Penellype's Weather Channel 2

[Penellype]

Autumn is here and the weather is about to turn distinctly autumnal, with several low pressure systems making their way across the country. It will become quite windy later today, but currently the main focus is on Wednesday, which could be quite stormy. The exact track of the low is uncertain, so keep an eye on the Met Office warnings for updates. Most models currently have the low moving through Ireland on Wednesday and tracking north east into Scotland, with the worst of the winds on the south and western flanks of the low. This brings gusts of upto 100mph just to the south of Ireland, and widely 60-70mph around western coasts. There are plenty of gusts upto 60mph inland too - how far south this gets depends on the track of the low, but currently anywhere from the midlands to the Scottish borders looks in for a battering on Wednesday into Thursday.

We haven't had many gales for a long time now. Make sure that any garden furniture, wheelie bins etc are put away or secure, close greenhouse and polytunnel doors to keep the wind out and anchor any tall structures such as runner bean supports as best you can.

[Bren In Pots]

Thanks Pen, we do appreciate your updates.

[Nicos]

Thanks for the heads up Pen.
I know we’re a lot further south than many grapes , but we do have similar weather at times, so these alerts certainly encourage me to check out if we will experience something similar.
Lets hope there won’t be too much damage.

[sandspider]

So apparently today is a wind day - the wind direction today shows the main wind direction up until 24th December. For me in the South West the wind is generally Westerly / South Westerly. So I suppose that means the weather will be warmish but wettish until 24th December. Maybe!

[Penellype]

Mmm, I'm not sure about that. I know there are certain days which are said to determine the wind direction for the next few months, but I think the best they could hope to manage would be to indicate the wind direction that is likely to be most common during that time, which would not rule out significant periods of wind from other directions. I don't know of any scientific basis for these "wind days", but it is true that certain times of the year do have a tendency to produce similar weather, for example the beginning of September tends to be mild and dry, and there are notable cold times in spring, particularly the "ice maidens" 15-19 May. However, if it was as easy as that we would not need all of these sophisticated weather models to give us the forecast!

[sandspider]

True enough! The Weather without technology chap makes a lot of wind days, but as you say, I'm not convinced. The weather will do what it does, regardless of natural lore and modern computer modelling! Doesn't stop me from looking at all the forecasts and trying to figure out what might happen

[Nicos]

I check most days to sandpiper but we’re in a strange corridor compared to neighbouring villages. I still like to check - and on where my children live…
This caught my eye the other day. I’ve seen others with loads of other weather situations but the idea still makes me chuckle!
https://www.geograph.org.uk/photo/6019372

[Plot70]

There is quite a few measurements missing from weather forecasting.
As an example how much solar energy does poison algae absorb?
Algae also changes the profile of wave crests. Remember the phrase "oil on troubled waters".
There are plenty more.
Digital weather forecasts are quite accurate up to a couple of weeks in advance.
There are many weather modelling systems and looking at all the forecasts does help.

[sandspider]

I check 3 or 4 forecasts if I really want to know. Usually they disagree, sometimes quite significantly. Sometimes one forecast gets it right and the others are wrong, but usually the weather is a mixture of what the various forecasts say. Difficult to forecast massive, complex systems I imagine.

[Penellype]

The issue with the models and forecasting is that any model has to divide the earth up into a series of equal squares to forecast for. The higher resolution models use more squares than the lower resolution ones and therefore should be more accurate. However, the squares are relatively big compared with local geography, so while a forecast might in general be accurate for the area, if you live in a frost hollow or in the shade of a hillside you may see significant differences. Similarly, large weather systems like a stable clear high pressure will lead to an accurate forecast, as will a well defined frontal system producing a wide band of heavy rain. Forecasts of sunshine and showers on the other hand can go badly wrong if the showers band together or if the conditions are fractionally different leading to lack of convection and therefore no showers. Snow and thunderstorms are particularly difficult to forecast.

The exact starting conditions are also critically important, and these come from real life measurements which are always subject to errors. An error of a fraction of a degree temperature today can lead to a huge difference in the predicted conditions next week, which is why some of the models have an ensemble consisting of many runs each with fractionally different starting conditions. If all the ensemble members forecast the same thing it is very likely to happen, if they vary a lot then you can expect it to be inaccurate.

[sandspider]

Makes sense, P. Thanks. Interesting subject, I do enjoy it!

[Penellype]

The summer-like conditions that many of us have had recently are about to come to an abrupt end tomorrow night. It could be cold enough for a ground frost in places, which will be a massive shock to the system. Check local forecasts and cover up anything fragile that you want to keep.

[Bren In Pots]

Thanks Pen I've just checked a couple of weather site and we're down to overnight lows of 3c in the next few days..

[Penellype]

Nights are forecast to get colder towards the end of the week and weekend, with frost possible even quite far south.

[Penellype]

Some ridiculous headlines are appearing in the usual newspapers concerning a "600 mile wide wall of snow". These headlines get further from reality each year.

The weather models are showing a change to drier weather next week as high pressure builds from the south west. Some model runs have the high drifting west later in the week, which is too far ahead for accurate forecasting and not all model runs agree. If the high moves west this allows colder air to move in on northerly winds. However, this is not a done deal, and as this scenario leaves us with relatively high pressure, any precipitation will probably be in the form of showers and is likely to be confined mainly to coasts and hills. There may be snow mixed in, particularly in the north, although the number of runs showing this are a minority at the moment.

What the newspapers will not tell you is that there are an approximately equal number of runs (both in the minority) showing quite mild weather as there are showing some snow. The majority option (but by no means certain) is cool and mostly dry, probably with frost and fog, but that does not make sensationalist headlines.

The really awful thing about this sort of newspaper sensationalism is that people believe it, and then when it doesn't happen they blame the weather forecasters, who have said nothing of the sort. Then when there is a real risk of severe weather people are less likely to take it seriously.