Penellype's Weather Channel

[Penellype]

Huge advances since the 70s. Satellites show you exactly where the clouds are and direction and speed of movement. High resolution radar coverage showing where it is raining. Lots of aircraft carrying pressure and temperature sensors. Far more monitoring stations and therefore much higher resolution. Much more computing power.

Quite how much better it can get is anyone's guess. The maths becomes fiendishly complicated, and there's the added problem that you start to run into uncertainties in measurements which simply can't be overcome. I think it will be a very long time before accurate medium range (2 weeks +) forecasts become the norm and it may never be possible to accurately forecast months ahead. You never know though - someone might come up with something that changes the game completely.

[Potstubsdustbins]

Yes that's exactly what they were saying on the program 'Storm Troupers' the spelling is correct. Since the relevance of 'chaos theory' was discovered everyone has realised just how difficult it is going to be.

The latest computer covers two large rooms and weighs as much as 7 double decker buses. From all the data obtained they get the computer to produce many different charts each time the data input is slightly different to try and replicate 'chaos theory' from this they can take a 'mean'.

Also they were saying that this way occasionally a seriously bad weather event comes to light and the possibility of this can be noted, mentioned in the forecast and authorities notified so they can be prepared just in case.

It was a very interesting hour of viewing not usual these days.

[Penellype]

Thanks for that Potty - I'd missed these programs as I don't tend to watch BBC4. The 3 programs are on iPlayer (not sure how long for) here: BBC iPlayer - Storm Troupers: The Fight to Forecast the Weather - Episode 1.

I was glued to the first one while I ate my breakfast - a fascinating account of the early history of weather forecasting, much of which I didn't know. Off to watch the 2nd one now

[Potstubsdustbins]

Glad you enjoyed number one, that bodes well for the other two.

[Penellype]

A very warm few days coming up with loads of dry weather apart from the north west which will have rain at times and more cloud (sorry).

A weak cold front moves south on Monday night bringing slightly fresher weather before the heat builds again mid week. This time it is less stable and I think by the later stages of the week we will see some thunderstorms breaking out, especially in the south.

Still uncertain by next weekend, but likely to becomes more unsettled especially in the north.

Today's ensemble chart for York shows the warmth well:



The dip on 20th is the cold front and this wants watching - current forecast minimum temperatures for early Wednesday around here are rather low for June:



This is right at the end of the "reliable" timeframe and is due to forecast clear skies and very light winds with the centre of the high pressure over Yorkshire. This sort of detail is not predictable at this range but highlights the possibility of a chilly night where winds fall light.

[Penellype]

Quick update:

The models have backed off such a cold night on Tuesday into Wednesday, with temperatures now showing generally in high single figures. I did think it looked rather extreme for June on the map in the previous post.

The models do occasionally throw up something rather over-enthusiastic even in the fairly short term. Yesterday this chart was posted on Twitter for Thursday:



This shows CAPE (convective available potential energy) and lifted index. Without getting too technical, this is a measure of the energy available to make large thunderstorms, and you can see that much of England is covered with extremely high values. These would give notable storms on the continent where CAPE is often much higher than here. To give some idea of the size of this, green colours indicate the possibility of storms, yellow and orange would be likely to give frequent lightning and hail. The grey colours are kitchen sink material - constant lightning, torrential rain, large hail, flooding and tornadoes possible.

Thankfully the models have backed off to a much more normal-looking chart, although thunderstorms are likely in places next week, the location varying slightly with the day. Today's chart for Thursday morning shows probable thunderstorms in the south east:



These CAPE values are still high for the UK and are due to the very hot weather which will have become very humid by Thursday, but they are nowhere near the top of the scale as they were on yesterday's chart.

If you are interested in the likelihood of storms (and possibly crop-damaging hail) in your area, the GFS CAPE charts can be found on The Weather Outlook Charts page:
Computer model weather forecast charts - scroll down and click "Other" on the left and choose UK CAPE-LI. As with all forecasting, the CAPE values are not telling you there will be thunderstorms, only that the potential is there. But current CAPE values will tell you when the potential is not there and there won't be storms.

[vixylix]

P, can you arrange some 'normal' consistent weather - I am done with all these extremes

[Penellype]

Glad you enjoyed number one, that bodes well for the other two.

Finished all 3 now - very good .

Thanks for posting that.

[Penellype]

P, can you arrange some 'normal' consistent weather - I am done with all these extremes

Err...

What exactly is normal? Dull, damp and drizzly? Temperatures around 30C are not unusual in summer .

Unfortunately I can't arrange anything, I can only say what's there. I think with social media nowadays there is a tendency to pick up on anything in the models that looks in any way unusual, even if it is only 1 run. I try to ignore the hype and present the facts, but that is not always as easy as it sounds.

With regard to the potential for thunderstorms, the CAPE is there for parts of the country (mainly the south and west on the latest run) from today until Thursday. However, that doesn't mean there WILL be storms, just that they are possible. As with all weather phenomena, there is more than one element to this, and there needs to be a trigger for the storms to develop. Its a similar situation to snow in some ways - if you have all of the atmospheric requirements for snow but there is no precipitation, you won't get snow.

With regard to the potential for a cold night into Wednesday, the models have given up completely on this idea, but tonight could be rather chilly in Scotland.

[Jimmy]

Has anyone ever compare the official weather forecast to that you would get if you just said tomorrow will be as today ?
Jimmy

[Potstubsdustbins]

#278 Glad you enjoyed them even I found them interesting and I am a 'look out the window in the morning' type person

[Jungle Jane]

Has anyone ever compare the official weather forecast to that you would get if you just said tomorrow will be as today ?
Jimmy

That's not very long range forecasting Jimmy,next day forecasting is quite simple red sky at night shepherds delight

[Penellype]

Has anyone ever compare the official weather forecast to that you would get if you just said tomorrow will be as today ?
Jimmy

This will work when the weaether is settled fine, or very unsettled and persistently showery. It won't work well in the typical westerly pattern of ridge - trough - ridge - trough, where you tend to get alternate fine and wet days, and it won't work whenever the pattern is undergoing a fundamental change.

In my experience the weather is rarely the same 2 days running anyway - there are differences in cloud amounts, wind direction and temperature even when things are settled.

[Penellype]

That's not very long range forecasting Jimmy,next day forecasting is quite simple red sky at night shepherds delight

Lots of weather sayings have some truth in them, and this is one of the best (with a few buts thrown in). The explanation behind it is that in general the weather comes from the west and a red sky at sunset (in the west) implies that the air there is dry. Logically therefore a red sky at night will lead to fine weather for at least a few hours, possibly much longer.

However...

Assumption is that the weather is coming from the west. If it isn't, then you can have nice dry air to the west and (for example) torrential thunderstorms moving up from the south, or even snow blowing in from the east (although that is less likely).

Identifying the correct sort of red is another sticky issue. In general soft pastel colours and pink-red hues are a good sign, angry orange, yellow and bright red might not be quite so nice. To have colour at all you need something in the atmosphere to scatter the light and dust or haze which is likely in dry air and high pressure will scatter the pinks and reds, whereas water vapour and cloud scatters more orange, yellow and even green.

I have a fabulous book (published in 1986) written by a sailor who has studied masses of these old weather lores and spent time observing what happened next. It makes fascinating reading:
https://www.amazon.co.uk/Weatherwise.../dp/071538788X

To quote the above book, "A truly 'red' good weather sunset sky is one that ranges from a virgin blush of pink to deeper, brighter, pastel hues of crimson plush; these are indeed shepherd's and sailors delights, with test results qualifying the adage for a reliability factor of close to 100%. A total of 97 fine nights and 77 fine tomorrows followed 102 observations of what I considered a 'proper' good weather red sunset. But a lurid evening sky - one that is angry, livid red or orange - is one to be wary of; furl your sails and guard your anchor, put away your walking boots and stay at home, for 77 garish, over-vivid evening sunsets observed during tests were followed by 74 bad weather nights and 61 grey, wet and gloomy days."

I find myself reading and re-reading that book, as some of the descriptions are superb.

[Penellype]

Met Office have issued a yellow warning of rain for northern England, Midlands and parts of Wales for tomorrow. The CAPE levels are still extemely high for this country, so while not everyone will get a storm, if you do it could be very intense with frequent lightning, torrential rain and large hail. This could result in local flash flooding and electricity outages.

I hate storms, so if one of these arrives over York I will probably be hiding under the table

http://www.metoffice.gov.uk/public/weather/warnings