The San Francisco call., 1896-05-30
WHAT CAUSES CYCLONES.
These Terrible Storms All Form in
the Arid Southwest.

"The st. Louis cycloDe-for tOrnadOeS
and cyclones are practically the same-was
fortunately forecasted by the Weather
Bureau as early as 10 o'clock yesterday
morning. After the morning map had
been made up, conditions were discovered
that gave rise to suspicion that cyclonic
elements were forming in the very heart
of the region that has OF late years been
marked by so many of these terrible vista
tons. A storm of considerable magnitude
and intensity was on its slow progress
from southwest to northeast with its CEN
ter over the greater part of the States of
Nebraska and Kansas.
''The following telegram was sent at 10
o'clock yesterday morning by the acting
chief of the bureau to Professor Garriott of
Chicago, who is in charge of the district of
the Mississippi Valley and middle States:
Conditions favorable for severe local
storms in the States of the lower Missouri
and Mississippi Valley, southern and
western Illinois and iowa this afternoon
or tonight. 1t might be well to announce
dangerous conditions in special telegranfs
if you have not already done so.'
IA duplicate of this dispatch was sent
to Professor Willis L. Moore, chief of the
bureau, who was at that hour in Kansas
City on an official errand. Professor Gar
riott acted Immediately on these instruc-
tions, and shortly after 9 o'clock, Chicago
time, he issued the following special fore
cast to every station within his district:
'Thunderstorms, severe in localities, fore
casted this morning for the States of the
lower Missouri, middle and upper Mssis-
sipni and lower Ohio valleys and this sec
tion.'
"These tornadoes need moisture in or
der to develop. The storms that give
them birth are formed in the treeless
plains of the arid Southwest, and there
they are severe sand blasts. The wind
blows straight ahead at a high rate for
hundreds of miles without meeting an
obstacle. Nearing the valleys of great
rivers, however, they begin to draw moist
ure into them, clouds form, velocties in
crease and cyclone conditions gradually
form. The wind sweeps down the slope
of the Rockies from the northwest to feed
the fury of the storm. At the same time
there floats from the gulf moist wind,
supplying the voids formed on the south
ern section OF the great whiri. These cur.
rents usually encounter each other on the
southwestern edge of the general storm.
A region of unstable equilibrium is formed.
There breaks off from the main whirl a
secondary twist of wind and rain. and the
tornado is upon the people without warn
ing.
"The cyclone area for the spring is
bounded on the west by about the hun
dredth meridian, and on the east by about
the eighty-fourth. West of the hundred
line there is not sufficient moisture to
create the torna1oes. East of the eighty
fourth the disturbances meet the Alle-
ghany mountains and are broken up.
They often drift off, too into the north
east, beyond the reach of the influences
that make the valley section so prolific OF
cyclones"
THE CALL correspondent was told how
these destructive tornadoes occur. They
usually follow the path of the general
storm conditions that move slowly from
west to east, or, as in this case. from south
west to northeast. At this time of the
year these storms are quite frequent
and cyclonic conditions may be produced
at any moment while such disturbance is
passing over the country. During April
and May the cyclone area is subject to
visitations of this character at almost any
hour. 1t is notable that in each of the
four cases that have occurred during the
past few days, storms have broken in
their intensity in the late afternoon or
evening, just as it is common for
severe thunderstorms to develop in
this section from to o'clock, after
the heat of the day has become intense
The cyclone or tornado is caused by the
meeting of two currents of air coming
from two different directions.
Sometimes these fierce torn ado-Iike
storms occur in the South. That is be-
cause the ordinary track of winter storms
in eastern sections of the country is from
the gulf northward or northeasterly. FIRE.
quently in July cycIonic disturbances take
place in the middle Atlantic States, but
not with the fury that characterizes the
blasts of the real cyclone region, where
winds have a sweep of thousand miles
before meeting an obstruction. The oues-
ton has often been asked, of late whether
these storms are not becoming more fire.
quent, and whether they are not in some
way due to an increase of city conditions.
The answer given to these queries by THE
CALL correspondent was that so far as
known. there are no more storms now
than ever before; and the handiwork Of
man on the face of the earth is not of the
slightest account in the formation of the
terrible disturbances. 1t has been thought
that perhaps the heat or great city. such
as st. Louis, might be factor in attract
ing violent conditions. The scientific an
swer is that the difference caused in the
general atmosphere by the artificial heat
of great city is of the very smallest mo-
ment when these gigantic riots of the eIe-
ments occur. They seem to be more fre-
quent now than before merely because
they are more fully and accurately re-
ported.
Cyclones are by no means modern in
ventions. They have been as long as the
world has existed, but when the country
was vast uninhabited waste, covered with
great forests, they swept and tore and de-
stroyed, without leaving their marks in
history. Perhaps the cutting down of
trees has had something TO do with the
modern violence of the storms, but they
would occur whether the face of the land
was wooded or barren.