Training Guide in Surface Weather Observations - Multiple Choices

does not mean that showers do not occur when thunderstorms are reported, e.g., the report may be “TS
SHRA.” Remember, thunderstorms can be treated as weather, even though it is a descriptor.
Example: TSRA or TS SHRA
Remember, a thunderstorm can occur without precipitation; it is the only descriptor that can be treated as
present weather and may be reported without precipitation.
Example: 10SM TS
When light precipitation is occurring along with a thunderstorm, following the rule of intensity before
descriptor puts the “” before the “TS.”
REMEMBER, THE INTENSITY REFERS TO PRECIPITATION, NOT THE DESCRIPTOR. THERE IS
NO SUCH THING AS A LIGHT THUNDERSTORM.
Example: 3SM TSRA
Using the same principle, when a “+” is placed in front of a “TS,” it is not an indication of a heavy
thunderstorm. Again, the intensity symbol relates to the precipitation, not the descriptor. An intensity
symbol is never used with “TS” if it is reported alone.
There are restrictions on the use of descriptors. The most significant restriction is: Descriptors are never
used with Mist (BR). A descriptor such as patches (BC) or partial (PR) used to describe fog (FG) always
implies that the visibility within the phenomenon meets the less than 5/8 statute mile criterion.
4.1.3 Obscuration
Obscurations when present with precipitation are in a separate group following the precipitation and entered
in order of dominance, e.g., RA BR HZ.
3 4
Shallow Fog (MIFG) is reported when the visibility at 6 feet above ground level is 5/8SM or more and the
apparent visibility in the fog layer is less than 5/8SM. This fog has a vertical extent of less than 6 feet.
3
Partial Fog (PRFG) is fog covering part of the station, which extends to at least 6 feet above the ground,
but not more than 20 feet, and apparent visibility in the fog is less than 5/8 statute mile. A substantial part
of the station is covered by fog while the remainder is clear of fog.
3
Patches of Fog (BCFG) are fog patches that randomly cover the station, which extend to at least 6 feet, but
less than 20 feet above the ground, and apparent visibility in the fog is less than 5/8 statute mile.
Freezing Fog (FZFG) is reported when the air temperature is 0.1°C or colder. This fog may produce a
deposit of ice known as rime ice. It is composed of grains separated by air, sometimes adorned with
crystalline branches. The visibility must also be less than 5/8 statute miles.
3 These are local phenomena usually formed by radiation cooling of the air. They often
form first in low lying areas.
4
May be reported with prevailing visibility of 7 statute miles or greater.
4-5