Southwest & Central Southern England Regional Discussion

[Wilxy]

Heavy shower here currently but not cold at a respectble 9°C.

Hopefully we can see a return of colder weather after xmas.

[Mark Parsons]

I may be wrong here, but i was fairly sure the effects of the strat changes or an SSW would only take 20-25 days to reach us, which is more 3-4 weeks?

Indeed, SSW come about quicker, if this is the case then the effects will be felt sooner, however SSW can be short lived compared to a gradual warming which is what I would prefer to see, then again I may be wrong!

[AWD]

All very quiet in here but then I suppose the weather is very quiet currently.

The warming up in the Strat is starting to become very interesting indeed. With a potential MJO shift into phase 3 which would be supportive of a MAH, and the first affects of the warming coming to fruition (hopefully) in the Strat at the end if the month, a MAH wouldn't be a bad thing IMO. If we can get a favourable PV position then that MAH would only go one way.........

GREENLAND.

That's my hunch & ramp of the day over.

[Mapantz]

A few short sharp showers here today, very gusty when they do pass through though. Plenty more of them to come!

I'm surprised there hasn't been much in the way of lightning detected? There's been a lot of hail mixed in to the showers which mean ELT's are good.

[AWD]

Lets see where we stand in the South West on the run up to Christmas then. Any snow likely? No, not this side of Christmas down here unfortunetly, although I can only say that with 80% confidence, transient snowfall has a very small possibility still.

Today, many inland areas look like having a dry & rather sunny day. Coastal areas will hang on to more cloud however, and this will produce a shower or two especially around Cornwall & Devon, working their way up the Bristol Channel possibly later;

Temperatures look like bring around average for most (High single figures or very low double figures);

Temperatures don't really change tonight, with the same sort of temperatures overnight, bar a degree or two lower maybe;

Tomorrow will see the same sort of temperatures as today, so I won't bother posting another temperature chart. It looks a dry day for most tomorrow, aside from an isolated shower in Cornwall. Cloud cover will increase in Devon, Cornwall, Dorset & Somerset as the day goes on, turning the sunshine more hazy here, and turning rather dull in the far South West. Regions further north & east, such as Gloucs, Wiltshire & Hampshire should have a dry & rather sunny day however, and feeling rather pleasent for December;

A few showers working there way up on a trough from the South West, are possible anywhere across the region tomorrow night. These shouldn't be too heavy though, temperatures again similar to previous values;

That's the next couple of days sorted, of which is as reliable as you can get with the UK weather. The above has a confidence rate of 90%. Now for the remainder of the working week, which has a slightly lower confidence rating of 70%. Wednesday looks like being a very wet day across the region, with heavy & possibly disruptive rainfall for much of the day & into the night. A band of rain moves up from the South West, giving us all a soaking;

With further heavy rain/showers moving in behind;

With isobars quite tight, winds will be rather gusty at times too, especially on channel facing coasts, succeptabke to southerly winds;

This is the areas that is causing a little confusion in the MOD thread, as you can see below with the temperature maps, that the SW & far south are mild with temperatures into double figures. However, north of the M4 & temperature are rather cool, stuck in mid single figures. It's the position of this depression to the west of the UK that is crucial in determining the temperatures we get on the ground here, hence why confidence has dropped in this part if the forecast, as a small difference of just a couple of hundred miles could make a big difference on the ground here;

You can see below, both the GFS & ECM send a surge of mild air into Southern England. If this "surge" is west of us, then we will see cooler conditions prevail;

At the moment however, the favourite scenario is for the milder air to affect the whole region, keeping temperatures mild, perhaps very mild briefly for the time of year, Wednesday & Thursday, this is shown in the GFS ensembles, with the majority clustering around mild uppers over the period in question;

More heavy rain for us all Wednesday night into Thursday morning, something which needs an eye kept on as this rainfall will start to mount up & is likely to cause further flooding problems;

This should clear Thursday morning, leaving behind a scattering of showers, some heavy with hail & thunder a possibility;

Mild temperatures for all;

A dry night for most Thursday night, with temperatures around the seasonal average;

You can see below now that winds start veering South Westerly as the Jet Stream starts to tilt SW-NE, never a good position for cold weather. This sets us up for a rather mild end to the week and weekend, with a mild flow, and rainbands crossing the country, the main theme:

I won't go into detail for the weekend, as we are now at such a timeframe where its worth looking at the wider picture rather than local detail, and where the word "trend" is ever more needed.

A mild, at times wet weekend is likely however, with temperatures in double figures for most, perhaps reaching the mid teens in Cornwall. Both the GFS & ECM send upper air of +10c over the south of the UK, something more akin to summer rather than winter;

Christmas week, will it be white or green? I have to say, realistically green is more likely than white currently, although I defiantly am not ruling out a Wintery blast that may bring a surprise or two over Christmas. The models have been hinting at colder weather over Christmas, but nothing sustained or substantial as of yet, hence why in our region, green is more likely than white. Below are the charts & ensembles for the festive period;

The GFS shoes temperatures returning to average values over the Christmas period, perhaps slightly below average on Boxing Day;

If you look at the ensemble graphs posted above, you can see a general cool down over Christmas is well supported, but a proper cold spell isn't. A frost might give something seasonal however.

The ECM shows the mild air taking a tad longer to get pushed away, resulting in a mild Christmas Eve, before cooling down a little more quickly than the GFS, with Boxing Day showing below average temperatures for our area. The lucky northerners might see a bit of snow too. Bah.

You can see below, a rise of pressure to the south of the UK;

Going forward to the new year, its this that I believe will influence our weather. If it sits over Southern Europe, the Jet Stream will ride over the top and give us mild, zonal conditions, if it retrogress's then we could give us hope for some colder weather into the new year. At this stage there is no clear signal for our weather beyond Christmas, so we will have to wait & see what happens.

What do I think the New Year will be like? Well, I think we will see a Mid Atlantic high pressure system set up, acting as a block to the Atlantic systems, and settling the weather down over the UK. Nothing particularly cold, but seasonal nonetheless.

Why do I think this? Well, the MJO looks like it could head into phase 3 at the end of the month, something supportive of a MAH. We also, at this timescale, should start to see the Upper Stratosphere warming as forecast, with wave breaking into the Lower stratosphere levels, then possibly into the troposphere afterwards.

Below you can see an extremely strong warming forecast by the GFS model;

Now don't worry that the chart is for 300+ hours away, the stratosphere forecasts don't work the same way as the NWP forecasts. FI is actually far more reliable in the Stratosphere than the troposphere. The above chart is probably equivalent to a T144 NWP chart. Fairly reliable but not inflammable.

What we need to see is the warming penetrate poleward into the vortex. As you can see above, the warming is currently forecast to "flow" around the core of the vortex. This needs to start making in roads into the vortex for maximum disruption to the PV. There are hints of this happening but that's all at this stage.

The ECMWF also starting to show this warming now;

When this model starts showing stratospheric warming's, you can be pretty confident a warming is now going to happen, to which it is likely now.

Signs of wave breaking to, which would only aid the warming, and possibly bring us a taster of what's to come earlier, before the "big blow";

I'm no expert on the Stratosphere, I find it absolutely fascinating but if you want further details & projections, then your best heading into the Strat thread, where far more knowledgable members will be able to help you.

My basic understanding and thoughts are:

- A taster cold spell at the beginning of the new year thanks to wave breaking into the troposphere.

- A brief recovery to more "normal" conditions second week in January

- A sustained and rather meaty cold snap the second half of January thanks to a major Stratosphere warming followed by a SSW, completely destroying the PV.

The bit of luck we do need is that if the PV does get destroyed, which is looking likely that it could, we need its reminants to settle somewhere favourable to the UK, ie: Scandinavia or Siberia area and not Greenland.

This is going to make January a very interesting month IMO:

Model watching is soon to take a turn for some very interesting & potentially dramatic charts. Lets see how it develops & hope it develops favourably for the UK.

Thanks.

Edited December 16, 2012 by AWD

[A.J]

A quality post, a lot of thought & time has obviously gone into it....Keep up the good work

[noggin]

What he said.^^^^^^^^^^^^^^^^

Thank you, AWD, for the time, thought and effort that you have put in here!

PS I see that there are slight glimmers of excitement in the model discussion thread........ha! I won't get fooled again.......

[Lewesdon]

The sky here in West Dorset looks as though its going to explode.

It has now.

Edited December 16, 2012 by Lewesdon

[stevofunnelcl]

Quick check on radar

purples and whites for south devon, into dorset

lightning strikes indicated in English channel

[BARRY]

Quick check on radar

purples and whites for south devon, into dorset

lightning strikes indicated in English channel

can you pop your location in your avater as it's nice to have anouther weather watcher in south devon as well

[kerensa]

hi all, thunder here and as dark as night!

[Valhalla]

Great post AWD, Thanks for that, it's nice to be able to read and actually understand it lol

I'm only a shadow lurker, love to read all the post in here and its mint that Ian has decided to stay in here with us.

Here hoping for loads of snow at some point this winter

[AWD]

Just has a rather heavy shower here too. Caused the few minutes of usual mayhem, everyone hiding in shop entrances etc.

[BARRY]

massive hail shower here more like night time.

[Andy Bown]

2 identical days this weekend ; sunny mornings and then troughs bringing heavy lines of showers by early afternoon.

[AWD]

Looks like a rash of showers coming up from the South West, mostly around coasts & up the Bristol Channel but there are a couple managing to get further inland into parts of Wiltshire & Hampshire now too.

A couple of thunderstorms off the channel coast too.

Edited December 16, 2012 by AWD

[Mapantz]

When the showers get here, they split over my area and then join back up when they've passed me. :lol:

Thunder in north Dorset though.

[TropicThunder]

Lightning accompanied by some loud cracks of thunder here!

[SupaSnowy]

I swear I just heard thunder. Big rumble

[AWD]

I swear I just heard thunder. Big rumble

Yep, thunderstorms around the IOW area, along the southern channel coasts.

Head to that big pointy metal tower thing at Gunwharf, Portsmouth. Should get s good view up there. lol.

[katemart]

After a beautifully sunny and warm day (two loads of washing on the line!) we now have a thunderstorm here in Southampton, with very black clouds and heavy rain.

Bit concerned about the convection because the clouds are behaving VERY ODDLY: either the cell was rotating or the clouds were piling upwards. They were kind of heading into the same direction from opposite sides, if you get me, and heading north-east of here.

[gottolovethisweather]

Could I strike lucky with an unexpected Thunder day here in Newbury.

That beefy cell looks a monster on the latest radar imagery and is moving in a general ENE direction. I will only be clipped by its Northern edge in any case but I remain hopeful of something interesting.

AT 6.8c after a Max of 7.5c, DP 6.4c, Barometer 998.8mb falling slowly and dark as night.

Edited December 16, 2012 by gottolovethisweather

[*Stormforce~beka*]

Thunder and lightning! It sounds a bit high up like.

[katemart]

That more southerly blob that is heading for the South-East coast is going to be a doozy, I reckon!

[AWD]

The netweather ATD shows where the strikes are currently, with cells moving in of the channel into the Southampton & IOW area;