The times., 1899-02-03
THUNDERsToRMs IN WINTER.
Visits Few and Far Between, But
Easily Explained.
From lie New York Tribune.)

tfTOm the New lOlh lIlDunt-J
Meteorological freaks like that which sur
prised and disturbed people in the vicinity
OF this city last Tuesday night are rare, to
be sure. but not altogether unprecedented
II one examines the records of the Govern
ment Weather Bureau for the whole coun-
try he will discover that there is not
month in the whole year when a thunder
storm is not reported from some place.
Like tornadoes, squalls. and other purely
local disturbances, they abound principally
in summer, but the conditions which pro-
duce them may and do occur in winter,
also, though much less frequently.
The prime cause of thunderstorm. ac
cording to the experts, is this combination
OF circumstances: y large amount OF mois-
ture in air the earth's surface, and a
certain difference of temperature between
the lower and upper layers of atmosphere.
There is a rate at which temperature nor
mally diminishes as one ascends. This is
about l degree Fahrenheit for every 800
feet. If. as sometimes happens, the dimin-
ution is less rapid than this. no special re-
suit is to be anticipated: but if on the
other hand the contrasts between the tem-
peratures at the surface of the earth and
two or three miles up should be much
greater, then the warm air below would
have disposition to break through the
everything cold stratum and rise above the
latter. A situation of this sort called an
unstable equilibrium" may be brought
about in two ways. The lower air may be-
come superheated by the sun. an upper
current of unusual coldness may sweep in
over the lower atmosphere.
The daily weather charts of the Govern
ment indicate the temperatures that pre-
vail at any one moment in widely scatter
ed places, but only on the surface OF the
earth. At the present time there is no
4
trasts that exist i'll a vertical direction for
two or three miles. Kite-hying may give
the Weather Bureau that information some
| day. and also furnish other much-needed
| data concerning the development and prog
| ress of storms.
| 1t is now almost generally conceded that
| the advance of the broad depressious. with
| in whose limits Il local storm always oc-
! ours, is controlled by the upper currents
| CT air, which over the United States are
at all times moving in an easterly direc-
ton. 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 moy-
| ed more briskly AT one time than another
| or as if the depression got a better grip
| on the cable under one set Of circumstances
| than under another. However this may be-
| il may be noted that the great trough Of
| low barometer that reached from the Lakes
to>he Gulf early in the last week showed
! sluggish disposition for n day or two:
| but on Tuesday afternoon and evening il
| Jumped forward-that is. TO the eastward
| with astonishing celerity. The perform
! ance justified a suspicion that the uppe:
part of a cold, hIgh-pressure area that was
! seen behind the depression had impatiently
| pushed ahead of the lower part and had
| spread out over the warm air in the
| trough, thus creating an exceptionally
| strong contrast between the surface tenn
| perature and that alOft. The abundant
| moisture in the air below supplied the
other essential factor in the production ol
| local storm.