Flight planning with this patchy weather

[CharlieDeltaUK]

This weather (I'm looking across the middle of England) looks like it presents some breaks in between the gloom. Do most VFR pilots abandon plans during this sort of weather or do they hope to nip out and get down during lulls? I suppose this question is really asking whether UK weather requires one to be opportunistic or is that the beginning of the slippery slope to get-there-itus?

[Guzzler]

I canned the the cross country part of my flight yesterday. Probably could have avoided the worst of the weather but was not prepared to take the risk. If the gaps would closed up things would have got very tricky.

Still did a little aerobatics though.

[Whiskey Kilo Wanderer]

You have enough fuel on board to divert or hold as required. Enough charts and airfield information to divert and know what’s there. Enough time before dark or other factors to get somewhere safely.

The storm cells yesterday were less of a problem because you could see them. It gets more difficult when the cells are embedded in the general clag. Knowing which way the cells are actually moving is useful. A large and active cell that passed over Headcorn yesterday laid down a white carpet (of hail) a couple of miles wide across the southeast. It made it relatively easy to see the direction of travel of the cell.

[gasax]

I think that UK weather requires the PPL to be somewhat pragmatic.

Much of the forecast information will give conditions which are 'conservative' - so frequently either the general situation will be better than forecast or specific aspects of it will be. I often note that the TAFs will oftne make a flight seem unlikely.

But - well there is always a but, now and then the shear variety of our climate will result in really much worst weather than forecast or localised conditions which really mean standing on the ground looking up is the only safe alternative. In about 300 hrs of proper cross country flying, I have made at least a dozen major diversions or U-turns and ended up on the ground omewhere I have no intention of being. I have also had probably a similar number of occasions where I have delayed leaving by at at least a day.

So as a 'dispatch rate' it starts to look like around 10% of my VFR cross country flights have had major alterations - but I do live in Scotland and by cross country I mean in excess of 2.5hrs..

But then even for 'local' flights I have had at least 5 major diversions in around 800 hrs - so approaching a 1% rate when you can simply look out of the window (mainly haar and localised rain / hale / snow).

[Captain Smithy]

Just one of these things we have to put up with. Some times you can be lucky with the Wx and get a half-decent break but up my way things have been decidedly dodgy for the past few days; not worth the risk.

If you don't like the weather, wait a while; it'll change :)

[Zulu Alpha]

It depends on what you want to do.
Generally you can see the cells quite clearly and assuming you are not limited by airspace restrictions, it is easy to detour around them. So circuits and short local flights are OK.
X countries are more challenging, but take a look at the weather radar to see how much space there is in between cells.

In addition early mornings and evenings are best when there is less heat from the sun.

[peterh337]

TAFs will always be pessimistic because the forecaster has to throw in anything remotely likely under the PROB30 heading.

The UK F215 is even more pessimistic, throwing in everything including the kitchen sink, and then adding moderate icing in all cloud even if the wx is CAVOK.

So one needs to have a physical look at the actual wx. One can use weather radar (http://www.meteox.com/h.aspx?r=&jaar=-3&soort=loop1uur), sferics (http://blitzortung.tmt.de/Images/image_b_eu.png?), satellite IR images (http://www.metoffice.gov.uk/satpics/latest_IR.html), etc.

And a quick look at the MSLP chart (http://www.mwis.org.uk/synoptic.php) will give you plenty of clues. The troughs (their actual position is meaningless; the forecaster just draws them in randomly) mean a PROB30 TEMPO of TS, and sure enough for EGKK you now have, for tomorrow,

PROB30 TEMPO 1313/1318 4000 +SHRA

I am no forecaster and would never suggest anybody can beat those who do it for a living, but it's not hard to get a rough grip on what is coming. It's just that in the PPL people spend hours on the stupid slide rule when they could be learning to read wx data presented to them on a plate, using that new fangled method (never mentioned in my PPL) called the internet :)

A while ago I knocked up this pic (http://www.zen74158.zen.co.uk/aviation/wx/wx.jpg), largely from the POV of high altitude IFR. It is self explanatory. One interesting thing I found repeatedly is that you get TS where there is a change from a cold to a warm front.

[1800ed]

I wish real charts were marked up like that - wold make things a bit easier :}

[flybymike]

Yup, loved the prob 100 really **** WX. I mean..no decode necessary or anyfink...

[Big Pistons Forever]

If I have to go anywhere a significant distance VFR and the weather is crappy I start out for the nearest airport more or less in the direction I with the the idea I will takeoff and have a look. If after takeoff I don't like what I see I just go back. If I get to it and things still look doable I set course for the next aiprort and repeat the process. There have been many days when I made 500 miles when I though I would be lucky to make 50.

But you have to have hard no go criteria. In other words you have a minimum altitude that you will not descend below. Anytime cloud forces you lower you turn around. The same for visibility.

[oscar romeo]

Ive had my IMC test at netherthorpe scratched last two days due weather, very frustrating!!!:ugh:booked for later today, still look marginal last time i looked but i have icing concerns but thats whats makes this counrty great the varied weather......yeah right.

[peterh337]

but i have icing concerns

What altitude are you flying at?

[oscar romeo]

Not sure today, my examiner may have changed plans, yesterday was 2 holds booked at doncaster 3500 then ILS. Other inbound traffic was diverting round weather yesterday.

Just want to get it knocked off now I am getting bored under the visor and ive got too much going on elsewhere to give it 100%

[peterh337]

This is a nice pic, from a couple of days ago

http://www.zen74158.zen.co.uk/aviation/wx/image.ashx.gif

[funfly]

From bitter experience the oft quoted remark "better being down here wishing you were up there...." is worth repeating

[FirstOfficer]

Peterh337,

Thanks for your links, I am just going through MET theory study for my forthcoming exam, and will start the practical flying soon. However I wanted to start getting use to MET planning from the start. Your links are most valuable. :ok:

I find MET an interesting subject, but quite a lot of information to get through and understand. :ooh:

[CharlieDeltaUK]

For someone wanting to get a good practical grasp of weather post-PPL, does anyone recommend any follow on training. I know Simon Keeling runs such courses. Are they effective? The Met Office seem to do some as well.

[peterh337]

IME, IMHO, they are not helpful because they just cover the same old met theory, which is almost impossible to use for anything practical because there is no website which can give you the data to "plug into" that understanding, so to speak.

That was my gripe with the JAA IR met also. Completely useless for understanding weather, I found.

What is needed is knowing how to directly use the various internet-sourced weather data to make practical go/no-go decisions. I am not aware of anybody doing that.

[abgd]

For someone wanting to get a good practical grasp of weather post-PPL, does anyone recommend any follow on training. I know Simon Keeling runs such courses. Are they effective? The Met Office seem to do some as well.

That's a really good question - weather is one of the things I feel I have the weakest practical grasp of post-PPL.

[peterh337]

This is why I think the way to approach this is by looking at hypothetical mission scenarios, in a classroom setting, using internet data.

It is completely wrong to think that one can (on any significantly reliable basis) outforecast the forecasters. Yet the way met is taught everywhere is just that... they teach you about polar tropical and maritime tropical etc etc airflows. I always find that stuff goes right over my head and I cannot see any way to relate it to reality. What matters at the end of the day is the tafs, metars, the frontal picture, radar, etc.

[FlyingGoat]

What is needed is knowing how to directly use the various internet-sourced weather data to make practical go/no-go decisions. I am not aware of anybody doing that.

Well, why don't you run an evening at Shoreham? You're seriously more clued-up than most of us and can sift out the b-****. I'll run the booking.....

[Halfbaked_Boy]

Google 'skew-T' diagrams, then learn how to use them.

Invaluable during the Summer months.

[peterh337]

How do you make use of them?

[Fuji Abound]

VMC

Its only partly about the weather.

Weather radar, METARs, and TAFs are without doubt the best sources for buidling a picture of the weather, and build a picture you should. It isnt of course just about the weather along your track, but the whats happening to the windward of your track that will give you a feel of how things might develop. Equally important is an assessment of your escape routes along your track - where do you go to get quickly on the ground if necessary and how might the terrain impact on your decision.

I find it interesting how often pilots plan for trouble. For example consider a typical trip from the south of England to Scotland - there are plenty of possible routes but why would you select a route over high ground if the weather is marginal - add on the extra miles and route up the coast.

and its also a lot about your piloting ability.

So many pilots seem very uncomfortable flying low level - is it stories of the dangers of scud running or other reasons? It takes time to be comfortable flying low level but once you are comfortable in reality it is very rare you cant stay under the weather in the UK. I can think of very few trips that I have wanted to do VFR that werent possible. Yes, that may well mean a circuitous route and there may be occasions when it clearly isnt possible or wise.

I would of course recommend time spent with an instructor or another pilot who is comfortable flying in these sort of conditions, the usual health warnings apply.

As to second guessing the professional forecasts I am less certain they are as consistantly accurate as some would have you believe. I can think of one pilot I know well who has a better than 90% record of predicting what the actual weather will be in those circumstances when he thinks it will be different from the met office forecast. More often that not it is better, but to be fair I can think of a few occasions when we have rightly predicted it would be worse.

Of course in these days of computerised weather forecasts local knowledge is particularly useful. There has been more than one occasion my flying partner(s) have been anxious to depart based on good TAFs - On a few of those I have been much more cautious and asked them to be certain that they really dont mind a train journey on our return to collect the car. Sure enough the fog has rolled in and all movements for the rest of the day have stopped.

[MichaelJP59]

One thing which seems to put a lot of people off is the ubiquitous PROB30 SHRA+ that we often get. It's not a 30% chance that you will get caught in a CB though. I guess most people build up enough experience to look at the F215, the rain radar and a range of TAFS/METARS and relate it to previous days.

[peterh337]

I find the F215 to be almost useless, because the forecaster chucks in everything he can think of.

The PROB30 has been degraded by the fact that only PROB30 & PROB40 are permitted under ICAO.

So PROB30 is now a shorthand for "a small chance of it happening but pretty unlikely" and normally you find that anytime there is a trough on the MSLP chart (see the link I posted) that appears as a PROB30 TEMPO TSRA in the TAFs.

PROB40 means that he thinks it will happen, probably.

What makes a massive difference is using GPS and doing things the "modern way". If you cannot navigate in haze then (sorry to say this) you are wasting your time doing a PPL, because you can be grounded for much of the summer.

[Phil Histine]

I do find myself envying the rich guys in Barons with weather radar, but this kind of extended CB activity is less usual that just yer regular low-level clag.

As a holder of a year-old IMC rating, my more common concern is the cloud tops, which are very hard to establish. I know that 1000' cloud will inevitably mean some IMC work leaving under the 2500' Class A that sits over my N London airfield, but having cleared that, if I was able to climb into clear air at, say 4,000' heading west I'd be out of it within 10 mins. But if it was XXX all the way to Wales or Cornwall, that would mean a great deal of hard work and, with no TCAS and without even a radar service in parts, I may not feel entirely relaxed flying blind all that way. But of course the 215 is far too general to give any real planning accuracy as to cloud tops over that distance.

[Prop swinger]

That's what skew-Ts are for (see above.)

You get a picture of the relative humidity of the atmosphere at various levels, & can use that to assess the amount of cloud.

You can also see the stabilty of the atmosphere & use the dry & saturated adiabatic lines to forecast the base & tops of convective cloud.


http://dl.dropbox.com/u/925530/skew-t.JPG

[Phil Histine]

Yes, perhaps I should make a concerted attempt to find a reliable source of t-skews and an even more concerted attempt to understand and interpret them. But wouldn't be nice if some met guys with a bloody great computer did it for us by providing a map of Britain witha cloud thickness forecast...

[BobD]

Well I am sat here feeling very frustrated, as I have just cancelled my planned flight today from Gamston to Leicester. The forecast today is very similar to that of yesterday, and certainly here in Sheffield, the day turned out better than expected. The bit that concerns me on the TAF's is the threat of thunderstorms en-route. During my training, I was advised that TS is a no-no.

My decision is also based on the fact that I would be taking two passengers (who I do not know), so their reaction to turbulence is unknown.

I have about 100 hours in my log book now, and have just completed the IMC, so I am still a relative novice. I would appreciate others opinions from the forecasts. Am I being over-cautious ??

[douglasheld]

No.

I'm in exactly the same position as you; I stayed on the ground today, too. I WANT to regret it, but I made my decision from the local TAFs. It's sunny and blue out the window, but it's also gusty, and those clouds look awfully tall...

[John R81]

I liked Fuji Abound's post 25.

I am a PPL(H) so most likely more comfortable than many posting here about flying under the weather. The ability to drop into a farmer's field and wait out the weather is also an important difference.

I have a minima rule that I have not so far broken (and I don't intend to); visibility to maintain 60knt airspeed and 600ft height OR turn back, divert or stick it in a field right now.

My normal airspeed is 110-120knt so I am aware of reducing speed to maintain VIZ, and I have a radar altimeter set to chime at 700 ft to remind me that things are getting tight.

I do take account of whether my direction of travel is with, or into, the oncoming weather.

PROB 30 I take note of but the likelihood is low. So, like FA's on Saturday 21 I headed to the airfield, and had a full day. Occasional heavy rain, with hail and gusting winds, to steer well clear of but nothing that caused problems, or even concerns given my fuel state and divert options.

So far, in total I have had 2x turn-back and give in, 1x land in a field for 40 minutes to wait for the weather to change, and no divert to alternate field. In addition, there have been a couple of times flying West to East when I have stayed on the ground waiting for a front to go through, and then lifted in the clear air ahead of the next wave of clouds to fly along with the clear air to my destination.

I do like to follow the METARs that are up-weatehr so I can get a more accurate understanding of what is going to hit me. Seeing airfield METARs dropping in succession also gives a clear view of the speed of advance.

Finally, on long N / S strips (EGKR to the Western Highlands) I have a number of alternate routes to provide for low-level options both West and East coast, depending on weather.

[CharlieDeltaUK]

You have expressed exactly what I was thinking in my original post, and I have about the same number of hours. I cancelled when faced with the same situation, and sure enough there were others at the airfield who would have flown. I can only say I was happy with my decision once the initial disappointment dissipated (and once I saw the actual weather which unfolded at my destination). I'm going to do the trip when the weather permits - the destination is still there.

If you had flown and had a bad experience, you would really have kicked yourself. And your passenger probably took comfort from knowing that you are the sort who is cautious.

At our level of experience, I think this is the sort of decision which becomes more tricky to make and others may have views on whether we worry too much. But, aside from mere disappointment, is there really any downside to erring on the side of caution? I guess it's more difficult if your flying is constrained to weekends. This weather has got to shift soon and we have some bank holiday s coming up, courtesy of HRH.

[Gertrude the Wombat]

During my training, I was advised that TS is a no-no.
I was told not to go within five miles of a CB, not to insist on staying on the ground whenever there's a PROB30 CB somewhere in the same county!

If the forecast is for embedded CBs I stay on the ground. If you can't see them you can't avoid them.

If the forecast is for isolated CBs, which you have a reasonable chance of seeing and avoiding, then I go flying. And on occasion have had to change my planned route to avoid thunderstorms, which I've seen from many many miles away.

It's in between that's harder - when they don't actually use the "embedded" word but also give the impression that there are more of the things closer together than justifies "isolated".

[peterh337]

If forecast skew-ts were accurate, they would be fantastic.

And weather forecasting would be exact too :)

In reality, these thermodynamic diagrams are just graphics which are generated from the same GFS computer model.

There is no magic here. The forecasters use these diagrams too, to generate their PROB30 TEMPO +TSRA etc. There is nothing a pilot can do with these things which will produce a more accurate TAF - unless the forecaster has done a cockup which is very rare.

The wx we have been having the last few days has indeed been unstable and this shows up on the skew-ts but the weather model itself is far too coarse to predict bases and (especially) tops accurately. This is why I use IR satellite images (http://www.peter2000.co.uk/aviation/ir-sat/index.html) (and other data) to get an idea of what is really out there, before the flight.

[FullWings]

If you're looking for a bit more detailed overview of UK/European weather, especially when it come to making go/no-go decisions, then I would recommend TopMeteo (http://www.topmeteo.eu/weather/aircraft!briefing_vfr) as a good service to subscribe to.

You get all the normal charts, METARS, TAFS, etc. but they also run models geared to light aviation on their servers and I have have found their predictions of cloudbase, wind, precipitation, cloud layers, etc. to be amazingly accurate.

[peterh337]

That is yet another GFS site.

Incidentally I wonder why they split the clouds into low medium and high? It is really a continuous spectrum, a lot of the time.

[FullWings]

That is yet another GFS site.

I regularly use two GFS-based forecast sites and they often give noticeably dissimilar forecasts, due to the different algorithms used on the basic GFS data. Both sites have their strengths and weaknesses, apparent after a period of usage. The one I linked to above is run by meteorologists who also happen to be private pilots and is optimised for typical European conditions.

In the last week or two's unstable airmasses, the showers have developed pretty much where they said they would - I was able to plan and successfully complete a fairly big flight in the UK by taking the forecast at face value, altering routings by as little as 20nm to stay clear of predicted adverse weather. This sort of precision hasn't been available at low cost to the average GA pilot until quite recently.

Incidentally I wonder why they split the clouds into low medium and high? It is really a continuous spectrum, a lot of the time.

Maybe it's because that's the way the met. professionals have always classified cloud types? Base at: low 0-2Km, mid 2-7Km and high 5-12Km. Lets them use all the Latin names and prefixes they learnt on the course...

When I did the ATPL, those were the standard definitions (I think!)

I tend to think of low cloud being associated with the surface in some way, either by convection or orographic influence, medium cloud as not being convectively connected and high as completely crystalline in content. Then you get a Cb which spans all three categories.

[mm_flynn]

If forecast skew-ts were accurate, they would be fantastic.

And weather forecasting would be exact too :)

In reality, these thermodynamic diagrams are just graphics which are generated from the same GFS computer model.
....
The wx we have been having the last few days has indeed been unstable and this shows up on the skew-ts but the weather model itself is far too coarse to predict bases and (especially) tops accurately.
I have been out a couple of times in the last week and found NWX's (navlost.eu) cloud profile was pretty accurate for my routes of flight with cloud density/ bases/ tops of the layers all pretty close to what I saw in flight. This is just a cut through the raw GFS model and seems fine for the overall cloud profile. Forecasting where Cells are going to be and when/where it is going to chuck down rain/hail is impossible. However, there was plenty of vis above the first cloud tops to eyeball the cells and avoid them.