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Freezing Rain
From SKYbrary Wiki
| Article Information | ||
|---|---|---|
| Category: | Weather | 
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| Content source: | SKYbrary | 
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| Content control: | EUROCONTROL | 
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| WX | |
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| Tag(s) | Weather Phenomena Icing |
(FZRA)
Contents |
Definition
Rain which freezes on contact with cold surfaces.
Description
Freezing Rain occurs when precipitation in the form of rain passes from a warm air mass into a cold air mass, becoming super-cooled. These super-cooled rain droplets freeze when they come into contact with the ground or other exposed surface. It is defined as either having droplets of diameter greater than 0.5 mm (0.02 inch) or, if droplets have less than this diameter, they are, in contrast to (freezing) drizzle, widely separated.
The winter storms which give rise to the phenomenon of freezing rain are often referred in North America as Ice Storms.
Effects
Freezing Rain can cause significant accumulations of Clear ice on upper surfaces which the aircraft anti/de-icing systems, being primarily designed to deal with ice accumulation caused by horizontal movement of the airframe, may not be able to cope with. Aircraft on the ground during freezing rain may become covered in thick layers of ice which will be difficult to remove; airfield operating surfaces and runways will also be affected, and all aircraft movement on the ground may be severely disrupted.
Solutions
- In Flight The best response is avoidance : aircraft should be routed away from forecast/reported freezing rain.
- On the Ground Check information on runway braking action before taxying for take off or attempting a take off or landing; ensure that all take offs made in freezing rain are within an applicable Hold-Over Time, noting that ground de/anti icing fluid Holdover Time (HOT) Tables for operations in conditions of moderate or heavy freezing rain.