knocker

Time for this again from an old forecaster

Tg -5C at Exeter this morning

Regarding Greenland that is a very simplistic comment and totally misleading The end of the northern-hemisphere summer brings to a close the Greenland ice sheet melt season and with it confirmation that 2022 was the 26th year in a row where Greenland lost ice overall. While much of Europe and North America sweltered this summer, Greenland was rather wet and cool, with the melt season delayed by snowfall in June. Melting came to a near-end in mid-August and the summer ended with a huge snowfall event dumping almost 20bn tonnes (Gt) of snow onto south-east Greenland. Nonetheless, taking into account surface melting, breaking off of icebergs and frictional effects under glaciers, the Greenland ice sheet lost 84Gt of ice over the 12 months from September 2021 to August 2022. Greenland last saw an annual net gain of ice in 1996. In this annual guest post, we discuss the processes of ice sheet melt, glacier calving, weather and climate that explain these losses. This year, we extend our discussion slightly and also look at the unusual warm period in the beginning of September 2022. (See our previous annual analysis for 2021, 2020, 2019, 2018, 2017, 2016 and 2015.) https://www.carbonbrief.org/guest-post-how-the-greenland-ice-sheet-fared-in-2022/

You can see the C3S outputs here mushy https://climate.copernicus.eu/how-read-c3s-seasonal-forecast

https://charts.ecmwf.int/

For what it's worth my two pennyworth on this discussion The green lines represent the height of the 500mb level in dm and indicate where the troughs and ridges are located from which much can be deduced., not least the flow of the upper wind. But in a fairly strong westerly flow as indicated they will not pick up. say, frontal wave developments in the flow which then track quickly east. And thus for a time the surface wind can be completely different in a particular region, albeit these developments should be consistent to the overall pattern. The dotted red and blue lines are the anomalies against climatology and not physical entities on the chart but their intensity should be noted

Well this morning's fax chart had a convergence zone across the south west for 1800 so it wasn't a complete surprise

They occur almost exclusively in winter in both hemispheres

I am sorry, but apart from the fact that there is no such thing as 'almost a polar low', to even mention polar lows in the context of this shallow wave feature is wrong and potentially very misleading. https://community.netweather.tv/learning/basics/polar-lows-r76/

Yes the ext mean anomalies are pretty broad brush but with the upper flow tending to diverge and abate, courtesy of the high in east Europe and slack low pressure to the south, then the idea of WAA drifting north obvioiusly cannot be ruled out, particularly at this range

Mushy for what it's worth this is how I see this. There are signs of weak positive anomalies across the Atlantic, and even a hint of a ridge, with a moderate W/NW upper flow towards a weak trough in the east before the upper flow backs quite sharply, courtesy of the strong high pressure in eastern Europe. Thus generally pressure very slack across the UK, and not particularly low with the detail a tad tricky at this range. Temps varying around the average

Oh my sainted aunt............surely not.

When I used to be a regular poster in here I oft made the point that the terms 'downgrade' and 'upgrade' are subjective and totally meaningless if not accompanied by some context and a more detailed objective analysis. They rarely are so ideally they should be dumped in the swear filter tout suite.

Never mind the impact on schools and kids what about the impacts in here. There are already signs of quite severe surface based instability developing.

A link to the latest comments by Will Hand in this thread https://www.ukweatherworld.co.uk/forum/index.php?/topic/128925-extreme-rainfall-weekend-18th19th/&tab=comments#comment-1166619

It has it in the same position as the METO and yes it becomes a tad more active But I would have thought the more convective activity down to the upper trough engaging with the cut off low and the extreme temp gradient to the east which could bring some heavy rain to the south west

I am not sure that I'm following much of this as the ecm is pusihng the front through early Saturday afternnon

But take a glance at the low level flow in relation to the temps. The exact position of the front crucial to the north south 'cut off'

But over last two days of the ecm run it develops a wave in the Denmark Straits on the elongated front that is running south from there and then develops it as it pushes through the ridge to be over Scotland at the end. I would have thought assuming that this will turn out to be anywhere near correct, withouy confirming evidence, to be fraught with danger.

But that is the point. Used correctly they produce the upper air frame work within which the determanistic runs will operate and thus likely signal whether something is out of kilter or whether a beady eye should be kept on it. For example this is the relevant 5 day anomaly chart from the ecm this morning for the period of the rapid wave delopment indicating the upper trough west of Ireland And these charts indicate the detail at t144 Now obviously if you just had the anomaly charts you would not spot these developments but, IMHO, you should recognise the possibilties of developments in this area if the models start indicating along these lines. And of course the ecm may well drop the rapid developments on the next run even though the framework still broadly correct

If that is meant to be a criticism I think it a tad unfair. They are not designed or meant to pick up rapid frontal wave development, such as the ecm is indicating this morning, along the base of the upper trough.

As far as I can see there has been a fair bit of uncerttainty regarding the interaction of the cold front moving east and the warm front feature tracking NNE from France. A couple of day ago the METO were going for moderate/heavy pulses of rain but last nigfht tracking the latter a tad further east not so much. It would seem the earlier interpretation was nearer the mark

A very important conversation was just published in NatureGeoscience on whether Atlantic Ocean circulation is (or has been) slowing in these two papers https://www.nature.com/articles/s41561-022-00896-4 https://www.nature.com/articles/s41561-022-00897-3 This new paper might be of interest (open access) https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL096527

I am not sure about the 'but we take from AROME' bit but a real-time sting-jet precursor tool for forecasters has only been developed over the last twelve months. Abstract Sting jets in European windstorms can cause damaging winds and gusts, but the resolution of global ensemble prediction systems is too coarse to represent them. Here we describe the development of a tool applied to outputs from these systems that forecasters can use to identify favourable conditions for sting-jet occurrence several days ahead. Plots generated by this tool have been available to Met Office forecasters since autumn 2019, and we demonstrate its usefulness for storm Brendan from January 2020. Damaging surface winds in some European storms have been attributed to descending mesoscale airstreams termed sting jets. The development of a prototype real-time tool that Met Office forecasters can use to identify favourable conditions for sting jet occurrence in extratropical cyclones is presented. The motivation is to improve national severe weather warnings. We have previously developed a convective-instability-based tool to identify sting-jet precursors for research purposes and applied it to storms in reanalyses and climate models with insufficient spatial resolution to represent sting jets. Here we describe the challenges of applying this research-derived diagnostic to output from an operational forecast system and demonstrate its usefulness for a recent winter storm. Through close collaboration with the researchers and forecasters from the Met Office, the diagnostic has been adapted to work on output from the Met Office's operational global ensemble forecasts as it becomes available. Since autumn 2019, forecasters have been able to view graphical output informing them whether storms impacting the UK and Europe (up to 7 days in the future) have the precursor. The tool has already proven useful in informing guidance for severe weather warnings, including those issued by the Met Office's impact-based National Severe Weather Warning Service that goes out to seven days ahead and is the primary hazardous weather warning service for the public and emergency responders. https://rmets.onlinelibrary.wiley.com/doi/10.1002/wea.3889

Cloud 'head' of developing Eunice south east of the cold air associated with the upper trough