Reported Visibility

NealRomeoGolf

NealRomeoGolf

Final Approach
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I just did my west bound trip of Central IL to Boise, ID. Fun adventure which I guess could have its own thread. The haze the whole way has been awful, but mostly visibility up in the 8000 to 11000 altitudes was 12 miles or better.

Yesterday coming into Boise, ATIS was at 4 miles most of the morning. I didn't want to do anything less than 5. So I had my backup to land short at Twin Falls and drive in. As I passed Pocatello the ATIS went to 7 miles. I soldiered on and still kept my out.

Lances have long noses and basically if you can see the ground in front of your nose it's about 6 miles. So I said if I lose my nose, turn around.

Boise stayed 7 miles on the ATIS and I was surprised to see the field at 10. So how could the ATIS be off by 3 miles? Maybe ground vis is worse than looking down and seeing it? Sure ended up being a non-event. Wish these fires would go away. Kinda ruined my pictures. :)
 
Ground visibility is not flight visibility. The AWOS is measuring the visibility over the space of a few feet and extrapolating it to a visibility in miles.
 
From the Belfort Instrument website:

"Visibility is detected using widely accepted principles of forward scattering. A high output infrared LED transmitter projects light into a sample volume and light scattered in a forward direction is collected by the receiver. The light source is modulated to provide excellent rejection of background noise and natural variations in background light intensity. "

They claim accuracy within 10%. Still doesn't really answer my question. Might have to go looking for technical data sheets.
 
From an AOPA article:

"What does three-quarters of a cubic foot of air have to do with visibility? It’s the volume of air an automated weather station uses to calculate visibility."
 
NealRomeoGolf said:
I just did my west bound trip of Central IL to Boise, ID. Fun adventure which I guess could have its own thread. The haze the whole way has been awful, but mostly visibility up in the 8000 to 11000 altitudes was 12 miles or better.

Yesterday coming into Boise, ATIS was at 4 miles most of the morning. I didn't want to do anything less than 5. So I had my backup to land short at Twin Falls and drive in. As I passed Pocatello the ATIS went to 7 miles. I soldiered on and still kept my out.

Lances have long noses and basically if you can see the ground in front of your nose it's about 6 miles. So I said if I lose my nose, turn around.

Boise stayed 7 miles on the ATIS and I was surprised to see the field at 10. So how could the ATIS be off by 3 miles? Maybe ground vis is worse than looking down and seeing it? Sure ended up being a non-event. Wish these fires would go away. Kinda ruined my pictures. :)
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All kinds of things can cause that. Surface visibility observations are taken many different ways. Some more accurate than others. Human vs automated observations can skew things. Another thing is what is reported is the prevailing visibility which is the best visibility through out at least half of the horizon. It could have been better in the direction you were coming from but worse in other directions. Kinda like just because you can see the airport from way up here between the breaks in the clouds doesn’t mean the ‘ceiling’ isn’t going to be way down there. Or maybe the Tower is making the observations and they need to clean their windows
 
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It might be accurate between the two sensors and still not be indicative of overall flight conditions.
 
So if I can see 5 miles and an AWOS is reporting 2 miles and I don't have an instrument rating, am I illegal?
 
Salty said:
Depends what airspace you're in.
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The FAR says flight visibility. So if what I see from the air is flight visibility and an AWOS is just ground visibility, I guess my eyes win.
 
Ok I lied, the FAR also has ground visibility in it. I love the FARs.
 
I've been "stuck" at towered airports when there's a single low cloud just above the weather station and the rest of the sky is clear. They can't let you out VFR until the station has high enough ceilings, even though we could all see it was perfectly safe.
 
Salty said:
I've been "stuck" at towered airports when there's a single low cloud just above the weather station and the rest of the sky is clear. They can't let you out VFR until the station has high enough ceilings, even though we could all see it was perfectly safe.
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That surprises me. Every Towered airport should have a certified weather observer and they can override the machine. Usually it’s the Tower controllers. What is an airport where this has happened to you?
 
NealRomeoGolf said:
In this case Charlie airspace. So thanks to subsection D, the answer is no.
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Ok. What are you doing in the Charlie airspace? Taking off from or landing at the primary airport? A satellite airport? Does the satellite airport have weather reporting? Or are you just passing through?
 
Smoke is weird stuff. You're better off being conservative with visibility related to smoke.
 
luvflyin said:
That surprises me. Every Towered airport should have a certified weather observer and they can override the machine. Usually it’s the Tower controllers. What is an airport where this has happened to you?
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It's happened to me twice. Once at KPIE and once at KBKV
 
Salty said:
It's happened to me twice. Once at KPIE and once at KBKV
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I just got off the phone with KBKV Tower. I found out what I expected to. There’s no NWS observer there so the controllers are LAWRS Certified. They can supplement the ASOS and call the Ceiling and visibility. He said they do it all the time, especially in the mornings. There was probably something else other than just what you saw that limited VFR
 
luvflyin said:
I just got off the phone with KBKV Tower. I found out what I expected to. There’s no NWS observer there so the controllers are LAWRS Certified. They can supplement the ASOS and call the Ceiling and visibility. He said they do it all the time, especially in the mornings. There was probably something else other than just what you saw that limited VFR
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Weird. The guy in the tower said wait a few for the station to update, so I did, and called him back and he cleared me out.
 
NealRomeoGolf said:
So if I can see 5 miles and an AWOS is reporting 2 miles and I don't have an instrument rating, am I illegal?
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At Boise or at any airport with airspace formerly known as a control zone, you can not take off or land, or enter the traffic pattern, if the reported ground visibility isn't 3 miles. Any other operation, it is only flight visibility that matters.

Note that the ground visibilities are in statute miles usually (though this won't get you from 7 to 10).
 
What about requesting special VFR? Not recommending it but if you are convinced a local phenomena is causing the restriction to visibility it is an option except where prohibited.
 
Arnold said:
What about requesting special VFR? Not recommending it but if you are convinced a local phenomena is causing the restriction to visibility it is an option except where prohibited.
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Another thing I found interesting is the same guy said “there are other options” but wouldn’t say what they were. I’m assuming special vfr and ifr are what he was referring to. I was in no hurry so I just waited a few.
 
iamtheari said:
Smoke is weird stuff. You're better off being conservative with visibility related to smoke.
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I'm sure it can be. But what I experienced yesterday was much ado about nothing. I had my outs ready though.
 
IIRC controllers are not allowed to suggest Special VFR or IFR. You must specifically request them.
 
luvflyin said:
Ok. What are you doing in the Charlie airspace? Taking off from or landing at the primary airport? A satellite airport? Does the satellite airport have weather reporting? Or are you just passing through?
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Yesterday I was landing at the primary Charlie. Monday I will be taking off from the primary Charlie.
 
Salty said:
Weird. The guy in the tower said wait a few for the station to update, so I did, and called him back and he cleared me out.
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Just a few minutes. Probably didn’t want to do a ‘special’ right then knowing the hourly was coming up in just few minutes. He still could have though.
 
NealRomeoGolf said:
Yesterday I was landing at the primary Charlie. Monday I will be taking off from the primary Charlie.
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Then it’s reported ground visibility like you said. In your you got 5 but they got 2, you wouldn’t have become ‘illegal’ until you entered the traffic pattern. But that would be a moot point because they wouldn’t have given you authorization to get that far
 
Everything is automated now. At my airpatch, weather has lasers at each end of the runway pointed straight up in order to get the ceiling height. On several occasions there was ONE rogue cloud directly over the laser which recorded a ceiling of something to every human as being ridiculous since the sky was otherwise clear.

Gone are the days when a weather observer would step out of his shop with their clipboard, stand on the yellow footprints and take observations of the sky and then go back in and type up the observation to be recorded on the ATIS.

I had a chief controller in Korea that walked up to the tower cab and asked the visibility. We told him a mile and a half. He looked around and told us "bull***t, I can see a mile and a half that way and a mile and half that way, visibility is three miles, we're VFR."

He was totally serious.
 
Timbeck2 said:
Everything is automated now. At my airpatch, weather has lasers at each end of the runway pointed straight up in order to get the ceiling height. On several occasions there was ONE rogue cloud directly over the laser which recorded a ceiling of something to every human as being ridiculous since the sky was otherwise clear.

Gone are the days when a weather observer would step out of his shop with their clipboard, stand on the yellow footprints and take observations of the sky and then go back in and type up the observation to be recorded on the ATIS.

I had a chief controller in Korea that walked up to the tower cab and asked the visibility. We told him a mile and a half. He looked around and told us "bull***t, I can see a mile and a half that way and a mile and half that way, visibility is three miles, we're VFR."

He was totally serious.
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ROTFL
 
Just got back from a similar flight: KLXT - KIDA - KRNO - KGCN - KLXT.

The smoke got so bad into Reno that I lost sight of the ground (at 4000 AGL).
However, the ATIS said visibility 3 mi, but clear below 12,000.
I ended up IFR into there.

I don't think it's just vertical vs horizontal.
I think it's looking for (bouncing off?) clouds.
 
Salty said:
I've been "stuck" at towered airports when there's a single low cloud just above the weather station and the rest of the sky is clear. They can't let you out VFR until the station has high enough ceilings, even though we could all see it was perfectly safe.
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Happens all the time. Murphy's Law says all ASOS/AWOS stations must be located on the foggiest part of the airport, and our airport is no exception. There have been lots of times an isolated low level fog bank formed right in the area around the ASOS and caused it to report 1/4 mi and 100 foot ceiling, when the airfield itself was clear and 10 miles.
 
luvflyin said:
Just a few minutes. Probably didn’t want to do a ‘special’ right then knowing the hourly was coming up in just few minutes. He still could have though.
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I'm not sure that completely explains it. He had just let me in VFR less than 30 minutes prior.
 
Salty said:
I've been "stuck" at towered airports when there's a single low cloud just above the weather station and the rest of the sky is clear. They can't let you out VFR until the station has high enough ceilings, even though we could all see it was perfectly safe.
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Did they deny an SVFR request?
 
The visibility in a METAR is prevailing visibility. How that is determined varies based on the specifics of each airport.

"Prevailing visibility is the horizontal distance over which objects or bright lights can be seen and identified over at least half of the horizon circle."
​
 
Larry in TN said:
The visibility in a METAR is prevailing visibility. How that is determined varies based on the specifics of each airport.

"Prevailing visibility is the horizontal distance over which objects or bright lights can be seen and identified over at least half of the horizon circle."
​
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That's fine if you got Timbeck2 or someone like him in the tower making the weather observations. If you're at a field where the observation is done via an AWOS, you get the visibility prevailing between the headsd of the unit which are all within about four feet of each other.
 
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