front.
C.
Clouds.
At 0630 local time, an even chance exists that the total
sky coverage (all clouds considered—low, middle, and high) will be
7/10 or more.
But overcast (10/10 coverage) conditions may be ex-
pected only about twenty per cent of the time,
There is a slight
tendency for overall cloudiness to increase as the season progres-—
ses into May; also for a daily maximum of cloudiness to occur near
sunrise,
About seventy-five per cent of the time, the "trade" cumulus—
normally based at 1,800 to 2,000 feet with tops at 8,000 to 10,000
feet—will cover 2/10 to 4/10 of the sky.
The middle clouds—-10,000
to 25,000 feet-—-will be associated with the eddies previously men=
tioned.
At times these clouds may become very extensive, very thick,
and remarkably persistent.
Cirrus clouds are very common.
Dif-~
ficulties in precisely observing and measuring these translucent,
hazy type clouds make a complete analysis of present data on cir-_
rus of dubious value.
D.
Winds.
At the surface, the persistent trade winds blow from east-
northeast to northeast at ten to twenty knots.
Although such ver~
sistence in direction and speed is not found aloft, westerly winds
are observed about sixty-five per cent of the time above 20,000 to
30,000 feet,
The frequency of occurrence of the westerlies above
25,000 feet increases as the season progresses.
163
The height at which