Ice warning - in VMC, below freezing level
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Rather than get bogged down in arguing the minutia of a particular aspect of meteorological theory (which, in any event, in the absence of an expert meteorologist is unlikely to be resolved satisfactorily), let me try and expand the issue.
Like many diligent pilots, I’ve expended vast amounts of effort over the years attempting to assimilate meteorology theory, not only for private and professional pilot qualifications, but also from the pragmatic position that herein lie many issues that can bust my a@se!
Like others, I regularly use my so-called knowledge of the theory to take a view on the particular conditions I’m going to encounter. That my predictions aren’t always borne out in practice is hugely more often than not, I believe, down to my lack of real understanding of the complexities of the subject than it is due to the fallibilities of the theory.
My experience, gained over three+ decades, is that aviation met. forecasting has got progressively better (thanks, presumably, to the enormous computing power increasingly employed), and is now pretty damn good. Where ‘actuals’ vary from forecast, it seems likely to me that this is not usually a question of erroneous theory about what happens given a particular set of conditions, but is more to do with the vagaries of the precise timing of occurrence of those conditions.
Where it is well less than perfect, however, is in the detail dissemination of the weather information. Get to talk to a real, live forecaster (increasingly rare these days), and you may well get a more useful and accurate picture of the weather as it is likely to affect you. Economics (and, perhaps, legal considerations) have determined that, in respect of en-route forecasts in particular, we have to live with more generalised forecasts that don’t give us what we really need, despite the theory being adequate for the task.
Other GA IFR pilots of non-pressurised aircraft that populate the FL100 to FL150 levels will be well familiar with this problem. Where will the cloud tops be? … dunno, there’s much less guidance available for your route than a real forecaster could give you (and, actually, less still now the new Met Form 215 doesn’t even bother with altitudes of 10,000 ft and above). Will I get moderate or severe icing in the cloud if the temperature is below 0 degC? … absolutely always, according to the Met Form 215, despite the fact that, more times than not in stratiform cloud, you won’t. Embedded Cb's? ... TEMPO, oh, that's helpful. And so on.
Now, if only we had real-time weather available in the cockpit – what a massive advance in safety and operational capability that would provide. Sadly, for us in Europe, the fabulous advance that Nexrad has offered in the USA will remain but a dream. Oh well, never mind, we can always look forward to the ultra-expensive benefits of Galileo instead … if anybody can recall exactly what they are.
Like many diligent pilots, I’ve expended vast amounts of effort over the years attempting to assimilate meteorology theory, not only for private and professional pilot qualifications, but also from the pragmatic position that herein lie many issues that can bust my a@se!
Like others, I regularly use my so-called knowledge of the theory to take a view on the particular conditions I’m going to encounter. That my predictions aren’t always borne out in practice is hugely more often than not, I believe, down to my lack of real understanding of the complexities of the subject than it is due to the fallibilities of the theory.
My experience, gained over three+ decades, is that aviation met. forecasting has got progressively better (thanks, presumably, to the enormous computing power increasingly employed), and is now pretty damn good. Where ‘actuals’ vary from forecast, it seems likely to me that this is not usually a question of erroneous theory about what happens given a particular set of conditions, but is more to do with the vagaries of the precise timing of occurrence of those conditions.
Where it is well less than perfect, however, is in the detail dissemination of the weather information. Get to talk to a real, live forecaster (increasingly rare these days), and you may well get a more useful and accurate picture of the weather as it is likely to affect you. Economics (and, perhaps, legal considerations) have determined that, in respect of en-route forecasts in particular, we have to live with more generalised forecasts that don’t give us what we really need, despite the theory being adequate for the task.
Other GA IFR pilots of non-pressurised aircraft that populate the FL100 to FL150 levels will be well familiar with this problem. Where will the cloud tops be? … dunno, there’s much less guidance available for your route than a real forecaster could give you (and, actually, less still now the new Met Form 215 doesn’t even bother with altitudes of 10,000 ft and above). Will I get moderate or severe icing in the cloud if the temperature is below 0 degC? … absolutely always, according to the Met Form 215, despite the fact that, more times than not in stratiform cloud, you won’t. Embedded Cb's? ... TEMPO, oh, that's helpful. And so on.
Now, if only we had real-time weather available in the cockpit – what a massive advance in safety and operational capability that would provide. Sadly, for us in Europe, the fabulous advance that Nexrad has offered in the USA will remain but a dream. Oh well, never mind, we can always look forward to the ultra-expensive benefits of Galileo instead … if anybody can recall exactly what they are.
Last edited by Islander2; 15th Mar 2006 at 21:18.
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Probably since America was invented 
The following hits the nail right on the head:
Other GA IFR pilots of non-pressurised aircraft that populate the FL100 to FL150 levels will be well familiar with this problem. Where will the cloud tops be? … dunno, there’s much less guidance available for your route than a real forecaster could give you (and, actually, less still now the new Met Form 215 doesn’t even bother with altitudes of 10,000 ft and above). Will I get moderate or severe icing in the cloud if the temperature is below 0 degC? … absolutely always, according to the Met Form 215, despite the fact that, more times than not in stratiform cloud, you won’t. Embedded Cb's? ... TEMPO, oh, that's helpful. And so on.
Actually F215 forecasts icing in all cloud, not just below 0C Very helpful (not).
Fortunately, there is GFS. One gets TAFs/METARs and MSLP and SIGWX charts from the usual aviation weather services, and then looks at GFS for the more detailed stuff. But it's changing, with more websites doing graphical presentations from GFS.
The following hits the nail right on the head:
Other GA IFR pilots of non-pressurised aircraft that populate the FL100 to FL150 levels will be well familiar with this problem. Where will the cloud tops be? … dunno, there’s much less guidance available for your route than a real forecaster could give you (and, actually, less still now the new Met Form 215 doesn’t even bother with altitudes of 10,000 ft and above). Will I get moderate or severe icing in the cloud if the temperature is below 0 degC? … absolutely always, according to the Met Form 215, despite the fact that, more times than not in stratiform cloud, you won’t. Embedded Cb's? ... TEMPO, oh, that's helpful. And so on.
Actually F215 forecasts icing in all cloud, not just below 0C
Very helpful (not).Fortunately, there is GFS. One gets TAFs/METARs and MSLP and SIGWX charts from the usual aviation weather services, and then looks at GFS for the more detailed stuff. But it's changing, with more websites doing graphical presentations from GFS.
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IO540
You appear to have shifted your ground.
If you are now arguing that we don't have the same richness of weather data in Europe that is available in the US, then few would disagree with you.
Your previous assertion, which appeared to suggest that real-world weather disobeys basic met principles more often than not, has rather less going for it.
2D
You appear to have shifted your ground.
If you are now arguing that we don't have the same richness of weather data in Europe that is available in the US, then few would disagree with you.
Your previous assertion, which appeared to suggest that real-world weather disobeys basic met principles more often than not, has rather less going for it.
2D
Avoid imitations
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"The Dry Adiabatic Lapse Rate (DALR) is actually 3 degC per 1,000 feet, and is the rate at which a parcel of unsaturated air will change temperature (solely due to change of pressure) when moved vertically through the atmosphere.
It is the Environmental Lapse Rate (ELR) that, in the International Standard Atmosphere, is 2 degC (well, actually 1.98 degC) per 1,000 feet. This is the variation in temperature with height within a non-moving column of air ... and in real life as opposed to the ISA may be greater or less than the DALR. Air forced to rise where the air mass ELR is greater than the DALR will continue to rise (unstable air mass).
The Saturated Adiabatic Lapse Rate (SALR) is the rate at which a parcel of air that has become saturated (i.e. visible moisture) will change temperature if it is forced to move vertically. Its value is half that of the DALR since latent heat is released as condensation occurs. The SALR has no bearing, as far as I'm aware, on the height of the cloud base."
---------------------------------
I don't think that's quite correct.....
Surely,
DALR = 3 degrees / 1000 ft
SALR = 2 degrees / 1000 ft
Both of the above relate to the ISA.
ELR = somewhere between the two, what you actually get on the day.
It is the Environmental Lapse Rate (ELR) that, in the International Standard Atmosphere, is 2 degC (well, actually 1.98 degC) per 1,000 feet. This is the variation in temperature with height within a non-moving column of air ... and in real life as opposed to the ISA may be greater or less than the DALR. Air forced to rise where the air mass ELR is greater than the DALR will continue to rise (unstable air mass).
The Saturated Adiabatic Lapse Rate (SALR) is the rate at which a parcel of air that has become saturated (i.e. visible moisture) will change temperature if it is forced to move vertically. Its value is half that of the DALR since latent heat is released as condensation occurs. The SALR has no bearing, as far as I'm aware, on the height of the cloud base."
---------------------------------
I don't think that's quite correct.....
Surely,
DALR = 3 degrees / 1000 ft
SALR = 2 degrees / 1000 ft
Both of the above relate to the ISA.
ELR = somewhere between the two, what you actually get on the day.
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2D in my Trevor Thom statement I was referring to the lapse rates being well off ISA figures, most of the time. I think that's correct.
Of course, the real weather always obeys met principles precisely, doesn't it Question is, which ones?
Of course, the real weather always obeys met principles precisely, doesn't it
Question is, which ones?
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Originally Posted by ShyTorque
Surely,
DALR = 3 degrees / 1000 ft
SALR = 2 degrees / 1000 ft
Both of the above relate to the ISA.
ELR = somewhere between the two, what you actually get on the day.
DALR = 3 degrees / 1000 ft
SALR = 2 degrees / 1000 ft
Both of the above relate to the ISA.
ELR = somewhere between the two, what you actually get on the day.
DALR ... correct.
SALR ... almost always incorrect, but unlike DALR it is a variable and depends on the amount of vapour condensed. At low levels in temperate climates it is around 1.5 degC per 1000 feet, which is the figure that tends to be used in the UK. It can be around 1 degC in the warm saturated air of tropical regions and can be (here's where your value may on the odd occasion be correct) 2 degC or more per 1000 feet where the temperature is below freezing.
DALR and SALR relate to the ISA ... no they don't!
ELR is somewhere between DALR and SALR ... not necessarily, indeed if this were the case unsaturated air could never be unstable - and that would transform our weather patterns!
Avoid imitations
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OOPssorry! Yes, Islander, of course you're quite correct. The ELR can be above, below or in between the DALR or the SALR lines.
Sixty lashes with a rolled up Tephigram for me!
ELR>DALR>SALR = Absolute Instability
DALR>ELR>SALR = Conditional Stability
DALR>SALR>ELR = Absolute Stability
DALR = rate of change of T within a vertical current of unsaturated air; this never changes and is reversible on ascent/descent.
SALR = rate of change within a vertical current of saturated air. This does not change from day to day but it does change with height. It is only reversible on ascent /descent if no water (precipitation) has been lost.
ELR = What you see is what you get.
That better?
BTW, reading back to the original question; formation of ice on an aircraft can occur from clear air, if the temperature is below the dew point and below 0 C, i.e. by sublimation.
Sixty lashes with a rolled up Tephigram for me!
ELR>DALR>SALR = Absolute Instability
DALR>ELR>SALR = Conditional Stability
DALR>SALR>ELR = Absolute Stability
DALR = rate of change of T within a vertical current of unsaturated air; this never changes and is reversible on ascent/descent.
SALR = rate of change within a vertical current of saturated air. This does not change from day to day but it does change with height. It is only reversible on ascent /descent if no water (precipitation) has been lost.
ELR = What you see is what you get.
That better?
BTW, reading back to the original question; formation of ice on an aircraft can occur from clear air, if the temperature is below the dew point and below 0 C, i.e. by sublimation.
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The question, chaps, is whether all this knowledge helps you in practice, with real flight planning.
Can you point me to a website where I can look up all these values, for different levels along a specified route?
No matter how much one understands met theory, one cannot, IMV, statistically significantly beat the forecasters who have all the data at their fingertips (including data which they don't publish, or do publish but only to fee paying customers) and who do this all day for a living.
I also don't think one can (statistically significantly) even beat totally dumb button pushing on a GFS website like e.g. http://www.arl.noaa.gov/ready/cmet.html.
If somebody with a JAA ATPL tells me they can out-do the pros, I suggest they start up their own weather forecasting company. They would make a lot of money. Or they could offer their services to the UK MO and help all pilots
I know this flies in the face of all the "professional" pilot training, which makes you sit through reams of this stuff, so if I have missed some essential point I would be (seriously) grateful if somebody could explain exactly what I am missing. In detail, so I can learn from it.
Interestingly, the FAA doesn't make pilots learn most of this stuff for the IR, but they don't find it a problem. Is the weather really so much more complicated (but predictable) in Europe?
Can you point me to a website where I can look up all these values, for different levels along a specified route?
No matter how much one understands met theory, one cannot, IMV, statistically significantly beat the forecasters who have all the data at their fingertips (including data which they don't publish, or do publish but only to fee paying customers) and who do this all day for a living.
I also don't think one can (statistically significantly) even beat totally dumb button pushing on a GFS website like e.g. http://www.arl.noaa.gov/ready/cmet.html.
If somebody with a JAA ATPL tells me they can out-do the pros, I suggest they start up their own weather forecasting company. They would make a lot of money. Or they could offer their services to the UK MO and help all pilots
I know this flies in the face of all the "professional" pilot training, which makes you sit through reams of this stuff, so if I have missed some essential point I would be (seriously) grateful if somebody could explain exactly what I am missing. In detail, so I can learn from it.
Interestingly, the FAA doesn't make pilots learn most of this stuff for the IR, but they don't find it a problem. Is the weather really so much more complicated (but predictable) in Europe?
Here's the sounding for Albermarle which is the nearest available. I'd imagine that the sounding for Blackpool, furtehr west, would have looked even more pronounced.
Note the layer between 850 hPa (5000 ft) and 920 hPa (abut 2700 ft) that gives the precip a chance to become liquid before plunging into the freezing air below.
Code:
03238 Albermarle Observations at 12Z 13 Mar 2006
-----------------------------------------------------------------------------
PRES HGHT TEMP DWPT RELH MIXR DRCT SKNT THTA THTE THTV
hPa m C C % g/kg deg knot K K K
-----------------------------------------------------------------------------
1005.0 141 0.6 -3.4 75 2.97 120 8 273.4 281.6 273.9
1002.0 163 0.2 -4.2 72 2.81 127 12 273.2 281.0 273.7
1000.0 177 0.0 -4.5 72 2.75 132 15 273.1 280.8 273.6
993.0 233 -0.6 -4.6 74 2.74 150 25 273.1 280.8 273.6
957.0 527 -3.5 -5.3 87 2.70 164 26 273.1 280.6 273.5
941.0 660 -4.6 -5.6 93 2.69 170 26 273.3 280.8 273.7
939.0 677 -4.7 -5.6 93 2.69 172 26 273.3 280.9 273.8
925.0 795 -4.9 -5.7 94 2.71 185 29 274.3 281.9 274.7
923.0 812 -4.9 -5.6 95 2.74 187 30 274.5 282.2 274.9
917.0 864 0.2 -1.8 87 3.68 195 31 280.2 290.6 280.8
913.0 899 3.6 0.8 82 4.46 195 31 284.0 296.8 284.8
908.0 944 3.6 -0.2 76 4.17 194 31 284.5 296.5 285.2
852.0 1457 0.3 -4.0 73 3.36 190 33 286.3 296.1 286.9
850.0 1476 0.2 -4.1 73 3.33 190 33 286.3 296.1 286.9
845.0 1523 -0.1 -4.2 74 3.33 191 32 286.5 296.3 287.1
829.0 1676 -0.5 -5.0 71 3.18 195 27 287.7 297.1 288.2
813.0 1832 -0.9 -5.9 69 3.04 213 22 288.8 297.9 289.4
811.0 1852 -1.1 -5.9 70 3.05 215 21 288.9 297.9 289.4
782.0 2141 -3.7 -6.0 84 3.14 220 17 289.1 298.4 289.6
779.0 2171 -3.9 -6.1 85 3.13 220 17 289.2 298.5 289.7
721.0 2779 -7.7 -7.8 99 2.96 235 21 291.5 300.4 292.0
701.0 2997 -9.4 -9.4 100 2.68 240 23 291.9 300.1 292.4
700.0 3008 -9.5 -9.5 100 2.67 240 23 291.9 300.0 292.4
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I wonder if anybody has done a comparison between the forecast skew-t data and the (just past) actual skew-t data. It would be a very interesting exercise, for skew-t diagrams contain so much useful info.
One would assume the GFS weather model is calibrated using the actual ascents.
One would assume the GFS weather model is calibrated using the actual ascents.
Why do it if it's not fun?
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This thread now contains a vast wealth of information - some of which I probably knew once but have forgotten, some of which is new information for me. Without a doubt, I am now significantly more experienced and more educated in this area (but still have loads more to learn too!)
One thing which is very good to see (at least, from a personal point of view it's good; from a professional point of view it's quite disappointing) is that I'm certainly not the only person on this forum whose understanding of this particular aspect of met isn't as thorough as it could be!
FFF
----------------
One thing which is very good to see (at least, from a personal point of view it's good; from a professional point of view it's quite disappointing) is that I'm certainly not the only person on this forum whose understanding of this particular aspect of met isn't as thorough as it could be!
FFF
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Just to put something to bed...Total beginner hit the nail on the head with regard to the 737 question..
I drive them, and they aren't particularly prone to icing. (Yesterday was another thing, the ice build up on the wing was quite another thing). Mostly due to the fact that apart from the last moments we drive them about 250 kts to 320 knots, so the the temp rise due to the ram effect will keep the leading edges warm enough to keep most of the ice away (in our temperate climate). We do have heated windscreens, but the heat doesn't do the whole windscreen so you get little patches of ice build up on the edges that are noticeable. Also there is a windscreen wiper nut that we use to observe ice build up, so they would have been aware. I think its just a difference in speed.....
I drive them, and they aren't particularly prone to icing. (Yesterday was another thing, the ice build up on the wing was quite another thing). Mostly due to the fact that apart from the last moments we drive them about 250 kts to 320 knots, so the the temp rise due to the ram effect will keep the leading edges warm enough to keep most of the ice away (in our temperate climate). We do have heated windscreens, but the heat doesn't do the whole windscreen so you get little patches of ice build up on the edges that are noticeable. Also there is a windscreen wiper nut that we use to observe ice build up, so they would have been aware. I think its just a difference in speed.....
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The mach heating should work in any climate.
You just need enough TAS to achieve a temperature rise whose magnitude exceeds the width of the temperature band (about 15C) over which liquid water can hang in stratus cloud. That is about 350kt TAS.
If you can get 15C of temp rise, all over (not actually possible all over due to local pressure drops) then you would "never" ice up.
You just need enough TAS to achieve a temperature rise whose magnitude exceeds the width of the temperature band (about 15C) over which liquid water can hang in stratus cloud. That is about 350kt TAS.
If you can get 15C of temp rise, all over (not actually possible all over due to local pressure drops) then you would "never" ice up.
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Originally Posted by IO540
The question, chaps, is whether all this knowledge helps you in practice, with real flight planning.
Can you point me to a website where I can look up all these values, for different levels along a specified route?
No matter how much one understands met theory, one cannot, IMV, statistically significantly beat the forecasters who have all the data at their fingertips (including data which they don't publish, or do publish but only to fee paying customers) and who do this all day for a living.
I also don't think one can (statistically significantly) even beat totally dumb button pushing on a GFS website like e.g. http://www.arl.noaa.gov/ready/cmet.html.
If somebody with a JAA ATPL tells me they can out-do the pros, I suggest they start up their own weather forecasting company. They would make a lot of money. Or they could offer their services to the UK MO and help all pilots
I know this flies in the face of all the "professional" pilot training, which makes you sit through reams of this stuff, so if I have missed some essential point I would be (seriously) grateful if somebody could explain exactly what I am missing. In detail, so I can learn from it.
Interestingly, the FAA doesn't make pilots learn most of this stuff for the IR, but they don't find it a problem. Is the weather really so much more complicated (but predictable) in Europe?
Can you point me to a website where I can look up all these values, for different levels along a specified route?
No matter how much one understands met theory, one cannot, IMV, statistically significantly beat the forecasters who have all the data at their fingertips (including data which they don't publish, or do publish but only to fee paying customers) and who do this all day for a living.
I also don't think one can (statistically significantly) even beat totally dumb button pushing on a GFS website like e.g. http://www.arl.noaa.gov/ready/cmet.html.
If somebody with a JAA ATPL tells me they can out-do the pros, I suggest they start up their own weather forecasting company. They would make a lot of money. Or they could offer their services to the UK MO and help all pilots
I know this flies in the face of all the "professional" pilot training, which makes you sit through reams of this stuff, so if I have missed some essential point I would be (seriously) grateful if somebody could explain exactly what I am missing. In detail, so I can learn from it.
Interestingly, the FAA doesn't make pilots learn most of this stuff for the IR, but they don't find it a problem. Is the weather really so much more complicated (but predictable) in Europe?
I am bemused, IO540 (and Fuji Abound). You seem to be suggesting that learning some meteorology theory is a waste of time since we will never be as competent as a professional forecaster. Sorry, but who was suggesting we would be? It was, after all, you (IO540) that pointed us towards skew-t diagrams … which are raw data diagrams REQUIRING a very good knowledge of meteorological theory to determine the weather that will result (for example in terms of cloud types, bases and tops).
IO540, skew-t diagrams display ALL the data we have been debating on this thread… from ELR, DALR and SALR to hydrolapse rate. Since it was you that provided the link, when you then ask: “can you point me to a website where I can look up all these values”, perhaps I can be forgiven if I question your understanding of skew-t diagram content! My sincere apologies if I’m doing you a disservice in making that observation.
For my part, I think I have made it clear that my knowledge of this complex subject is extremely limited, and that I would always bow to the views of a professional meteorologist. But this leaves me with two problems:
1) in planning, whilst terminal forecasts largely give me what I need, en route forecasts are really lacking (a point, IO540, on which you had previously agreed ); and
2) in flight, especially on a long sector, the situation can change markedly from that forecast, and I tend not to have a met. specialist sat alongside me in the cockpit (neither do I have, regrettably, the NEXRAD resource that is available to our U.S. companions).
In consequence, us pilots are FORCED to make some judgements about the weather … and, let me make it absolutely clear, this has got nothing whatsoever to do with any egotistical belief that we “know better than the professional forecasters.”
I’ve no idea what the FAA requires in terms of met. knowledge, since I went the CAA route. What I can say, though, is that when I was at PPSC in the mid 1990s, the time I wasted studying irrelevant material (including ‘nav. plotting’ and ‘Decca’, for gawd’s sake!) did not extend to meteorology … ‘twas two papers in them days: ‘Theory’ and ‘Practical’, and every single bit of the course material I still view as good, useable stuff, even if I do struggle with the concepts.
So, IO540, what would your proposed ATPL/CPL/IR met. course contain? Would it be sufficient for a student to take a stab at estimating the cloud tops from a skew-t diagram? And would that student be able to recognise the met. conditions on the day of FFF’s flight (as reported at the start of this thread) as classic ‘rain icing’ conditions … one of the truly big ‘avoid’ areas for GA flight?
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As an 'umble PPL with an FAA IR, I know very little about weather other than how to read the charts, TAFs and METARs on offer. I fly an Arrow with no deicing equipment of any kind, so if it's close to freezing and cloudy, I stay down here wishing I was up there.
But I did, some years ago, spend a fascinating evening with a senior guru from the British Antarctic Survey, who explained a load of stuff about weather. Most of it has faded into the background, but I do remember 3ºC per 1000 feet as the DALR, and the helpful phrase "drier is higher". I think there was something about the saturated adiabatic lapse rate being constant (might've been 1.5ºC per 1000 feet, I dunno) but the "wet, humidity not defined" one being unpredictable. That may be my brain seizing up.
I also remember on my FAA IR oral being given a METAR with the dewpoint higher than the actual temperature, and being asked what it meant. I don't know what the expected/correct answer was, but I said someone had just taken a leak onto the wet bulb.
But I did, some years ago, spend a fascinating evening with a senior guru from the British Antarctic Survey, who explained a load of stuff about weather. Most of it has faded into the background, but I do remember 3ºC per 1000 feet as the DALR, and the helpful phrase "drier is higher". I think there was something about the saturated adiabatic lapse rate being constant (might've been 1.5ºC per 1000 feet, I dunno) but the "wet, humidity not defined" one being unpredictable. That may be my brain seizing up.
I also remember on my FAA IR oral being given a METAR with the dewpoint higher than the actual temperature, and being asked what it meant. I don't know what the expected/correct answer was, but I said someone had just taken a leak onto the wet bulb.
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"Perhaps pilots place too much reliance on the forecaster and met observer. The rules require that you consult the available information. However the interpretation and use of that information is up to the Captain. The forecaster will never say don't fly today. That decision is up to the aircraft commander.....so don't try to pass the buck if the decision made is incorrect."
Islander2
It was that quote that caught my attention.
Islander2
It was that quote that caught my attention.