How do you judge VMC?

LongRoadBob

LongRoadBob

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Im not even sure what to ask here, but when weather is marginal how do you exeperinced VFR pilots judge the viability, if you can fly?

My CFI started right at the beginning of wanting me to judge if we could fly, but I just plain don’t have enough experience, all I can really do is tell what I think t this point.

So on the evening before the flight I’m looking at the TAFs, Metars, and other weather info.
Then comes the morning and I look up and see scattered clouds. I know my job/task is to find out the heights of those cloud, and the density, and all that, but I have a very hard time understanding if I am able to fly within the VFR requirements. If I can avoid coming too close either above, below or to the sides of clouds.

It would be a huge help for me, and I am guessing a lot of other students, to hear the basic though process you experienced pilots use to judge if you can fly...

Is that too vague?
 
One tip, if you are based at a busy training field is; if no one else is flying - there might be a reason.
That is not meant to be flippant; many such accidents happened where no one else was flying (except for the IFR guys), in fact the guys staying on the ground often urged the accident pilot to stay.

Another; even now I am not ashamed to ask other pilots what they think of the weather. Use all available resources.
 
Bare bones VMC is 3 mi visibility and 1,000 foot ceiling. Not saying necessarily smart VMC, but it can be done legally anywhere. Anything beyond that comes down to personal minimums. 3 mile visibility can be quite startling if you've never done it. Same with having to fly 500 foot AGL to stay the required 500 feet below a cloud base. For a local pleasure flight, I usually want closer to double that to be 100% comfortable, 6 miles and 2000 foot. Going somewhere VFR, it would depend on how far I'm going and my familiarity with the area.

Granted, I'm also instrument rated, so file IFR and go a lot of times. But even IFR I have personal minimums, I'm not about to fly in 200 feet and 1/2 mile in a single engine airplane. That is just a level of risk I am not personally comfortable with.

All of this discussion falls under Aeronautical Decision Making, and making safe decisions based on your capabilities, experience, and comfort. Some people are most accepting of risk and push minimums, others are more risk adverse. I lean towards the risk adverse. With weather, I always want a plan B.
 
I would try to think if you can be in suitable airspace to practice that your are VFR for what your plan is.
Can you stay below. Or get above. What are predictions for clearing vs accumulating?
Ceilings a bit low and overcast. Probably can just stay in pattern and do pattern work as a student.
If lightly scattered or few and they look small probably can easily get above.
Think about the time of day as well. Morning things stay calmer but this time of year the afternoon can start to develop some stuff.
In the beginning it can be hard to get a feel for what is happening. Study weather. Pick up a book. Look at it at times your not flying just for fun so you can pay more attention to what is happening. I find reading the weather “discussions” in ForeFlight to be invaluable. I’m sure you can find them around without FF.
 
For pattern work 1500-3. For the practice area 2500-5. For XC 5000-5.

All visibilities are flight visibility and ceilings are AGL. Mist, smoke, haze are weather items that reduce flight visibility.
 
Keep in mind your CF I is wanting you to get used to how to make these decisions on your own. I doubt they are gonna let you fly with him or solo in very questionable weather. Because remember they are not always going to be there to make the decision for you. I would get used to making that decision on your own, but keep in mind be prepared to be able to discuss it with regulations in mind as well as personal minimums
 
Find a visible landmark (antenna? Tower?) that is 3-4 miles cr9 the field. If you can see it, you have visibility. Can't judge cloud height accurately from the ground, you'll need a report from somewhere--ATIS, ASOS, AWOS, pilot reports, etc.
 
Hank S said:
Find a visible landmark (antenna? Tower?) that is 3-4 miles cr9 the field. If you can see it, you have visibility. Can't judge cloud height accurately from the ground, you'll need a report from somewhere--ATIS, ASOS, AWOS, pilot reports, etc.
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:yeahthat:

I have a tower on a hill near my home 'drome. If I can see the hill, I have visibility. If I can see the tower, I have ceiling.
 
Hank S said:
Find a visible landmark (antenna? Tower?) that is 3-4 miles cr9 the field. If you can see it, you have visibility. Can't judge cloud height accurately from the ground, you'll need a report from somewhere--ATIS, ASOS, AWOS, pilot reports, etc.
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If you are standing on the ground and looking at an antenna 3-4 miles away you established the ground visibility.

To determine the cloud bases find the difference between the surface temperature and the dew point. This value is known as the "spread". Divide the spread by 2.5 (if temperatures are in °C), then multiply by 1000. This will give the altitude of the cloudbase in feet above ground level.
 
[snarky comment]
If I can't see Pikes Peak, weather is questionable.
[end snarky comment]

Why? Haze, smoke, fog, snow, rain. Any or all.

Same for Long's Peak or Mt Evans.
 
Dean V said:
If you are standing on the ground and looking at an antenna 3-4 miles away you established the ground visibility.

To determine the cloud bases find the difference between the surface temperature and the dew point. This value is known as the "spread". Divide the spread by 2.5 (if temperatures are in °C), then multiply by 1000. This will give the altitude of the cloudbase in feet above ground level.
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Is there a formula like this for figuring out what the tops are for say an overcast layer?? I usually check area forecasts for this but they cover such a large area... would be nice if TAFS would also say what the tops were.
 
Here's what I would have done when I was still a VFR only pilot. I'm not a fan of having hard rules and limits, I prefer guidelines. Every flight is different, the weather is always different, the terrain is always different, the pilot's skill level will change. Playing it safe is always a good choice especially when you're new to this.

Look at the current general(not aviation) forecast, look at the METARs along the area of flight. Look at the TAFs along the area of flight. Look at the radar returns(if any) along or near the route of flight

Winds- do *I* feel safe landing in the current and forecast winds at the intended airport(s) I'll be landing at with some margin for safety if the winds are a bit more than expected? You judge this by knowing what winds you've landed in successfully before and how comfortable you feel in them. This is pretty easy to explore with a CFI on a windy day.

Thunderstorms- noooope, I don't mess with that stuff, if it's a relatively stationary storm and I can stay at least 30 miles out maybe I'll go around it but I prefer to just avoid them altogether. Pop up scattered t-storm conditions are usually a big nope from me even (or especially) IFR

Precipitation- tricky to predict but anything more than a few light green patches along the route is something to avoid. If temps are below freezing just don't.

Ceilings/clouds- 1500-3 is good enough for staying in the pattern. Beyond that it gets more complex, one has to take terrain into account in some areas. Flying around here in the mostly flat midwest I'm ok with making a short hop or flying towards improving conditions for a short period under a 2,000' ceiling as long as I'm confident said ceiling is not getting lower(this is where monitoring the METARs for a while to see what's happening and knowing the TAF is important). By short I mean less than 30 minutes. For going any significant distance I really want to be at least 3,000AGL above any terrain along the route and at least 1,000' below the clouds so around a 4,000' ceiling in flat areas. I'll determine this again primarily by looking at current actual METAR data and TAFs along the route.

For night flight as a new pilot- clear below 12,000 and GPS equipped... with more experience and comfort level those minimums could be a lot less but get experience with the easy stuff first.
 
I’m not super experienced but your CFI is doing you right on this. Flying requires a lot of personal decision making skills. Even if it’s clear forever, do you like the winds? Are you comfortable with VFR on top? One of my first long XC flights I found myself unexpectedly VFR on top. How about being prepared to land if the wx turns sour? Happened on another long XC when clear forever turned to mush within minutes. Thankfully I had an airport just behind me so 180 and landed. That was like a 5 hour wait for things to improve. Oh the winds. Even if it’s clear forever will you fly with huge gusting winds? I chose to once, just local practice area. One pilot was talking to the local bravo approach control about banging his head pretty hard. Flew once with a CFI in a checkout of a new aircraft, with deteriorating wx. We were trying to get to the practice field but it went from forecasted wonderful VFR to do not touch. On the way back while dodging clouds and requesting a lower altitude he was asking me if I would fly in these conditions solo. That was a big nope.

It will only get more difficult after you are on your own. Be honest with your CFI. If the clouds or winds are outside your comfort level tell him/her. They may say otherwise but it’s a very good topic of conversation.
 
Dean V said:
For pattern work 1500-3. For the practice area 2500-5. For XC 5000-5.

All visibilities are flight visibility and ceilings are AGL. Mist, smoke, haze are weather items that reduce flight visibility.
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Thanks all, this is what I was hoping for with information.
One thing though, you say it is AGL, but weather reports TAF, METARs are all in MSL I thought. You are pointing out that I need to think in AGL, correct?

I understood that the CFI was trying to get me to start right away with making decisions and of course would correct me if I was wrong in my assessment. I use the reports, but I guess I just need more experience of seeing, when it is scattered clouds etc. what that really means as far as ability to stay the required distances from them. I imagined that sometimes with the information a pilot might think it is doable, but end up having to “slalom” all over trying to avoid clouds and find out it isn’t a good day to fly after all.

That a great point also from benflyguy about adjusting the plan, doing pattern work if it is low ceilings.
I’d still have to be able to fly to another airport since ours doesn’t allow touch and go, or pattern work.

This was all very helpful.
 
LongRoadBob said:
Thanks all, this is what I was hoping for with information.
One thing though, you say it is AGL, but weather reports TAF, METARs are all in MSL I thought. You are pointing out that I need to think in AGL, correct?

I understood that the CFI was trying to get me to start right away with making decisions and of course would correct me if I was wrong in my assessment. I use the reports, but I guess I just need more experience of seeing, when it is scattered clouds etc. what that really means as far as ability to stay the required distances from them. I imagined that sometimes with the information a pilot might think it is doable, but end up having to “slalom” all over trying to avoid clouds and find out it isn’t a good day to fly after all.

That a great point also from benflyguy about adjusting the plan, doing pattern work if it is low ceilings.
I’d still have to be able to fly to another airport since ours doesn’t allow touch and go, or pattern work.

This was all very helpful.
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Correct.
Think of it this way, if the field is at 1000' MSL and the METAR is reporting overcast at 500', then the clouds would be underground.
So yes, those reports are always AGL, not MSL.
 
"If there's a question, there's no question."

If I'm not sure if it's a good idea, I don't do it.
 
A great way to force your brain into the proper decision making mode:

Think of every decision as a bet. In other words, 'would I bet $10,000 the decision I'm about to make is the correct one?'
If the answer is no, the problem is one of two things... 1.) You don't have enough information to make a proper judgment and decision. The solution is to get more information.
2.) It's the wrong decision.

it's interesting what happens to your brain when you start thinking like this. Seriously changes your perspective on the decision making process.

Sent from my Pixel 2 XL using Tapatalk
 
What if I have a gambling addiction?
Is that really sound advice? :D
 
EdFred said:
What if I have a gambling addiction?
Is that really sound advice? :D
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Hehe. Sure it would! You just have to make the stakes for losing unpalatable.

Sent from my Pixel 2 XL using Tapatalk
 
I don't do poor visibility, unless I know the terrain and the weather patterns enough to believe that it's no problem. It's too easy to get into a situation where the visibility decreases suddenly and you lose contact with the ground. That's illegal and unsafe. If I can see the horizon though, I am not too shy to squeeze into a mail slot under rather low ceilings (over unpopulated areas and flat terrain). Also, I never try to beat a deteriorating weather. I can try and beat the motion of fronts and the like, where I can see 30 miles on one side, and their location and movements agree with the prog chart. But if clouds are coming down, I land immediately.

Last Tuesday I tried to get into Denver and after a 5 hour flight had to turn back from halfway between Springs and the destination. Centennial and FTG were 800 broken. I overnighted in Limon, just 40 minutes short. On Wednesday, Centennial started to report clear. I took off and had to return, because it closed completely. On a 40 minute flight! I stayed at Limon for another couple of hours until another window at Centennial.
 
Here is my basic go/no-go question: What is my plan B? If the answer to that question is not adequate to accomplish the mission, then I do not fly.

To answer that basic question, a few others come up:
* How much time do I have to accomplish the mission?
* What do all the available, relevant weather reports say?

Once in the air, judging distance from clouds in any direction is hard. Nobody is good at this. Assume your estimates of distance are off by 75%. Visibility is easier if you know what to look for. Here in the Great Plains, there is a 1-mile square grid of section line roads. So it’s easy to count section lines and see how many miles of visibility you have. You can also use landmarks measured from where you are and, if you’re accurate in your position, know whether you are in decreasing visibility.

Personal minimums should respect all of your limitations. If you’re just getting started on judging flight visibility, then taking off in reported conditions of 5 miles visibility would be a bad idea since you won’t be able to tell that it’s closing in to 3 miles, then 1 mile, then zero. If you are not instrument rated, current, and proficient or you are not in an instrument qualified airplane, then flying into reported legal VFR minimum conditions is a bad idea because you don’t have a backup plan (filing IFR in the air) if they close in on you.
 
iamtheari said:
Once in the air, judging distance from clouds in any direction is hard. Nobody is good at this. Assume your estimates of distance are off by 75%. Visibility is easier if you know what to look for. Here in the Great Plains, there is a 1-mile square grid of section line roads. So it’s easy to count section lines and see how many miles of visibility you have. You can also use landmarks measured from where you are and, if you’re accurate in your position, know whether you are in decreasing visibility.
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In the air, you can often judge your distance from clouds by looking at shadows.

To estimate visibility if you’re not someplace with section lines, look ahead of you and note some terrain feature as it just comes into view, time how long it takes to get to that terrain feature, and you can determine what the visibility was “back there”. When visibility is minimal, I do that fairly regularly.
 
I will say that "three and one thousand" is simply no fun (and conflicts with pattern altitude). If I'm sightseeing, seven or eight miles and 2K on the ceiling, adjusted by what I observe.
 
zaitcev said:
I don't do poor visibility, unless I know the terrain and the weather patterns enough to believe that it's no problem. It's too easy to get into a situation where the visibility decreases suddenly and you lose contact with the ground. That's illegal and unsafe. If I can see the horizon though, I am not too shy to squeeze into a mail slot under rather low ceilings (over unpopulated areas and flat terrain). Also, I never try to beat a deteriorating weather. I can try and beat the motion of fronts and the like, where I can see 30 miles on one side, and their location and movements agree with the prog chart. But if clouds are coming down, I land immediately.

Last Tuesday I tried to get into Denver and after a 5 hour flight had to turn back from halfway between Springs and the destination. Centennial and FTG were 800 broken. I overnighted in Limon, just 40 minutes short. On Wednesday, Centennial started to report clear. I took off and had to return, because it closed completely. On a 40 minute flight! I stayed at Limon for another couple of hours until another window at Centennial.
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Ah yes, Limon. Did a quick FTG - LIC a few years ago and got stuck in Limon when the unforecasted weather attacked. I kept calling back to FTG about the weather. Finally, after a few hours, I could get back. I've also been stuck in Colorado Springs, a mere 50 nm from home at FTG. Parked the cherokee, borrowed a car and drove home. Came back the next day and flew back.Unfortunately, no cars at Limon.
 
zaitcev said:
Last Tuesday I tried to get into Denver and after a 5 hour flight had to turn back from halfway between Springs and the destination. Centennial and FTG were 800 broken. I overnighted in Limon, just 40 minutes short. On Wednesday, Centennial started to report clear. I took off and had to return, because it closed completely. On a 40 minute flight! I stayed at Limon for another couple of hours until another window at Centennial.
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5 Hours? From ABQ area to APA? Even in my slow cherokee, it's only 3 hours. Coming from someplace else?
 
midwestpa24 said:
Bare bones VMC is 3 mi visibility and 1,000 foot ceiling. .
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That's only partially true (you forgot the other cloud clearance rules) and only true down low in the surface area. Elsewhere it might be a mile and clear of clouds or it might be 5 miles and 1000/1000/1 and ceiling is irrelevant.
 
LongRoadBob said:
Im not even sure what to ask here, but when weather is marginal how do you exeperinced VFR pilots judge the viability, if you can fly?
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How do I judge the viability of VFR flight? I don't want to be flippant here but I get a weather briefing. Actually that's not exactly true. Before I get a briefing I look online at all the data that I will get when I get an official weather briefing. I pull the TAFs and METARS. I also look at the prog charts of course.

One of the things I do (but certainly not the only thing) when I'm looking at all that data is to use the TAF to figure out the trend of the forecast i.e. is the weather supposed to improve or go downhill and on what timeline. Then I look at METARS from the previous few hours to see they match up with what the TAF was predicting for that time. From that I get an idea of if the weather is sticking to forecast or not. If the forecast is for better vis and ceilings as the day goes on, are the METARS showing that?

If its marginal but forecast to improve as the day goes on and the METARS are showing that ceilings and visibility are trending up as predicted, then I go get and official briefing and make sure everything still lines up there. If conditions are not improving as predicted, I'd wait it out to be on the safe side.
 
A mile and clear of clouds where I live. At 100 mph that's not a comfortable scenario. You need to know where you are and what's in front of you. Especially when maintaining 1 mile means your topping out at 400-500'.
 
flyingron said:
That's only partially true (you forgot the other cloud clearance rules) and only true down low in the surface area. Elsewhere it might be a mile and clear of clouds or it might be 5 miles and 1000/1000/1 and ceiling is irrelevant.
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Oh I didn't forget, but I do not consider 1 mile and clear of clouds VMC for my own personal use. Even the FAA generally accepts anything less than 3 mi and 1000 feet to be IMC conditions, even if the airspace requirements allow for it.
 
murphey said:
5 Hours? From ABQ area to APA? Even in my slow cherokee, it's only 3 hours. Coming from someplace else?
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I moved to Austin 2 years ago. And I had to deviate south to Clovis for weather. Came through Raton.
 
For lessons I established personal minimums. Then checked the weather. Forecast, prog charts, tafs, metars, radar. Before I leave for the flight, I check the tafs and metars, usually in the form of a briefing. Your instructor wants you to cancel flights when necessary, it's part of developing your weather and flight awareness. What I would do on the questionable days is first tell my instructor what I would do in the situation were I flying alone. Most of the time, when conditions were below my mins, I would say cancel. If it was questionable, then I would take into account the conditions and the forecast. More importantly what were the conditions doing relative to the forecasts. Is the forecast accurate and calling for clearing? Then I would probably go to the airfield and make the decision there. That would be my discussion for my minimums. Then we would talk about the instructor minimums. Which generally are lower than mine. You are flying VFR, after a few lessons and discussing it, you should have an idea of what his tolerance is and be able to decide if you can go or not. The important thing is not to worry about being right every time in the beginning, but to understand why a go/ no go decision is made and be able to differentiate between your mins and his mins. After a few times you should get an I concur response with your decision. That said, sometimes you'll get an I think we are ok, let's do it. When that happened to me, I would do it, it's a great experience to see what marginal conditions are really like. It's not a nice feeling when ceilings are lower than you thought or visibility is worse than you had planned on when that instructor is not next to you. Don't be afraid to make the call.
 
midwestpa24 said:
Oh I didn't forget, but I do not consider 1 mile and clear of clouds VMC for my own personal use. Even the FAA generally accepts anything less than 3 mi and 1000 feet to be IMC conditions, even if the airspace requirements allow for it.
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Got a reference for that? If you’re referencing what I think you are, then you’re also saying it’s not VFR unless it’s 3000 & 5 or better.

(I’m picking nits here...I’ve gotten a “full standard brief” of “It's IFR, you cant go.”)
 
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MauleSkinner said:
Got a reference for that? If you’re referencing what I think you are, then you’re also saying it’s not VFR unless it’s 3000 & 5 or better.

(I’m picking nits here...I’ve gotten a “full standard brief” of “It's IFR, you cant go.”)
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Just referencing the definitions of VFR, MVFR, and IFR. For personal use, MVFR doesn't usually bother me much. For that matter IFR doesn't anymore either, as long as I'm in a properly equipped aircraft I'm familiar with.
 
midwestpa24 said:
Just referencing the definitions of VFR, MVFR, and IFR. For personal use, MVFR doesn't usually bother me much. For that matter IFR doesn't anymore either, as long as I'm in a properly equipped aircraft I'm familiar with.
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keep in mind that those are weather descriptors that have nothing to do with it actually being VFR or IFR. “IFR” weather simply means I’ve got an 80% chance of completing my VFR flight without deviations.
 
As I mentioned, I do always read weather reports, METAR, TAF, NOTAMS, etc, and have been working on looking for trends to build up experience.

Mainly what I was looking for, and many here have posted very helpful ways to evaluate this, is to get a mental picture of what it is going to be like to fly on a day with some weather. Some of this I will just have to experience. Sometimes, maybe most, clouds for instance are contained at certain altitudes, or range of alt, and other times varied throughout, peppered all over and where a pilot might have to change course a lot to avoid.

Also, so far I find it very hard to judge distance from clouds. I hope this comes with time, but without feedback as to what the distances really were (verification somehow) I can’t really improve on that.

Not sure how I would judge, except someone here mentioned shadows on the ground, where I could get an idea when I know the ground distance, can see the clouds shadow and my own shadow.

But there were many many helpful posts here. Thanks!
 
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