Icing G-Airmet accuracy

[skidoo]

I would like to get some input from real experiences on icing tops as related to g-airmets. More specifically, how accurate did you find the forecast to be when you climbed above the forecast icing tops. I'm trying to determine how conservative the forecast may be.

For example, say the icing forecast for an area was freezing level to 160. More often than not, would you have actually broken through on top at less than 16K, or more often than not, would you have broken out on top above 16K?

For those non-KIKI flights, consider when you have flown over those areas.


Additional comments or input welcome on your experiences.

 

[Alexb2000]

I fly a non-fiki aircraft within an icing airmet several times a year. I never really like to trust the forecast as much as a pirep. Although the forecast makes me take serious pause and careful planing. I usually ask someone taking off to radio back the tops and any icing conditions or have the tower get that information. Of course if it is a jet then I take what they say with a grain of salt given their climb rate and deicing capability.

I left Memphis about a 1.5 years ago with an icing airmen tops at 16K. I waited until a regional jet went up reported they broke out in a valley at 14K negative icing but moist buildups all around the area with tops to 16. I had the tower put me out on the same path and a circling climb, broke out, climbed on top went home.

Said simply I prefer pireps in the exact area and time I am flying. Also, 100% know the freezing level, write it down on your way up. Have an out and all of that.

 

[poadeleted20]

The Airmet Zulu is an extremely blunt instrument. It will encompass a very large area (both horizontally and vertically) in which icing might be encountered. It is not by itself a forecast that icing conditions will exist throughout the area it encompasses. One must also avail oneself of all the other weather data (area forecasts, winds aloft, temperature aloft, CIP/FIP, PIREPs, Skew-T's, etc) before one can begin to make a reasonable estimation of whether one is likely to encounter structural icing in any particular location within the area covered by the Airmet Zulu.

To learn more, go visit Scott Dennstaedt's aviation weather training website http://www.avwxworkshops.com and take some of his courses.

 

[Threefingeredjack]

In my home area we have significant orthographic lifting along the windward side of the Cascades which,(obviously), alters the moisture profile depending on where along the crests you cross. Most airways select the crossing points which offer the lowest MEAs, (10-13K). I have never trusted the blanket forecasts and hold the same philosophy Ron stated above. Learn what you can from the information available then go see what reality is. If I am filing a GPS direct route I always take the underlying terrain and wind velocity into account when guessing how much moisture is getting stuffed into the air.

 

[skidoo]

I sure would like to see input from more of POA.

I'm not trying to gauge how much moisture exists. But, rather, I am trying to determine what reality to expect for the level of tops. I can easily see the bottoms and compare to ceilings forecast since I am mostly on the ground. But, I have never been able to compare actual cloud tops with forecast icing. I'm not looking at convective or summer weather, but rather I'm most interested in the cold season inversion layers that tend to plague the NW.

I just got my IR in mountainous icing country, and need to be extra conservative for my upcoming cross countries. Often, it looks like it is good VFR here, good VFR at the destination, but clouds, and potential icing in between. I can easily get to 20K ft, as long as I know the clouds and icing will be below.

I may be looking at a trip from Montana to the Oregon coast sometime next week, if the weather is decent.

 

[poadeleted20]

You can be pretty sure that you won't collect ice outside the AIRMET Zulu zone. Beyond that, see post #3.