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11-20-2011, 08:13 AM
Is there any way to determine cloud tops other than PIREPS? Last week I put the first few hours of hard IFR into my logbook. During the first leg of the trip we were in IMC the whole time. I could catch glimpses of blue skies above every so often so we must have been skimming the tops. Sure I could have requested higher, but it would have been nice to know tops before I filed. There has to be a reason clouds stop forming at this magic altitude. Is there any guesstimate type formula, anything to get an idea?
11-20-2011, 08:19 AM
Might not be useful for tops, but here is some useful information on clouds in general that you can put in your back pocket:
Temperature(F) minus dewpoint divided by 4.4, then multiplyed by 1000.
Temperature(C) minus dewpoint divided by 2.5, then multiplyed by 1000.
temp - DP X either 200 (if using C) or 400 (if using F)
If reading temps from a digital ATIS, use the T000000 series of numbers for the exact temp spread.... IE temp 6 C and Dewpoint 7 C in the ATIS can be found again at the end as T056074 meaning 5.6 degrees C temp and 7.4 degrees C on the DP... the difference being 1.8. 1.8 x 200 = 360 feet estimated bases... with just the ATIS 6/7 you'd come up with 200 for the bases and be significantly off....
yes, if you HAVE to be mr perfect, use the 4.4 and 2.2 OR 440 feet and 220 feet per degree.
11-20-2011, 08:27 AM
This is one of my "stump the chump" questions I give on my BFR's. The answer: Area Forecast.
Here's the current FA for WI.
NRN HLF...BKN030 TOP 140. OCNL VIS 5SM WDLY SCT -SHSN BR. BECMG
1619 SCT030 BKN050. ISOL -SHSN. 22Z SCT050. OTLK...VFR.
SRN HLF...BKN025 TOP 140. ISOL -SHRA. 12Z BKN035 LYRD FL250. 17Z
11-20-2011, 08:36 AM
Right, I ususally check the FA before each flight. It seems like it will usually only report tops associated with convection or really thick layers. Like tops FL200 - FL400. Obviously from your example that's not always the case, but I don't think I've ever seen like OVC010 TOP 050. I just need to keep reading them, most of the summer none of this mattered. It was either VFR or raining... easy go-no-go.
Not to mention these are probably not geared toward the guy flying IFR in a Cessna 150 :)
USMC - Thanks for the refresher. I remembered there were formulas from my PPL days and have thought about this a few times. Never got around to looking it up again though.
11-20-2011, 08:48 AM
I really seldom read the Area Forecast. But when I need info on Tops that's where I go. I do find it to be pretty accurate. Here's another example. I am pretty sure anytime there is a "ceiling" reported they will include the tops.
MA RI CT W HLF... SRN CT...BKN015 TOPS 030. 15Z SCT015 BKN060 TOPS 080. OTLK...VFR.
11-20-2011, 09:05 AM
Nice. Alright, thanks guys.
11-21-2011, 12:51 PM
It is what it is:cool:
11-24-2011, 07:44 AM
That's a perfect question for any flight instructor to add to their repertoire of questions. Thanks for posting!
11-24-2011, 06:13 PM
I knew that fact from Richard Collins "Air Facts" videos. Not a very sexy show for the most part. But Collins knows a ton about aviation, and he was also the son of Leighton Collins, the aviation author from the 50s.