Blessed Weather

December 6, 2023

Plenty of discussions around the accuracy of models in forecasting the MJO. Here's another paper (in addition to the one posted on the previous page by Downburst) which identifies a known weakness of underestimating the amplitude of the MJO as it progresses across the Maritime Continent and Western Pacific:

"One of the greatest challenges in current dynamical forecast systems is the fast damping of the MJO signal as the forecast lead time increases, which results in a rapid decrease of forecast skill. This systematic damping of the MJO convection signal is particularly apparent when the MJO starts over the Indian Ocean and is expected to propagate through the Maritime Continent and move further into the western Pacific. The frequency of MJO events not crossing the Maritime Continent in forecast models is more than twice as large as it is in observations, known as the Maritime Continent prediction barrier."

Does this help explain the slump of amplitude in many of the RMM forecasts we are currently seeing? Here's the ECM Ensemble Extended Range marked as illustration:

In the same paper the Average forecast errors by model (unfortunately no BOMM inclusion):

Source: Deep learning for bias correction of MJO prediction

I've put both papers into the Netweather Research Library where there's lots of other MJO papers.

December 3, 2023

11 minutes ago, andy989 said:

I know it varies but Is there an average/typical lag time between an SSW and its effects being felt? Asking because I’m working in India for 2 weeks on February and it would be my luck that I miss all the action

6 minutes ago, Liam Burge said:

I believe the average is 2 weeks, however I could be completely wrong on this.

Here's a couple of extracts from an easy-to-read article from the Royal Met Org:

Polar vortex, sudden stratospheric warmings and the Beast from the East
.......not all sudden stratospheric warmings are the same, and so the impacts they have on the weather in the UK can vary a lot.
......A sudden stratospheric warming typically takes a few weeks to have maximum impact on our weather, but its influence can last for up to 2 months.

Article: https://www.rmets.org/metmatters/polar-vortex-sudden-stratospheric-warmings-and-beast-east

December 3, 2023

4 minutes ago, MattH said:

Just flicking through some of the EC46 plots, amongst a busy weekend shift, and I think there is already some evidence for changes in there, for towards and beyond mid-December.

As ever the usefulness of the layout of the EC46 images on a day-by-day basis allows you to see clear trends and a few links to some of the more interesting ones are as follows...

The regime changes are trending away from a resolute 'blue' or +NAO to now a very uncertain 'no regime' signal in the latest plot. You can see how the predicted +ve NAO has been nibbled away at in recent days to now the most recent one nearly losing that strong signal altogether.

The other series of plots which have changed is the VP signal, obviously no surprises on this one after numerous comments and discussions on this thread, but the last few runs highlight that strengthening signal.

Lastly, the one that stood out the most to me was the general 500mb height anomalies - We can see how the signal was for -ve 500mb height anoms over NW Europe a week or so ago, with a cyclonic signal through the 18th to the 25th Dec. However, note how that signal has been nibbled away at as well with now the most recent signal showing something far more blocked.

Whether this is just run-to-run variability, time will tell, but I don't think it is. Again this is why viewing these plots in this format is better than looking at them individually as you can visually see and extract potential trends and there are certainly trends there in my opinion already.

Once this -VP200 signal and associated MJO event pushes further into the W Pacific with a resultant +GLAAM/+GWO rise, it should be a fascinating watch from an NWP perspective in the 10 to 15-day time period, again as I mentioned the other day, covering the final third (20th-31st) or so, or now perhaps even earlier...

Cheers, Matt.

Looking at the latest BOMM projection of the MJO going into Phase 8 around the 12th Dec and this morning's GFS 0z 500hPa forecast for the NH way out at T384 (19th Dec), it's a very good match with the MJO composite for Ph8/Nino. It's tempting to think that the GFS is starting to take onboard the signal as the 12th plus the typical 7 to 10 day lag gets us to the 19th to 22nd. Any thoughts Matt?

BOMM RMM

GFS 0z for 16th

MJO composite Ph8/Nino

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4968676

December 3, 2023

4 minutes ago, MattH said:

Just flicking through some of the EC46 plots, amongst a busy weekend shift, and I think there is already some evidence for changes in there, for towards and beyond mid-December.

As ever the usefulness of the layout of the EC46 images on a day-by-day basis allows you to see clear trends and a few links to some of the more interesting ones are as follows...

The regime changes are trending away from a resolute 'blue' or +NAO to now a very uncertain 'no regime' signal in the latest plot. You can see how the predicted +ve NAO has been nibbled away at in recent days to now the most recent one nearly losing that strong signal altogether.

The other series of plots which have changed is the VP signal, obviously no surprises on this one after numerous comments and discussions on this thread, but the last few runs highlight that strengthening signal.

Lastly, the one that stood out the most to me was the general 500mb height anomalies - We can see how the signal was for -ve 500mb height anoms over NW Europe a week or so ago, with a cyclonic signal through the 18th to the 25th Dec. However, note how that signal has been nibbled away at as well with now the most recent signal showing something far more blocked.

Whether this is just run-to-run variability, time will tell, but I don't think it is. Again this is why viewing these plots in this format is better than looking at them individually as you can visually see and extract potential trends and there are certainly trends there in my opinion already.

Once this -VP200 signal and associated MJO event pushes further into the W Pacific with a resultant +GLAAM/+GWO rise, it should be a fascinating watch from an NWP perspective in the 10 to 15-day time period, again as I mentioned the other day, covering the final third (20th-31st) or so, or now perhaps even earlier...

Cheers, Matt.

Looking at the latest BOMM projection of the MJO going into Phase 8 around the 12th Dec and this morning's GFS 0z 500hPa forecast for the NH way out at T384 (19th Dec), it's a very good match with the MJO composite for Ph8/Nino. It's tempting to think that the GFS is starting to take onboard the signal as the 12th plus the typical 7 to 10 day lag gets us to the 19th to 22nd. Any thoughts Matt?

BOMM RMM

GFS 0z for 16th

MJO composite Ph8/Nino

December 2, 2023

Model output please folks. Thanks.

December 2, 2023

5 hours ago, Shaunado said:

Do you know of a radar history app that goes beyond the 6 hours of the Met Office app? I want to work out which side of midnight my overnight dusting came. Thx

31 minutes ago, Harry's House said:

According to the Met Office rainfall radar map, it would seem that for you at Egerton, precipitation occurred not far from midnight both before and after.

Indeed Harry. Looks like Kent enjoyed a streamer last night that lasted just under an hour. It started as a rain/sleet mix around 22.45 but it turned to snow as it moved inland and temperatures dropped. It finally died out around 00.15 today. Here's the radar at 23.35 (blue rain, green sleet, pink snow):

December 2, 2023

Certainly a cold day. The Netweather Extra temperature feed from Met Office automated weather stations showing most of the Region remaining sub-zero at around 13.00. (The feed lags the radar time stamp by an hour or so). I've just listened to John Hammond on the TV and he's talking about it turning mild, wet and windy by the weekend following, i.e. by 7 days time.

December 2, 2023

3 minutes ago, MattStoke said:

I don’t know why people pay any attention to the BBC forecasts when they can just look at the second to last ECM operational run.

MeteoGroup provide the BBC with their forecasts that we see on the TV. They use input from 3 different models and then 'add value' by allowing their meteorologists to make human input/tweaks before issuing a forecast. Here's some snippets about how they arrive at the forecasts:

The making of : a weather forecast
MeteoGroup uses a combination of three weather prediction models to arrive at the best result. These are the European model (operated by ECMWF), the American model (operated by US NCEP), and the British model (produced by UKMO). Our long-standing use of each of these models has taught us how well each scores on the various elements, which allows us to give a certain weighting in relation to each weather element to be calculated.
The most important step in our production of the specific forecasts we offer customers involves adding value to the data we buy. Our innovative, cross-functional Weather Systems Team is responsible for a bulk of (machine learning) post-processing algorithms we run on all of the data obtained from the models. Post-processing is used to correct the quite coarse-scale nature of model output; these corrections are necessary to ensure that local effects are taken into consideration. The process outlined above is at the heart of our high-quality forecasts and results in the MOS (Model Output Statistics). The meteorologists on duty are responsible for putting the finishing touch to the ultimate weather forecasts to be issued; of course, they have the full width of MOS data at their disposal. Senior forecasters are allowed to make changes to the MOS via the MeteoBase system.

Full article: https://medium.com/@meteogroup/the-making-of-a-weather-forecast-4ee5bfcc942e

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4966567

December 2, 2023

3 minutes ago, MattStoke said:

I don’t know why people pay any attention to the BBC forecasts when they can just look at the second to last ECM operational run.

MeteoGroup provide the BBC with their forecasts that we see on the TV. They use input from 3 different models and then 'add value' by allowing their meteorologists to make human input/tweaks before issuing a forecast. Here's some snippets about how they arrive at the forecasts:

The making of : a weather forecast
MeteoGroup uses a combination of three weather prediction models to arrive at the best result. These are the European model (operated by ECMWF), the American model (operated by US NCEP), and the British model (produced by UKMO). Our long-standing use of each of these models has taught us how well each scores on the various elements, which allows us to give a certain weighting in relation to each weather element to be calculated.
The most important step in our production of the specific forecasts we offer customers involves adding value to the data we buy. Our innovative, cross-functional Weather Systems Team is responsible for a bulk of (machine learning) post-processing algorithms we run on all of the data obtained from the models. Post-processing is used to correct the quite coarse-scale nature of model output; these corrections are necessary to ensure that local effects are taken into consideration. The process outlined above is at the heart of our high-quality forecasts and results in the MOS (Model Output Statistics). The meteorologists on duty are responsible for putting the finishing touch to the ultimate weather forecasts to be issued; of course, they have the full width of MOS data at their disposal. Senior forecasters are allowed to make changes to the MOS via the MeteoBase system.

Full article: https://medium.com/@meteogroup/the-making-of-a-weather-forecast-4ee5bfcc942e

December 1, 2023

ICON 12z very interesting. Big low unable to make progress against an emerging Scandi High:

December 1, 2023

I learnt to ski in Solden whilst on a school trip aged 14 - you can imagine the fun that was had. A great resort although spread out along the steep valley.

Another snow storm to hit the Alps later today and into Saturday and with tightly packed isobars it could be blowing about a bit. For lower level resorts and pistes this could start as rain today before colder air digs in tomorrow so turning to snow before dying out. Then a bit of a milder week ahead before maybe a repeat of today/tomorrow taking place in a week's time (i.e. 8th/9th Dec). Overall this is a great build-up to the new season.

Big picture (Sat):

Precipitation (Fri):

850hPa (Sat):

Freezing level (Fri):

Freezing level (Sat):

Sources: Meteociel and Netweather Alps Charts.

November 30, 2023

Nice tho the pics and stories of snow are, it's maybe time to head over to your Regional threads please guys. There's lots of model shenanigans to be discussed in this thread. Thanks.

November 29, 2023

1 hour ago, Methuselah said:

So what caused the cold weather (along with a few blizzards) between Xmas and early January then? It seems to me, that the extreme cold had set-in weeks before the Canadian warming exerted its effect?

1 hour ago, Cold Winter Night said:

1962-1963 had a Canadian Warming in late November, but that one was, like most CW's, no formal SSW with a 10 hPa reversal.
Later on, at the end of January, there was a proper SSW.

1 hour ago, feb1991blizzard said:

i thought there had been a canadian warming in nov 62, hence why the usual excitement in here whenever those type of winters analogue vaguely with whats happening now.

1 hour ago, Mike Poole said:

Yes, I thought that as well, Canadian warmings are an early season phenomenon, and one that seemed until this year to be a thing of the past.

That’s why it is so interesting to see one, and even though it is not a reversal, it seems to have a very clear signature on the model output. One more thing very much in our favour as we head towards the heart of winter

Thanks guys. The frustration of scientific papers that are behind a paywall and you can only read the abstract and first page. The abstract says "The stratospheric warming and circulation change of January and February 1963 are discussed....... ........warming initially appeared at 10mb over southeastern Canada....... ......the subsequent events..... .....destruction of the wintertime polar cyclone......"

And the last sentence of the first page says "Beginning in mid-January 1963 the stratospheric circulation was interrupted by intense temperature and height changes of a scale as large as any previously documented".

I concluded the Canadian warming was early January, leading to a full-blown SSW late February, but I'm happy to accept that the Canadian Warming was in November, leading to the above in Jan/Feb. Have you guys got a source of info to confirm Nov 1962 please? There are precious little scientific papers on the phenomenon, although last week Prof. Judah Cohen stated he was involved in a study, so that's good news.

Whatever, for those of us with a cold persuasion, let's keep our fingers crossed that this Canadian Warming has a similar impact to the winter of 1963.

November 29, 2023

30 minutes ago, Bricriu said:

Just a thought on this, given background drivers are always in a state of flux, it would seem that on very rare occasions the background signals can be overridden. Look at the winter of 1962/63, I presume the MJO and AAM weren't conducive to blocking through that extremely long lasting spell,but the intense blocking must have overriden them. Perhaps if we had an omega block this time with the cold well entrenched the same thing might have happened this time. I take your point though that they generally have a huge bearing on what type of weather we are likely to have .

A Canadian Warming of the stratosphere in January and February 1963 played a big part in making that winter very special. Such warmings don't always have such an impact (some have very little impact) but this type of warming puts pressure on the SPV and can weaken, displace and lead to a full blown SSW.

Source: The Mid-Winter 1963 Stratospheric Warming and Circulation Change

The current warming expected to rumble on for a couple of weeks yet; here's the geopotential height and temperature anomaly at T384 14th Dec from this morning's GFS 06z.

November 29, 2023

Good morning all. The frustration of a failed chase fully understandable, but please stick to discussing model output in this thread and use the Winter Moans, Ramps & Chat thread for non-model and more general chat. A few posts have been moved over there.

Many thanks.

November 28, 2023

Confirmation of the promising lead-up to the 23/24 season. Fingers crossed we can avoid any hair dryer warm southerlies between now and the season start.

November 28, 2023

16 minutes ago, The Enforcer said:

How's that Canadian warming coming along - 7th December wasn't it?

Coming along nicely. Forecast to peak around the 5th - 7th December. Here's the geopotential height and heat temp anomaly at 10hPa. The SPV literally feeling the heat and being encouraged to move towards the European side of the hemisphere.

28th Nov

05th Dec

Source: http://www.weatheriscool.com/prod/ztemp_multilevels.html

Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4962207

November 28, 2023

16 minutes ago, The Enforcer said:

How's that Canadian warming coming along - 7th December wasn't it?

Coming along nicely. Forecast to peak around the 5th - 7th December. Here's the geopotential height and heat temp anomaly at 10hPa. The SPV literally feeling the heat and being encouraged to move towards the European side of the hemisphere.

28th Nov

05th Dec

Source: http://www.weatheriscool.com/prod/ztemp_multilevels.html

November 26, 2023

The posts discussing the BBC forecasts and how they arrive at their forecasts have been moved to the following thread:

November 25, 2023

13 minutes ago, weathercold said:

London

Why not add your location to your profile? It's always nice for other members to see what part of the country you're from, especially if you're in your Regional thread and post about the snow in your back yard. I've marked a screen grab showing how:

November 25, 2023

8 minutes ago, winterof79 said:

I wish to god that someone hadn't started to use the term "phasing" some on here will be asking for their roasties to be phased with their gravy on Christmas day

A coming together would have been nicer

Hereby known as the Fujiwhara Effect:

The Fujiwhara effect, sometimes referred to as Fujiwara interaction or binary interaction.....
The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described the effect in the 1920s. Binary interaction of smaller circulations can cause the development of a larger cyclone, or cause two cyclones to merge into one. Extratropical cyclones (mid and high latitude lows) typically engage in binary interaction when within 2,000 kilometres (1,200 mi) of one another........
......with significant acceleration occurring when the low-pressure areas are within 1,100 kilometres (680 mi) of one another. Interactions between their circulations at the 500 hPa level (18,000 feet above sea level) behave more predictably than their surface circulations. This most often results in a merging of the two low-pressure systems into a single extratropical cyclone, or can less commonly result in a mere change of direction of one or both of the cyclones. The precise results of such interactions depend on factors such as the size of the two cyclones, their distance from each other, and the prevailing atmospheric conditions around them.

Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4958927

November 25, 2023

8 minutes ago, winterof79 said:

I wish to god that someone hadn't started to use the term "phasing" some on here will be asking for their roasties to be phased with their gravy on Christmas day

A coming together would have been nicer

Hereby known as the Fujiwhara Effect:

The Fujiwhara effect, sometimes referred to as Fujiwara interaction or binary interaction.....
The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described the effect in the 1920s. Binary interaction of smaller circulations can cause the development of a larger cyclone, or cause two cyclones to merge into one. Extratropical cyclones (mid and high latitude lows) typically engage in binary interaction when within 2,000 kilometres (1,200 mi) of one another........
......with significant acceleration occurring when the low-pressure areas are within 1,100 kilometres (680 mi) of one another. Interactions between their circulations at the 500 hPa level (18,000 feet above sea level) behave more predictably than their surface circulations. This most often results in a merging of the two low-pressure systems into a single extratropical cyclone, or can less commonly result in a mere change of direction of one or both of the cyclones. The precise results of such interactions depend on factors such as the size of the two cyclones, their distance from each other, and the prevailing atmospheric conditions around them.

November 24, 2023

Could we stick to model output discussion in here please folks. There's a bit too much off-topic chat in here tonight so I'm afraid posts will likely start disappearing. Please use the Winter Chat thread. Many thanks.

November 24, 2023

Is this the one @Battleground Snow:

November 23, 2023

2 hours ago, WINTRY WALES said:

Where can one find the latest METO update?

There is a dedicated thread on the forum for posting and discussing Met Office and BBC updates:

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