Prob30 TSRA
 

What do you do when faced with a reasonable looking TAF which ends with PROB30 TSRA?

That's the situation that I found myself in yesterday, and I'm not sure that I made a good call. I was planning a solo landaway at Shoreham, and while the weather at Goodwood quickly picked up from a rather grotty start, Shoreham kept reporting 3000 SCT005 BKN009 until mid-morning. It gradually improved, and by lunchtime the METARs were reporting 9999 FEW012 SCT018, and I started to think about going. I was aware that by that point we were into the bit of the TAF which included PROB30 TSRA, and Shoreham ATIS was reporting a Thunderstorm warning. However the METARs seemed fine, PROB30 wasn't much, and, after all, I could always turn back. I went.

I made it to Shoreham, landed, put on my high-vis jacket and headed off to the terminal. After the novelty of looking at the 'Arrivals' monitor wore off I headed back to my aeroplane, thinking that I'd better get a move on because it was looking a bit grim to the east. With perfect timing a bl**dy great bolt of lightning hit the hills to the north-east, and within minutes Lancing college disappeared in the mist and the rain started. It took me rather a long time to get back home....

Was I dumb to head off in the first place, or was I just unlucky in getting the PROB30's 1-in-3 chance of bad weather? What would you have done? I'm not worried about safety, as getting rained in was probably the worst that could have happened - if the weather had been bad before arrival I would have just turned around and headed back west. However, it's the first go/no-go decision that I've had to make and it didn't turn out quite as planned... :)

My only advice, and this is very subjectve, is that I would have looked at the thunderstorm activity we have had over the last few days. These have all been quite lively and builds-ups have been quite rapid. When I see Prob30 I always expect the worst. However, I'm just a dumb air traffiker with a shiny new PPL.

The unofficial interpretation I would use is....

PROB30 = good chance of
PROB40 = very good chance of

Most times when I've seen a PROB30 of TS, they have happened.

When thunderstorm activity occurs in the UK, it tends to take the form of quite specific individual cells. Whole lines of storm cells of the sort seen in the US at certain times of year are far less common.

So, with this in mind, normally, when a storm arrives at your airfield, sit it out for 30-40 minutes and you will find that it clears and you are good to go again. Just occasionally, you are unlucky and it clears in the direction of your destination.

PROB30 is often associated with TSGR and similar because since by their nature the storms are specific individual cells. The forecaster cannot be sure that any cell will pass over any particular airfield, even though he can be pretty sure that there will be storms over a wide area.

So, when you see PROB30 TS, assume that you will be flying in or around storms with some certainty. You just can't be sure that one will pass over your airfield.

When you see TEMPO 1015 TS you can assume that the storms are rather closer together, since in this case multiple storms are predicted to pass over the station in the TEMPO interval.

Hope this helps

Evo

2 Donks calls it well. Some of the best flying I have done has been with CB activity in the locale, but you have to keep your escape options open all the time.

You say that you weren't worried about safety, so IMHO you made a good call.

When you have fairly low hours these sorts of decisions seem troubling at times, but you'll get used to them as you build your experience.

As the old cliche goes, "go by air, if you've time to spare!" - so as you rightly point out, your worst option was a delay.

What I'd be looking for would be the possibility of TS squall lines associated with frontal activity - these can be nasty as they tend to be many miles (perhaps over 100NM) across, thus making circumnavigation difficulty; thats when I tend to stay in the bar.

;)

Evo 7

I had a similar situation on Wednesday with a PROB 30 TSRA for the afternoon, when I was due to come back from a day trip to Le Touquet.

With hindsight I think the fear of CBs was a bit overstated on my part, but chatting it through with the CFI and others at my flying club, I was enlightened. I had made some decisions that were perfectly acceptable and I was not a danger, but my planning could be improved.

I will remember the experience next time I plan a trip and so my flying skill will be improved. A lesson learnt. I had just got 100hrs total time at the end of the trip.

I want to be as safe as I can but just waiting for clear blue skies will not improve my flying skills or judgement.

Good luck with your flying Evo

REX:)

Thanks all - some very useful feedback there. I was left with a feeling that 'I learned something from that', but wasn't quite sure what that something was. Bit too keen to go maybe, but I learned plenty from it... :) :)

There is a good website showing lightning strikes here Link NOT removed......... :D so I'll have a glance at this before heading off. If lightning strikes are reported in the area and the TAF reports TS then I will consider very carefully if I'll go or not.

You are right to fear CB's though, as my instrument instructor once said "with an IR you can go anywhere pretty much...except near a CB...these will rip your wings off" :)

Cheers
EA:D

By the way, you probably made a good call, you made it there and back without any drama, and you got into the air this weekend, which is more than I did!

In addition to englishal's lightning strikes site, I'd also suggest taking a lok at the wx radar on the Met sight... can help form a picture of how bad, from what direction, and when to expect TS/RA.

englishal

I did get to fly, but the last three days have been....

Saturday - Solo landaway Shoreham. Get stuck under a Cb for hours. Got wet. :(

Sunday - Solo Navex. Take off, weather looks dire to the west. Circuit and land. Got wet. :(

Monday morning - Sunday's Solo Navex. Didn't get wet, but 12kt crosswind too much for student solo. :(

Monday afternoon.... :confused:

Bloomin' 'eck, it's bl**dy August! :rolleyes:

I got as far as the pub the last few days...and my roof started leaking in the rain on Friday, which it didn't do all winter.....is it August???

EA:D

I was looking to do EGBB - EBOS on any one day last week.
No Wx radar in the plane and recent days have shown heavy squall lines over a wide front with no gaps between the CB's.
Originally Wed looked good.
- clear to the east and a front out to the west not due to arrive until the night.
Forecast changed with the front coming in earlier and prob 30 TS thrown in. :eek:
Decided against it..........usual route LAM-BPK (overhead LTN) dct EGBB. This takes you overhead Milton Keynes and on the news later that evening, the heaviest downpour had been Nr. M.K. with 60mm in about 30 mins.:) :)

Right decision. Why risk it if you don't have to. There will then be another opportunity so don't be pressured.

Going this week.........forecast good too:D :D

:D :D :D :D :D

Since Evo has pointed to this thread I thought I might as well revive it with the observation that wycombe's law of probabilityis similar to another another natural law covering the forecasting of cloud cover:

FEW = can see the ground quite often really
SCT = Ground visible from time to time in the distance
BKN = Solid overcast, though you may be able to claim you caught a glimpse of the surface within the last half hour
OVC = The only reliable forecast of the lot.

And by the way what happened to Evos 1 to 6? I hope no violence was involved! :uhoh:

Way back when I was a new PPL(A) in my first summer of flying, a friend and I flew from Welshpool to Blackpool for the day. The TAFs wer givng PROB 30 TS, but it was a lovely day, and no-one expected the TS to amount to much. We had lunch etc, and set out to leave in late afternoon. We were told there was thunderstorm activity, but again, no-one seemed to think it was that bad. Well, before reaching the Liverpool area we reached a black wall of cloud, heard various other pilots calling that they were diverting or returning to Blackpool, and we made it back there 5 minutes befiore a massive storm hit, with pink forked lightning and almost non-stop thunder. Blackpool was awash with people on mobile phones reorganising their lives, there was an impenetrable line of TS from Liverpool to Leeds, and virtually everyone was stuck overnight. We eventually made it back to Welshpool the following morning.

Since then I carry a toothbrush and spare underwear in my flight back, and treat PROB 30 TS with a great deal of respect.

I can never understand the concept of 30% chance of rain - either its going to rain & I'll get wet, or it isn't.

Where has this thread been hiding for the last few montsh? I'm sure I don't remember it the first time around...

Seems like the general advice is to treat any forecast which contains CBs with lots of caution, which makes sense - but I'd also add that there are so many other factors to take into account it's impossible to give a definitive answer.

First of all, it's much easier to see the weather from the air than the ground. It's always worth calling anyone and everyone en route to see what their weather is, but failing that nothing can beat going up to have a look. Do one circuit, land, then evaluate what you saw, and make a decision. (Easier to make a decision on the ground than in the air, I find, which is why I'm suggesting just one circuit to start with).

Other things to take into account include: Where are you going? I would say that, in general (and I'm sure someone can find an exception), doing circuits with this type of forecast is fine - you can get down before the weather arrives. Flying across a deserted part of the country probably isn't. If you are flying cross country, how many alternates are there? Is there any high ground that may make it difficult to turn back? Controlled or restricted airpsace that makes it difficult to fly around any weather?

As well as flying considerations, there are practical considerations. If it's a hired or shared aircraft, do you have to have it back for someone else? Do you have to be at work the next day? Of course if you do get caught out by the weather, these things musn't influence your decision to stay on the ground and find a hotel.... but that doesn't mean that they can't influence your decision to go or not in the first place.

Someone mentioned the difference between the single-cell CBs we often get in the UK, and huge lines of CBs that occur in other parts of the world. I've not yet encountered CBs outside of the UK, so all my experience and suggestions are entirely based on UK weather - but you should certainly take local weather patterns into account.

Also, are you going VFR or IFR? I would never consider flying in IMC if CBs are forecast unless I had weather radar (and I've never yet been allowed anywhere near the controls of anything that does have weather radar!)

And probably loads more stuff that I can't think of right now!

FFF
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PS - :D @ Kolibear

Nice lunch down the Pub, FFF...? :D

This has been hiding for well over a year, just linked to it because The Phoenix Rises isn't the only student to head solo into a thunderstorm...

Isn't that what I said? I'm sure I said something like "Where has this thread been hiding for well over a year"! :O One day I'll learn the difference between 2002 and 2003!

FFF
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To reply to the original (regardless of age) thread, you can look up the applicability of TAF's in an IFR route manual, meteorology section.

The given example 'PROB30 TSRA' situation for a destination or alternate is a transient/showery type of deterioration which is not applicable.

Thus Evo's decision to go was sound and legal.

That it may not be applicable does not mean that you shouldn't consider it as a possibility. Just not a major part of the equation.