Weather Classes; Weather Code Selection; Table 7 Wmo Metar Code Limits - Vaisala PWD22 User Manual

Chapter 3________________________________________________________ Functional Description
VAISALA ________________________________________________________________________ 31
Thinner
Fog is reported to get thinner (32) if the last 20-minute average minus
the first 20-minute average is more than zero ( >0 ), and the difference
must be greater than 30 % of the first 20-minute average.
Stable
Fog has been stable (33) if the last 20-minute average minus the first
20-minute average is less than 20 % of the lower average visibility.
Thicker
Fog is reported to get thicker (34) if the last 20-minute average minus
the first 20-minute average is less than zero ( < 0 ) and the difference
is more than 30 % of the new 20-minute average.
Table 7 WMO METAR Code Limits
Code
None
MIST
(BR)
FOG
(FG)

Weather Classes

The weather classes are continuous, and showers or intermittent.
The weather class is continuous if there are fewer than two clear (no
precipitation) periods during the preceding hour.
The weather class is showers or intermittent if there are more than two
clear periods during the preceding hour in precipitation.
However, if more than 30 minutes have elapsed from the last detected
precipitation, the "PRECIPITATION DURING THE PRECEDING
HOUR" code is used.

Weather Code Selection

PWD22 presents the weather type using the World Meteorological
Organization (WMO) code table 4680. Precipitation type is also
reported using the United States National Weather Service (NWS)
abbreviations. The complete list of WMO and NWS codes used in
10-minute Visibility Average
Higher than 5 km.
Higher than or equal to 1 km but
lower than or equal to 5 km.
Lower than 1 km.