As the days grow longer…

The latest run of the GFS has come back into line with the ECMWF model in establishing a cold anticyclonic easterly across the country by T+144. After that the GFS enters the twilight zone by introducing a number of cyclonic outbreaks that get embedded in the cold easterly flow, these suggest a high chance of substantial spells of snow especially in eastern districts by the end of the month (fig 1).

Figure 1 – Courtesy of www.wxcharts.eu

Even the Met Office are now warning of the increased chances of this happening thanks to the recent Sudden Stratospheric Warming event above the North Pole. Professor Adam Scaife, of the Met Office Hadley Centre, said:

“Signs of this event appeared in forecasts from late January and in the last few days we have seen a dramatic rise in air temperature, known as a Sudden Stratospheric Warming, at around 30 km above the North Pole. This warming results from a breakdown of the usual high-altitude westerly winds and it often leads to a switch in our weather: with cold easterly conditions more likely to dominate subsequent UK weather.”

Frank Saunders the Met Office Chief Operational Meteorologist said

“A Sudden Stratospheric Warming implies around a 70 per cent chance of cold conditions across the UK.  There tends to be a lag of about 10 days before we see the downstream effects on the UK’s weather, as it takes time for the influence in the upper atmosphere to feed down to those levels where our weather happens. The outcome for the UK’s weather is still uncertain, but forecasts from computer models at the Met Office and at other centres are beginning to coalesce around a greater likelihood of cold conditions in the days and weeks to come.” 

Model uncertainty about any block

Figure 1 – Courtesy of www.wxcharts.eu

Just when we thought that we finally might see some winter down here in the south it now looks like two of the three main NWP models can’t agree with how things will work out in just 6 days time. The difference at T+144 between the GFS and the ECMWF models is massive, with the GFS going for a cyclonic SW’ly (fig 1), and the ECMWF for an anticyclonic E’ly (fig 2). All I can think is that it must be how each model handles the current SSW that is behind these two widely different solutions.

Figure 2 – Courtesy of www.wxcharts.eu

The position of any upcoming block

Figure 1 – Courtesy of www.wxcharts.eu

There is no doubt that a change of type will occur in the next week or two because of the SSW that started late last week. The next problem is where the actual block will be positioned and orientated. The two main available NWP models at T+240 have different views on that matter at the present time. The ECMWF has the block centred over the southern North Sea at the 500 hPa level and aligned northeast-southwest (fig 1), whilst the GFS has it centred over NE Greenland, and ridging more or less north-south across Iceland towards western Ireland (fig 2).

Figure 2 – Courtesy of www.wxcharts.eu

The exact position of where any block sits at the 500 hPa level, will make a big difference at the surface, because it dictates the surface flow and the source of the coldest air. As you can see the ECMWF at T+240 has higher than average 850 hPa temperatures across the UK in a strong SE’ly flow, and the coldest air over SE Europe and the Balkans (fig 3).

Figure 3 – Courtesy of www.wxcharts.eu

Meanwhile the GFS model has the coldest air at 850 hPa over Scandinavia with the UK in a much colder regime and the flow more easterly and not as strong (fig 4).

Figure 4 – Courtesy of www.wxcharts.eu

Here’s what the experts are saying down at the Met Office about the medium term (fig 5).

Figure 5 – Courtesy of the Met Office

Latest GFS run nominated for Hugo award

The Global Forecast System has been nominated for a Hugo award for its latest model run for the UK (fig 1)! The Hugo Awards are a set of literary prizes that are given annually for the best work of science fiction or fantasy. This is the first time that a piece of software has ever been nominated, but the trilogy of T+288, T+312, & T+336 forecast charts do meet the essential criteria for any nomination, in that they are both science and fiction.

Figure 1 – Courtesy of www.wxcharts.eu

Despite this tongue in cheek humour, and as a snow lover, I would love something like this to happen, and perhaps now that the polar vortex is split we will finally see a change in type that means something like is possible and not just science fiction.

Saturday night’s low

Figure 1 – Courtesy of www.wxcharts.eu

I wonder if Met Éireann will end up naming the low that runs across Northern Ireland later on Saturday? It looks like the Met Office are more concerned about the snow from it over SE Scotland and NE England. This low is not hanging about though, so I can’t see that being a big problem. The latest GFS run does have the low undergoing rapid cyclogenesis, deepening by 30 hPa by the time we get to 06 UTC on Sunday morning (fig 1), and more markedly than do the UKMO in their latest forecast charts (fig 2).

UKMO Chief Forecaster’s assessment

Rain and hill snow, accompanied by some strong winds, is expected through Saturday evening, clearing eastwards overnight. Above around 200 metres, 2-5 cm of snow may accumulate although there is a small chance of 5-10 cm falling over the Southern Uplands. As skies clear from the west overnight into Sunday morning, ice is expected to form on any untreated surfaces“.

Figure 2 – Courtesy of the Met Office

Could this be it?

Figure 1 – Courtesy of www.wxcharts.eu

I notice that the Met Office have now picked up on the change of type that the GFS seem to have been hinting at since the New Year and never seems to happen. The latest run shows this block establishing itself by T+312, with an easterly regime developing across northern Europe, with high pressure over Iceland and Scandinavia and low pressure over Iberia and the northern Mediterranean (fig 1). It’s essential that you get high pressure over Iceland to stop warm air riding over the top and collapsing the block as so often does.

It’s still a couple of weeks away, and we know just how highly unreliable NWP can be at this range – especially the GFS model, but it is at least supported by the latest medium range outlook (fig 2) from the Met Office – so we live in Hope – well we would if we could afford the house prices there.

Figure 2 – Courtesy of the Met Office

More explosive deepening and severe gales

Figure 1 – Courtesy of www.wxcharts.eu

The next Atlantic low is poised to run in later today and overnight and introduce gales across the whole country, with gusts to severe or even storm force across the northwest of Scotland. Low ‘Helene’, as the Institute of Meteorology at the Free University of Berlin have called it, will deepen according to the latest GFS model (o6 UTC) by around 29 hPa in 18 hours or so as it tracks across the Isle of Lewis and clips Caithness by 06 UTC tomorrow (fig 1).

The Met Office at the moment have issued a yellow warning for strong wind from 01 to 14 UTC tomorrow for gusts of 60-70 mph with some to 70-80 mph but it’s only for the northwest of Scotland (fig 2).

Figure 2 – Courtesy of the Met Office

The GFS model is forecasting severe gale force gusts ahead of the cold front across the whole of England and Wales later in the night (fig 3). There has been no word on any additional warnings for England and Wales from the Met Office, so I can only assume that the UKMO model is at odds with the GFS, or maybe that the fire at the Met Office this morning on a server, has been more serious than we thought and is somehow hampering them being issued?

Figure 3 – Courtesy of www.wxcharts.eu