Penellype's Weather Channel

[Potstubsdustbins]

I seem to remember a week ago we were being promised a white very cold Christmas, reading this mornings rag we are now being told it could be the hottest Christmas since records began.

Think I'll wait for Pen to come along with her ideas, much more reliable.

[Penellype]

I seem to remember a week ago we were being promised a white very cold Christmas, reading this mornings rag we are now being told it could be the hottest Christmas since records began.

Think I'll wait for Pen to come along with her ideas, much more reliable.

Always remember that the press will jump on anything that might be unusual, or a possible record, regardless of how likely or unlikely it is, and blow it up out of all proportion.

I have been very careful not to mention Christmas because there has been a huge amount of uncertainty. At one point some of the models were showing a possible UK wide white Christmas, but it is only now beginning to come near to the reliable timeframe.

Currently the weather is warming up as mild air moves in, with the flow coming from the south west. How much of this warmth we actually feel depends a lot on the amount of fog. Warm air moving over cold, wet ground is a perfect recipe for dense fog, and with high pressure for the next couple of days there will be little wind to shift it. The sunshine is very weak at this time of year (we are less than a week off the shortest day) so it won't burn off easily. Anywhere from Yorkshire southwards away from the west coast is vulnerable to fog.

Therefore, although some parts of the west have already warmed up after today's rain, further east the ground is very cold and the milder temperatures will take another day or 2 to make their presence felt. By Wednesday the high is moving slightly to the east allowing more of a breeze to shift the fog, and is likely to be warmer, with temperatures into double figures. However, on Thursday a weak cold front is likely to move south through the country introducing cooler air from the west or north west. This is where the uncertainty starts. Most models are predicting a swift return to high pressure, but then another cold front moves south on or around Christmas eve. If this is correct it will be cooler on Christmas day, with the possibility of some snow or wintery showers in Scotland, although further south any precipitation is likely to be rain:



Do not take this as the probable outcome - this is what the GFS model is predicting at the moment, but there is plenty of time for it to change. However at present all the models are seeing the cold front and the "hottest Christmas on record" looks highly unlikely to me.

After Christmas the current thinking is that it may become rather stormy for a while, and it is possible that this could be brought forward to Christmas day.

This is the latest ensemble chart for York:



The warmer upper air temperatures are clear to see, as are the 2 cold fronts around 21st and 24th/25th. There is a noticable increase in rainfall after Christmas and the sharply pointed peaks and troughs in the temperature graph indicate the possibility of stormy weather, but much could yet change.

Finally an illustration of the radical change that has happened over the past few days. Here is the chart for a week ago:



Note the high pressure to the west and over Greenland, and the low extending towards Spain. The jet stream (black line) is well to the south, with the wind coming down from the north.

Tomorrow's chart looks like this:



The high over Greenland has been replaced by low pressure and high pressure is established over Spain. The jet stream is now well to the north, pulling up the air from the south west.

[bikermike]

I do enjoy this. I have just enough meteorological understanding to have a clue what is going on. And various hobbies that make one an amateur meteorologist...

[Penellype]

The Met Office have issued a yellow warning for fog https://www.metoffice.gov.uk/public/weather/warnings

The Daily Express have invented a "fog bomb".
https://www.express.co.uk/news/weath...morrow-tonight

Words fail me.

[Chippy Minton]

Fogbomb

Love it.

Does this mean we can have any weather related bombs? Sleetbomb? Mizzlebomb? Due to the expected high pressure approaching the country we have to expect a Breezebomb?

[Penellype]

Time for a quick update.

The models have been disagreeing about what happens on Christmas day. Up to then the mild weather continues but with more of a breeze from tomorrow which will hopefully shift any remaining mist and fog. On Christmas day a cold front is due to move in bringing colder and wetter weather, and the disagreements are all about the timing of this - it seems to be getting later with every run. This means that away from Scotland the prospects of a white Christmas are remote, but there could well be some snow later in the week, although conditions will be marginal, which will make forecasting it difficult. Some forecast snow may fall as sleet or rain, and factors such as how heavy the precipitation is can make the difference.

The trends to colder and wetter weather show up well on the ensemble chart for York:



Beyond the cold front on Christmas day/boxing day there is a lot of scatter and uncertainty both with the timing of the rainfall spikes and with the upper air temperatures, reflecting the uncertainty in the models. Some of the ensemble runs go for stormy weather into the first week of 2018 while others build high pressure over us or over Scandinavia. I'm not even going to try to guess which is right at this stage, but I don't think we will be seeing the last of this winter's cold weather next week!

[Mark_Riga]

"I don't think we will be seeing the last of this winter's cold weather next week".

I hope not, I've still got to clear around my raspberry patch as they can be badly affected by slugs, snails and particularly white fly. The white fly were not too bad this year and I put it down to clearing most places they might want to overwinter.

[Penellype]

"I don't think we will be seeing the last of this winter's cold weather next week".

I hope not, I've still got to clear around my raspberry patch as they can be badly affected by slugs, snails and particularly white fly. The white fly were not too bad this year and I put it down to clearing most places they might want to overwinter.

I may not have put that very clearly!

There will be a cold snap - colder today and even colder tomorrow, which is likely to last until Friday. Some areas may well see snow, but it is not likely to be as snowy or as cold as last time.

What I meant at the end of my previous post is that while it is forecast to warm up a bit after this, I would be surprised if we don't have more cold snaps this winter. There is still a long way to go before spring!

[Penellype]

Plenty of warnings of snow and ice for tonight and tomorrow, including an amber warning of snow for parts of northern England for tomorrow https://www.metoffice.gov.uk/public/weather/warnings.

Becoming generally wetter and windier from tomorrow, milder over the weekend into the first half of next week, after which it could all go downhill.

As always, anything more than a few days ahead is open to big uncertainties.

[Penellype]

More yellow warnings this time for wind, for much of England and Wales and for southern Scotland tomorrow night into Wednesday. https://www.metoffice.gov.uk/public/weather/warnings This particular storm coincides with high spring tides caused by the full moon, which is also at perigee (which means it is at its nearest point in its orbit to earth) - this is why it looks bigger than usual at the moment. The combined effects of the spring tides and strong winds mean that flooding is possible along western coasts.

The rest of this week will be wet and not particularly cold, but on Friday high pressure starts to build over northern Scotland and this could turn the wind into the east. This is very cold at this time of year and frost and snow are likely in some places. As always details are uncertain at this timescale, but be prepared for another cold snap at the weekend. I don't think this will last too long as the atlantic is still active, as is shown by the purple colours on Sunday's chart:



The ensemble chart (for York) shows the cold spell well, with the white average line dropping below -5, so snow is a possibility:



The GFS is predicting that the cold snap will be over by mid next week. It probably will, but always remember that bringing the atlantic westerly wind back is the default position for these charts, and next Wednesday is a long way away so things could change.

[Penellype]

The met office have updated their warning to amber for wind in parts of Ireland, northern England and the very south of Scotland tonight and into tomorrow as Storm Eleanor passes over. This is in a somewhat different position to where it was forecast to be yesterday. https://www.metoffice.gov.uk/public/weather/warnings

[bramble]

The west of Ireland was hammered by storm winds, heavy rain and severe flooding thid evening thanks to storm Eleanor.
55 thoussnd homes without power and another high tide forecast for morning.
Very severe.
Stay safe all.

[Penellype]

Indeed, stay safe - even though the worst of the wind has passed there will still be very high seas crashing into the west coast due to the storm and spring tides.

[Penellype]

Following on the heels of storm Eleanor, another load of wet but at least rather less windy weather is due tomorrow. This low pressure will slip to the south and drag the wind into the north, bringing in colder air. There is a serious disagreement between the models as to what happens next, and it will make a very big difference.

The situation by Sunday is not really in doubt and is still predicted to be much the same as in the chart in post #490 above. Note the huge green U shape south of the UK - the jet stream (thick black line) is over Africa, with the remains of Thursday's low over Spain. High pressure is building over Scotland and this is pulling the wind into the east (cold).

The GFS still wants to bring another low pressure system in fairly quickly, so by Tuesday the high has moved east and the wind is starting to come from a more southerly direction, with lows beginning to move back in. These still move down to the south rather than the normal northeast track, so this is not particularly warm, but it is basically not desperately cold:



The ECMWF model is having none of this. It builds the high pressure over Scotland, but does not really allow the atlantic low in, so the wind turns to the south east (still cold), but the low dives south before reaching us, and the high builds back more strongly to the north. By Friday 12th Jan we have this:



This is really cold and this sort of pattern does not move very fast. There is a real risk of an extended and very cold spell of weather, which would probably be mostly dry with hard over night frosts with this. Pay no attention to the orange and yellow colours showing with this high. These are upper air temperatures and at this time of year the colder surface air is what matters. This situation, where cold air runs underneath warmer upper air, is called an inversion. Depending on the amount of moisture in the air, this could be crisp, clear and frosty or dull and cloudy with freezing fog. I don't know enough about air masses to predict which it would be, but it would definitely be cold.

The Canadian GEM model (usually less reliable) agrees with the ECMWF on this one. I am not going to predict it, as the GFS has been rock solid in bringing the atlantic lows back in, and the ECM equally solid with its easterly wind. But the message is clear - there is the possibility of a longer cold spell than we have seen so far this winter, which could potentially last quite a long time.

[Penellype]

Something had to "give" at some point, and the cold fans will be gnashing their teeth this morning, because all the models are now showing a return to less cold weather by the middle of next week. The downside is that it means more in the way of rain, particularly in the west.

Note that I say less cold, not mild. We will still be on the cold side of the jet stream, with the air coming from a more northerly direction at times, but this is not the freezing cold "beast from the east" that the ECMWF was seeing until this morning. There is still some potential for snow this weekend, particularly in parts of Scotland and on higher ground in the north.

The pattern next week is still not a "normal" mild, wet and windy one, with high pressure not very far away to the east, and the jet stream still diving south over Spain. It would not take much adjustment to put this back into the colder category, so I expect that the general uncertainty and the swings between cold snaps and less cold spells will continue for a while.

Interestingly the longer range models have not seen the cold position at all, going unanimously for a mostly milder and definitely wet to very wet remainder of winter. It is unusual to say the least for the long range models to be more accurate than the short range ones, and for the moment I'm not convinced.