109 - Sky Conditions

Define point of observation

Out-of-doors location at ground or water level where a minimum of obstacles to the view of the full circle of the horizon and a full celestial dome exist

Define celestial dome

Portion of the sky which is visible in all directions of the local horizon from the point of observation

Define obscuring layer

Non-cloud layer which wholly or partially prevents an observer from seeing the sky or clouds at higher levels. can be aloft or surface based

Define single layer

Cloud or obscuring phenomena with bases of the same height

Define multiple layers

Cloud or obscuring phenomena with bases at different heights

When is trace reported

Less than one okta

Define summation point

The amount of oktas of the whole sky that is covered by layers at and below that level

For summation amount, what is trace considered?

Zero

Define total amount

Amount in oktas of the whole sky that is covered by all layers observed

When a layer consists of 2+ cloud types, what is reported?

The predominate type

When a layer has equal amounts of different cloud types, what is reported?

The convective cloud

When a layer is composed of CB and TCU, what is reported?

CB

When a layer contains convective clouds that are not predominant, what is reported?

The convective cloud is reported in the remarks

Orographic clouds are observed, how are they reported?

In remarks, even if predominate

Define vertical visibility

The distance an observer on the ground can see vertically into a surface based layer

Up to what height are layers reported to the nearest 100ft?

10,000ft

Above 10,000ft at what interval are layers reported?

1000ft

Within what distance does a pilot report have to be regarded as representative of conditions at the observing station?

1.5NM

What is the convective cloud base formula?

Temp - dew point x 400

What are the requirements for variable ceiling?

Ceiling 3000ft or less and rapidly fluctuating up and down by ¼ of the mean value

Order of priority when determining height of a layer aloft and vertical visibility

• Measured

• Aircraft

• Estimated

Define ceiling

Lowest layer aloft reported as OVC or BKN or the vertical visibility

How shall a variable ceiling be reported?

In the remarks with the lowest value first

How long must contrails persist to be reported?

15min +

In what order do remarks appear?

1. Layer type and amount

2. General aviation remarks

3. MSL pressure

What indicated a cloud base on a ceilometer?

Black