Penellype's Weather Channel

[Penellype]

Quick update for the bank holiday on current thinking.

Today and tomorrow will be increasingly warm and humid with temperatures in the high 20s likely in the sunshine. On Saturday a low pressure system moves over Ireland and this is likely to introduce thunderstorms especially to the north and west, moving east over night but probably missing the south and south east.

Sunday looks drier and still pleasantly warm before another low moves up from the south on Monday. The position of this 2nd low is uncertain and forecasts for Monday and beyond keep changing, but the general idea seems to be for cooler and more unsettled conditions to take us into the start of June.

Some of the thunderstorms over the weekend could be accompanied by hail - if you have seedlings outside that can be moved under cover briefly and you see very strong signals on the radar (eg on Weather Radar - Live UK Rainfall Radar - 5 Minute Updates - Netweather.tv) heading your way, it might be prudent to move them indoors until the storm has passed.

[Jonny.D]

I love it when it rains overnight and you wake up to see that everything has had a growth spurt and looks invigorated

[Penellype]

Beware of a rather cooler night tonight than we have seen recently. This is the GFS minimum temperature forecast for 6am tomorrow morning:



If you live in one of the colder areas it will be worth closing greenhouse doors and windows and covering anything vulnerable with fleece. This sudden change to a colder night is the result of a combination of a cooler air mass, light winds and clear skies. It appears to be one on its own, with the remainder of the week looking less cold at night.

Currently we are under a ridge of high pressure, giving a couple of mostly dry days with a few showers possible, but with more rain in the north and west. A large low pressure system is out to the west, trying to move in. Western areas will see rain first, and this will spread slowly eastwards, probably on Friday. The weekend is likely to be changeable with most places seeing some rain.

As always the longer term is very uncertain with the models swinging wildly between low pressure dominating with cool and changeable weather, and high pressure ridging from the azores bringing warm and drier conditions. I think this is one of those times when looking beyond the 5 day forecast is probably a waste of time.

[Jay22]

Thanks Penellype, have just this minute brought in my toms...far to cold and it's a cold wind too!

[Penellype]

The models now seem to be firming up on what is going to happen in the next couple of weeks, and it doesn't look great.

This is the position at the moment:



There is a large low pressure in the atlantic, and the front that gave yesterday's rain and storms lies roughly along the middle of the elongated section of the 1015 isobar. This is now moving away to the east to give a weekend of sunshine and showers. Notice the ridge of high pressure over Europe, which is preventing that low from going anywhere fast, and the relatively high pressure to the north and over Greenland.

This pattern means 2 things. Firstly the trough of low pressure in the atlantic can't escape to the east because of that ridge. Secondly the jet stream is being forced south because of the high pressure to the north. This sort of thing is not uncommon in early June and has been termed the June monsoon. We are in for a week or 2 of weather that (apart from the temperature) would not look out of place in November. Temperatures should remain average to warm because we will mostly remain on the eastern side of the trough.

This is the chart for Tuesday:



This has actually been moderated quite a bit in the last few runs of the GFS - it was a vicious looking dartboard type low centered smack over the top of us at one point. Even so this system will bring a lot of rain and some very strong winds to parts of the country on Monday into Tuesday, timing depending on where you are. The jet stream, which broadly divides the yellow and green areas, is now to our south and we are in the firing line for a series of low pressure systems originating along the east coast of America and rolling across the atlantic. It will therefore be changeable, wet and windy at times until something happens to break this pattern.

This, for example, is the chart for Monday 12th June:



You can see that not a lot has changed - the highs are still there over Europe and to the north, and the low is still in the atlantic. The jet stream is still close enough to be bringing in low pressure systems which are basically skimming across the atlantic and rotating around the main centre of the low.

The ensemble chart for York shows the situation well:



The rainfall spike on Monday night into Tuesday is huge and lasts over 24 hrs. There are plenty more following on as the lows move in.

It is early days yet, but this does not look great for summer. Comparison with previous years which have had similar patterns is always a dodgy business, but putting together what I have seen from the models and from past years with a warm and dry spring and similar El Nino situation it looks more likely than not that we are in for a wet summer. There are exceptions and some of them were very good summers indeed, so all is not lost, but I suspect at least the first half of June to be something of a washout. At some point, hopefully sooner rather than later, something will happen to change the positions of the highs. Either the high over Greenland will weaken and allow the jet stream to move north, or the high over Europe will change its position to allow the trough to move away. The GFS shows the first of these scenarios happening by the very end of the run (the thick green line on the ensemble chart goes quite hot):



However, this is far too far in the future to be taken anything like seriously at this point.

[Potstubsdustbins]

I told you so!

Son returned from a week in Salcombe Devon today. North Devon gets lighting storms, son in Salcombe gets 7 days no rain, bright sunshine, romping on the beach and sailing. He's got to go wrong soon.

[Penellype]

Some disgusting weather on the way for Monday and Tuesday as an active low pressure gets stuck over the country. Most places can expect constant heavy rain and gales. This is the accumulated precipitation forecast upto 6am on Thursday (as far as the model goes) from the high resolution Arpege model:



The worst of the wind will be in the southern half of the country - timing of the strongest gusts can be found here: Arpege charts

Batten down the hatches and be prepared for surface flooding (possibly worse). The Met Office will probably issue warnings - check Weather warnings - Met Office and https://flood-warning-information.service.gov.uk/map for details nearer the time.

More heavy rain is expected on Thursday.

[Potstubsdustbins]

Thanks for the heads up Pen going out now to close up.

[Penellype]

After an unsettled week things look like improving, particularly the further south and east you go, but by next weekend most places look like becoming mostly dry.

Tomorrow looks showery with a band of cloud that produced rain across the north of England today moving south and weakening. The jet stream is slowly moving north, so low pressures will increasingly affect only northern and western areas.

By Wednesday we have this:



This chart clearly shows the higher pressure to the east and low to the west which will still be bringing showery rain to Scotland while the south could be quite warm and humid. There is also a "heat low" developing to the south and this could well produce thunderstorms in the south east on Thursday.

By Friday high pressure is ridging up from the azores. Notice that this is a much stronger high at 1030mb rather than the 1020 of the high earlier in the week.



This should give some very pleasant weather to the whole country for next weekend, although with the high positioned slightly to our west, this is not going to be a heatwave.

As always, beyond 5 days the forecast becomes much less reliable, but current runs of the GFS have the high drifting into the atlantic which could pull down some northerly winds. Its June, so unless you live on a Scottish mountain it shouldn't get too cold, but it may become more unsettled, particularly in the east if this sort of chart comes off:



This is a long way off though.

The ensemble chart for York picks up the possibility of showers from the low pressure on Thursday, but otherwise looks pretty dry for the next week or so:



The northerly wind forecast around 19-21 June shows up as the thick green line being one of the colder runs at that point, and this is followed by an increase in the number of rainfall spikes (= more unsettled), although these are not very big.

[Nicos]

Best get the suncream handy then?
Thanks Pen!

[Penellype]

Not promising wall to wall sunshine, as there could well be thunderstorms at times particularly in the south and over France. But I expect a gradually improving picture through the week, after which everything depends crucially on where that high pressure goes. This morning the ECMWF is seeing it drifting north by the middle of the week after next:



This would be very bad news, as if the high got stuck up there we would be in the firing line for a series of lows running underneath it.

This is only one solution and at the moment is not seen by the other models, but it does illustrate that things are not straightforward at present.

[Ms-T]

Thanks Pen .just wish the wind would calm down.

[Penellype]

Thanks Pen .just wish the wind would calm down.

So do I! My fruit cage frame is rocking alarmingly.

[Penellype]

Quick update on what might happen after the weekend. There are huge uncertainties and a significant difference between the models.

The GFS is still going for a northerly or north westerly air flow to develop with high pressure drifting into the Atlantic:



This would be fairly cool but most places would be mainly dry.

The ECMWF has the high building to the east, which has exactly the opposite effect:



Here the air is coming up from the south, and this would be a heatwave, with temperatures in the south very likely to top 30C.

As you can see, the general pattern between the 2 models is similar, but the strengths of the 2 ridges (compare the positions of the 1020 isobars) are different and it makes a huge difference to our weather.

[Potstubsdustbins]

Type of Assembly forecasting I believe guess who........................watched a TV programme last night

T'was interesting though seeing how things have advanced in the last few decades. One comparison was a 5 day forecast is now as good as a 1 day forecast in the 70s.

I'm voting for option 2 if I may please