Is VV limiting when choosing an alternate?

grimey · Post by **grimey** » Sat Jan 07, 2006 11:22 pm

lilfssister wrote: If the ceiling is 1000 feet or more but the visibilty is reduced to 3 miles or less by precipitation, smoke, or fog, it is still IMC/IFR.

If the ceiling is 900 feet or less and the visibility is 4 miles or more, it is still IMC/IFR.

Less than 3 miles, and 3 miles or more.

lilfssister · Post by **lilfssister** » Sun Jan 08, 2006 6:51 am

grimey wrote:
lilfssister wrote: If the ceiling is 1000 feet or more but the visibilty is reduced to 3 miles or less by precipitation, smoke, or fog, it is still IMC/IFR.

If the ceiling is 900 feet or less and the visibility is 4 miles or more, it is still IMC/IFR.
Less than 3 miles, and 3 miles or more.

You are correct sir! I have corrected my post. Another good reason not to post, chat, watch a hockey game, and talk to the person beside you at the same time!

split s · Post by **split s** » Sun Jan 08, 2006 10:06 am

Anyone remember approx what year the metar was first introduced?

squawk 7600 · Post by **squawk 7600** » Sun Jan 08, 2006 10:28 am

It does make sense that a VV condition would be considered a ceiling as the value of the VV does determine a limit...so therefore treat it as a ceiling. I just wasn't sure if it was a limiting factor in determining an alternate because it doesn't state this fact clearly anywhere. A good place to put it would be in the CAP GEN I would think....same place where they make mention of TEMPO and PROB. Might help out alot of people.

On the other hand, there is one problem I do have with the VV phenomenon in the fact it is not as restricting as an OVC or BKN condition. Like I said before, you can most often see throught it at 005 when it is reported at 003 so how much reliablity does the TAF really have? Plus in a VV condition when related to FOG or SN, these conditions change rapidly and the TAF might not hold true for these reasons. I'd sure hate to scrap a flight because I can't hold my alternate based on a VV because of some SN condition.

zzjayca · Post by **zzjayca** » Sun Jan 08, 2006 11:18 am

split s wrote:Anyone remember approx what year the metar was first introduced?

I can't remember exactly but it was either 95 or 96 when we underwent our training for the conversion from the SA's.

Cat Driver · Post by **Cat Driver** » Sun Jan 08, 2006 11:25 am

Why doesen't Canada use ICAO units for measuring visibility in METAR's?

Every time I read a Canadian METAR ( which ain't very often ) I have to convert to get the picture for visibility.

Cat

split s · Post by **split s** » Sun Jan 08, 2006 1:32 pm

[quote="zzjayca"][quote="split s"]Anyone remember approx what year the metar was first introduced?[/quote]

I can't remember exactly but it was either 95 or 96 when we underwent our training for the conversion from the SA's.[/quote]

Man time goes by fast, I guess it's been more than a couple years since vv did not count as a ceiling.

grimey · Post by **grimey** » Sun Jan 08, 2006 1:59 pm

Cat Driver wrote:Why doesen't Canada use ICAO units for measuring visibility in METAR's?

Every time I read a Canadian METAR ( which ain't very often ) I have to convert to get the picture for visibility.

Cat

Probably because we're right next to the US, and they don't either. I'm not saying it's a good reason, but...

swede · Post by **swede** » Sun Jan 08, 2006 3:16 pm

I do not ever recall seeing V V in a TAF because it is striclty an observed phenomena, therefore it is not limiting because it is non existent in terms of flight planning.

Cat Driver · Post by **Cat Driver** » Sun Jan 08, 2006 3:28 pm

" Probably because we're right next to the US, and they don't either. I'm not saying it's a good reason, but... "

Then why does Canada claim they use the ICAO format when they obviously do not?

I truly find your system to be difficult to understand, especially your CAR's.

Cat

chipmunk · Post by **chipmunk** » Sun Jan 08, 2006 3:30 pm

swede wrote:I do not ever recall seeing V V in a TAF because it is striclty an observed phenomena, therefore it is not limiting because it is non existent in terms of flight planning.

Check out page 1 of this thread.

onezerotenthousand · Post by **onezerotenthousand** » Sun Jan 08, 2006 4:15 pm

VV you'll USUALLY only see the under 300 feet so unless you going into a 2+ precision approach A/D it doesn't really matter, too low. Do you really want to make VV in the actual a safe alternate? Carry more gas if you can.

TeeKay · Post by **TeeKay** » Sun Jan 08, 2006 7:55 pm

Swede -

Yep, VV is (part of a TAF, sure as BKN or OVC), and VV does, absolutely, just the same as OVC or BKN. Like Chipmunk wrote, see P. 1...

grimey · Post by **grimey** » Tue Jan 10, 2006 9:56 am

squawk 7600 wrote: On the other hand, there is one problem I do have with the VV phenomenon in the fact it is not as restricting as an OVC or BKN condition. Like I said before, you can most often see throught it at 005 when it is reported at 003 so how much reliablity does the TAF really have?

This probably depends on how the observer is measuring the VV that the METAR and TAF are reporting and forcasting. If it's based off of a PIREP, you'll likely have ground contact at or near the stated VV. If it's based off of a balloon estimate, you could have ground contact at a significantly higher altitude, especially if there's any significant wind. Because the baloon rises at a fairly fixed rate, but gets blown around horizontally by the wind, the observer will end up measuring a vertical visibility by timing the balloon when they really observed a slant visibility. If there's a cloud base with little obstruction to vision below, it doesn't really matter much how far away the balloon is, so long as the observer still has it in sight when it enters cloud.

Note that I'm not advocating considering VV to be "better" than a similar overcast or broken ceiling, I'm just trying to explain why a pilot may see one as better than the other. With the METAR format, there's no real way to tell how the ceiling was measured. Assume the worst, and give a pirep if you see different on your way in or out.

ahramin · Post by **ahramin** » Tue Jan 10, 2006 10:05 am

split s wrote:Anyone remember approx what year the metar was first introduced?

zzjayca wrote:I can't remember exactly but it was either 95 or 96 when we underwent our training for the conversion from the SA's.

I am sure it was before 96 so i'm guessing 95.

Big Bird Anonymous · Post by **Big Bird Anonymous** » Thu Jan 12, 2006 1:59 pm

No one has answered the question yet.

If planning an IFR alternate and the TAF indicates a V V which shows a condition in which the vert vis is below alt. min's, is that limiting?

yes or no

zaac · Post by **zaac** » Thu Jan 12, 2006 3:16 pm

Yes

Alternate operating minima is decided by vis and ceiling.

VV is a ceiling.

TeeKay · Post by **TeeKay** » Thu Jan 12, 2006 5:37 pm

Big Bird -

I answered the same thing as zaac back on Jan 8... and even before that on p. 1. Absolutely, it is treated as a ceiling, and it appears on TAF's all the time.