Boating: How to Boat: Safety
Weather 101: How to Read Clouds
Before
leaving the dock, you can get weather information from TV, radio, your VHF radio
and on the Internet. While on the water, your VHF radio is the best source for
weather warnings. Even so, at certain times of the year weather can change rapidly
and you should continually keep a "weather eye" out, especially to
the west, in order to foresee changes that might be approaching.
Clouds
are a tool you can use to predict or forecast weather. The type of cloud and
direction of movement can warn you of weather changes that are imminent. Clouds
are categorized by the altitude at which they appear and the shape that they
take.
(This
is not an in-depth study of clouds, but an attempt to simplify the subject for
use by recreational boaters.)
| Cloud Group |
Cloud Height |
Cloud Types |
| High Clouds
= Cirrus |
Above 18,000
feet |
Cirrus
Cirrostratus
Cirrocumulus |
| Middle Clouds
= Alto |
6,500 feet
to 18,000 feet |
Altostratus
Altocumulus |
| Low Clouds
= Stratus |
Up to 6,500
feet |
Stratus
Stratocumulus
Nimbostratus |
| Clouds
with vertical growth |
|
Cumulus
Cumulonimbus |
It is
helpful to remember the following definitions of cloud shapes:
|
Cumulus
meaning "heap, a pile, an accumulation" |
|
Stratus
meaning "spread out, flatten, cover with a layer" |
|
Nimbus
meaning "rainy cloud" |
Variations
of cloud types are created by combining the cloud's shape/description with the
altitudinal names as a prefix or suffix.
Cirros
(high) or Cirro can be used with cumulus (heap) to indicate a
cirrocumulus or high, lumpy cloud. Cirrocumulus clouds, sometime called
"mackerel skies", can indicate the approach of a hurricane in the
tropics. It can also be used with stratus (flat, layered) as in
cirrostratus to indicate a high, flat or layered cloud.
Alto
can also be used with cumulus and stratus to indicate altocumulus
and altostratus which are middle altitude lumpy clouds and middle altitude
layered clouds respectively.
Nimbo
or nimbus might be used with cumulus or stratus to indicate
a cloud formation that is producing precipitation. These clouds could be either
cumulonimbus which would be a lumpy, vertically-rising rain cloud or
nimbostratus which would be a sheet or flat-looking rain cloud.
High
clouds exist above 18,000 feet and are cirrus clouds.
|
Cirrus
clouds are the most common of the high clouds. They are composed of ice
and consist of long, thin, wispy streamers. Cirrus clouds are usually white
and predict fair weather. Sometimes called mares tails, they stream with
the wind. By watching the movement of cirrus clouds you can tell from which
direction weather is approaching. The appearance of cirrus clouds usually
indicates that a change in weather will occur within 24 hours. |
|
Cirrostratus
are sheet-like, thin clouds that usually cover the entire sky. The sun or
moon can shine through Cirrostratus clouds. Cirrostratus clouds usually
come 12-24 hours before a rain or snow storm. |
|
Cirrocumulus
are small, rounded puffs that usually appear in long rows. They are usually
white, but sometimes appear gray. Cirrocumulus are usually seen in the winter
and indicate fair, but cold, weather. In the tropics, they may indicate
an approaching hurricane. |
Medium
high clouds occupy altitudes of 6,500 feet to 18,000 feet. These clouds
are called alto clouds. Alto clouds are used to predict weather changes
in 6 to 12 hours.
|
An Altostratus
cloud usually covers the whole sky. The cloud looks gray or blue-gray. The
sun or moon may shine through an Altostratus cloud, but will appear hazy.
An altostratus cloud usually forms ahead of storms with continuous rain
or snow. |
|
Altocumulus
clouds are grayish-white with one part of the cloud darker than the other.
Altocumulus clouds usually form in groups. If you see Altocumulus clouds
on a warm, sticky morning, be prepared for thunderstorms by late afternoon.
|
Low
clouds, called stratus clouds, are at altitudes up to 6,500 feet.
These clouds form a solid sheet or layer of cloud mass.
|
Stratus
clouds are uniform gray in color and almost cover the entire sky. Light
mist or drizzle is sometimes associated with Stratus clouds. |
|
Stratocumulus
clouds are low, lumpy and gray. Most form in rows with blue sky visible
in between. Precipitation rarely occurs with Stratocumulus clouds, however,
in frontal weather they may turn to Nimbostratus. |
|
Nimbostratus
clouds are dark gray with a ragged base. Rain or snow is associated with
Nimbostratus clouds. |
Clouds
with vertical growth
|
Vertically
developing clouds are the Cumulus type. These small, lumpy
clouds are low "fair weather" clouds. However, as they develop
vertically (by rising hot air) they may go from small, fair weather clouds
to large, boiling, vertically-growing monsters called cumulonimbus. |
|
Cumulonimbus
are generally known as thunderstorm clouds. High winds will flatten the
top of the cloud into an anvil-like shape. Cumulonimbus are associated with
heavy rain, snow, hail, lightning, and tornadoes. The anvil usually points
in the direction the storm is moving. |
If
you still can't remember all of the cloud names and formations, you can always
watch the clouds for two specific weather situations that indicate a high probability
of a storm:
A
"lowering ceiling": This means that the height of cloud formations
continues to get lower and lower, usually caused by a warm front. As the ceiling
lowers you will see clouds in the following order:
- Cirrus
- Cirrostratus
- Altostratus
- Stratus
- Nimbostratus
- storm clouds!
On
the other hand, watch for cumulus (puffy) clouds that start to rapidly develop
vertically to become cumulonimbus thunderstorm clouds. On hot and humid days,
these storms occur over water as the radiant heat from the land absorbs moisture
from nearby water and rises to produce thunderheads. These storms can also indicate
a cold front and may be preceded by squall lines, a row of black storm clouds.
Wind shifts unpredictably and accelerates dramatically. Lightning can occur
for miles in front of a storm and after the storm appears to have passed.
Other
things to look for that indicate an approaching weather change:
- Weather
changes generally come from the west so scan the sky with your weather
eye, especially to the west.
- A
sudden drop in temperature and change in the wind (increasing winds and/or
seas) often means that a storm is near.
- If
you have a barometer on your boat check it every two to three hours. A
rapid drop in pressure means a storm is approaching.
IF
A STORM IS NEAR…
- Reduce
speed and proceed with caution
- Put
on PFDs.
- Close
all hatches and ports.
- Head
for the nearest shore that is safe to approach and duck into the lee of
land.
- Put
the bow into the wind and take waves at about a 40-45 degree angle.
- Watch
for other boats and floating debris.
- Pump
out bilges and keep dry.
- Change
to a full fuel tank.
- If
there is lightning, unplug electrical equipment and keep away from ungrounded
metal objects.
- Secure
loose items which could be tossed about.
- Keep
everyone low in the boat and near the centerline.
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11 through 20 of 20 total.
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