Visibility 10+ SM (9999+ m)

[Simicro 247]

Hi everybody,

I use Active Sky and very often the METAR reports: Visibility 10+ SM (9999+ m)

But in reality, in my GA aircraft, under 10 000 ft, I have much less visibility.

I know aviation is not an exact science but the difference between what is reported and what I see is huge.

What do you think?

 

[downscc 1,327]

Active Sky is very dependent on METAR reports, which only report visibility up to 10 nm (9999 m).  The actual visibility can be anything from 11 nm to severe clear and its up to Active Sky to make a guess.  A good guess can be made by looking at the temperature/dew point spread.  If the spread is less than 5 deg C then expect the visibility to decrease.  Humidity is the primary visibility obstruction, then there is smoke and smog as well but these are usually reported as well as any precipitation.  I've flown on hot summer days where there is a high pressure dome over the entire Southeast and it's like an ocean below with deep haze up to 16000 then clear and tall cumulus look like icebergs floating in the brown soup.  Really something to fly along just above that haze line.

[lownslo 592]

In Active Sky, what value do you use for the "Maximum upper visibility" setting?

Greg

[Michael Moe 495]

Maybe I am wrong but i always believed that METAR vis is measured on the ground Straight ahead?

So there could be forinstance overcast at 2000feet and again at 4000feet and still vis at 9999+?

Horizontally and vertical vis?

EKCH131650Z OVC6700/// 9999 VV0300 for instance .This would stille be a ILS CAT1 to 22L but with not a clear sky.

Might plan for a CAT2 on hand but not mandatory 

Used to determine RVR and DA/DH on the Approach chart? 

 

 

Michael Moe 

 

Edited August 13, 2019 by Michael Moe

[Simicro 247]

Thank you all.

@downscc Why am I not surprised to see you in this thread? I think I can guess the thread you jump into 😉 Maybe you can guess where 'aviation is not an exact science ' in my initial post comes from!

If I understand well, Visibility 10+ SM (9999+ m) is not the actual visibility but the range of the report? I've never seen things like 3/4/ SM or alike.

My Maximum upper visibility in AS is: 199

 

 

[Michael Moe 495]

1 hour ago, Simicro said:

Thank you all.

@downscc Why am I not surprised to see you in this thread? I think I can guess the thread you jump into 😉 Maybe you can guess where 'aviation is not an exact science ' in my initial post comes from!

If I understand well, Visibility 10+ SM (9999+ m) is not the actual visibility but the range of the report? I've never seen things like 3/4/ SM or alike.

My Maximum upper visibility in AS is: 199

 

 

As i explained what I believe is that METAR vis is shown as Horizontal and sometimes VV. but from the ground. 

You could  as an example  have this in the METAR: 0100 VV075 meaning that 100m is vis ahead and VV75feet is below most Cat 2 approaches because mostly Cat 2 is About 100feet AGL(DH)

EHAM and sometimes EKCH have these situation. I have seen 75m vis with VV00 in EKCH.

VV (ceiling) is only present in the METAR when relevant (Fog,ovc etc)

Michael Moe 

Edited August 13, 2019 by Michael Moe

[downscc 1,327]

I am now aware of any NWS product that has upper level visibility.  Yes, a METAR is by definition the surface visibility usually either reported by a ground observer or measured with a transmissometer.  I've seen pireps that report haze layer but those are pretty rare, I've never seen it reported in a Area Forecast (FA).  Not even cloud tops or top of overcast is normally found in NWS products.