The record-union., 1895-08-05
THE WET AND DRY SEASONS HERE.
interesting Facts Explanatory of Cali
fornia Weather.
Causes of Our Long and Dry Summers
Where Storms Come From,
and Their Nature.

cial at San Francisco, has favored the
public with another article on "Wet and
Dry Seasons IN California" in which he
says:
The periods of the year IN California
are more generally spoken Of as the wet
and dry season, rather than by the name
OF one of The four seasons IN vogue III Inc
greater portion of the world. The term
s'wet' season does not IN this sense mean
continuous wet, nor does the term dry"
mean no rainfall. They are used in
comparative sense and mean the wet
season, that rain is more probable; and
the dry season, that no rain is more
probable than the reverse.
This paper is based entirely on the rain
fall at san Francisco, which is very close
TO the mean between the heavy and light
rainfall OF the State, hence it represents
very largely the whole State. Rain
has fallen every month Of the year
at San Francisco. August has a mean
rainfall OF 00l Of an inch, July 0.02
September or, June 90, May 90,
October lbs, and the other months
have averages of from to inches.
From May Ist to October 1st, five
months. have an average rainfall OF
LIB inches, and the remaining seven
months have an average of 22.I0 inches,
making an annual average of %. 90 inches.
At the present time, August lst, we are
in the middle, or little past the middle,
OF the dry season, and it will not be long
until many viii be making inquiries as
10 the commencement OF the rains. Con-
sidering the record of the past twenty
five years, made in San Francisco by the
United States Weather Observer, it is
found that the average date of first 0.05 OF
an inch OF rainfall occurs by September
9th. Considering June 30th as the Off
Cial end of one season, and July lSt the
commencement of the next season. We
find that the earliest date OF 0.05 of an
inch OF rain is July 5, 1885, and the
latest October II, 1919; that Is, from July
LIST to October II. 1875, only 0.05 of an
inch of rain fell.
AS 005 Of an inch of rain is such a
small amount, II has been deemed best to
consider that when one-quarter (0.Z5) of
an inch OF rain has fallen that that date
be considered the commencement of the
rainy season. Using this, then, as the
basis, we find that the rainy season be-
gins on October Sth. The earliest date of
quarter OF an inch is Septem Der s, 1854
an0 the latest not until November %, 1880.
as one-quarter of an inch OF rainfall at
San Francisco is hardly sufficient to allow
OF rainfall over the southern portion of
the State, basis OF one inch at san Fran
CISCO was considered for the southern por-
ton as the commencement OF the rains
there, and this is found to be November
1st.
The earliest date of l inch of rain is
September 10, 1855, and the latest Decem-
Der ), 1890 One inch OF rainfall at San
Francisco is not sufficient for the interior
OF the State TO allow OF good blowing and
seeding, hence q total of inches at San
Francisco was considered, and with :
inches of rainfall ct San Francisco up to
November 18th, that date can be said to
be the date of commencement Of good
blowing.
Five inches is considered as the rainy
season being here III full effect, and it is
found that inches does not fall before
Decem Der 10Th, and that the earliest date
that inches have fallen is October u,
1889, and the latest February ), 1891. In
this latter season February was very wet
ana the total for the season was lbs
inches.
To summarize. we have; First rains,
September Eth; the rainy season begins
October Sth, and in the southern part OF
the State. November LIST; ground moist
ened for blowing, NOvem Der 18th, and
rainy season in full effect Deem Der 10TH
These facts have not been presented here
tofore. and may be found OF interest and
value TO many. for it shows the average
OF the past twenty five years. The great
est seasonal rainfall at san Francisco was
in l0S9-90, when 1915 inches fell, the least
being ll.04, in 1901.
IN this connection the causes of these
seasons and the cause of tins great Yaria-
ton in the amount of rainfall may be of
interest. The amount OF rainfall III Cali
1Ornia is dependent upon the north or
south DETECTION of the storm areas. The
food OF a storm is heat and moisture.
With the approach of the summer
months the heat is increased and with
this increase of heat the moisture becomes
less. hence the storm areas retreat north
ward to obtain their greater supply of
moisture. As the storm areas seek their
more northerly path, the rainfall over
California becomes less and less. and
with the passing of the summer heat the
path of the storm areas move southerly
and the rainfall then increases.
The normal path of storm areas across
the Rocky Mountains from Novem Der to
April is about the fittieth degree OF north
latitude, and when the path is south of
this latitude the rainfall over California
Is increased, when to the north it is de-
creased. From April the path of the
storm areas AREAS of low barometric
pressure are called cyclonic or storm
areas moves northerly until July and
August. when II is at It's farthest point
north, which is about or above the Iati-
tude of Sitka. From August they adj
vance southwark, and the rain then be-
gins in the north, in British Columbia
then in Washington and Oregon, and
finally in California.
The daily weather map is now dis
1ornia, and will be sent to many places.
free OF charge, il requested, and a study
OF the map, Observing the progress and
course OF the storm areas marke ed Low
on the map, the public can form very
good ideas as to the approach of the rainy
season SO long as the ''low" is not seen
off the Northwest Washington coast.
there need be little or no fear of rain in
California, but when it appears there,
then rain over California 10 probable and
is made possible by the ''low" moving
southwark along the coast, the barometer
falling over California and the winds
backing or shifting to the south and
southwest.
Rain IN California. unless it is local
showers, seldom occurs with winds from
any point OF the compass except the
south, southeast or southwest. This has
caused the idea among some that the rain
came from the south. This is an error
The causes which produce the rains come
from the north, though the winds are
southerly. The air is light and with an
upward movement, like the drRught UP
q chimney. In storm center, the air
from the surrounding sections moves
spirally inward to fiji up this lightness or
hollow IN the atmosphere
AS storm areas move southwark along
tue coast from Alaska, and cease their
southerIy movement about the Column bia
River. the wind to the south OF the storm
centers are southerly. They blow into
the storm area, give it more food or en-
ergy. and the influence Of the storm is
extended southwark. allowing the rain
to fall over California The more extern
siye the storm area, and the greater the
Impure Blood