Defining severity of icing

Flysher

Flysher

Well-Known Member
Ive been reading a book called severe weather flying and it made some interesting points on the way we forecast and report ice. Basically the author says that we need to revamp the way we forecast ice. The current means, trace/light/moderate/severe are methods of reporting ice, not forecasting them.

What is a weather forecast really telling you when it forecasts "moderate" icing? Moderate ice is more or less defined as accretion that demands continuous use of deice/anti ice equipment to continue flight in that area of icing. The point he brings up though is that accretion can differ vastly between different types of aircraft due to wing shape, aircraft size, speed, etc... so what is a forecast report of moderate ice really telling you? not much in my opinion. A 737 may experience light ice while a light twin may experience moderate or greater. He suggests that they come up with some alternative way of predicting ice, such as probability of ice based on cloud type/temp/dewpoint/ etc... much like aviationweather.gov has now. Save the trace/light/moderate/severe stuff for pireps and extremely likely severe situations like FZRA.

I went to an FAA caravan winter seminar last night and it seems that they were using the terms trace/light/moderate/severe with regards to where the ice formed on the plane rather than accretion rate. They showed several slides with pictures of wings loaded with different amounts of ice and asked us to identify the severity of it. Several pictures had very minor amounts but were classified as severe due to the fact that the ice was on the unprotected area of the wing. Im not sure if this was a caravan specific way of reporting ice or if its maybe a new method that the FAA will try to implement.

Anyway just curious as to everyones thoughts on the items I brought up.
 
Hey Jaron,
So Pissed I wasn't able to make it to that presentation. Are they going to publish it at all? Was there anything good that you remember?
 
I have this information from a ground school I took -


Light is occasional use of de-ice equipment and ¼” within 15-60 minutes
Moderate is keeping de-ice protection on and ¼” within 5-15 minutes.
Heavy occurs when your ice protection gear is unable to get ahead of icing

 
Those are the definitions everyone knows now, but what Im saying is that isnt a good way to forecast icing. Those are ways of reporting it.
 
I don't do any hazard forecasting, specifically, so I really can't go into what we use to forecast icing over our areas.

We pretty much use a namogram, which is available publically. We take into consideration the type of clouds forecasted, their relation to frontal boundaries (cold or warm - post or pre frontal), temperature changes through the levels, how much during how large or small a vertical column, etc etc.

A lot more goes into forecasting ICG than pilots really want to know.

The conditions of trace, light, moderate, severe are yes, simply reporting statements on how the ICG is impacting flight controls, and are not terms that us forecasters use when actually forecasting it. We, like you suggested, use cloud type, placement, temp contrasts, moisture advection, etc etc etc, things I already listed.

jfleisher, are you a forecaster? If not, do you have any suggestions on how forecasters can better forecast ICG? Or is this just pilot complaining because they lack the understanding of what actually goes into the product.

I hear this complant from a number of pilots, civilian and military. It's easy to complain about it, but until one actually does it and understands the systems and processes needed to go into the forecast. . . one really dooesn't have much foundation to offer a better suggestion. Forecasting ICG on the synoptic level is not a very easy task.
 
surreal1221 said:
I hear this complant from a number of pilots, civilian and military. It's easy to complain about it, but until one actually does it and understands the systems and processes needed to go into the forecast. . . one really dooesn't have much foundation to offer a better suggestion.
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My suggestion is to not forecast The Apocalypse when the weather is not going to be that bad. My flight school has good standardization and adherence to weather minimums and bum TAFs have cost me money when conditions have not deteriorated as predicted. Today, the opposite happened. It was supposed to be P6SM OVC050 for the rest of the day but that turned into 1 1/4 BKN005 a few hours earlier than forecast.
 
surreal1221 said:
The conditions of trace, light, moderate, severe are yes, simply reporting statements on how the ICG is impacting flight controls, and are not terms that us forecasters use when actually forecasting it. We, like you suggested, use cloud type, placement, temp contrasts, moisture advection, etc etc etc, things I already listed.

jfleisher, are you a forecaster? If not, do you have any suggestions on how forecasters can better forecast ICG? Or is this just pilot complaining because they lack the understanding of what actually goes into the product.
Click to expand...

But that is the way its forecast to pilots. Any airmet/sigmet or area forecast always mentions moderate icing/severe icing etc in such and such area.

Is it just me or does someone always seem to get offended anytime something even remotely debatable is brought up? Im not a forecaster and I'm not complaining, heck this wasnt even directed at forecasters. Im just suggesting that whoever is in charge maybe revamp the way it is forecast to the pilot. Right now when im about to go fly somewhere in the van or the 'jo and I see a forecast that says " moderate icing between freezing level and 12000" it pretty much means nothing to me, other than I am probably gonna get some ice on my trip. I wasnt tryin to p!ss in anyones cereal:whatever:
 
Van_Hoolio said:
My suggestion is to not forecast The Apocalypse when the weather is not going to be that bad. My flight school has good standardization and adherence to weather minimums and bum TAFs have cost me money when conditions have not deteriorated as predicted. Today, the opposite happened. It was supposed to be P6SM OVC050 for the rest of the day but that turned into 1 1/4 BKN005 a few hours earlier than forecast.
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ICAO? I get pretty pissed about busting a TAF, but then again. . . the NWS may be a bit more relaxed when it comes to verification of their products.

Weather forecasting is very pessimestic. . . you don't want to be that one forecaster that said no to +FC across an area. . . send out the product without it, end up AMD'ing the product hours down the road when a SVR weather outbreak happens, and when it all is said and done. . . a number of people are dead, and millions in property damage has occured. (Let it be known though. . . that nothing like the just mentioned situation would ever occur. . .) Just remember that, it's pessimestic (on the NWS side) for a reason, and it's very much the same on the DoD side as well. I hate it, but we can't be optimistic 100% of the time.

jfleisher said:
But that is the way its forecast to pilots. Any airmet/sigmet or area forecast always mentions moderate icing/severe icing etc in such and such area.

Is it just me or does someone always seem to get offended anytime something even remotely debatable is brought up? Im not a forecaster and I'm not complaining, heck this wasnt even directed at forecasters. Im just suggesting that whoever is in charge maybe revamp the way it is forecast to the pilot. Right now when im about to go fly somewhere in the van or the 'jo and I see a forecast that says " moderate icing between freezing level and 12000" it pretty much means nothing to me, other than I am probably gonna get some ice on my trip. I wasnt tryin to p!ss in anyones cereal:whatever:
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The category of ICG is told to pilots in the way as to indicate what sort of impacts to flight controls you could experience. Drawing a couple of SFC progs and HWDs right now, but when done - if I remember. . . I'll break each down to you from trace to SVR.

What good would it do for an ICG product to tell you an accumulation rate? It's going to vary between aircraft types. The rate of moderate ICG on a 767 or 757 is going to pretty much be SVR on a single engine aircraft. I find the system to be very effective when used in combination with general weather knowledge, and the knowledge of your aircraft.

Trust me, you didn't piss in my cereals - nor did you offend me. I'm just a person that if I see or think something is wrong, I'm not just going to moan and suggest it be changed. One must also suggest what they feel would be a good suggestion as to whatever the complaint is.
 
surreal1221 said:
The rate of moderate ICG on a 767 or 757 is going to pretty much be SVR on a single engine aircraft. I find the system to be very effective when used in combination with general weather knowledge, and the knowledge of your aircraft. .
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I think you are even understating it a bit. I have had zero or trace when light aircraft were reporting severe!
 
I think icing is one of the hardest areas to predict- specifically because of the reasons you mentioned. The pireps are best for this, because they include aircraft type in the body of the report- thus you can see "MOD RM" or whatever it is, and then "BE9T" in the type and use some knowledge to know about where the report was coming from. For a C172, moderate rhime can quickly become severe as it loads up on the aircraft. I remember the AOPA publishing an online article last year about how the FAA determines "known icing"- if I remember correctly, anytime there is visible moisture and the temperature is below freezing, you can assume that a possibility for icing exists, and the accidents that have occured in this weather have come with the FAA blaming the pilot (well, don't they almost always blame it on pilot error?).

My company has a specific definition for severe icing (accreting faster than it can be removed, and past a certain mark on the prop-spinner). This thread kinda hit home as last night flying my last leg we were getting quite a bit, and it was interesting to see the decay in performance followed by the performance restoration after the boots popped and the ice was shed.
 
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