The National tribune., 1890-04-17
THE WEATHER.
Some Facts About the Development Of Thunder
storms.
BY LIEUT.. J. P. FINLEY. U. g. sroSAL SERVICE.

correspondence invited. suggestions desired,
and information cheerfuiiy furnished. Every cf-
fort employed To make this Bureau Of practical use
to tie readers OF THE NATIONAL TnIHUsE. All
communications should be addressed Weather,
THE NATIONAL TRIBUNE Office. Washington. ID. CT
In the formation OF thunderstorms there Is
usually very little OF either cyclonic or tornado
violence, aud the wind accompanying them,
when strong. Is more OF the character Of sud
den aud violent sqnai. though il often amounts
10 nothing more than gentle wind blowing
out beneath the thunder cload.
Thundcrstorms appear To be small and Inn
perfectly developed cyclones in which there 10
little or no gyrat0ry motion or barometric de-
preston. They are purely Summer storms and
develop under abnormal conditions of heat aud
moisture. Sometimes they are experienced in
Midwnter, but only when these abnormal
conditions are present in a marked degree, aud
the precipitation may be either snow rain.
The electricity present is merely AN attend
ant feature, aud not the cause OF the disturbance
As has been stated in other articles atmospheric
electricity probably arises from the operations
evaporation aud condemnation, but just how
how We arc unable TO tell.
The barometric oscillations and cyclonic mo-
tions frequently cover considerable area and
are not so easily or generally observed ms tho
changes In temperature, wind direction and
wind velocity.
The sudden change In temperature Is usually
100 To 20' or 25', while tho corresponding
changes in barometTic pressure rarely amount
10 AZ much as o. Of an inch. aud these changes
take place mostly in about 10 minutes. In
| India the change Of temperature Is said 10 be
only TO- To 10, while the change OF pressure is
! from 10 to OILS of an inch. the greater part Of
| which always occurs very suddenly.
In the United Stasts the corresponding sud-
| den increase OF the wind often amounts TO from
| 40 10 60 miles an hour.
| The changes of temperature and the corre-
| spending reverse changes of relative humidity,
| necessarily take place from the changes OF
| capacity OF the air for moisture with changes
of temperature and do not indicate any CORE
| spending changes in the absolute amount Of
| moisture in the air before and after the thun-
derst0rm sets IN. Although the relative
humidity is greater, yet il is most probable
| that the absolute amount Of VapOr Is less after
than before the storm.
According to observation thunderstorms
often appear in groups all progressing east
wardly, in parallel directions. some abreast
and others following after. Hence there is
often succession of such storms at tho same
place within short period Of time, ss, the
same afternoon. Thus, on July 90 1855, five
separate storms were traced in the southern
part OF New Hampshire and tho eastern part
Of Massachusetts,. On July 3 Of the same year
there was group Of thunderstorms ia the
central aud southern portions OF the above
States, of which no less than 10 could
be traced from the observations There may
have been a hundred different centera Of action
around which rain and thunder occurred over
progressive areas, of greater or less extent
aud Of various times Of DURATION from which
no reports were received.
| In such thunderstorm area there NAV b,
such a blending Of the different storms tha
, | there are few places where rain does moi
fall and thunder Is not heard, and So from re
ports received from limited number of stations
IL may seem 10 be one homogeneous storm area
But even reports often indicate that this is no
. the case, for what at first appears to be well
united storm IL later found to consist of nu
merons loosely connected parts, from which
showers Of varying strength arise. In al
such cases the relation Of each distinct storm
area 10 the general storm area is tn
same as that Of heavy showers 10 the gen
eral rain area on larger scale, where th
atmosphere over large area is in the unstab
state but in which the conditions have no
been such as 10 give rise 10 Il cyclone (iow). |
Is simply one Of the numerous places Wher
ascending currents are for some reason starte,
more than at other places, which give rise {
rain, and generally thunder, but in which til
condition is generally absent which gives ris
to rotary circulation.
Tho general form of the rain area at an
given time in compact group of simultaneOu
storms and even where il may be regarded a
one solid storm, is no doubt very different i
different cases, aud in the same storm diiiereu
at different times.