Jacques Wardlaw Redway

“ Fog and cloud are the most striking examples of condensation on a large scale; in weather science it is commonly called volume condensation. One cannot readily make a distinction between fog and cloud; in general, fog is cloud on the ground, while cloud is fog high in the air. When the blue sky becomes white, the change in color is due to condensation—perhaps water dust, perhaps ice dust. If the condensation thickens, distant objects become blurred by the accumulated condensation; a moisture-haze, quite distinct in color from the blue dust-haze, occurs. ”

“ Inasmuch as the sky is almost always wholly overcast during a steady rain or snow, the ragged edges are rarely visible. The foregoing description is hardly true of tropical rain clouds with their sharp, greasy-appearing edges. The observer will not be in serious error in designating any low cloud from which rain is falling as nimbus. The flying scud, its top pointing with the wind, drops no rain. The breaking of a nimbus usually denotes the clearing of a storm ”

“ A theory that the cloud particle is repelled from the earth because it is charged with the same kind of electricity has been advanced; but it is not certain that this theory satisfies all conditions. That clouds form and disappear in accordance with the laws of temperature and dew-point is the fact that is important in weather science.
For convenience, cloud matter may be considered to be in a stage of condensation intermediate between vapor and liquid—a condition which may be brought about by several means:
Local ascending currents, or updraughts, which are vertical or nearly vertical ”

“ The details of cloud photography are described in the Monthly Weather Review, August, 1920.
the chilling of the air progresses. Advection fogs are more apt to follow gentle movements of the air; gale winds may create mixing to the extent that dew-point temperature is not reached. The advance of a cold wave moving gently into a region of warm, moist air—the fog in front of a high—is an example of advection fog. ”

“ Where the movement of the cloud is very slow, a rest for the head and shoulders may be necessary. The direction is best observed when clouds are near the zenith. The movement and direction of horizon clouds are apt to be decep- tive, giving to the observer an imperfect perspective. ”

“ It is not always easy to distinguish alto-stratus from cirro-stratus clouds. One cannot always estimate its altitude and, if the cloud is thin, it may be about as white as a cirro-stratus formation. The lower edge may be undulate, but it is hardly
↑ Not every “thin whitish sheet of cloud” is a cirro-stratus formation. The low, white cloud veil of winter days may produce a halo; but it is not a cirro-stratus cloud.
Ellerman, photo.
Turreted alto-cumulus below developing into thunder-heads, curro-cumulus above. Cirro-stratus at right center. ”

“ Thin alto-stratus (lower middle) merging into alto-cumulus. Dense alto-stratus (right) , Mount Weather, Va.
Tradition has made the long, flat cloud-streak near the horizon the type form of stratus cloud. But if that same cloud-streak were overhead it would appear merely as a low cloud covering more or less of the sky. When a fog lifts, it forms a stratus cloud; and if it floats away toward the observer’s horizon it becomes a long gray cloud streak. In the first case one is looking at the under side of the surface ”

“ Mammato alto-stratus in the wake of a thunder-storm. Strato-cumulus in lower left side.
camp in the Sierra Nevada Mountains overlooking the Sacramento Valley, clouds formed by dust, smoke and fog are sometimes the only ones visible for a considerable period.
Along the Atlantic Coast and the Mississippi Valley a cloudless sky for more than one or two days is unusual; for a period of three days it is very rare. During the moist periods of midsummer a very thin cloud veil may prevail for a week or more at a time. ”

“ The Distribution of Cloudiness.—In the Pacific Coast region of the United States, cloudiness is more or less seasonal. Practically all the lower clouds are prevalent during the winter months—that is, during the rainy season. During the summer the lower clouds may be absent for weeks at a time. ”

“ Cumulo-nimbus (Cu-Nb) , Thunder-cloud, Shower-cloud.—Heavy masses of cloud rising in the form of mountains, turrets, or anvils, generally surmounted by a sheet or screen of fibrous appearance (false cirrus) and having at its base a mass of cloud similar to nimbus. From the base local showers of rain or snow (occasionally of hail or soft hail) usually fall. Sometimes the upper edges assume the compact form of cumulus, and form massive peaks
Cumulo-nimbus cloud resulting from eruption of Vesuvius, Note the heavy rain falling from lower part of cloud. ”