Penellype's Weather Channel

[Chippy Minton]

And the tabloids have already started with the "Come on Aileen" jokes.....

So altogether now, after 3.....

Gives us something to hum as w chase the blow-away / wheelie bin / [insert wind driven object] down the street....

[Penellype]

And the tabloids have already started with the "Come on Aileen" jokes.....

So altogether now, after 3.....

Gives us something to hum as w chase the blow-away / wheelie bin / [insert wind driven object] down the street....

Except that the song was about Eileen, not Aileen...

[Chippy Minton]

Never let reality get in the way of a good tabloid headline....

[Jay22]

You can pronounce Aileen as Eileen though.

[Penellype]

Aileen is one of those storms that developed very rapidly from what looked like almost nothing this time yesterday. It is now giving the continent a battering, and strengthening as it does so - these were the latest gusts at about 11.35am:



map is from Weatherobs.

The numbers are in km/hr - to quickly convert to mph multiply 6 and divide by 10 (multiply by 0.621371 to be more accurate).

[Jungle Jane]

I don't think wind needs to have a name,if it's a hurricane it's ok but to name just the wind seems wrong. Apparently it makes people more aware & to get things bolted down etc but I didn't do anything & it just knocked a bucket over because it's just wind

[1Bee]

There was really very little to show for it up here. Even my 12 foot sunflower is still looking unruffled.

[Penellype]

The policy is to name storms for which the Met Office produce amber warnings. Probably the idea is to draw attention to the fact that there is an amber warning for parts of the country, but these warnings rarely cover the whole of the country. Today's amber warning seemed to be somewhat further north than the strongest winds, which illustrates the difficulty in precisely forecasting the tracks of rapidly developing storms.

[veggiechicken]

Aileen broke branches on 3 mature trees in the garden and brought down trees, blocking roads, locally.
Raining heavily throughout the day.
Hope she's gone now.

[Penellype]

Sorry to hear about your trees VC. Yes she has gone off into the continent now and shouldn't give us any more trouble.

[Gillykat]

We didn't see much of Aileen up here in Northumberland - a bit of heavy rain overnight and that was it

Fingers crossed it stays dry next week (between Sunday 17th until Saturday 23rd would be purrfect!) as I'm on holiday and am wanting to knock the plot into shape!

[Penellype]

I think you are likely to have some dry weather, but always remaining a bit changeable. The models are really struggling with the forecasts due to massive uncertainties about the position of hurricane Jose in the atlantic and if/how it interacts with the jet stream when it eventually drifts north. Currently anything from landfall on the eastern seaboard of America (fairly unlikely) to it disappearing slowly into another low pressure in the mid atlantic could be on the cards, and this crucially affects development or otherwise of high pressure to its east, which in turn affects us. Until yesterday most of the models were predicting a drier and warmer spell, but they have backed off this and although some increase in temperature is likely, currently they are showing low pressure never particularly far away, with the south and east getting the better weather, as usual.

Ensemble forecast for York this evening:



Note the increasing uncertainties in upper air temperature and the size and positions of the rainfall spikes after about 19th September.

This could all change again tomorrow.

[Penellype]

Still massive uncertainties about the effect of hurricane Jose on our weather. The short term forecasts have been accurate, with chilly days, cold nights (zero reached at Tyndrum in the Scottish glens last night) and widespread showers on a northerly wind. This will continue for the next couple of days, although the showers will become less widespread and probably less heavy as the high topples in from the west. Watch out for a particularly chilly night into Tuesday morning if you are in a frost-prone area as the air mass is still cool and winds will be light.

Once the high moves over us it will change the direction of the flow to the south west and this will bring in warmer weather, particularly in the form of less cold nights, for a day or 2 before falling off again as another low moves through. It is what happens next that has the models chopping and changing.

Here is the York midnight ensemble:



You can clearly see the dip in temperature on Monday night followed by the rise into mid week and the fall towards the weekend. The rainfall spikes at the bottom show the fronts or showers that go with the low pressure. But after that the individual members of the ensemble are all over the place. My guess is that what looks like a possibly extended period of above average upper air temperatures (associated with southerly or south westerly winds) may actually turn into a series of ups and downs as high and low pressure systems arrive in turn. The rainfall spikes at the bottom sort of give the game away.

We shall see.

[Penellype]

Another chilly night tonight as the cold front currently bringing rain to the west moves eastwards across the whole country. This can clearly be seen on today's ensemble chart with the rain from the cold front showing at the bottom:



Into the weekend it becomes warmer and drier (but not completely dry) as high pressure becomes more influential from the east.

What is developing is a classic "battleground UK" scenario, with high pressure to the east over Europe, stretching up to Scandinavia, and low to the west over the atlantic. Saturday's chart shows this well, with the flow coming up from the south between the low and the high, which is why things warm up:



This is not a heatwave, but will be pleasantly warm.

Despite the high pressure, things will not be completely dry. Showers are still possible as the low pressure is not that far away, especially to the north and west. However it will clearly be warmer (particularly at night) and drier than recently.

Notice that there is some variation in temperature and considerable variation in rainfall amounts on the ensemble chart even within the "reliable" 5 day timeframe, with one member (orange) showing a drop in temperature and a big rainfall spike on 25th. This highlights the uncertainty of this battleground scenario in that small shifts in position of the blocking high to the east can have big consequences for our weather.

The blocking high is not going anywhere fast, but what tends to happen with these is that they drift slowly north and flatten out towards Greenland, allowing the low pressure to break through underneath. Currently the lows are forecast to start having more influence in around a week, with Thursday's chart looking like this:



This corresponds with the start of the bigger concentration of rainfall spikes on the ensemble chart. Note the large dartboard low off the coast of America - that is hurricane Maria which has just battered Puerto Rico, and could be heading towards us as an autumn storm if it gets caught in the jetstream (too soon to tell).

Currently the most likely scenario is a gradual change towards more unsettled and autumnal conditions towards the start of October, probably starting in the south west as the high forces the lows underneath it. Timing is very uncertain.

The latest run of the GFS has Maria getting caught up in the jet stream and arriving as a very autumnal looking storm around 4th October:



This is just one possible scenario, but Maria is definitely worth keeping an eye on for its affects on our weather, particularly as any storm in this position would be blocked by the high over Europe and might hang around for a day or 2.

[Penellype]

Its all about Maria...

Treat all forecasts beyond about Thursday with huge caution. There are enormous discrepancies between the models depending which side of the jet stream Maria ends up.

This is this morning's GFS run for a week today:



Note the position of Maria, due south of Greenland, with its centre above the thick black line, ie to the north of the jet stream. In this position Maria sucks up warm air to its east, resulting in a ridge of high pressure building towards the UK, so that by 4th October we have:



While possibly not completely dry, this would be calm and fairly pleasant.

The ECMWF develops things quite differently. On 1st October the ex-hurricane is still close to the east coast of America:



It then moves north west, crucially staying south of the jet stream - due south of Greenland on 2nd October:



In this position it is lined up to get caught in the jet stream, develop rapidly into a storm, and arrive here on 4th October:



Don't pay much attention to the exact timing or position of the low (its far too early for that), the point is that this would be wet and very windy, probably stormy to the south and west of the low. Totally different to the GFS run above.

Over to you Maria (go north please!).