Blessed Weather

That's an ECM chart I believe, available on their website here. It has the legend (description) below it. In laymans terms the velocity potential regions shown with green are regions with enhanced convection and brown suppressed convection and is particularly useful for monitoring the MJO. This description on the Quora website I thought was a nice easy way of getting an understanding: "......the only things that can cause a [velocity potential] divergence at that height are tall cumulus towers from whose tops there is an outflow of air transported up from the atmospheric boundary layer due to condensational heating. Therefore, the 200 mb velocity potential can be used as a proxy for deep convection in the tropics." And a neat technical description from ChatGPT on the same Quora website: The 200 mb velocity potential in atmospheric science represents the large-scale, non-divergent flow in the upper troposphere. It is a measure of the tendency for air to accelerate in the horizontal direction due to changes in the distribution of temperature and pressure. This quantity is useful for understanding the dynamics of the atmosphere at high altitudes and can provide insights into the behavior of weather systems and the large-scale circulation patterns. Hope that helps.

Time to move on please folks. The thread is now being clogged with the debate. If you want to carry on please head over to the Winter Chat thread. Thanks.

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. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4971007

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.

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

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

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

Model output please folks. Thanks.

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):

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.

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

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

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

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.

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.

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.

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.

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.

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.

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

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

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

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:

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

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.