# taf question

#### SEAN

##### New Member
FM0000 VRB03KT P6SM OVC040 PROB30 0612 4SM -SHSN=

can someone tell me what the Prob means in this taf

\thanks

Probability is 30%-39% that from 0600z-1200z 4SM visibility in light snow showers.

Ive also had a DE tell me that the Prob30 meant that 30% of the forecast area would see these conditions, but that isnt what my college weather classes have been saying.

[ QUOTE ]
Ive also had a DE tell me that the Prob30 meant that 30% of the forecast area would see these conditions

[/ QUOTE ]

And what's the forecast area for a TAF?

Well, I know its a 5SM radius, but its used by pilots in a much wider radius. Im not sure what he was referring to when he made that statement, I just nodded and we moved on.

[ QUOTE ]
I just nodded and we moved on

[/ QUOTE ]

Probably a good thing!

[ QUOTE ]
[ QUOTE ]
I've also had a DE tell me that the Prob30 meant that 30% of the forecast area would see these conditions

[/ QUOTE ]

And what's the forecast area for a TAF?

[/ QUOTE ]sounds like one of those "correct, but who cares?" situations.

From a meteorological standpoint, precipitation probability is a number that is the product of two others:

probability that precipitation will occur in the area
X
the amount of the forecast area that is expected to be covered

So, 30% probability for an area can mean a 30% chance that the forecast area will be 100% covered by precipitation or a 50% chance that 60% of the forecast area will be covered by precipitation or a 100% chance that 30% of the forecast area will be covered by precipitation, or anything in between.

=Maybe= some sense in the general Area Forecast since a general knowledge that it includes elements of both rain and area probability can assist our planning. 80% may mean that there's a good chance that we will get wet, but also that we will have some viable alternates enroute, although even then, being a calculation, neither we nor our briefers know which of the infinite possibilities it is. But it's definitely not as meaningful when we're talking about a 5 NM radius TAF (although I have seen a small storm pouring rain down 1 mile east of a runway with not a cloud in sight anywhere else)

taf was correct...although a little late. Went out last night and encountered snow at 1500 ft. Immediately diverted back to teh airport and landed. No need to mess around. Taf said early morning.....i was out at 7 pm.Oh well, pretty wild when you level off andlookinto the landing light and see snow whistling past. TAf was for Dulles, and I was in Manassas(khef) about 10 miles to the west.

The only thing you can be 100% sure about with the weather is what you see out your windshield. And that is only good for the time that you're actually looking. Look down at your charts and all bets are off.

Yeah, very true. A meteorologists best friend is his office window. Although I have found TAFs extremely accurate, I never put all of my faith in them.

Replies
7
Views
546
Replies
1
Views
273
Replies
32
Views
2K
Replies
48
Views
4K
Replies
17
Views
3K