User's Guide _______________________________________________________________________
112
_____________________________________________________ M210296en-A
a.
Fog patches: Fog patches (code 31) are detected from
rapid changes in visibility across the one-kilometer fog
limit. If the visibility of the one-minute average is more
than twice or less than half of the two-minute average,
then the internal patch indicator is set for about 30
minutes.
b.
Thinner fog: Fog is reported to become thinner (32) if
(latest 20-minute average - earliest 20-minute average) >
0, and the difference is greater than 30 % of the earliest
20-minute average.
c.
Stable fog: Fog has been stable (33) if the
Absolute
(latest
20-minute average - earliest 20-minute average) is less
than 20 % of the lower average visibility.
d.
Thicker fog: Fog is reported to become thicker (34) if
(latest 20-minute average - earliest 20-minute average) is
less than zero and the difference is more than 30 % of the
new 20-minute average.
Haze and Mist
If no precipitation is detected, a visibility code is generated. The
HAZE code (04) is used when the DRD12-estimated, relative
humidity is low and the visibility during the 10-minute average is less
than the
Haze limit
. If the estimated humidity is high, the MIST code
(10) is used instead of HAZE. If the estimated humidity is low and the
visibility during the 10-minute average is less than 1000 m, then code
05 (smoke, dust, or sand) is used.
When visibility increases above
Haze limit
×
1.2, the FD12P will
report CLEAR (code 00).
Weather Classes
The weather classes are continuous, showers, or intermittent.
The weather class is:
- Continuous, when there are less than two clear (no
precipitation) periods during the preceding hour, the
precipitation is continuous.
- Showers or intermittent, when there are more than two clear
periods during the preceding hour in the precipitation, the
weather type is intermittent.
