New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1899-01-29
THTN DERSTORnS IN WINTER.

J.. Lii
EASILY EXPLAINED.
Meteorological freaks like that which surprised
and disturbed people in the vicinity OF this city
last Tuesday night rare, to be sure, but not
altogether unprecedented. II one examines the
records of the Government Weather Bureau for
the whole country he Will discover that there
is not a month in the whole year when a thun-
derstorm is not reported from some place. Like
tornadOes, squalls and other purely local dis
turbances. they abound principally in summer,
but the conditions which produce them may and
do occur in winter also. though much less fire.
quently.
The prime cause Of a Thunderstorm, according
TO the experts, is this combination OF circum-
stances A large amount Of moisture In the air
the earth's surface, and a certain difference
of temperature between the lower and upper
layers Of atmosphere. There is rate at which
temperature normally diminishcs as one as
cends This is about | degree Fahrenheit for
every 300 feet. IT. as sometimes happens, the
diminution is less rapid than this, no special re-
suit is to be anticipated; but II, on the other
hand the contrast between the temperatures at
the surface of the earth and two or three miles
up should be much greater then the warm air
below would have a disposition to break through
latter A situation of this sort called an 'un-
stable equilibrium" may be brought about in
two ways. The lower air may become superheat-
ed by the sun, or an upper current Of unusual
GOODNESS may sweep in over the lower atmos
phere.
The daily wea her charts Of the Government
indicate the temperatures that prevail at any
one moment in widely scattered places. but only
on the surface OF the earth. At the present
time there is no systematic means of ascertain
ing the contrasts that exist in vertical direc
ton for two three miles. kite-fying may
give the Weather Bureau that Information some
day and also furnish other much-needed data
concerning the development and progress OF
storms.
II Is now almost generally conceded that the
advance Of the broad depressons, within whose
limits a local storm always occurs, is controlled
by the upper currents Of air. which over the
United States are at all times moving in an
easterly direction. But the most casual student
of weather charts knows that the rate at which
these depressions travel varies greatly. just as
if the upper currents moved more briskly at one
time than another or as if the depression got
better grip on the cable under one set Of cir
cumstances than under another However this
may be. it may be noted that the great trough
of low barometer that reached from the Lakes
to the Gulf early in the last week showed
sluggish disposition for a day or two; but on
Tuesday afternoon and evening 1t jumped for
ward-that is to the eastWardwith astonish-
ing celebrity. The performance justified a sus
picion that the upper part OF cold, high pres
sure area that seen behind the depression
had impatenty pushed ahead OF the lower part
and had spread out over the warm air in the
trough thus creating exceptionally strong
contrast between the surface temperature and
that aloft The abundant moisture in the air
below supplied the other essential factor In the
OF a local storm