IntuVueRDR-7000 Weather Radar Pilot's Guide
D201911000094 Principles of Weather Radar Use
Rev 0, Feb 2020 47
results from much more widespread and much less vigorous uplift.
As a result, stratus precipitation is more layered in form with much
lower gradients in radar reflectivity. However, the reflectivity of
stratiform weather can be sufficient to cause yellow and red on the
radar display. These high reflectivities result from relatively high rain
rates, as well as from enhancement of reflectivity due to melting of
snow particles just below the freezing level. High reflectivity of stratus
weather does not indicate any significant hazard (with the exception
of any potential for icing, or takeoff and landing performance issues
associated with high rainfall rates).
ICING
Updrafts in thunderstorms support abundant water; when carried
above the freezing level, this water becomes supercooled. As the
temperature in the upward current cools to about -15°C, much of the
remaining water vapor sublimates as ice crystals. Above this level, the
amount of supercooled water decreases.
Supercooled water freezes on impact with an aircraft. Clear icing can
occur at any altitude above the freezing level; but at high levels, icing
may be rime or mixed rime and clear. The abundance of supercooled
water makes clear icing occur very rapidly between 0°C and -15°C,
and encounters can be frequent in a cluster of cells.
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