Instructional Materials on Making Weather Observations
Adapted to the World Wide Web from a file on the University of Michigan
Gopher. Another adaptation was done on a file describing a
Weather Forecasting Contest
for the schools in which the students use the
real-time weather information on the Michigan Weather
Underground.
This file contains the procedure on how to make a weather observation.
It also contains sources (phone numbers) on where to get information
on weather instruments.
Procedure for making a weather observation.
Temperature :
Use a thermometer and read it to the nearest integer.
Do not measure temperature directly in the sun or very
close to the ground.
Clouds :
Type - Cloud charcteristics vary depending on their
altitude as well as the atmospheric conditions.
Altitude:
Low clouds: Stratus (dull gray,usually
overcast, associated with steady
precipitation). Some other species of low
clouds include nimbostratus, cumulus,
stratocumulus, mamatocumulus.
Middle clouds: Begin with the prefix alto.
Examples include altocumulus, altostratus.
High clouds: Cirrus, cirrocumulus,
cirrostratus. Usually appear "feathery".
Weather conditions:
Many times you can identify the current (or
future) weather situation by analysis of cloud
type and coverage, for example:
Cirrus clouds are fair weather clouds, they
usually indicate an approaching front.
Cumulonimbus clouds are indicative of
significant upward motion (due to warm humid
air at the surface rising, then condensing) that
leads to thunderstorm development
(convection).
Stratus clouds are good indicators that
precipitation is approaching.
Brief descriptions of some cloud types.
Stratus
The uniform dull gray colored clouds that
often cause completely overcast skies. The gray
underside of the cloud is shapeless and may resemble
fog. The clouds are layered and formed largely from the
nearly horizontal motion of air with one air layer
slidding over another. These clouds are found at low
altitudes.
Stratocumulus
Clouds that consist of masses or rolls
of cumulus clouds, usually arranged in a pattern with
narrow breaks between the individual clouds. They often
form "cigar shaped" rolls. The bases of the clouds form
at low altitudes. They are common in the late fall and
winter.
Cumulus
Detached clouds, generally dense and with
sharp outlines, developing vertically in the form of
rising mounds, domes or towers, of which the bulging
upper part often resembles a cauliflower. The sunlit
parts of these clouds are mostly brilliant white; their
base is relatively dark and nearly horizontal. Expansion
of rising air results in adiabatic cooling thus forming
cumulus clouds.
Nimbostratus
Grey cloud layer, often dark, the
appearance of which is rendered diffuse by more or less
continuously falling rain or snow. The clouds are
shapeless and of a low altitude. Slow steady rain or
snow may develop from these clouds.
Altocumulus
Clouds found at middle altitudes that are
similar in appearance to cumulus clouds. Altocumulus
clouds are composed of white or gray, rounded patches
with sky visible between the patches. These clouds are
often arranged in groups or lines.
Altostratus
Middle altitude stratus clouds. They are
smooth on the underside forming a uniform gray sheet.
The faint image of the sun can sometimes be seen through
them. These clouds sometimes appear bluish.
Cumulonimbus
Heavy and dense cloud with a considerable
vertical extent, in the form of a mountain or huge
towers. The upper portion of the cloud spreads out in
the shape of an anvil. Under the base of this cloud
(which is often very dark) there are frequently low
ragged clouds either merged with it or not, and
precipitation sometimes in the form of virga.
Mamatocumulus
These clouds extend downward from a
cumulonimbus cloud, they appear as bubble like bulges.
They are formed by a cold downdraft near the edge of a
thunderstorm and as a result can accompany severe
weather conditions and in particular tornadoes.
Coverage
Cloud coverage is classified into the following
four categories.
- Overcast - The sky is completely (or greater
than 90%) covered by clouds.
- Broken - Mostly cloudy skies (50%-90% of the
sky covered by clouds).
- Scattered - Partly cloudy skies (10%-50% of
the sky covered by clouds).
- Clear - The sky is cloud free (or less than
10% cloud coverage).
Movement
Clouds move in the direction the wind is
blowing at the altitude of the clouds. Clouds
can be moving a different direction than the
observed wind at the surface. If a cold front
just passed through the winds will be
backing with height (counterclockwise shift
in wind direction). If a warm front is
approaching the winds will be veering with
height(clockwise shift in wind direction).
Precipitation:
Rainfall is recorded by a rain gauge.
Snowfall can be measured by using a
ruler to record the depth.
Precipitation amount is always given as the amount of
precipitation that fell over a given time period
(generally 24 hours, midnight to midnight).
If the precipitation occurs while the wind is strong
precipitation measurements must be measured carefully.
Rain would fall more horizontally which means the
instrument wouldn't "catch" all the rain that actually
falls. Snow depth would vary considerably because of
drifting so measure the depth at many flat, open
locations and take an average estimate. In making an
observation while there is precipitation, note the time
precipitation began and ended.
Wind:
Wind has a speed and a direction.
Wind speed is measured by an anemometer.
Wind direction can be estimated by noting
which way a flag is blowing. Remember wind
direction is taken as the direction the wind
is coming from.
Present weather:
Weather is constantly changing and
can change in many different ways.
Is it precipitating, if so, what kind of
precipitation is it (rain, snow, ice pellets, hail, mix)
and what is the intensity of the precipitation (light,
moderate or heavy). Visibility is generally a good
indicator of precipitation intensity. Note the distance
to landmarks near the observation spot and determine what
landmarks are visible when there is significant
precipitation.
Is the precipitation associated with a
thunderstorm, if so the intensity of the thunderstorm
should be noted. Is there lightning associated with the
thunderstorm, if so how what is the intensity (frequent
or occasional, cloud to cloud or cloud to ground). Is
there hail with the thunderstorm, if so what is the size
of the hail (its diameter). Is there a tornado associated
with the thunderstorm.
Sources for weather instruments.
Nimbus instruments 1-800-633-1033
The Weather Store (617) 742-3045
Weather Station 1-800-321-9542
American Weather Enterprises (215) 565-1232
Wind and Weather (707) 964-1284
Texas Weather Instruments 1-800-284-0245
Meteophysics Corp. (415) 331-5181
Texas Electronics Inc. (214) 631-2490
Maximum Inc. (508) 995-2200
Magnaphase Industries, Inc. (206) 735-0374
They have many different weather instruments:
Thermometers, rain gauges, wind measuring instruments,
to name a few.
Prices are highly variable.