New-York tribune., 1905-07-12
TRAITS OF SUMNER STORMS.

One Of the most striking differences between
such storms as have occurred in this vicinity
within the last few days and those Of winter is
seen in the distribution OF the attendant rain
fall. At both seasons a wide area is likely to
be affected at any one tne but the actual re-
suit is not the same. In cool weather the pre-
cipitation is usually almost uniform over the
whole of the region favored. which may en-
brace several large States, and it is practically
continuous for several hours. In warm weather
it is concentrated over many widely separated
spots Sunshine often intervenes between these:
and where there is a downpour at all 1t is gen.
orally swift, sudden and copious. That which
visited New-York City Monday almost
without precedent in this respect for northern
ATTITUDES; but it illustrated the extremely local
character Of such meteorological episodes.
Summer and winter storms are dissimilar also
in the changes in wind direction and tempera-
ture which accompany them. In cool weather
the wind usually holds from the same quarter
from the beginning TO the end of the period of
precipitation and finally shifts to the north
west, where it stays for day or two. Previous
20 that occurrence the air Is mild, if not really
warm, but the mercury takes an abrupt drop
when the sky clears In July another pro-
gramme is observed. Nine times out of ten the
wind goes back after a shower to the same quar-
ter as before which is generally the southeast
while given locality is under the influence of
one particular barometric depression. The move
ment of 'Iow' in summer is almost invariably
sluggish, and not until the centre of it has
passed to the eastward does any lasting change
come in the wind or temperature. A shower
is often ushered in, to be sure, with a gust of
greater or less violence from the west, but its
duration is brief The phenomenon is attributed
by meteorologists to a convulsiye descent of air
though the volume of atmosphere which is
thrust downward may be large enough TO pro-
duce cooling effect that lasts an hour or so,
the benefit is shortlived. No permanent relief
can be expected until the low area of barometer
is followed by high one and the wind comes
steadily from the northwest.
Observations made with balloons and kites in
thousands Of instances show that with increasing
elevation above the earth there is usually a slow
fall in temperature The average difference is
about degree Fahrenheit for every 300 or 325
feet On occasions. however. notable depart
ures from this standard are observed Some
times the dimnution is not so rapid as might
be expected and when such situation exists
no particular consequences need be looked for.
When, on the other hand, at an elevation of
few thousand feet stratum of air is found
which is much colder than the established for
inula demands trouble is almost sure TO follow.
At one point or another the hot air below will
force its way upward, an exchange will take
place Oh a greater or a smaller scale, and thun-
dershowers, wind squalls, tornadoes or hail
storms viii follow. A large brood Of these local
demonstrations is generated almost slmultane-
ously, their intensity being governed mainly by
the extent to which the lower air is saturated
with water yapor and by the temperature de-
ficiency of the upper stratum.
The task Of forecasting local disturbances Is
beset with peculiar difficulties. 1t is compare
lively easy for the expert TO recognize on a
weather map the conditions which are favorable
10 their development. These are likely TO pre-
vail over wide area at one time. and warning
OF their existence ought always to be given. II
is practically impossible, however, TO foresee
precisely where any particular outbreak will
begin. The most that can be done ordinarily is
TO say that there is chance that such storms
viii form. After one does, its progress can be
reported by telephone; but the responsibility OF
doing that has never been assumed by the ma
tonal government and probably never viii be.