going from average to 2-3c above, by the end of FI. The OP run according to the ensembles is similar to the mean plot, tempering recent colder outlier Op runs. However the T850's (London) have a 10c spread at the end of FI, so the second week of April still very uncertain. The Op run (London) has precipitation at around zero for the whole of the 0z run!

GFS steadfastness with the HP keeping hold over this weekend, looks to now be the most likely scenario, now ECM has followed suit. Still some divergence early next week but by the end both models are on the HP bandwagon again, though with cooler T850s and T500s always close by, temps will remain subdued compared to the last 10 days.

[Thundery wintry showers]

The ECMWF ensemble support for that brief northerly outbreak next Tuesday and possible wintry showers in north-eastern districts appears to have increased on the latest run, but the GFS and UKMO operational runs continue to show nothing of the sort.

The key period of divergence is on Sunday/Monday regarding the behaviour of a trough off northern Scotland. The ECMWF has the trough deepen and slide down the North Sea introducing the northerly outbreak but the GFS has the trough shunted out to the east, and the UKMO has it stick around to the north-east. The weekend is looking set to be dry but rather cooler than we've been used to recently, probably with plenty of sunshine in the west but a fair amount of broken cloud in the east.

The latter part of next week looks pretty clear too as a couple of others have mentioned- all routes lead to high pressure.

[PersianPaladin]

Looking out towards the boundaries of F.I. – it seems at T216, all models seem to agree on a potential pattern change for the UK – with the formation of a significant shortwave depression near Iceland. The GFS evolves this so as to bring the shortwave over the whole UK – introducing much colder and showery weather, with likely periods of rain. The feature also develops at T216 on the ECM, albeit with a slightly different orientation. By T240 the system has intensified significantly and looks set to sink south-eastwards. The GEM also picks up the same evolution. ECMWF ensembles also suggest a pattern change from around the 6^th of April, with a potential north\south split with respect to rain – albeit that split could disappear if the operational signals of the models turn out to be true.

Still – it’s high-pressure for the “reliable†time-frame. However, T120 on the GFS shows an important change in the behaviour of the northern-arm of the jet. The energy flow over Greenland starts to migrate southward and by T144 the jet bows NNE towards Iceland rather than over southern Greenland and round the north of Iceland as its done thus far. This allows shortwaves to develop in the region and to make progress westward. Our high sinks southward but if the same jet-profile persists into F.I:-

http://www.wetterzentrale.de/pics/Rtavn18615.png

We are likely to get an erosion of the block and a NW incursion sooner or later. How far south the trough sinks is anyone’s guess. I’m still going with a period of wet weather for western Scotland beginning around 7^th April, with possible showers for northern England. Could remain dry for most of England probably until the 15^th of April onwards. Interestingly, the ECM ensemble mean suggests a strong signal for a significant development of an Icelandic low from the 7^th – with that feature shown as much more vigorous on the ECM than the GFS.

[SMU]

UKMo 144 has 528 Thickness across the UK & for scotland & the NE a higher probability of snow with thicknesses around 515 dam & uppers around -8c.

Certainly not like we have been used to this week, Scotland could see maxima of around 3c in this type of condition & dropping close to freezing in the snow flurries- with possible cover over the higher ground-

England especially the NE could see some snow flurries with very dry lapse rates, temps up to 6/7- dropping in the showers-

feeling very chilly if this varifies-

http://www.meteociel.fr/ukmo/runs/2012032812/UW144-21.GIF?28-18

[johnholmes]

now that is unusual in March Steve

[Geordiesnow]

Indeed Steve and the first signs that the UKMO has more firmly want to develop some sort of Mid Atlantic ridge which allows a unstable shot coming in from the North although the GFS wants to erode the block somewhat.

Still looks a dry outlook for the foreseeable though, not an awful lot of rain in the outlook and unless the unstable Northerly comes off(which I hope it does because of the wild veriation of the very warm to below average temps) not an awful lot of excitment in the outlook after these warm and sunny days are over and done with.

[Methuselah]

UKMo 144 has 528 Thickness across the UK & for scotland & the NE a higher probability of snow with thicknesses around 515 dam & uppers around -8c.

Certainly not like we have been used to this week, Scotland could see maxima of around 3c in this type of condition & dropping close to freezing in the snow flurries- with possible cover over the higher ground-

England especially the NE could see some snow flurries with very dry lapse rates, temps up to 6/7- dropping in the showers-

feeling very chilly if this varifies-

http://www.meteociel...44-21.GIF?28-18

And the emphasis is very much on the word, IF...

[Cloud 10]

Looks like next week is going to be a bit different!

[SMU]

http://www.meteociel.fr/modeles/ecmwf/runs/2012032812/ECH1-120.GIF?28-0

Heavy snow showers moving into NE scotland & the NE

S

[phil nw.]

The 12z outputs show differing solutions wrt to how far west the cold air incursion affects the UK early next week.

http://www.wetterzen...cs/Rukm1441.gif

http://www.wetterzen...cs/Rgem1441.gif

http://www.wetterzen...cs/Recm1441.gif

http://www.wetterzen...s/Rtavn1441.png

The UKMO much more bullish with the extent of the cold affecting the UK and GFS very much a milder solution early next week with the high rebuilding quickly nearby.

These differences underline the low confidence expressed in last nights discussions by the American forecasters.

Either way it looks a brief affair but temperatures will be much lower generally after tomorrow and with more cloud around.

Again little in the way of meaningfull rain in the next week.

Edited March 28, 2012 by phil n.warks.

[Thundery wintry showers]

The likelihood of one of those "spring switch-arounds" has increased on the evidence of tonight's runs- both UKMO and ECMWF support a northerly incursion on Tuesday/Wednesday with a belt of rain and sleet followed by probable wintry showers for northern and eastern districts (though only light-moderate showers, we'd need to see more of a cyclonic influence to expect thunder and large hail from it). I see that the GFS 18Z has also joined in with the idea. It's not guaranteed though as it is still 5 days out and there is plenty of scope for backtracking.

Little change in the outlook for this weekend which looks dry but rather cooler and cloudier than we've been used to recently- broken stratocumulus cloud and sunny intervals will probably be the norm.

For the longer-term outlook all routes still lead to high pressure but the extended ECMWF runs cast doubt on whether it will stick around for long. As others have noted, though, no sign of significant rainfall for the drought-affected areas.

[Weather Wizard]

Chilly 18z FI

The perfect synoptics for winter (low pressure to are east)

Edited March 28, 2012 by Weather wizard

[The PIT]

00 oz upgrades the cool down into a proper cool down with some proper frosts around in FI. So a trend of proper cool down was replaced by a drop to normal which has now been replaced by a cool down.

[Polar Maritime]

It seems like we are in for one big cool down from the N/E for April if the GFS came into fruitation.

The ECM is also showing the same trend this morning.

At least we have some interesting weather to look forward to, we need the rain and in any case im getting bord of this high pressure.

Edited March 29, 2012 by Polar Maritime

[Methuselah]

The far-reaches of FI look quite interesing (don't they always!). A large blob of cold around the Greenland area and sustained heat building away to the south and south-east. What a potential for some wild swings??

[Alex]

The models today remind me of April 2008. I just hope they are wrong as I don't think I bear going back to very cold conditions again!

[summersnow]

But also of interest is how consistently GFS is showing a sustained cool down after about 10 days. It has been showing this scenario in FI for some time now and has been fairly consistent with it. Clearly well into FI, it should be treated with extreme caution but when GFS is as consistent as this in FI, the synoptics do often gradually filter into the reliable time frame before other models start picking up on it. It's often at this stage GFS seems to wobble about a little and then jumps back on board within the even closer time frame! It's quite odd!

As I pointed out above, 2 days ago, the cool down that has been quite consistently showing on GFS in FI, is gradually now filtering into the reliable time frame. Still a great deal of caution needed, but if GFS 06z verifies then we'll be having a late winter in the north and plenty rain for the south!

Edited March 29, 2012 by summersnow

[SP1986]

As the NAO and AO don't join the party with regard to northern blocking (a lack of negative indices), I'm not buying anything any models shows at the moment. At this time of year the GFS in particular may seem to be seen going gung ho with the amount of cold modelled.. certainly a surface temperature mean of -4C in FI on the lower members, is pushing it a little too far for believability, as I'm not sure you'd even get that often in mid-winter.

Certainly cooling down, but as yet, not convinced by the wintriness and hard frosts being forecast to head our way.. hard frosts? not in April (except inland perhaps and localised)

(Hard frosts is defined as an airfrost of -5C or lower, and whilst I'm aware this has happened inland in the past.. having -5C on the coast in April is rare, if not unheard of in some parts)

[Bottesford]

At the moment it looks like an area of cold high pressure will be in charge the middle of next week.

Not the worst outlook for those of us taking some holiday next week although nothing like as great as its been this week (how nice it looks from the office window...).

So some sharp overnight frosts but generally looking dry.

[IDO]

The ensembles for the GFS 0z indicated the Op run was a modest cold outlier (from T192) so its no surprise the 06z tames down the Easter cold PM excursion. It also pushes the trough further east and flattens things. Still the outlook cannot be ignored as there will be a large dip in max temps. compared to the last week. The GFS ensembles have little inter-model support; for instance the T850's in London have a scatter of over 10c from about the 7th April, so confidence is low for the Easter weekend as to how cool it will be, and the 6z run is more hopeful of the south having a couple of good days.

ECM has now pushed back the cold uppers again (T850's), this time by 24 hours (was 2nd-4th previous run), now from the 3rd, and this is close to the GFS, though their (GFS) influence is for less time (c.36 hours). For the south this weekend is still influenced by HP but with temps tempered to only 2-3c above average, away from the cloud. Still low confidence for any significant rain for the south in the short to medium term.

We will see if this cold FI eye candy of the GFS 0z is yet another false dawn for cold lovers; the potential is there but lots of uncertainty at the moment.

[picog]

Bye, bye summer (perhaps)

http://www.wetterzentrale.de/pics/MT8_London_ens.png

[stewfox]

As the NAO and AO don't join the party with regard to northern blocking (a lack of negative indices), I'm not buying anything any models shows at the moment. At this time of year the GFS in particular may seem to be seen going gung ho with the amount of cold modelled.. certainly a surface temperature mean of -4C in FI on the lower members, is pushing it a little too far for believability, as I'm not sure you'd even get that often in mid-winter.

Certainly cooling down, but as yet, not convinced by the wintriness and hard frosts being forecast to head our way.. hard frosts? not in April (except inland perhaps and localised)

(Hard frosts is defined as an airfrost of -5C or lower, and whilst I'm aware this has happened inland in the past.. having -5C on the coast in April is rare, if not unheard of in some parts)

Yes but we dont ALL live on the coast ??, it was -4c in Chesham not far from here the other day

Edited March 29, 2012 by stewfox

[johnholmes]

the 500mb anomaly charts have been not very helpful for several days but they are perhaps coming round to a consensus of a cooler/colder interlude with upper air heights low to the north/NE of the UK and a ridge of sorts to the west; that position yet to be decided.

This would indicate an usettled spell, the more so the further north you live.

[Cloud 10]

We apologise for the delay of the 12z gfs.

NWSTG Operations Status

In the meantime,here's some music....