Penellype's Weather Channel

[Penellype]

Latest run of the GFS is starting to line up with the ECMWF producing a much colder outlook than previous runs. This is the chart for next Wednesday:



This shows the high pressure building over Scandinavia and the winds turning into the east. While there is still plenty of uncertainty as this is a week away, it is looking increasingly likely that the cold at the end of this week could turn into something much more prolonged than was at first apparent.

Things can change at this distance but be prepared for cold next week, and if charts like the one below are right, quite a bit of snow!



This is a long way off but it needs watching.

In the shorter term tomorrow is looking very windy for northern areas and yellow warnings for wind have been added to the previous ones for snow. Keep an eye on the met office warnings page for details Severe weather warnings - Met Office.

[Penellype]

If my Twitter timeline this morning is a reasonable guide, there is likely to be huge confusion about what is happening with the weather over the next few days. Weather apps, which take their data directly from the models without any human interpretation, are likely to be confusing and inaccurate at best. Snow is the hardest weather type to forecast as half a degree either way can make the difference between wet sleet and snow that settles. In heavy showers a process called evaporative cooling can make this amount of difference and more. This means that even short term forecasting can get things quite badly wrong, especially as showers can be very hit and miss locally in any case.

From what I can glean from the models and by cutting out the near-hysterical snow mania, the following looks a reasonable interpretation at present:

Today - a low pressure to the east of Iceland with a secondary low to the north east of Scotland is coming up against cold air and high pressure over Europe and stalling:



This low is responsible for the strong winds currently over the northern half of the country. There are cold fronts associated with this, behind which there is much colder air. Further troughs and fronts associated with the low will move across the country today with associated showers, probably mainly snow, across Scotland, N Ireland, north west England and north Wales.

Tomorrow - winds will ease as the secondary low moves away to the east. Snow showers will continue in the north and west, moving south to include the pennines and much of Wales by afternoon. Some of the showers may make it to the east particularly through the Cheshire gap. These are likely to be of snow. Meanwhile, and this is the tricky bit, a small disturbance to the south west will move into the south, bringing warmer air and rain:



This will run up against the cold air and may turn to snow along its northern edge. There is potential for significant snow, but it could be sleet or rain. There is also uncertainty about how far north this feature will get. Keep an eye on the latest forecasts, preferably those with a human interpreter rather than weather apps, and look at radar maps such as Weather Radar - Live UK Rainfall Radar - 5 Minute Updates - Netweather.tv which has an option to turn on weather type and show snow in pink.

Friday - By early Friday the low is starting to move south down the north sea:



The strong winds will return, this time straight from the north pole, so it will feel bitterly cold. There will be snow associated with this, particularly in the east, as fronts move south. Meanwhile the flow is more westerly further west and the dividing line between rain and snow is difficult to judge.

Saturday - all the models are now in agreement that as high pressure builds the source of the winds will become more westerly.



While not exactly warm, this is not as bitterly cold as the easterly some of the models were predicting earlier.

There is still huge uncertainty about what happens next. The ECMWF is sticking to its easterly idea, the GFS keeps changing its mind, the midnight run cutting off the easterly very quickly, the 6am run (only just available) keeping the easterly going. There is so much inconsistency between runs that the only thing to do is to wait until it settles down.

[Penellype]

Already things are not quite panning out as expected, with snow confined to Scottish hills and the showers over the west falling mainly as rain with sleet over higher ground. Some of this may turn to snow later.

[Lumpy]

Thank You P.

I don't watch the weather on the news anymore just read your posts as you are far more accurate.

Could we have a sticky p;ease for this if Penellpe does not mind.

[Penellype]

Thank You P.

I don't watch the weather on the news anymore just read your posts as you are far more accurate.

Could we have a sticky p;ease for this if Penellpe does not mind.

I don't mind, just as long as people realize that I am totally unqualified with respect to weather forecasting.

[Nicos]

Done!
I really enjoy your posts..thank you for doing these...

[Scoot]

Thank You P.

I don't watch the weather on the news anymore just read your posts as you are far more accurate.

Could we have a sticky p;ease for this if Penellpe does not mind.

Great idea for the Sticky. Hopefully we carry on getting the weather reports for longer than "Winter weather 2016/2017". Maybe just call it "the weather thread".

[Penellype]

I'm happy to post weather updates when the weather is likely to be of interest. We may find once we get into spring or summer that there are fairly long periods when it really isn't very interesting or relevant, so updates may be less frequent then.

[Bigmallly]

Good work Pene, it's always nice to have a heads up when extremes in the weather are possible.

[Penellype]

One aspect of this current very active and interesting weather setup that I haven't mentioned is the likelihood of coastal flooding. Strong winds coupled with high tides are likely to cause problems around the coasts, particularly but not exclusively north sea coasts. The highest risk is on Friday with high seas caused by the low pressure system as it moves south down the north sea, but if you live near the coast please do keep an eye on the flood warnings https://flood-warning-information.service.gov.uk/map and be aware of the possibility of dangerous conditions on coastal paths etc from large waves which could overtop flood defences.

[Penellype]

Latest ideas about the expected location of the snow over the next couple of days from the excellent Gavin Partridge:
Snow Watch | UK Snow Events | Severe Weather

[Thelma Sanders]

I haven't looked at his forecasts for ages, I hope he is better now than he used to be lol!

[Penellype]

Still vast uncertainty in the location and amounts of snow this afternoon, with huge differences between the models.

The GFS has this for 6pm this evening:



The pink area is heavy snow.

The higher resolution Arpege model has this for the same time:



of which this is snow:



Personally I think the GFS is over-playing this somewhat, but it is always wise to over rather than underestimate the possibility of snow. Check the radar if you need to know nearer the time.

It is now looking increasingly likely that after a brief warm up Sunday/Monday (which may not reach eastern areas at all) the winds could turn into the east bringing colder frosty weather which could last for some time, starting in the south and moving north to include Scotland later in the week. Amounts of snow with this would depend crucially on the position of the high pressure over the continent - the further north it is the more snow we are likely to get. Current model runs are placing the high over Denmark or Germany which would put us in a cold but mostly dry airflow with little snow, but this could easily change, and there is still some possibility that the easterly will not develop or not last for very long. Anything beyond this weekend is still very uncertain, as is the depth of cold (and hence the minimum temperatures).

[Potstubsdustbins]

A mate of mine lives in Caithness he has had some pretty bad snow today, but having a quick whip round the webcams elsewhere it seems confined to the hills at this time.

[sparrow100]

SNERRRRRRR! Snowing in south London! Wooot wooot!