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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.

Outlook up for grabs

Posted Wed, 23 Jul 2014 17:18:07

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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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.

Chart viewer

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.

Chart viewer

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


Thunderstorms are go

Possibly! There’s always a lot of uncertainty with thunderstorms in the UK and experience suggests they miss more often than hit. Nonetheless, as well as becoming very hot in the coming days it looks like there’s a risk of severe thunderstorms affecting parts of the UK. The highest temperatures from this Spanish Plume probably on Friday when 32C (90F) could be reached if there’s enough sunshine. The worst of the storms hitting on Friday and Saturday.

The CAPE and Lifted Index charts from this morning’s GFS6z run give some pointers to developments. The chart below is for Friday afternoon and shows a wide area of instability. The expectation is for a trough to push northwards across central and western regions bringing heavy showers and possibly thunderstorms. The east remains under the influence of high pressure so more focus on dry weather although isolated thunderstorms could be breaking out.

06_57_ukcape

Saturday currently looks like the day to watch with the main action. Once again there’s a lot of energy and instability, and with pressure falling thunderstorms could break out widely becoming severe. The general picture may be for heavier and more persistent rain in central and western regions with more hit and miss thunderstorms in the east.

06_81_ukcape

Keep up to date because there could quite a lot of severe weather to contend with. You can check the rainfall and lightning strikes picture using the rainfall radar page. There’s also the geolocation rainfall radar optimised for smartphones

By Sunday it’s likely to be warm or very warm rather than hot. There’ll probably be fewer showers too, so it could turn out to be a pretty good day. As I’ve been saying the ‘breakdown’ may be quite half hearted and there’s plenty of evidence from the computer models of high pressure building back in next week.

Looking good and this summer is now shaping up to be a pretty decent one despite the storms I’ve just been talking about. Given the mild winter and spring as well as the warm start to summer there must be a good chance of 2014 being the UK’s warmest year on record. I’ll take a look at the stats as we head through the coming months.

Chart viewer

Posted at Wed, 16 Jul 2014 13:06:43


Summer nails its colours to the mast

Very interesting weather during the next few days. The heat is set to build as the Spanish plume displaces very warm air from Spain to north western Europe, and there could be some torrential downpours and thunderstorms to accompany it. I’d not be surprised if 32C (90F) is reached on Friday making it the hottest day of the summer. With Thursday also looking hot one of the thresholds to describe this spell as a ‘heat wave’ will probably be reached.

During the weekend cooler air is set to return from the west but as I said yesterday the details are uncertain. It still looks like there’s a good chance of high pressure building as we head through next week bringing more dry weather and another warm up.

The overnight ECM computer model run showed high pressure in the ascendancy ones more by the middle of next week. The chart below is for Thursday 24th July and the pattern it suggests at this time of year is a hot one.

ecm

The GFS6z model run from this morning shows something a little different but the general picture is also a high pressure dominated one bringing a good chance of another hot shot during the next couple of weeks. The chart below is from the GFS6z for Thursday 24th July.

gfs

In summary it’s hot and thundery in the next few days. The details for next week and beyond remain uncertain but the computer models runs suggest summer is nailing it’s colours to the mast this year. The next few weeks are hopeful, but of course in the UK the weather is never in the bag.

Chart viewer

Posted at Tue, 15 Jul 2014 14:25:46


Britain set to bake?

The hot weather for later this week is still on track with 30C+ looking likely on Thursday and/or Friday. Into the weekend a thundery breakdown from the west looks likely to develop as the Spanish Plume gets shunted back eastwards into the near continent. However, that may not be it.

On some computer model runs the breakdown looks a very half hearted affair, especially in southern parts of Britain. The overnight GFS operational run shows high pressure taking back control and the heat building again next week. Here’s the chart from the GFS run for 0GMT Wednesday 23rd July which shows high pressure centred over Scotland.

00_216_mslp500

When looking at these blocked high pressure dominated charts in summer the same rules as winter apply. Most importantly don’t jump to conclusions based on one run. With the UK sitting on the edge of maritime and continental air masses very small adjustments on the global scale can mean a huge difference to the weather we experience.

Nonetheless if the GFS is correct we could be heading into a classic British heatwave like the one we had last July. If things are going to rival 2003, 1995 or 1976 then we need the hot weather to persist through this month and August. With variability in computer model output and uncertainty even about next week it’s far too early to be talking about that as an outcome, but don’t rule it out just yet!

In summary the short term outlook is for it to become very warm or hot, and thundery later this week. A breakdown develops this weekend, but the extent of this is uncertain. Next week may turn out be changeable but at the moment I’m optimistic of summer keeping the upper hand and another spell of fine weather developing.

Check the charts for yourself
 

Posted at Mon, 14 Jul 2014 09:07:55


Hot before it goes bang!

The mercury still looks set  to soar later on this week with 30C (86F) probably being recorded for the first time this summer as a Spanish plume weather pattern develops over Britain. The details need watching and there is uncertainty about how long the heat will last before a breakdown takes place.

This morning’s GFS6z run shows very warm air pushing up from the south by Wednesday. By Thursday it’s a mainly hot and dry picture with the 564dam thickness values (often indicative of a ‘heatwave’) or higher over much of southern and eastern England.

Then on Friday heavy showers and thunderstorms break out! The CAPE and Lifted Index forecast chart suggests a widespread risk of thunderstorms. The oranges and reds show where the CAPE values are favourable for thunderstorms and with the Lifted Index (LI) contour plot negative numbers are the thing to look for.

06_129_ukcape

In summary hot weather looks odds on for later in the week. A thundery breakdown then probably develops but the timing and details of this are uncertain. After the breakdown high pressure may then build back from the south to another taste of summer.

Chart viewer

Posted at Sun, 13 Jul 2014 10:45:09


Plumetastic next week?

The outlook for next week remains very interesting and the computer models are still signalling the possibility of a Spanish Plume pattern developing. This occurs when very warm air from southern Europe or North Africa is pulled northwards towards the UK, often due to low pressure to our west and high pressure over the continent. It can bring temperatures of 30C (86F) or higher to the UK for a time before cooler air begins returning from the west and a thundery breakdown ensues.

The overnight operational ECM computer model run shows the potential development quite well. Recent GFS model runs have shown something similar but with a less intense plume not lasting as long. The chart below shows 850hPA forecast temperatures for next Friday from last night’s ECM operational run. The hottest air is pushing northwards through Spain then France and into southern England. If this was the outcome 30C (86F) could easily be reached in a few places if cloud cover holds back.

144_mslp850

My take on things is that very warm weather is likely to develop through next week. The ECM model does seem to have a tendency to slightly overcook the development of high pressure over the continent (we’ve seen this a number of times in the winter when the cold fails to materialise!) but conversely GFS can rush the Atlantic through too quickly. What all that means is a good chance of a King George II hot blast before a breakdown occurs, perhaps just in time for next weekend.

Chart viewer

Posted at Sat, 12 Jul 2014 13:19:05



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