DECEMBER, 1897. MONTHLY WEATHER REVIEW. 545.
over the continent, descendiug here and there to the earth’c
surface. All that portion of the continent that is under the
influence of this descending wind is subject to dry, warm
fcehn winds, and, a t the best, relatively light rains. If the
lower current on the windward side of the range is relatively
feeble and but little rain is deposited on the windward side
then but little wind will flow thence over the continent, the
volume of the descending dry fcehn winds will diminish, and
the chances for local rains in the interior will increase.
In general, the quantity and frequency of rain dependr
upon the heights of clouds whose very formation itself de.
pends upon the upper and lower winds. The absolute quan-
tity of rain depends, also, upon the dew-point, and, othei things being equal, is, therefore, greater for moist wiuds than
for dry ; but the relative quantity and the relative frequency of rain in successive seasons are the features that determine
a drought, in ordinary agricultural usage, for any locality
and these depend essentially upon the relative movements oi
the atmosphere in the respective seasons. If the movementr
are downward, or feebly upward, or if they introduce coolei
or drier air than ueual, the result is drought; if they arc
more strongly upward than usual, they bring cloud and rain
These principles are abundantly illustrated by the winds and
rains that prevail in the interior of India, Australia, and
North America.
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WATHR MEBSUREMENTS FOR IRRIGATION.
The attention of the Editor has been called to the fact thaf
on page 209 of the MONTHLY WEATHER REVIEW for May, 1897;
he has adopted the British Imperial gallon, which is used in many parts of this country, and has said nothing about the British wine gallon, which is also used. The imperial gallon
contains 10 pounds of water, or 277.274 cubic inches. The
wine gallon contains 8.3389 pounds of water, or 231 cubic inches. Records expressed in imperial gallons may be con-
verted into wine gallons by multiplying them by the factor
10/8.3389 or 1.21.
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CHINOOKS IN IOWA.
If the term ‘‘ foehn wind ” is to be used as a general nanie
for all warm,:dry, descending winds then, of course, there may
be a similar propriety in the use of the word “chinook,” but
as “ foehn ” has the priority of many years of ineteorological
usage, and as we have both dry chinooks in Montana, and wet chinooks in Oregon and Washington, the Editor would
prefer the unambiguous Swiss or Helvetian word “ fehn.”
The Climate and Crop Report from Iowa for the month of December contains two interesting notes by observere. At
Clarinda, A. 8. Van Sandt says :
On the morning of the 29th the wind was in the northwest, so011 veering to west. It was as mild as May and reminded me of what I have read of the chinook. Query: Was it the tail end of one? The snow, which was very compact from:previous melting, lost one-third of
ita depth.
At Odebolt, E. Starner says :
December 4.-Chinook atzmidnight that settled >lie snow about 6 inches.
Before studying the weather maps to ascertain whether conditions were favorable for descending winds on these dates,
the Editor would say that, in general, such winds may occur
at any spot on the globe. The fact that they are peculiarly
frequent and effective in certain regions, such as Switzerland,
Greenland, western Montana, New Zealand, and northern
India should not prevent us from recognizing the fact that
they are recurring frequently in almost every other region. Whenever some air ascends other air must descend. There
can be no doubt but that the famous hot winds that occur occa-
sionally from Texas northward to Canada are descending
winds.” It is acarcely proper to speak of the fcehn wind in Iowa as the tail end of a chinook that had spread from Mon-
tana down to that State, because both these terms are gener-
ally more restricted in extent. The hot winds of Iowa and of Montana are generally separate local chinooks.
On examining the weather maps for December 4 and 29,
we find that on the morning of the 4th the temperature
had risen remarkably in western Nebraska, eastern Wyoming,
and northward through Dakota and Montana into Canada.
The winds were from the southwest, t.he air was descending
the eastern Rocky Mountain Slope, the pressure was 30.70 over the region around Salt Lake City, and 29.70, or less in
Manitoba, everything was favorable for a chinook in the
intermediate regions. By the 5th, a. in., the warm winds had
covered a large region southeastward to the Mississippi Val-
ley. Evidently the whole mass of air flowing eastward from
the region of high pressure was descending along the surface
of the ground and did not begin to rise until it came within
the influence of the low pressure near the Lake Region. On
the 4th, a. m., a t Havre, Mont., the temperature was 5 6 O
higher than on the 3d, a. m. This was an intense chinook. Iowa had temperatures 13O or 14O higher, aud during the
whole day experienced a moderate chinook. All the inter- mediate regions had their descending dry and relatively warm
winds. On December 29 the conditions were very similar. The high
pressure was over the Salt Lake region ; the lowest pressure
was over Lake Superior ; the whole eastern Rocky Mountain Slope was covered with a layer of descending air, clear and
dry, and, in general, warmer to such an extent that Iowa,
Minnesota, and Wisconsin were from 20° to 60° warmer than
on the 28th. The chinook-if it nirty be so called-prevailed from the Rocky Mountains eastward to the Mississippi. Iowa
did not get the tail eiid of i t but was in the midst of it. If LLchinook” and ‘Lfcehn” are terms that are to be re-
stricted to intense local manifestations of descending winds,
and if by the “hot winds’’ of the western plains we desig-
nate only those that occur a t the time of the ripening of the
wheat and corn, when they do such injury to crops, then we
ought perhaps to devise some term specifically appropriate
to these widespread areas of descending winds that briiig dry,
clear, warm weather to one-half of the Mississippi watershed. Not only does the eastern slope of the Rocky Mountain
region have its descending chinook winds, but so also has the
eastern slope of the Appalachian range, a fact that was
pointed out by the Editor as long ago as 1872. Thewesterly winds that bring fog and possibly rain or snow to Buffalo,
Pittsburg, Knoxville, and Chattanooga frequently descend
upon New York, Washington, Lynchburg, Columbia, S. C., and Atlanta as clear dry winds, and on the average a very
little warmer than on the windward side of the mountain
range. One of the first indications of this action of descend-
ing winds was observed soon after the station a t Lynchburg was opened in 1871, wheu it w&s found that so-called clearing
up weather and the first clear sky began a t that station some
hours before it reached Washington, and even a whole day earlier in the case of very slowly moving changes.
An area of high pressure apparently represents a region
in which air is descending so slowly to the earth’s surface
that it cools by radiation faster than it warms up by com-
pression. When such an area is central, as occurred so fre-
quently during December, over the middle Plateau Region,
the atmosphere is pushed not merely eastward down the
3astern slope, but also northwestward into California, Oregon,
tnd Washington. It is the relatively rapid descent down these
slopes that causes the air, which is compressed by ita own
*See the article “ Suniiner Hot Winds on the Plains,” b Dr. I. M. ;line, Weather Bureau Observer, in the Bull. Phil. SOC. dshington,
... - ---- -__
KII, 1894.
646 MONTHLY WEATHER REVIEW. DECEMBER, 1897
weight, to become heated so rapidly as to produce a decided chinook ; consequently, during the current December Mr.
B. S. Pague, Section Director for Oregon, reports t h a t
The month was enerally warmer than usual, that in fact it waa abnormal so far as t%e absence of any extreme cold is concerned. Two well-defined chinooks were experienced; viz, from the 5th to the 8th and from the 26th to the 238th.
These dates correspond to bhose of the wa.rni witids on the
edstern slope, showing that the same area of descending air
can produce chinooks on both sides of the Plateau Region.
Mr. Pague says:
The cause of the mild temperature throughout the month was the dynamic heating of the air, due to the high ressures over the Plateau Region and the hi h latitude in which the pow pressure8 passed from the ocean eastwarf. Had the high pressures been persistent to the north of Montana, then the HTould not have been over the Plateau Region, and the result woud have been different; the low ressures would have traveled south of the normal path, and the col$a.ir from the northeast would have lowered the temperatures much below the normal.
If the dry air from the Plateaii Region descends with
sufficient slowness i t may cool by radiation rapidly enough
to counterbalance the warming by compression. This latter
warming is quite an exact quantity and amounts to about lo
C. for every 100 meters of descent, or to lo F. for every
188 feet, consequently air that has descended 5,500 feet vertically must have been warmed up 30° E’. Now, clear, dry air, rolling alung on the surface of frozen or snon-covered
ground in the winter season when the sun is low, can easily
cool more than 30° in twenty-four hours. Thns, northerly
winds and cold weather in Texas niay sometimes he a direct
continuation of air that was quite warn1 when it rapidly
descended the eastern slope of the Rocky Mountains a few
days before in Montana, Nebraska, or Kausas. But most
frequently the cold waves of Texas are due to the southward flow of cold air from the Canadian regions into the Mississippi
watershed ; the divide between the Mississippi and Canada is
scarcely 2,OOO feet above sea level and the cold air generally lies below the 3,000-foOt contour line. The progress of such
a cold wave, south and east., i R frequently described as dense
air underflowing, pushing aside, and lifting up the warmer,
lighter air of the hIiesissippi Valley. Above this cold air the observers on mountain tops and plateaus, or in balloons,
generally find air that is potentially warmer, that is to say,
air that if brought down to the earth’s surface would by com-
pression have a higher temperature than the air of the cold
wave.
METEOROLOGICBL TABLES AND CHARTS.
By A. J. HE~EY, Chief of Divislon of Reoorde and IYIeteorolo~cal Dab.
Table I gives, for about 130 Weather Bureau stations
making two observations daily and for about 20 others
making only the 8 p. m. observation, the data ordinarily
needed for climatological etudies, viz, the monthly mean
pressure, the monthly means and extremes of temperature,
the average conditions as to moisture, cloudiness, movement of the wind, and the departures from normals in the case of
pressure, temperature, and precipitation ; the a1 titudes of the
instruments, the total depth of snowfall, and the mean wet- bulb temperatures are now given.
Table I1 gives, for about 2,400 stations occupied by volun-
tary observers, the extreme maximum and minimum temper-
atures, the mean temperature deduced from the average of all the daily maxima and minima, or other readings, as indi-
oated by the numeral following the name of the station ; the
total monthly precipitation, and the total depth in inches of any snow that may have fallen. When the spaces in the
snow column are left blank it indicates that no snow has
fallen, but when it is possible that there may have been
snow of which no record has been made, that fact is indi-
cated by leaders, thus ( . . . . ).
Table I11 gives, for about 30 Canadian stations, the mean
pressure, mean temperature, total precipitation, prevailing
wind, total depth of snowfall, and the respective departures from normal values. Reports from Newfoundland and Ber-
muda are included in this table for convenience of tabulation.
Table IV gives detailed observations a t Honolulu, Repub-
lic of Hawaii, by Curtis J. Lyons, meteorologist to the Gov-
ernment Survey. Table V gives, for 26 stations, the mean hourly tempera-
tures deduced from thermographs of the pattern described
and figured in the Report of the Chief of the Weather Bureau,
Table VI gives, for 26 stations, the mean hourly pressures as
automatically registered by Richard barographs, except for Washington, D. C., where Foreman’e barograph is in use.
Both instruments are described in the Report of the Chief of
the Weather Bureau, 1891-92, pp. 28 and 30. Table VI1 gives, for about 130 stations, the arithmetical
1891-92, p. 29.
means of the hourly movements of the wind ending with the
respective hours, as registered automatically by the Robinson
anemometer, in conjunction with an electrical recording mechanism, described and illustrated in the Report of the
Chief of the Weather Bureau, 1891-92, p. 19. Table VI11 gives, for all stations that make observations at
8 a. m. and 8 p. m., the four component directions and the
resultant directions based on these two observations only and
without considering the velocity of the wind. The tots1 movement for the whole month, as read from t.he dial of the
Robinson anemometer, is given for each station in Table I. By adding the four components for the stations comprised in
any geographical division one may obtain the average resultant
direction for that division.
Table IX gives the total number of stations in each State from which meteorological reports of any kind have been re-
ceived, and the number of such stations reporting thunder-
storms (T) and auroras (A) on each day of the current
month.
Table X gives, for 56 stations, the percentages’ of hourly
sunshine as derived from the automatic records made by two
essentially different types of instruments, designated, respect-
ively, the thermometric recorder and the photographic
recorder. The kind of instrument used a t each station is
indicated in the table by the letter T or P in the column fol- lowing the name of the station.
Table XI gives a record of rains whose intensity a t some
period of the storm’s continuance equaled or exceeded the following rates :
Dmation,minutea.. 5 10 16 a0 26 80 86 40 45 50 (10 80 100 is0
Rateapr.hr.(lns.].. 8.001.8o1.4Ol.a0l.Oel.OOO.Q4O.sOO.SeO.UO.76O.aOO.#O.aO
In the northern part of the United States, especially in the
colder months of the year, rains of the intensitias shown in
the above table seldom occur. In all cases where no storm
of sufficient intensity to entitle it to a place in the full table has occurred, the greatest rainfall of any single storm has
been given, also the greatest hourly fall during that storm.
Table XI1 gives the record of excessive precipitation at all
stations from which reports are received.