I am reliably informed that the spring vernal equinox will occur at precisely 1615 UTC today this 20th day of March 2018, but the weather is in a fickle mood at the moment, and spring, well at least the start of it, looks like it will be a cold affair in our part of the world. The Met Office in their extended outlook till the middle of April (fig 1) is being its usual unequivocal self about the possibility.
In line with that outlook, the GFS model for April 1st (fig 2) is forecasting a northerly outbreak which is not at all unusual for spring across the British Isles.
Cold springs are somewhat of a rare commodity these days, and the last one to produce negative anomalies in Central England was back in 2013 (fig 3), and in the last 30 year there have only been three cold springs (2013, 1996 and 1991).
Rather surprisingly Dublin is as snowy as any other station in this mornings 06 UTC SYNOPs, reporting a level snow depth of 16 cm from showers coming evening off the Irish Sea.
On what is probably going to be the coldest day of this present cold wave across our part of Europe, there has been a widespread severe and penetrating frost overnight. Thanks to a snow surface (I’m guessing there is one there even if they didn’t report one), the coldest low-level station was South Farnborough where the temperature fell to -11.7°C.
Even by 09 UTC this morning, the only station in the British Isles to have an air temperature above freezing was St Mary’s on the Scilly Isles with 0.2°C (fig 2), after reporting a rare frost with a minimum [18-06] of -0.5°C.
The snow showers have just kept coming, and it looks particularly bad today over SE Scotland and NE England, with more snow showers in a strong easterly wind that must be causing some pretty deep drifts. I wonder if the Met Office will issue a red alert for snow and blizzards for the borders or the central belt of Scotland before it’s done?
The spell of snow forecast for the southwest later on Thursday could produce some large snowfall totals before milder air eventually clears it all away. I’ve got a feeling that we might get fed up to the back teeth of March before it’s done, as it looks likely to remain cold and cyclonic till at least mid-month in the latest GFS model run.
Here’s how the Met Office see March panning out (fig 3):
I find the line “towards the middle of March it may turn more unsettled and less cold” rather strange. Do they mean unsettled compared to how the weather is now, or over the next few days? It’s as if the medium range forecaster hasn’t seen the latest NWP, because the scenario that he describes may happen mid-month, is already forecast to happen at the beginning of the month (fig 4).
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).
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.”
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).
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).
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).
Here’s what the experts are saying down at the Met Office about the medium term (fig 5).
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.
The latest 3 month outlook for contingency planner from the Met Office is flagging February as likely to be a much colder month than average for a number of reason (fig 2). The MJO is apparently active and is forecast to enter a phase that may lead a negative NAO. All that basically means is the pressure is lower in the Azores than it is over Iceland, and indicates that the north Atlantic circulation has been blocked, with the usual zonal westerly flow becoming either easterly or meridional. In the month of February that basically means colder and more anticyclonic over western Europe. The outlook goes onto say that at the moment there is little likelihood of a SSW event in February but we live in hope.
Things may already be getting underway judging by the latest set of forecast charts from the Met Office (fig 2).
The latest offering from the GFS model predicts a rather cold northwesterly airstream on Christmas Day, a bright looking day with wintry shower especially across northwestern areas. This brief cold snap may well be the last in a series of cold north or northwesterly incursions that you can trace back to the end of October (fig 1).
As so often happens between Christmas and New Year, the weather drastically changes in mood, and this year doesn’t fail to disappoint in this regard, as it turns progressively milder on Boxing Day, and by the start of 2018 its super mild across the British Isles and the bulk of Europe, if this chart for January 1st is to be believed (fig 2).
The GFS solution does contradict the latest extended outlook from the Met Office though, which suggests that in the final days of December “Temperatures will be near to or below average and snow is likely, at times”, they go on to imply that things might turn more settled and anticyclonic as we go into January 2018 (fig 3). As always, it will be interesting to see what transpires in a couple of weeks time.