Hi there,
This is a question that I don’t know the answer to and haven’t flown in enough ice to learn about.
One can assume that the probablity of ice at 1050mb is zero – no cloud, no visible moisture, no ice. It can also be assumed that at 950mb, rising air provides ample conditions for icing. However, between these two values, is there a relationship between changes in pressure and probability of icing?
For example, is there is a pressure value in winter time where one hasn’t experienced ice? Sort of a cut off point?
Hopefully those more meteo savvy can advise?
DMEarc
Sorry no. Ice is very hard to predict.
DMEarc wrote:
One can assume that the probablity of ice at 1050mb is zero – no cloud, no visible moisture, no ice.
Eh? No, you can’t. High pressure areas can have both cloud and visible moisture. It depends very much on the airmass and the age of the high.
You can pretty well guarantee ice in anything between 0C and about -15C, with some cases below that (I have got thin rime at -15C, just once, and posted a photo of it here). The worst for icing is around -5C.
It’s just a question of when it will start, not if.
I don’t think the pressure is much to do with it except obviously it will largely determine whether you will get “wx” in the first place. In 1030+ CAVOK seems assured but in the winter one often gets high pressures where you have a thin layer, base say 500ft, very hazy underneath, tops 1500ft, but the icing hazard in that is very low.
Doing more research on the topic and reading the FAA AC91-74B which was posted on another thread, it states:
Air Temperature and Pressure. Icing tends to be found in low-pressure areas and at
temperatures at or around freezing. Pilots can reference the surface analysis charts to identify
areas of low pressure. Freezing levels can be determined from the winds aloft forecast.
I do think the is a risk relationship between pressure and icing…
DMEarc wrote:
Air Temperature and Pressure. Icing tends to be found in low-pressure areas and at
There is a relationship in the sense that low pressure areas are associated with convection, which increases icing risk – but it is not the pressure in itself which causes the risk but rather the large-scale weather situation associated with a low.
