Penellype's Weather Channel 2

[Nicos]

I notice my weather forecasts ( northern Normandy so similar to southern England) say rain daily as from Tuesday…. Thanks for the heads up confirming it.

[Penellype]

Quite a chilly night coming up tonight before the weather starts to break over the weekend. Low pressure pushing in off the atlantic will turn things much more wet and windy, probably for the rest of October, although things could change if another hurricane appears (nothing happening in that department at the moment). Although it will be quite warm at first with the air coming up from the azores, there is the potential for some colder weather with northerly winds towards the end of next week. This can of course change, but the models are fairly consistent with this signal at the moment. Frosts could be possible even in the south if the currently forecast pattern arrives.

[Gillykat]

Thanks Pen

I'm getting stuck in to my allotment from tomorrow morning with my new brush-cutter so hoping to get as much done as possible before winter's bad weather does arrive. After a few years of being in a mental fug it feels good to actually feel excited and have plans for Plot 34

[Nicos]

Thanks Pen...much appreciated as I'm torn between gardening and indoor renovations at the moment, so high pressure for a bit longer is good news for me as it gives me more time!

[Penellype]

Sorry, been really busy and struggling to keep everything up to date!

The current warm and humid weather is a result of ex-hurricane Sam, which is currently to our west, drawing up warm air from the Azores. This is causing high pressure to build to its east, over us. During the weekend the low that was Sam moves south, and an associated cold front which is dumping rain over Scotland at the moment, will weaken and move south east, introducing cooler and less humid air from the west. There will be cloud and possibly a little rain associated with the cold front as it does this, but the high pressure remains basically in control.

Over the next week the temperature will depend on the position of the high pressure and the amount of cloud, which is always tricky to forecast with high pressure. There will be a risk of fog in places but I don't think it is likely to be cold enough for frost except on high ground. The high pressure looks well and truly stuck for probably at least the next 10 days, with the remains of Sam blocked to our west.

In the longer term what will probably eventually happen is that another ex-hurricane or tropical storm will join forces with Sam and become strong enough to shift the high pressure either to the east or south. When this will happen is very uncertain as these things are highly unpredictable due to the small size of the storms relative to the resolution of the weather models. Currently the models are forecasting the possibility of more unsettled weather from around 10 days time (but this is highly unreliable), and there is the possibility of colder weather arriving as a result of this around the last week of October (huge uncertainties).

In my opinion the possibility of a cold November and December is still on the cards. Remember though, this is little better than a guess.

[Nicos]

Any Autumn updates Pen?…this warm spell is sure to break soon?

[Penellype]

28 / 29C forecast today! Rain tomorrow or Thursday, but still quite warm. Rather pleasant in fact, though still cool at night.

The high pressure has finally shifted a bit further south and east, which has turned the wind from east or north east to south or south east, which is a much warmer direction and involves a lot less cloud. The rain later in the week may be in the form of thunderstorms and things are likely to cool down by the weekend.

[sandspider]

28 / 29C forecast today! Rain tomorrow or Thursday, but still quite warm. Rather pleasant in fact, though still cool at night.

[Penellype]

Wow, thanks Pen. What a fantastic and detailed post.

Please do remember that forecasting beyond 5 days is little better than guesswork and I could be completely wrong.

[Mr Bones]

Wow, thanks Pen. What a fantastic and detailed post.

[Nicos]

Thanks Pen…brilliantly explained as usual

[sandspider]

Thanks P, I appreciate the detailed write up. Better batten down the hatches, as usual!

SS

[Bren In Pots]

Thanks for the info Pen.

Last winter we had some snow but nothing to stop traffic moving but it looks like this year might be different and much colder with it.

[Penellype]

Hi Penelope. Hope all is well! Wondering if you have any thoughts on what autumn is likely to be like? The chap at weather without technology thinks it's going to be mainly wet and cold, and the chances are he's right, I fear!

Sorry, been really busy with work this last couple of weeks. I've been meaning to post about the impending "heatwave" for the last week of August, that the models have been showing and which has now pretty much completely disappeared. Every single one of the short range models got this wrong, although they were flipping about like a fish out of water at times. The one thing that does seem to have been pointing in the right direction (assuming the heatwave doesn't arrive) is atmospheric angular momentum (AAM), which seems to be linked to something called the MJO (Madden-Julian Oscillation), which is to do with the state of the atmosphere around the equator. I do not pretend to understand the first thing about how this works, and I rely on my information about it from following Matt Hugo on Twitter. Consistently throughout this year, when models have been uncertain the AAM seems to have pointed vaguely in the right direction. The latest I can find from Matt about this is that the AAM remains negative, which does not bode well for late August and early September, and that an extended period of heat is unlikely. High pressure is not to be ruled out at this time of year - one of the difficult things about the MJO is that the same thing results in different weather here depending on the time of year.

Higher pressure does seem to be likely over the next couple of weeks, and as always it is the position of the high that causes all the headaches. Current models have the centre of the high mostly to the west of us, which brings the wind in from a north or north west direction, so in general rather cool. Some of the models have the high moving further north, and this can allow low pressure to develop to the south, which is what has happened a couple of times already this year. This turns the wind into the east, which can be warm or hot, if there is a southerly component (of which there is little sign on the charts I have seen).

One of the big unknowns at this time of year is what happens to ex-hurricanes as they move towards the north pole. After a quiet month or so there are signs of the hurricane season waking up and this can dramatically change the weather pattern for us. There is therefore always more uncertainty at this time of year than in the summer.

Other drivers that are important are the developing, probably weak La Nina, the stage of the solar cycle and the QBO which is now in its easterly phase. The recent weather and these drivers, along with the sea surface temperatures in the Atlantic all bear quite a striking similarity to 2010.

So, the autumn. If pressed, my forecast would be tentatively for higher pressure through September, probably centred somewhere north of us, resulting in mainly dry conditions (particularly the further north you go) but with the potential for more unsettled interludes if an ex-hurricane heads this way. October could also be high pressure dominated, with the possibility of a late burst of warmth (which I seem to remember happened in 2010). I do not expect either September or October to be particularly wet (except possibly in the south) from the charts I have seen. All the while I expect to see high pressure building over the arctic and the effects of this to start to be felt in November. I think November will be cold, potentially with some snow, and I expect that to continue into the first part of the winter at least. ALL of the drivers that I know about are pointing to a cold winter this year.

There, I have stuck my neck out this time. Remember, I have no training at all in meteorology, and therefore at best my forecast is a very slightly educated guess.

I hope I am wrong about winter - I hate cold winters.

[sandspider]

Hi Penelope. Hope all is well! Wondering if you have any thoughts on what autumn is likely to be like? The chap at weather without technology thinks it's going to be mainly wet and cold, and the chances are he's right, I fear!