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Regularly updated thoughts from from Brian Gaze, TWO's founder. Use the Follow @TWOweather button to keep up to date with Brian on Twitter.

Heat hanging on

Posted Tue, 29 Jul 2014 19:11:12

The outlook remains similar to the one I described yesterday with low pressure having more of an influence on the weather further south east later this week. The details remain up for grabs though and the warm continental air looks reluctant to give way.

The GFS12z chart below is for next Monday and shows the +10C 850hPA isotherm still flirting with southern England. With breaks in the cloud maximum temperatures would still be close to 27C (71F) in the south. Not as hot as earlier this month but still very warm.

12_147_mslp850

The GFS12z model run goes on to show the warm air remaining over the south and east for much of next week before the Atlantic pushes cooler air through for a while around 8th August.

So the warmth could hang on for quite a while yet in the south east, but often cooler in the north western half of the UK.

Rainfall is a different matter though. As we head through the second half of the week there is a risk of heavy and thundery showers becoming more widespread. These probably heaviest away from the south eastern corner, but even here I’d not rule out showery rain at times.

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Living on the edge

It still looks like we’ll see low pressure pushing unsettled weather across all of the UK later this week. The details need watching carefully as we’ll still be close to the edge of the hot continental air mass, so it wouldn’t take much rearranging of the jigsaw pieces to bring a much warmer and drier outcome to southern and eastern regions at least.

This morning’s GFS6z run shows the +10C 850hPa line just straddling the south east of England. There’s nothing special about the +10C 850hPa but it does indicate warm conditions down at ground level if the cloud holds back, so even by Friday 25C (77F) or so is possible in the south east.

06_105_mslp850

Assuming cooler Atlantic air does push through later this week will that mean we’re cueing up an unsettled pattern for August? Not necessarily. Last night’s GEFS runs gave some suggestions of pressure rising again next week. That would suggest drier conditions returning. It’s not a done deal though with the GEFS surface level pressure plot below showing quite a spread of outcomes becoming possible next week.

gefsensmslplondon

In summary the next few days should bring more fine weather to the south with the north remaining changeable. Friday onwards looks increasingly iffy in all regions with an increasing chance of low pressure areas pushing unsettled weather over all parts of the UK. The south east most likely to hang on to the warmer and drier conditions for the longest.

Next week a range of outcomes are possible, but there is a signal (albeit quite a weak one) for high pressure to return.

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Posted at Mon, 28 Jul 2014 12:15:57


Hot or not?

The next few aren’t looking bad for most of us but keep an eye on the forecasts and homepage updates because nationwide it’s a more mixed picture than recently. There will be wet weather at times but also spells of warm sunshine.

What happens later in the week is interesting. It’s still looking like areas of low pressure will begin to have more influence on the UK’s weather and this could mean more unsettled weather extends south for a time. However, it wouldn’t take much change  for hot conditions to return to the south.

The chart below which is from one of the 20 GEFS6z model runs illustrates this. The +10C 850hPa line is just clipping the south eastern corner of England with a massive reservoir of heat over the continent. 30C (86F) would be back on the menu if this outcome which was also flagged up as a possibility on last Thursday’s 14 day discussion forecast is realised.

17_168_850tmp

An interesting week ahead and although it’s generally more mixed there will still be quite a lot of fine and warm weather in southern and central regions. Later in the week the questions increase! Hot or not?

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Posted at Sun, 27 Jul 2014 12:36:40


Unsettled conditions heading south?

Today looks like being the last hot day in this spell of fine weather but it’s not all doom and gloom. At least not in the short term! During the next few days it should often be pleasantly warm in southern and central regions with dry and bright weather for much of the time. I’d expect more cloud than we’ve had recently as decaying weather fronts push further south eastwards, but not much rain down here.

Further north and west a more changeable picture with a greater risk of showers or longer spells of rain.  All in all more typical British summer fare as it says on the site homepage today.

Unfortunately the current trends later next week are for a further downturn in the weather as low pressure gradually extends it’s influence further southwards. It’s too early to be certain of how this will play out but both  the European ECM and American GFS models are supporting this idea. I’m always more confident about the mid term outlook when they are in rough agreement with each other.

The chart below is for next Sunday and is generated from last night’s operational ECM run. I’d not worry about the details but just note that areas of low pressure are pushing in across north western Europe with a trough at the 500hPa level supporting this.

192_mslp500

The chart below is from this morning’s GFS6z run (so is slightly newer than the ECM) and shows a very similar picture. Again don’t worry too much about the details just yet.

06_192_mslp500

In summary the GFS and ECM runs are both favouring more unsettled conditions gradually pushing further south during the week ahead. If correct early August may well be quite mixed. To finish on a positive, the GEFS/GEFS ensemble model has been indicating that high pressure will build back later on so even if we do go into an unsettled period it may not last too long.

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Posted at Sat, 26 Jul 2014 14:47:18


Heat ebbing away?

Make the most of the next few days because we may not see temperatures as high again for a while. A transition to cooler conditions still looks set to take place through the coming weekend as a cold front gradually pushes south eastwards. The rain associated with this is likely to become patchy as it moves down across the UK, but there could be a few hefty showers around in the south east before it clears away.

By early next week a ridge of high pressure will probably build back from the south west. This probably bringing decent weather again to southern and central regions, and although temperature are likely to remain above average they’ll probably be lower than present values. At this point I’m expecting more changeable weather in the north.

The second half of next week and beyond are up for grabs. I’m hoping we’ll see the Azores high pressure building quite strongly towards the UK with more fine and very warm conditions developing. Unfortunately, on balance I’m expecting a more mixed picture with low pressure areas influencing things across the UK, but particularly central and northern regions.

This would mean temperatures trending back towards the average or perhaps still a little above. Also there’d be a greater risk of showers or longer spells of rain, mostly but not exclusively in the north. The pressure chart below is for Friday 1st August and plotted using the average values of all the GEFS6z runs. It shows a fairly typical picture for summer with high pressure centred over the Azores and a westerly drift over the UK.

21_192_850tmp

In summary the weather after the next few days doesn’t look too bad, but not as good as we’ve had recently. It’s still too early to ‘bank’ this outlook and I’d still not be surprised if the computer models tilt back towards a hotter scenario.

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Posted at Thu, 24 Jul 2014 14:37:15


Outlook up for grabs

Developments later this weekend and through next week are still uncertain. I heard people today saying the very warm weather is set to continue for the next 3 weeks. I’m inclined to agree that the outlook is a promising one, but less settled and cooler options still can’t be ruled out. Here’s why:

By this weekend high pressure is probably going to be sitting further west with pressure ebbing away to the north east of the UK. This will bring more of a westerly influence to the weather in northern parts of the UK, and quite possibly to the south too.

The extent of this remains uncertain with some computer model runs keeping it warm or very warm in the south with little disruption. Others make more of the westerly Atlantic influence with cooler air and the risk of showery rain pushing right down across all parts of the UK.

Today’s GFS12z run is closer to the latter category. By Monday  it has maximum temperatures of about 22C (72F) in the south. This still isn’t too bad of course, but much lower than what many of us have become accustomed to recently. Here’s the GFS temperature forecast chart for the afternoon of Monday 28th July.

12_123_uk2mtmp

This run then goes on to show quite a mixed and changeable picture with low pressure bringing the risk of showers or longer spells of rain and closer to average temperatures.  The operational run of the UK Met Office model also looks quite mixed with a north westerly influence developing.

At this stage I still think the data on balance favours a pretty good mid term outlook, but if more computer model runs in the next 24 hours follow today’s GFS and UK Met Office operational runs the question marks will begin to increase.

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Posted at Wed, 23 Jul 2014 17:18:07


Cooler early next week?

The next few days are looking very warm or hot, but there’s a reasonable signal for cooler Atlantic air to push in from the west by early next week. The extent and duration of this is less certain.

This afternoon’s GFS/GEFS data for London shows a cooling trend developing after July 27th. This is clear on the top plot on the chart below, where the thick white line shows the average of all the runs. There’s reasonable agreement for the cooling trend, but note there are still some runs which keep it very warm. In other words it’s not a done deal yet.

Look a little further ahead and you’ll see the white line creeping upwards again indicating warmer air returning. Virtually all the runs are showing this which means the confidence level in it happening is quite high.

gefsens850london0

The latest ECM operational run shows the cooler air from the north west making it further south than most of the GEFS runs. Nonetheless, even the ECM warms things up through the second half of next week with high pressure building back in from the south west.

In summary the extent of the ‘cool down’ early next week remains uncertain. It may not last for long and before then we’ve got more fine and very warm or hot weather to come.

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Posted at Tue, 22 Jul 2014 19:11:29


Hot then a passing Atlantic influence?

Mostly fine and warm weather during the next few days. During the second half of the week it still looks as though temperatures will tick back up towards 30C (86F) or perhaps a little higher. There could also be an increasing risk of thunderstorms breaking out, but again these hit and miss. Probably less widespread than the ones in the last few days too.

The chart below shows today’s GFS12z temperature forecast for the afternoon of Friday 25th July. As I’ve pointed out before it’s not unusual for local values in a few places to come in slightly higher than suggested.

12_99_uk2mtmp

What happens later in the weekend and early next week is still up for grabs. The computer model output today has been favouring more of a west or north westerly influence early on as an Atlantic influence pushes through for a time. This would bring cooler and cloudier conditions with rain most likely in the north. When I say cooler that is relative because temperatures in the south would still be mostly above the late July average.

Today’s chart plotted using the average of all 20 GEFS12z runs gives a reasonable illustration of this. If a pattern like this was the outcome the warmest air would be pushed further away from the UK for a while at least.

21_192_850tmp

It looks like there’s a reasonable chance of this happening early next week, but then what? The good news if you’re hoping for summer to continue is the majority of the GEFS runs go on to show high pressure building back bringing more very warm or possibly hot weather later next week. Any Atlantic interruption in our summer next week could therefore only be a blip!

Chart viewer

Posted at Mon, 21 Jul 2014 18:44:58


Weekend storms and heat

The potential for severe storms during the next couple of days is widespread but there are likely to be big local variations in the weather. This morning GFS6z run gives a decent indication of the areas probably most at risk.

By Saturday morning the rain and storms are shown to be affecting southern and central regions. The worst conditions probably mostly west of London but the south eastern corner could also be experiencing cloudbursts.

06_24_precipratec

Through the morning the storm risk moves further north. The chart below is for 9GMT and by then a central area stretching approximately from Birmingham to Manchester could be bearing the brunt of the storms.

06_27_precipratec

During the afternoon the storm risk continues pushing northwards and there could still be torrential rain along with hail and thunder. There’s also the possibility of more storms triggering in the south later in the day as it becomes hot again in sunny spells.

06_33_precipratec

The storms could be severe so keep up to date with the latest forecasts and rainfall and lightning radar.

By Sunday heavy showery rain and storms are most likely in eastern and north eastern regions.

Early next week there could still be a risk of thundery showers but it looks like the focus will switch back to drier and hot weather with temperatures climbing back to 30c (86F) or above. The heat probably lasting through the rest of the working week and into the weekend, but again it could turn thundery. Beyond that perhaps a transition to cooler weather from the west, but that’s a long way off.

Chart viewer Rainfall and lightning radar

Posted at Fri, 18 Jul 2014 14:20:56


Storm and heat news

Several opportunities for thunderstorms in the next few days. Tonight showers and thunderstorms will push northwards across western and possibly central regions and then possibly extend further east as they move into northern Britain tomorrow. The south east probably missing them to keep dry and hot weather on Friday. The hottest day of the year so far I think.

A more widespread and potentially severe storm risk is likely to develop on Friday night and into Saturday. The chart below is from this mornings GFS6z run and is valid for 6GMT on Saturday 119th July. It’s showing torrential rain into parts of the south. Subsequent charts have this heading north over Wales and much of western England.

There’s still uncertainty about how this will unfold, but things on the last couple of runs have been positioned a little further west. This means the worst of this batch of storms could be in central and western regions, but it is very uncertain and eastern and south eastern parts could also experience some torrential downpours with hail and thunder.

06_48_precipratec

By Sunday the storm risk is probably more focused on eastern and north eastern England. Through the period remember to check the rainfall and lightning radar because conditions could vary enormously over short distances.

Early next week the storm risk should fade with very warm or hot and sunny weather returning.

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Posted at Thu, 17 Jul 2014 15:04:35



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