Model Output Discussion - 18z 31/10/15 onwards

[johnholmes]

There are differences between the ECMWF-GFS upper pattern and that of NOAA. This in the ne Canada/Greenland area and further north. It is unclear just yet which pattern will be nearer the mark. It is not often that NOAA is wrong in these pattern changes but we have to wait and see.

links below

http://www.cpc.noaa.gov/products/predictions/814day/500mb.php

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

[Liam J]

ECM shows a number of depressions crossing the UK with bouts of wind and rain, so a pretty unsettled outlook especially further north & west where rainfall totals will be piling up.  

 

Oh dear Frosty, if that's the best you can find things must be dire...   

Edited November 9, 2015 by *Sub*Zero*

[Summer Sun]

Bar some slightly cooler air on Saturday taking temps back down to around average ECM has mild air quickly coming back in all parts will see rain at times, though the south has the best chance of seeing some longer drier spells

 

 

The air right at the end of the run could be cool enough for some wintry showers on the high ground in the north elsewhere and temps gradually falling back to around average

 

[MP-R]

ECM shows a number of depressions crossing the UK with bouts of wind and rain, so a pretty unsettled outlook especially further north & west where rainfall totals will be piling up.  

 

Oh dear Frosty, if that's the best you can find things must be dire...   

 

Those charts he posted aren't bad too be fair, the only problem is they're right out in the far reaches of FI. Need to start seeing upstream signals in the next week or so for those to come into fruition. Certainly the GFS is showing the traditional November Atlantic train with a progressive cool down through this week, peaking on Friday, before the super mild returns at the weekend for a couple of more days. Thereafter the run shows drastic changes towards a cooler/colder outlook but lots of water under the bridge first.

 

I'm just glad it actually feels more like November out there this morning. Will be a very mild night again tonight though.

[Vorticity0123]

The weather is really feeling like autumn currently with an unrelenting westerly to southwesterly flow established over the UK. Low pressure areas frequently sweep over and to the north of Scotland, bringing lots of rain and strong winds. Who sees this pattern in November would not think that a tropical system from the Atlantic could affect our weather. Yet, though indirectly, this could be the case as a new tropical depression has given birth near the Bahamas. Here, I will present an insight in how this depression (TD 12) could influence our weather.

  

Short-lived system forms near the Bahamas

 

As mentioned before, a new tropical depression has formed in the Atlantic. More about this system (including further updates) can be found here: https://forum.netweather.tv/topic/84379-tropical-depression-12/#entry3280246. The system is forecast to recurve out to sea and be absorbed by another low pressure area in about 3 days’ time. Below is the latest track forecast of the system.

 

NHC track forecast of TD 12.

 

Absorption into an extratropical storm

 

The low pressure area absorbing 12L will do so just off the Eastern Seaboard. This all is visualized in the ECMWF forecast below.

 

ECMWF surface pressure (contours) and 500 hPa heights (shades) 00Z T+48 (forecast for the night from Tuesday to Wednesday).

 

The tropical system (TD 12) is encircled in black, whereas the extratropical low which will absorb 12L is encircled in blue.

 

The low pressure area containing the remnants of TD 12 will slowly traverse the Atlantic, as can be seen below:

 

ECMWF surface pressure (contours) and 500 hPa heights (shades) 00Z T+96 (forecast for the night from Thursday to Friday).

 

The low pressure area is located at about 65W 45N.

 

Blocking high pressure à over or under the block?

 

If we focus ourselves more towards Europe, we can see that a high pressure area lies to the west of Portugal. This high pressure area is associated with a building ridge at 500 hPa over Europe (which we have seen a lot this fall). And this high pressure area will be a key player in the future of the low pressure area containing the remains of the tropical cyclone. The difference appears to be related with a possible cut-off low which may or may not develop. To show this, here the GFS and ECMWF are compared. This time the maps are more focused on Europe.

 

GFS:

 

GFS surface pressure (contours) and 500 hPa heights (shades) 06Z T+136 (forecast for the night from Saturday to Sunday).

 

ECMWF:

 

ECMWF surface pressure (contours) and 500 hPa heights (shades) 00Z T+144 (forecast for the night from Saturday to Sunday).

 

The general picture is that the low pressure area is being forced over the European ridge of high pressure. For clarity, the ridge of high pressure is centered over France whereas the low pressure area is located to the northwest of Scotland.

 

However, upon a closer look, there is an important difference between the ECMWF and the GFS. The GFS shows a cut-off low developing from this low pressure area near Scotland (indicated in black). Coincidentally, the low pressure northwest of Scotland area is forced more to the north, enabling high pressure to build further northward. With a little bit of fantasy, one could even see a nice example of an Omega block in here.

 

In the ECMWF, no cut-off low develops, and coincidentally the low pressure area to the northwest of Scotland is able to move more to the south. As a result, the high pressure area over mainland Europe is not able to build up that far northward. This would imply unsettled weather to prevail over more areas of the UK.

 

Does this all have to do with differences in modelling of the tropical system over the tropical Atlantic? Most likely yes, but it is not the only player on the table. Nevertheless, it will be able to force the weather forecasts for Friday to Saturday to flip over the next few days, as tropical systems tend to magnify the uncertainty in weather forecasts.

 

Summary

 

A weak tropical system has developed in the tropical Atlantic ocean. This system will be absorbed quickly, but the resulting low pressure area could have an influence on our current weather by the possible formation of a cutoff low. The north of the UK will most likely remain unsettled, but the cards for the South have not been shuffled yet. Definitely an interesting period of model watching coming up with a tropical cyclone about to influence our weather.

 

 

 

[ANYWEATHER]

A positively Bracing day on Friday, compared to the recent warmth.....

[knocker]

Someone correct me if I'm wrong is this not a classic Nino patterm?

[Frosty.]

Maximum temperatures at this time of year should be in the range of 9-11 c 48-52 f from north to south but they are still way above that, however, for the first time this autumn, an incursion of cold polar maritime 528 dam thicknesses are set to sweep across northern britain on friday with blustery showers turning to sleet and snow on northern hills and mountains of n.ireland, n.england and especially scotland according to the Gfs 6z with temps in the south falling back closer to average for a day or so. The 6z also shows high pressure at times across the south from sunday and during next week.

[Thunderbolt_]

I'm going to try a daily break down of the 06z run, since it looks like we're in for a very topsy-turvy week...

 

Tuesday will see pretty much a continuation of what we have had so far this November. It will be very mild and cloudy, though maybe some eastern areas could see a bit of brightness later on. There will also be some rain for the far north west of Scotland too.

 

 

Wednesday will then be another wet and windy day, especially for the northern and western areas. It again will be very mild for time of year.

 

 

On Thursday we start to bring in some cooler air from a bit more of a westerly direction, so temperatures will be down a degree or so on Wednesday. They may still be slightly above average however. It will also be very breezy with some persistent rain over Scotland.

 

 

Friday should then see quite an interesting day, as a large incursion of Pm air moves of the UK. It again will be very blustery with some pretty heavy showers rattling through. These showers could also contain hail and thunder in northern and western parts of the country. The biggest detail however will be the temperatures, which will be significantly lower than what they have been (maybe even slightly below average).

 

 

By Saturday however, we bring the mild air back as quite an active warm front moves across the country. It will be a wet day, but temperatures could vary by quite a lot over different parts of the UK. Under a milder air mass, behind the warm font we could see temperatures reaching the mid teens in the south west, however they will be limited to only single digits in the north east, ahead of the front.

 

Edited November 9, 2015 by Thunderbolt_

[radiohead]

The GEFS is not without some interesting members.  

 

[Pennine Ten Foot Drifts]

A couple of things are catching my eye on the latest GFS output:

 

Firstly, the first 'proper' Atlantic storm of the season (at least that will affect a larger swathe of the UK) as we go through Thursday evening and into Friday, firstly affecting primarily North and West Scotland on Thursday night, with gusts potentially topping 80 mph in the most exposed spots:

 

Then transferring to cover a wider swathe of northern Britain on Friday morning, with the strongest winds across northern England, where gusts could top 60 mph on coasts and higher areas:

 

 

And then a few days later on Sunday a complete change as a ridge of high pressure nudges across most of the UK, which may well make for a very pleasant day indeed for more southerly and easterly areas, with temperatures possibly getting up to 16 or 17 degrees:

 

Edited November 9, 2015 by Pennine Ten Foot Drifts

[knocker]

A positively Bracing day on Friday, compared to the recent warmth.....

 

And a positively toasty day on Sunday compared to recent bracing

Chart weatherbell

[Ali1977]

No sign of any flips to colder weather yet, the NH does still hold some interest though...no PV over Greenland which could be expected at this time of year. . I'll be keeping an eye on the METO long range as I for one think a big flip to cold will happen before 2016.

The charts aren't that far off delivering in 10 days time with a few tweaks...much more interesting than the last 2 years

Edited November 9, 2015 by Ali1977

[fergieweather]

No sign of any flips to colder weather yet, the NH does still hold some interest though...no PV over Greenland which could be expected at this time of year. . I'll be keeping an eye on the METO long range as I for one think a big flip to cold will happen before 2016.

The charts aren't that far off delivering in 10 days time with a few tweaks...much more interesting than the last 2 years

 

There's absolutely no current sign (stress current) of such a turnaround before January (note too today's update of the GloSea5 prognosis for D-J-M on the UKMO website and the switch towards +ve temp anomalies - albeit rather weakly - versus the October output looking into same period).

 

Shorter-term, the overnight EC and GloSea output has effectively zero sign now of even transient blocking spanning the next 15 to potentially 30 days inclusive. Broadscale W'rly zonality - albeit with some Pm incursions - is absolutely the form horse looking ahead and may dominate for a good part of winter too, if cross-model consensus (and equally the shared opinion of every seasonal forecaster I know) is on the money. The next key point of interest will be updates soon to EC Seasonal Model, to see how closely it mirrors - or not - the latest GloSea prognosis. The critical juncture remains later into winter and whether any colder swing then emerges (courtesy SSW).

Edited November 9, 2015 by fergieweather

[Ali1977]

Well, there's the answer....a long few months ahead by the sounds of it....Ski resorts will be hoping for some pattern change to get some moisture into the Alps .

[Polar Maritime]

Well, there's the answer....a long few months ahead by the sounds of it....Ski resorts will be hoping for some pattern change to get some moisture into the Alps .

Just remember Ian stresses what the Models currently show, So its certainly not a given. With the models certaily showing a typical late Autumn pattern.

Edited November 9, 2015 by Polar Maritime

[fergieweather]

Just remember Ian stresses what the Models currently show, So its certainly not a given.

Correct. Moreover, returning to the UK, the predominant expected pattern doesn't preclude colder spells especially in the north (Pm or even Am incursions). However, at least over the next 11-30 days, there's now very little (i.e. only a couple of EC ENS members!) showing any blocked pattern throughout the period.

But yes, the point to stress is 'currently'.

[bradymk]

Not much to add today and not much change in the outlook for the near future. Friday will certainly feel colder after what we have had recently but other than that the exceptionally mild weather continues with night time lows for here not dropping below 14c next two nights haha.

 

Today ECMWF ENS showing that the stubborn Euro high may finally be starting to depart at the end of the run.

 

 

Day 7 (left) euro high still strong as ever.  Day 11 euro high starting to regress southwards with lower heights over UK and a return to more average temperatures for the time of year but staying unsettled.

 

Below on the left is the Canadian seasonal model showing the expected December at the moment. Pretty dire if its cold you are after but the image on the right does show a change for Feb maybe highlighting what some others have been saying in regards to later in the winter but its just another seasonal model.

       

 

Patience and a waiting game required for now, it looks like it may be a long few weeks in here but interesting to keep track on everything as always.

 

Latest value for ENSO 3.4 now +2.576c making it at almost record levels. nino 4 also setting a record weekly but 1.2 anomaly dropping suggesting a more central based ENSO? Maybe...

[Hocus Pocus]

Correct. Moreover, returning to the UK, the predominant expected pattern doesn't preclude colder spells especially in the north (Pm or even Am incursions). However, at least over the next 11-30 days, there's now very little (i.e. only a couple of EC ENS members!) showing any blocked pattern throughout the period.

But yes, the point to stress is 'currently'.

Without a major shift in the upstream pattern and with heights being maintained over Europe then any hope of a major pattern change won't be anytime soon, certainly not this month for sure.

[Nick F]

Just remember Ian stresses what the Models currently show, So its certainly not a given. With the models certaily showing a typical late Autumn pattern.

 

Does look like we are stuck in a rut though with this current pattern which, IMO, appears to be predominantly driven by the current strong El Nino, which typically manifests in late autumn/early winter with a strong Alaska low driving a Strong pacific jet feeding through to a strong Atlantic jet - which doesn't encourage a blocky pattern, so we have the +AO/+NAO with flattish ridges over SE Canada and mainland Europe, with little scope for amplifcation.

 

The strong El Nino, however, does look to peak in November and December looking at some most recent forecasts (see NMME forecast below), with a weakening in magnitude as we head into mid to late winter. This *may* mean a change colder a patterns at times in Jan and Feb, though dependent on rate of decline of El Nino.

 

 

In the meantime, as others have said, the tropospheric polar vortex has not become deeply rooted over the Greenland area yet, so there is scope, if we get any waves in the progressive flow showing enough amplitude, for ridges to build in the right place, albeit probably briefly, for cold Pm or Am flows as we head into late Nove and early Dec.

 

But Ian's post re: signs from the EC and GloSea output is no surprise.

Edited November 9, 2015 by Nick F

[johnholmes]

before too many show 'like' for this post it is NOT anywhere a done deal yet, and I only suggested hours NOT days IF it does happen, and not a major pattern change!

Edited November 9, 2015 by johnholmes

[MP-R]

 

The strong El Nino, however, does look to peak in November and December looking at some most recent forecasts (see NMME forecast below), with a weakening in magnitude as we head into mid to late winter. This *may* mean a change colder a patterns at times in Jan and Feb, though dependent on rate of decline of El Nino.

 

 

Is there a place where one can find out when previous El Nino's peaked i.e. to get an idea of which period was most affected by the Atlantic? Did 2009 peak in November?

[carinthian]

Lots of difference in the up stream pattern compared to this time last year. Could be a complete reversal to the previous N. American winter. Already we see a strong development of Gulf Alaskan Low driving in unsettled conditions to Western Canada and the Rockies States. All this after a drought of a summer here. So the El Nino creating a swift change in this location. High Pressure holding over the Great Lakes operating in tandum with the Euro high and keeping the cold at bay for the great populated centres of both the Eastern USA and Europe. Variables will come into account, mainly as I see it the low sea temperatures persisting in much of the NW Atlantic Ocean to include Baffin and Labrador Seas and the continued forecast to show negative anomalies of the coming 30 days. Westerlies may dominate for sometime yet but the variable I highlight and a strengthening High over NE States/ SE Canada could easily change the dominant winter patterns as shown for the previous two over both sides of the Atlantic.

C

[summer blizzard]

09 peaked in Feb 10 I believe.

[Frosty.]

The Gfs 12z op run shows very mild weather quickly returning to most of the uk during the weekend following the cooler blip on friday, temperatures again into the mid teens celsius across many areas on sunday, even eastern Scotland is exceptionally mild on sunday and parts of the south seeing locally low 60's F, even a coldie like me who is searching for our first cold snap thinks it's very impressive how temperatures have been generally above and sometimes well above the seasonal average during the autumn so far. The very mild conditions on this run continues next monday in the s / se but cooler air then spreads south on monday night so that next tuesday has a weak ridge pushing east with temperatures closer to average but then it becomes milder again with low teens celsius across southern uk for a while but also windier and more generally unsettled, it's an unsettled run but temperatures through low res are closer to average.

Edited November 9, 2015 by Frosty.