Prob30 Prob40

[FullTravelFree]

Question:

How do you deal with PROB30/PROB40 indicating nonVFR weather?
Especially when planning a long flight with a long 'wait' before returning.
I have said quite some times, 'nogo' because these PROB's, ugly looking PROBs
The way I look at it 30-40% change of getting stuck or getting in trouble.
But....
...a lot of times, a lot more then 60 or 70% nothing happens, nice VFR or even clear blue skies...
There I am, looking at the blue skies, not flying, unhappy boss...

Here in Poland it seems the met-man puts out a PROB almost every day,
and a lot of times they range from morning to evening.

Any tips/hints/trics? All thoughts appreciated.
FTF

[DeltaNg]

In IFR flight planning - some ops manuals will say

PROB 30 = Captains discretion.

PROB 40 = Assume Valid.

[Stuck_in_an_ATR]

I think that basing a "nogo" decision solely on PROB30, or even 40 without any further in-depth analysis is an overkill. Especially if that "PROB" is followed by "TEMPO", or "LCA". That might work o.k. for leisure flying, or training, but not for commercial applications - especially in places, where "PROB" is, more often than not, nothing more but forecaster's CYA exercise...

For me "PROB"= take more fuel, plan for alternate scenarios, monitor the wx more carefully. Also, I think that safe, yet efficient "go/no go" decisions, should be based on the "big picture" (ie. wx forecasts from various sources, taking in to account terrain, possible alternates, local knowledge when applicable etc.) and taken "case by case" - that's what we are paid for after all... :ok:

Re. your scenario getting stuck somewhere with your boss... IMHO, once you have determined that you can safely complete your flight to your destination OR alternate, the rest are "commercial" decisions and therefore, your boss's call... Your job is to present him all possible safe alternatives and let him choose. What I mean by that is telling him: "Boss, I can fly you to XXX, BUT as per the weather forecast, we have a a 30% chance of getting stuck there overnight, or landing in ZZZ instead. Do you want to go?". From my (limited) experience, that usually does the trick. If he says "no go", it's his decision, so he shouldn't be angry with you, even if the skies turn blue. If he says "go", then he'd been made fully aware that he might end up stuck someplace else if the weather goes bad, and shouldn't be too unhappy about that either...

Cheers!
Stuck.

Disclamer: My experience is mostly based on FW ME IR ops, which are generally less prone to WX. Nevertheless, I think that basic principles hold true for all kinds of flying.

[topik22]

You should fly in military...prob 30 to be alive...:)

[FullTravelFree]

Now this is interesting. Thanks for the replies so far.

I'm also more and more convinced about the CYA factor involved...
So you could say there's more difference between the PROB30 and 40 then just a 10% chance. I wonder if the met-man also keeps this in mind when making the TAF.
And why there's no PROB20 ( like a met-CYA) or a PROB50 (a real 'warning').

Hope there are some met-people active on PPRUNE, maybe they can 'enlighten' us.
More thoughts of the old-and-bold..???
FTF

[Spanish Waltzer]

Interestingly :8 I have started to see some prob10 & prob20 appear in forecasts although not as yet anything greater than a prob40. Is this a recognised change or just local interpretations of the rules by forecasters?

SW

[douglasheld]

When I was in flight training I asked an instructor about this and another instructor said his friend was doing aviation meteorology in the area.

According to him, his Met friend said that PROB40 means there is some weather there, a big front or something, and they don't know if it will move over and get you or whether it will stay where it is.

PROB30 is when the landscape is expected to be peppered (or polka dotted) with weather. All these things will be drifting by, but you don't know whether one of them is going to target directly through your aerodrome.

[Lindsay55]

In Australia the significance of a probability is that if there is a chance (ie any prob) of the condition been below the alternate minima for the aerodrome or if a chance of thunderstorms, then fuel must be carried to make it to a suitable alternate.

[Helinut]

My feeling is that you are probably correct that the forecaster raises the probability for his TAF, or put another way the met forecast is cautious. That seems reasonable to me, given what we do with his forecast.

In general, there are more options than going or not going. As others have said, there are various things you could do, other than decide to stay at home. Take extra fuel, plan out in your head your options for diversions etc. Depending upon what sort of flying you are doing and how important the task is, you also have the option of making a precautionary landing. This is a more easily adopted option for a hele than a FW. Having recently started flying non-helicopters VFR again, I am reminded hat I am much more careful about weather than with heles, because the precautionary landing is much less of an option.