Penellype's Weather Channel

[bikermike]

gosh! excellent stuff.

[Penellype]

Time for a quick update.

As mentioned in my last post, the GFS got it right, and the weather has turned a little less cold. A front associated with a low pressure system is moving in off the atlantic, bringing some rain from the west during today and tonight. Another small low will slip south over western Ireland tomorrow night, ending up in the Bay of Biscay - this is very unusual. The flow over us is very slack by this time and for the remainder of the week, with light winds leading to damp, grey and potentially very foggy weather as a weak ridge of high pressure follows the low, eventually joining up with the high that is still there over Scandinavia.

Meanwhile, the very cold weather that has begun to loosen its grip over the USA looks like having another go, and this will strengthen the jet stream and push a more vigorous low towards us. By Sunday/Monday it could turn quite stormy for a short while. However, the Scandinavian high is not budging and once more this low is predicted to slide to the south rather than taking the more normal north easterly track, pulling the winds into the north west. This air would be cold, originating from Greenland, and there would be fronts associated with the low, with snow likely in some areas, particularly the north. It is too soon to say where exactly, but the possibility of some snow accumulations is definitely there.

While this is happening high pressure is forecast to build over Greenland and this would eventually force the winds round more to the north. It is looking possible that we could be in for a week or so of cold, and at times snowy weather from early next week. However this is far enough ahead for things to change considerably by the time we get there.

Finally, the GFS model is consistently predicting a "sudden stratospheric warming" (SSW) towards the end of January. This happens when the high pressure which usually forms over Siberia at this time of year causes the air high above it to warm (don't ask me why, I don't know), and this warmth spreads over the north pole, causing the temperature over the pole in the stratosphere to warm up very quickly by upwards of 50 degrees C. It is generally agreed that when this happens it tends to increase the chances of blocking high pressure over the pole a couple of weeks later. We already have some high pressure over the pole, and the crucial factor is where it is positioned. If in the "right" position, this can lead to very cold weather for the UK. At present this is a long way off in forecasting terms. Last year we were forecast one of these things, and a warming did occur, but not strongly enough to be designated a SSW. Last year we didn't get any cold weather associated with the warming.

So, as the forecasters would say, there are some very "interesting" signals. When weather men use the word "interesting" it often means something nasty may be on the way!

[Penellype]

Models are firming up on the ideas in my previous post. This weekend will be relatively mild with rain starting to push into the west. By Monday a strong area of low pressure starts to make inroads into the high that is currently keeping most of us dry and fairly cloudy (at least in the east). The mist and fog will be blown away as winds strengthen.

Monday's chart shows the low pressure, with a weather front across the country bringing rain (snow in Scotland):



Notice that the air in this low is coming from Greenland - this is due to the north west - south east slope of the jet stream (thick black line). Unusually this gives us cold weather from the west (called cold zonality).

The low pressure sinks south east across the country, leaving us in a cold and showery flow. The showers could well be snow and will be heaviest in the west. By Wednesday a small low pressure is developing to the west of Ireland:



This could bring a more substantial period of snow to much of the southern half of the country on Wednesday into Thursday - the exact track of this low is uncertain and it wants watching.

As the low moves away to the south east the wind moves round to the north, keeping us cold. The latest run of the GFS model then has the wind pulling round to the north east by Sunday, which is even colder.



Note the high pressure developing over Greenland. This is not at all far from becoming much more than a cold snap, and could, if this continued, become quite a long and severe cold spell. However, at the moment it is a long way off.

What is not in doubt is that the current calm and relatively mild, gloomy weather is going to change to a wetter, windier and then colder regime during Monday. After that, we are cold and in some places (details to be determined) snowy for the reliably forecastable future. The GFS ensemble chart (for York) shows the change to colder weather well:



After Monday the white predicted average line does not rise above the red 30 year average line at all until the very end (unreliable part) of the chart, although some of the individual ensemble members do. The rainfall spikes during the colder period could easily fall as snow.

[Penellype]

The little low pressure that I mentioned in the previous post, due to cross the country on Wednesday night is giving all sorts of headaches as to exactly where it is going. This low is going to get caught up in the jet stream and strengthen rapidly, bringing very strong winds on its southern side as well as potential snow to its north and east. Winds could include damaging gusts of 70-80mph just to the south of the low, which is currently forecast to mean northern England. However anywhere to the south of the low will be very windy. The storm is likely to be named storm Fionn.

The met office have issued a series of yellow warnings from today to Thursday for ice and snow, snow and wind www.metoffice.gov.uk/public/weather/warnings.

Batten down the hatches and secure anything loose that might blow about.

[Penellype]

So, last night there were strong winds to the south of a line between north Wales and the Humber, and snow in many places north of this line, most in the west. Storm Fionn?

Well, yes and no, but mostly no. The Irish Met Agency named a storm Fionn yesterday as it battered the south of Ireland. I'm not sure that this was actually the same storm that we got last night. But although there was actually an amber warning last night (the criterion for naming a storm), this was for snow, not wind. Even so it was very windy with gusts of over 80mph in places. The Met Office decided not to name the storm, but in Europe it has intensified even more, and the Netherlands have had a real battering this morning. So the French (I think) have named the storm David, and the Dutch seem to be calling it Friederike.

Confused? I certainly am!

[Penellype]

The currently chilly weather is due to come to an end soon. The weekend will be cold, with frost and snow at times - there is currently an amber warning for snow in parts of southern Scotland and various yellow warnings for snow and ice for the northern half of the UK over the weekend. See https://www.metoffice.gov.uk/public/weather/warnings for details.

On Sunday a warm front is due to move in from the atlantic and this will be coming into cold air. There is likely to be snow on its leading edge, and quite a bit of snow may fall in northern areas before it turns to rain, hence the warnings. The air will be much warmer behind the warm front as it will be coming from the south or south west, as illustrated on the current ensemble chart for York:



Temperatures could reach double figures at times next week, particularly if the sun comes out. Pressure is relatively low, so bands of rain can be expected at times, and it will probably become cooler towards the end of the week as the low moves away and the wind swings briefly round to the north.

There is still uncertainty about what happens next, but most of the ensemble members seem to favour high pressure building to our east, keeping the wind from the south west. The rainfall spikes on the ensemble chart are decreasing, so providing this is not a damp and foggy high, this could be looking quite nice for the last week of January.

Much could change though at this range - if the high to the east moves further north there is still potential for a bitterly cold easterly wind...

[geepee]

The currently chilly weather is due to come to an end soon. The weekend will be cold, with frost and snow at times - there is currently an amber warning for snow in parts of southern Scotland and various yellow warnings for snow and ice for the northern half of the UK over the weekend. See https://www.metoffice.gov.uk/public/weather/warnings for details.

On Sunday a warm front is due to move in from the atlantic and this will be coming into cold air. There is likely to be snow on its leading edge, and quite a bit of snow may fall in northern areas before it turns to rain, hence the warnings. The air will be much warmer behind the warm front as it will be coming from the south or south west, as illustrated on the current ensemble chart for York:

[ATTACH=CONFIG]78254[/ATTACH]

Temperatures could reach double figures at times next week, particularly if the sun comes out. Pressure is relatively low, so bands of rain can be expected at times, and it will probably become cooler towards the end of the week as the low moves away and the wind swings briefly round to the north.

There is still uncertainty about what happens next, but most of the ensemble members seem to favour high pressure building to our east, keeping the wind from the south west. The rainfall spikes on the ensemble chart are decreasing, so providing this is not a damp and foggy high, this could be looking quite nice for the last week of January.

Much could change though at this range - if the high to the east moves further north there is still potential for a bitterly cold easterly wind...

Great info, Pen', might I be right in thinking from experience, once that Easterly, chilly wind comes on us at this time of year, it often stays that way for a while ? ie A cold but maybe dryer early window to please farmers and growers ????

[Penellype]

Great info, Pen', might I be right in thinking from experience, once that Easterly, chilly wind comes on us at this time of year, it often stays that way for a while ? ie A cold but maybe dryer early window to please farmers and growers ????

Easterly winds are a result of high pressure to the north east. The wind circulates clockwise around a high, so that position puts us in the firing line for an easterly. How long it lasts usually depends on the strength of the high. If it is just a transient ridge in a more mobile westerly flow, we may get a brief easterly that doesn't last long. But more often, if the ridge builds over Scandinavia at this time of year it is difficult to shift. A true blocking Scandinavian high can last for a couple of months, so yes, in this situation you often get locked in cold that lasts a fair while.

The models, particularly the ECMWF, have been keen to predict this situation this winter and have already had a few failed attempts at it. However, current model runs don't show this happening. My point was that presented with a chart like this (by the GFS model) for 10 days time:



it doesn't take a huge amount of imagination to shift the high a couple of hundred miles north east, which would be enough to pull in an easterly wind. This is well beyond the reliable timeframe, and the other models do not currently see quite such a strong high, or have it quite so far north, which would keep us in the warmer southwesterly flow around the western side of the high.

[Penellype]

A potentially snowy day for many parts, with snow already falling in some western areas. Keep an eye on https://www.netweather.tv/live-weather/radar if you are going out. If you turn weather type on at the top the snow will show in pink, sleet in green and rain in blue. It is not absolutely accurate but gives you an idea of what is coming your way.

[KevinM67]

Just checked that website Pen - cheers.
I'm currently sitting about the house, peeved off, waiting for that big band of cr@p to pass over Dublin. Luckily for us though it's just rain.

Such a weird difference in temperatures over the UK and Ireland at the moment and expected.

[Penellype]

The big difference in temperatures is the result of a warm front dividing different air masses. Recently we have been in a cold polar maritime air mass, which originates from Greenland, but behind the warm front we (probably) have a tropical maritime air mass, bringing much warmer air from the south west. Where the 2 air masses meet the warmer air is forced above the cold air, causing cloud and rain or snow along the line of the front. As the warm front passes over the temperature will rise noticeably.

[Penellype]

Quite a stormy night on the cards tonight as a rapidly deepening low moves in from the atlantic. The Irish met agency has already named this Georgina. The Met office is less impressed and has a yellow warning of wind for parts of Scotland https://www.metoffice.gov.uk/public/weather/warnings. There is also a yellow warning of rain for some pennine areas.

The models are making a bit of a meal of this one, and some have much stronger winds than the Met Office are suggesting, with gusts of 70-80mph much further south than the warning area. The focus is likely to be on a cold front which could develop a squall line - a tight band of torrential rain and very gusty winds that only lasts for a few minutes. Be prepared for this - you will see it on the radar pictures nearer the time as a brightly coloured line of heavy rain. It will in any case be windy and tomorrow will start wet.

Today has been warm for the time of year, but the cold front will bring a cooler (though not particularly cold) few days as the wind swings round more towards the north. Friday night could be frosty as winds fall light before things warm up again over the weekend. High pressure then seems likely to build to the south, turning the wind back into the south west. Anything beyond that depends critically on where the centre of the high pressure sits, and there is considerable uncertainty over this at the moment.

[bramble]

Penn. We had 13 deg here today. Crazy weather.

[Greenleaves]

Question for you Penellype?

We have an old chap (93) over the allotment who's a bit of believer in old sayings....he is convinced February's weather is going to be very cold....any indications he may be right?

[Penellype]

Penn. We had 13 deg here today. Crazy weather.

Yes, warm south westerly air flow today.