Skew-T/Log-P Experts: Icing likely?

Discussion in 'Cleared for the Approach' started by iamtheari, Feb 4, 2017.

  1. iamtheari

    iamtheari Line Up and Wait

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    I'm still slowly working on my instrument rating. The weather on the ground is just barely MVFR: 31011KT 3SM -SN FEW001 SCT014 BKN030 M13/M15 A2980. On days like today, I like to ponder "Could I fly IFR?"

    Here is an excerpt of the current sounding from https://rucsoundings.noaa.gov/. It looks like I would have smooth air in the clouds up to about 8,000 MSL and it may be a little bumpy above that. But what about icing? The inversion starts just above the surface with a temperature of -13C and 88% RH. The bend starts at 7293 ft, temperature -4.8C and 85% RH.

    My gut tells me that it's too warm above 4770 ft where the temperature goes above -10C and that there is at least a decent chance of picking up some ice. Anyone care to share some thoughts about reading this diagram?

    Screen Shot 2017-02-04 at 10.15.34 AM.png
     
  2. James331

    James331 Touchdown! Greaser!

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    Simply put, it's below freezing on the deck with a ceiling of 3k and you want to go IFR, sure you'll probably be ok....but I wouldn't do it ;)

    I don't really need a diagram, and I've picked up ice when my IOAT was at the temps that's talking about, if you go into a cloud and it's below freezing and you're not FIKI, you're likley not going to have a good time, even if you're running LOP with a AOA and the latest version of fore flight
     
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  3. iamtheari

    iamtheari Line Up and Wait

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    I've read that sufficiently below freezing makes icing unlikely, but can't find a lot of straight answers on particular numbers. You're not the only person I've talked to who has picked up ice in this particular range (down to -10C). How cold does it have to be before it's somewhat safe?
     
  4. neilw2

    neilw2 Pre-takeoff checklist

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    :yeahthat:

    Like James says, for me IFR in the winter is simple. If it is below freezing (or close to freezing) at MEA I don't fly in the clouds. If I can't fly VFR I don't go. You can be fancy with all the skew-t but for me as a single engine non-fiki plane I don't play with ice- at all.

    Although it is true at very low temps the risk of icing goes down it's something I am not interested in trying my luck with.
     
  5. iamtheari

    iamtheari Line Up and Wait

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    Thanks for the responses. I was notified of a comment, not showing up at the moment (deleted probably), asking if there is an icing airmet or any pireps. There is an icing airmet for moderate ice between 5,000 and 16,000. There are not any pireps, but mostly because we're in the middle of nowhere and the only pireps we normally see are airliners saying they found smooth air now that they're not over the mountains anymore. And don't worry, I'm not going to take the J-3 Cub up just so I can make a pirep about the ice. :)

    But the whole point of armchair flying is to learn. Why is that airmet only above 5,000 feet? That seems to match my reading of the Skew-T/Log-P (see above where I said it looked ripe for icing above 4,770) but I don't want to suffer confirmation bias so I'm hoping to gain some insight into reading the sounding and having a more detailed understanding of what the atmosphere is doing than I can get from one airmet zulu that stretches from here to Lake Huron and another that stretches nearly to Sacramento.
     
  6. NoHeat

    NoHeat En-Route PoA Supporter

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    An airmet is for 3,000 sq miles or more of icing. A skewT is for a single location, so it tells you nothing about conditions in a wide area.

    The SkewT you posted tells me there is an ugly chance of icing at every altitude from ground up to about 13000' or 15000' at your location only, and nothing more.
     
  7. bbchien

    bbchien Final Approach

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    Yoikes! I would not be flying that.
     
  8. midlifeflyer

    midlifeflyer Final Approach

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    My sentiments exactly. Others point out the good chance of picking up ice at altitude. But I also see about zero chance of getting rid of it if you do pick it up. I don't like that combo. Not sure I'd like it any better with piston FIKI.
     
  9. iamtheari

    iamtheari Line Up and Wait

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    That's definitely true. The minimum IFR altitude in the area is 4800 so you're not getting out of the clouds by descending, at least not on purpose, and, if you started picking up ice in a light plane, you're not going to climb from 5,000 all the way up into the flight levels to get out of it.

    I'm still curious, though: How much colder does it have to be for the chances of icing to go down significantly?
     
  10. coloradobluesky

    coloradobluesky En-Route

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    Skew T might be interesting and informative but its NOT going to keep ice from sticking to your airplane.
     
  11. Ghery

    Ghery Final Approach

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    Me, neither. I live in the PNW and we have this wonderful ice machine called the Cascades. Your conditions look like prime icing conditions to me. If the temperature in the clouds is conducive to ice you won't find me flying. This is supposed to be fun, and ice in a non-FIKI airplane is NOT fun.
     
  12. midlifeflyer

    midlifeflyer Final Approach

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    I don't have the reference handy but, as I recall, it's -20 C. Basically, it's too cold at that point for supercooled drops to form or maintain their supercooled status. They become ice crystals that are relatively dry and bounce off rather than adhere. But as Neil said earlier, I'm not likely to want to use that information to plan a flight, at least in the aircraft I fly.
     
    Last edited: Feb 5, 2017
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  13. denverpilot

    denverpilot Taxi to Parking

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    Don't like the looks of that here, either. Too long in a thick layer that's getting warmer as you go up.

    I initially liked the -13/-15 at the surface but the inversion that that kills it for me.

    If it was going to get COLDER going up, that wouldn't look so bad but I'd want a lot more information about the bigger picture for the route.

    About the only way you get that massively cold stuff from the surface on up is 12-24 hours after a deep "arctic blast" slams through and the bases usually don't look that ragged behind one of those. Usually solid and very frozen with clearing weather coming along soon. The front "clears out" any moisture usually.

    SkewT screams "too wet and too warm" climbing into it for me in something that can't handle ice.
     
  14. midlifeflyer

    midlifeflyer Final Approach

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    I really like that way if putting it: "too wet and too warm." It sounds so counterintuitive, associating too warm with icing. But the countintuivety makes it memorable and it's incredibly accurate.
     
  15. azure

    azure Final Approach

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    I hesitate to mention this, but there is a characteristic feature on a Skew-T sounding that identifies a cloud that is glaciated or mostly glaciated. And, ironically, it resembles the OP's sounding low down in that the temp and dew pt curves parallel each other. Here, with a strong inversion and the temp climbing into prime icing territory, I'd not touch it with a ten-foot pole. And I would want to be an expert in reading the Skew-T before relying on it to identify clouds that are made of ice. One or twice I thought a posted Skew-T was glaciated, and Scott D said nope, it's not.
     
  16. James331

    James331 Touchdown! Greaser!

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    Y'all must really need to get somewhere, bad.

    When it's right near freezing or below and you fly non FIKI into a cloud, based on it being too cold for ice to form, to me, as someone who fly in ice all the time, that's like taking a bullet, based off its weight deciding it doesn't have any powder in it, chambering it, putting the pistol to your temple and squeezing the trigger.

    Even as a medevac, presuming a deice failure, I have never had to be somewhere bad enough to try what you have mentioned.
     
  17. aggieaviator

    aggieaviator Filing Flight Plan

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    Agree with everyone so far. That's pretty cold on the surface but it's prime for ice most of the way up to your normal cruising alts. No thanks.

    Its rare in most parts of the US to get temps too cold to pickup ice without encountering the "wet" ice along the way up and that's only wise if in a FIKI and even that depends on other variables. If it was -18 at the surface and getting colder all the way up, that's something else entirely. Again, risk/reward, pireps, airmets, aircraft, escape plans considered.
     
  18. jordane93

    jordane93 Final Approach PoA Supporter

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    You're going to have a bad time.
     
  19. rocketflyer84

    rocketflyer84 Line Up and Wait

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    Stay out of the clouds when they're below (or close to) freezing if you have a non-FIKI aircraft. Keeps it simple. Trying to predict if you'll get icing under various conditions or not is a pointless excercise. Don't go in there.
     
  20. GeorgeC

    GeorgeC Pattern Altitude PoA Supporter

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    Even if it's legal VFR under the layer, give yourself lots of margin. On a recent flight, I thought freezing OATs would be no factor because I was under an inversion and no precip was forecast. Imagine my surprise when I started to see water droplets...
     
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  21. azure

    azure Final Approach

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    Yup... inversion means it's warm up above and any precip is going to fall as rain. If the OAT is below freezing at your altitude... unforecast virga is bad news even if it's very light. :(
     
  22. GeorgeC

    GeorgeC Pattern Altitude PoA Supporter

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    I just went to pick up my son from school. It was cloudy. Nothing on the radar, no umbrella required, right? Get outside and it's drizzling. Check the sounding, and unsurprisingly, there's a huge saturated layer. The question is, absent a lifting mechanism... how and why does the precipitation happen?
    Screen Shot 2017-10-11 at 5.52.25 PM.png
     
  23. Clark1961

    Clark1961 Touchdown! Greaser!

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    Did you just ask why the temperature drops on a cloudy day?
     
  24. GeorgeC

    GeorgeC Pattern Altitude PoA Supporter

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    No, but the forecast discussion had my answer:
     
  25. rocketflyer84

    rocketflyer84 Line Up and Wait

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    If you are not FIKI and it’s below freezing inside the clouds then don’t go in there. Simple.

    Sure you could get all fancy and try to predict if there will be icing and how bad and such but why take such risks? You only need to see one plane fall out of the sky in winter (I’ve seen it) to say “yeah, not gonna mess with that.” If you want to fly in the clouds below freezing then you need an airplane made for that. Trying to do otherwise is not wise IMO.
     
  26. Ryanb

    Ryanb En-Route PoA Supporter

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    The Metar alone should be enough to determine the probability of ice, no skew-t needed. Temp is already below freezing on the surface, so any moisture would be conducive to icing.
     
  27. TheGolfPilot

    TheGolfPilot Line Up and Wait

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    I don't look at charts like that very often... But The fact that it is minus 13 on the ground and icing is supposed to be present 5k and up, tell me there is an inversion and the warmer air put you closer to 0 and I have seen ice build up on my strut when my temp gauge showed 0.

    Good rule of thumb, as mentioned already. freezing temperatures overlapping possible visible moisture= no go.
     
  28. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    holy mackerel where is it winter already? Its not even hallowe'en yet!
     
  29. Clark1961

    Clark1961 Touchdown! Greaser!

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    Had first snow of the season on Monday.
     
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  30. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    no location. AK?
     
  31. Clark1961

    Clark1961 Touchdown! Greaser!

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  32. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    Surely at higher elevations? Not eastern Co or even Denver? Brrr.
     
  33. Clark1961

    Clark1961 Touchdown! Greaser!

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  34. Brad Z

    Brad Z En-Route

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    This thread started in February and got necroposted. The Skew-T in the original post was from North Dakota. Would expect snow in ND in February.
     
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  35. iamtheari

    iamtheari Line Up and Wait

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    Ding-ding-ding, Brad wins the prize. Although we had some snow last week, it's been back to beautiful fall conditions since then. I still have high hopes of completing my two-day camping trip around the state in the Cub (to get the stamps from all the unpaved airports in my ND Airports Passport book) before winter hits.

    Fun factoid, though: North Dakota's record high is 120F and the record low is -60F. Only six states have been hotter while seven have been colder, although they all had help from mountains. Our record high and low were set months apart in 1936 at roughly the same elevation. And I have personally been snowed on in North Dakota every month but July.
     
  36. labbadabba

    labbadabba Pattern Altitude

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    Original post was from last Feb...