Snow

[flyingcheesehead]

So, it was kinda snowy here tonight, and that got me thinking about flying in snow.

Having lived in WI my entire life, I've had more than a little exposure to the various varieties, and I know pretty well how to keep it off the windshield of my truck too. But, that brings up questions as well.

For instance, there's the "dry", fluffy snow. When that's falling, I will try to keep the windshield as cold as possible, and that keeps the snow from sticking. But, when it's snowing like that on the surface, what's going on up in the clouds?

In comparing dry, light snow vs. wet, heavy, sticky snow - Does one generally form at a higher altitude than the other? Is the wet snow a result of falling through a warmer layer, or is it a sign of an inversion (rain that slowly freezes on the way down)?

Bottom line, what's safe to fly in in an airplane that's not certified for flight into known icing? And, what can the various types of snow tell us about icing aloft?

Thanks,

A weather retard.

 

[kevin47881]

Great question Kent. As one who has very limited flight in snow (one to be exact), I'm interested to hear responses from those with more experience and knowledge than myself as I'm thinking about flying to northern Indiana this Christmas.

 

[bbchien]

So, it was kinda snowy here tonight, and that got me thinking about flying in snow.

Having lived in WI my entire life, I've had more than a little exposure to the various varieties, and I know pretty well how to keep it off the windshield of my truck too. But, that brings up questions as well.

For instance, there's the "dry", fluffy snow. When that's falling, I will try to keep the windshield as cold as possible, and that keeps the snow from sticking. But, when it's snowing like that on the surface, what's going on up in the clouds?

In comparing dry, light snow vs. wet, heavy, sticky snow - Does one generally form at a higher altitude than the other? Is the wet snow a result of falling through a warmer layer, or is it a sign of an inversion (rain that slowly freezes on the way down)?

Bottom line, what's safe to fly in in an airplane that's not certified for flight into known icing? And, what can the various types of snow tell us about icing aloft?

Thanks,

A weather retard.

If you promise not to disseminate it, I have an article for you....that I wrote on this very topic.

Bruce

 

[EdFred]

The old timers round here say if it's snowing on the ground you can fly in the clouds. Ummmm...I wouldn't go that far. Gotta really get a temps aloft, and know where the cloud bases are. If below -10C (?) at your altitude then you should be ok being in the clouds - the precip is already frozen.

 

[gprellwitz]

Great question, and one I would love answered for myself and for the weather ground school I'll be teaching in a couple of weeks. I was actually wondering this very thing earlier this week.

Bruce, I'd love a copy of that article, and I promise not to disseminate it. Could I, however, disseminate some of the knowledge I gain from it in my class?

Thanks!

 

[flyingcheesehead]

I was really wishing I could go flying last night so I could shoot some approaches. It was snowing at a pretty good clip (1.75 mi vis under a 400 foot ceiling). There were no airplanes available though, and even if there were, I obviously don't have the knowledge to make a good go-no go decision.

Airmets said freezing level between 3,000 and 7,000, DBQ winds/temps aloft showed 0 C at 6,000. Theoretically do-able around here, MVA east of the field is 2700 and that's the altitude at the IAF on most of the approaches as well. But, not much of a margin when I couldn't get into any other fields in the immediate area and the closest reasonable alternate was RFD. OK, so the "no go" part wasn't really that hard, but I'm curious for next time.

I was mostly worried about the potential for freezing rain and the associated quick buildup of clear ice... So I'm looking forward to Bruce's article so I can see if that's a potential problem when it's snowing.

 

[cwyckham]

...
I was mostly worried about the potential for freezing rain and the associated quick buildup of clear ice... So I'm looking forward to Bruce's article so I can see if that's a potential problem when it's snowing.

I'm not a weather guru or an IR guy, but I grew up in Canada, so I've seen snow a couple times (though I've only flown in it once). I don't know about icing potential in general, but I'd say that the chances of freezing rain are nill unless you're seeing something other than regular snow on the ground. Largish droplets of liquid water, supercooled or not, can't suddenly develop into fluffy snowflakes. You'd be getting freezing rain or rain (or maybe graupel) on the ground if you had a potential for scary freezing rain conditions at altitude, I'd think.

That said, I'd also assume that you could get rime ice buildup in the clouds at altitude if it's snowing lower down.

Just a theory, though.

Chris

 

[tonycondon]

i flew in snow once and picked up no ice. i was with my instructor and didnt get in on most of the weather brief, and it was dang near 3 years ago. i generally just wasnt paying much attention so i dont remember the exact circumstances. we were in the clouds most of the trip though and wings stayed clean. just one guys experience.

 

[flyingcheesehead]

I'd say that the chances of freezing rain are nill unless you're seeing something other than regular snow on the ground. Largish droplets of liquid water, supercooled or not, can't suddenly develop into fluffy snowflakes.

Suddenly no, but with several thousand feet...

It was kind of "in-between" snow - Not bog-down-the-blower wet, but it wasn't perfectly dry and fluffy either.

 

[DJones]

One additional thing to be aware of when flying in heavy snow... snow can stop up the air filter depending upon the location, orientation of the filter. Combustion engines tend to not run very well without oxygen

Doug

 

[ScottM]

One additional thing to be aware of when flying in heavy snow... snow can stop up the air filter depending upon the location, orientation of the filter. Combustion engines tend to not run very well without oxygen

Doug

Wouldn't switching the carb heat on solve that issue? I know in the fuel injected Cessnas if the filter clogs up there is on a spring loaded door so it would open like a flap and take in air from the engine compartment bypassing the clogged filter.

 

[ScottM]

Bruce can you post the article and if not I would also like a copy.

 

[W.O'Boogie]

If you promise not to disseminate it, I have an article for you....that I wrote on this very topic.

Bruce

No dissemination from me if you'll pass it to me too. Officer & Gentleman's Word on it.

 

[Everskyward]

That said, I'd also assume that you could get rime ice buildup in the clouds at altitude if it's snowing lower down.

This is very true. I saw it early yesterday morning. Snowing lightly on the ground, rime ice in the clouds. Temps were around -5C.

Dry snow doesn't stick so much especially if the airframe is cold, but that's when you're beneath the clouds. When you're up in the clouds it's a different story and there's definitely a chance of getting ice.

 

[Baron 55]

Another thing about snow...when you are landing, after breaking out on an ILS or whatever, if the snow is blowing across the runway, it can be a weird optical illusion, particularly at night with the lights of both the runway and airplane on. Very weird. The sensation of sideways movement is palpable. Sideways movement of the airplane or even the runway, though you know it can't be. I've never had a problem landing, but the visual effect is quite odd and with one student in a twin once, I had to take the plane as she was unable to "see" past the illusion. [Perhaps she could have if she'd had to, as in the case if I wasn't there with her.]

 

[gismo]

IME, picking up ice when flying in snow (wet or dry, heavy or light) is unlikely if not impossible. You can however find (typically light rime) ice in the tops of clouds above the snow but even that's not very common. In any case large droplets of water won't form into snowflakes, which are crystals of water that grow by adding miniscule (almost molecular) bits of water at a time. And if snow falling through a warm layer melts and then refreezes it becomes sleet or snow pellets and that's not a good time to be flying because the refreezing part will occur on your airplane if you are at the correct band of altitudes.

So:

In snow: no ice (but watch for air filter plugging).
Above snow: could pick up ice, but not rapidly.
In snow pellets or sleet: Serious ice lives at or above your altitude.

And IME the most serious hazzard of snow is that the visibility can go below most approach minimums quickly and whiteout conditions are a possibility anytime there is heavy snow especially with wind.

 

[jesse]

I've flown in light snow. Never had an issue.

It's pretty cool flying at night in snow. The strobes light all the snow flakes up.

 

[gismo]

I've flown in light snow. Never had an issue.

It's pretty cool flying at night in snow. The strobes light all the snow flakes up.

JOOC, if you are in light snow, how can you tell it doesn't become more than light ahead? For that matter, it's not uncommon for a wide area to go IMC real quick when the snow begins to thicken. Or were you just flying around the pattern?

 

[jesse]

JOOC, if you are in light snow, how can you tell it doesn't become more than light ahead? For that matter, it's not uncommon for a wide area to go IMC real quick when the snow begins to thicken. Or were you just flying around the pattern?

If I remember correctly it was XC at night RST to LVN. Clouds were something like 7,000 SKC or FEW. One of those deals where there really was nothing to be concerned with on radar nor was there any thing mentioned by flight service.

You now how sometimes in Minnesota you get some snow flakes that pretty much come out of no where and it's all over with after a few minutes. It was like that. When it comes to weather I have always been extremely conservative. It wasn't like there was a snow storm coming through.

 

[Ghery]

I remember flying through some snow with my CFI once. In flight visibility stunk. No build up on the airframe, however. That was that day. YMMV.

 

[gismo]

If I remember correctly it was XC at night RST to LVN. Clouds were something like 7,000 SKC or FEW. One of those deals where there really was nothing to be concerned with on radar nor was there any thing mentioned by flight service.

You now how sometimes in Minnesota you get some snow flakes that pretty much come out of no where and it's all over with after a few minutes. It was like that. When it comes to weather I have always been extremely conservative. It wasn't like there was a snow storm coming through.

I get it now, and your encounter sounds quite benign. I was responding to your:

"I've flown in light snow. Never had an issue."

...which sounded like you thought that flying under VFR in snow was no big deal.

 

[Cap'n Jack]

Before I soloed, wewere doing pattern work when snow was coming in, and flying VFR in light snow. We could see the heavier snow come closer on each trip around the pattern. The snow didn't accumulate on the plane, and we landed for good before the heavier band got to us.

I don't know what it's like in the clouds. My opinion is that stratus or cumulus clouds when it is freezing or colder on the ground=ice in the clouds. I don't have any real world knowledge to back that up.

 

[BobS]

Bob Miller wrote a good article in this month's IFR Magazine. The legal answer is that flying in visible moisture at or below the freezing temperature is prohibited for planes not equipped for known icing. Snow is visible moisture, so flying in snow is technically prohibited.

For those of us who don't park our planes six months a year, snow gives an indication that there is a lot of moisture in the clouds. In my experience the cloud tops of clouds that are snowing are usually going to produce rime. Near the Great Lakes, the clouds are often low and stratus in the wintertime, and one can get on top quickly, but this is not legal and risky in planes that lack good climb performance. The only times I've experience static interference on the radio were in snow. I've never had snow stick to the airframe, but it is a source of worry about what I might be climbing towards.

 

[gismo]

Lance,

Yes, snow grains and/or ice pellets (sleet) are good indicators that liquid water exists in the clouds above. Serious ice? Perhaps, but not always.

Yeah, WRT weather, never say never and never say always.

Snow is an excellent depletion mechanism and will typically harvest most (but not all) of the supercooled liquid water in the cloud. Supercooled droplets will rime onto the snowflakes as they fall through the cloud. A snowflake has a lot of arms or branches to collect water. However, icing is possible in all parts of the cloud even if snow is falling from the base of the cloud. If the cloud is vertically-developed, such as a cumulus cloud, a mixed phase cloud is extremely likely with moderate or greater icing potential. This is especially true of clouds that form via orographic effects.

JOOC, with any significant vertical development in a snow producing cloud, where is there significant liquid moisture to be lifted? I must admit that I've never tangled with any significant cumulus clouds that were producing snow AFaIK (I try to avoid anything that shows up on the radar in winter, will that keep me out?) and I don't doubt that there's potential there for ice. And just for the record, my experience says there's no ice below snow producing clouds IE in snow but not in cloud. And as to expand on what I said, I've never found anything beyond light rime ice inside snow producing clouds (so far), and IIRC when I was picking up ice, I was above the snow.

This past March I had a chance to visit one of my collegues who is the lead icing researcher at the National Center for Atmospheric Research. I asked him if a pilot could use any rules of thumb about snow and icing. He said that it would be a very bad choice to assume that snow falling from the cloud implies little or no icing potential. Snow decreases icing potential, but doesn't eliminate it. There are a lot of factors to consider.

Certainly true. The plane I fly is a de-iced twin so I'm generally willing to fly where ice might exist as long as I have a reasonably plausible escape route if it does exist. One such card to play is turning back and/or landing early, but so far I've managed to keep that card in my hand unplayed.