San Fernando Valley State College
A NOVEMBER RAINFALL SINGULARITY
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A thesis submitted in partial satisfaction of the
requ irements for the degree of Master of Arts in
Geography
{Climatology)
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by
Robert de Violini
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June 1969
The thesis of Robert de Violini is approved:
San Fernando Valley State College
June 1969
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CONTENTS
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1
Page
Abstract
Chapter 1.
v
Introduction
1
1.1 Singularities
1
1.2 Earlier Studies of Recurring Weather
Phenomena
3
Chapter 2.
Areal Extent of the Mid-Novewber
Precipitation Singularity
2.1 Extent of the Singularity in Ventura County
7
7
2.2 The Singularity in California
10
2.3 The Singularity in the Mountain States
13
Chapter 3.
Precipitation Occurrence by Date
3�1 Examination of Daily Data
Chapter 4.
Eastward Propagation of the Singularity
18
18
22
4.1 The European Late November Storminess
22
4. 2 November Data at Mid\-lest and East Coast
Stations
24
Chapter 5.
Storm Tracks and Pressure Changes
26
5.1 November Storm Tracks
26
5.2 Five-day Mean Charts
28
5.3 Tracking Problems
33
Chapter 6.
Possible Causes
35
6.1 Possible Upper-air Influences on the
Singularity
35
6.2 Conclusions
37
References
40
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' Fig.
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1.g.
Fig.
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Ii Fig.
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3.
Frequency of days with measurable preci­
pitation at selected stations in Ventura
County, 11 Oct � 20 Dec, 1946 - 1965.
11
Number of days with at least 0.0 1 inch
of precipitat ion, by pentad, 13 Oct 31 Dec, 1946 - 1965, California stations.
15
Number of days wiL� precipitation and
average amount of precipitation, by pentad,
13 Oct - 31 Dec, 1946 - 1965, California
stations.
16
4.
5.
6. · Number of days with precipitation and
average amount of precipitation, by
pentad, 13 Oct
31 Dec, 1946 - 1965,
Mountain States stations.
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Fig.
9.
i Fig.
10 .
Fig.
11.
17
and 8 . Num�er o f days with precipitation
and average amount of precipitation, by
date, 23 Oct - 31 Dec, 1946 - 1965.
Fig. 7. California stations.
Fig. 8.
Mountain States stations.
20
21
November daily precipitation data for
Urbana, Ill. , and Woodstock, Md. , 1946 1965.
25
Principal tracks of low pressure centers
across the United States in November.
27
Five-day mean sea-level pressure and
pressure change charts, 7 - 26 November.
Fig. l la.
7 - 17 November.
Fig. llb.
12
21 November.
Fig. llc.
17
26 November.
30
31
32
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Location of selected Ventura County
.rainfall stations.
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2.
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Frequency of days \¥i th measurable precipitation at Point Mugu by ten-day intervals, July 1946 - June 1966.
1.
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FIGURES
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-···---···-···-- ·--···----··--·----
--
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ABSTRACT
A NOVEMBER RAINFALL SINGULARITY
by
Robert de Violini
I
Master of Arts in Geography (Climatology)
June 1969
! A precipitation maximum in mid-November is demonstrated
lj for
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Point Mugu, California,
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j locations
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and at a number of other
in California as well as at a few locations in
the Mountain States and the Midwest.
Peaks are found
between 14 and 16 Novenilier in both daily precipitation
! occurrence and
I! through
daily average amount during the years 1946
This singularity may be related to the
1965.
late November storminess common in Europe, and may
! possibly
! Northern
I1 summer
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be generated by perturbations induced in the
Hemisphere circulation as the stratospheric
easterlies break down after the autumnal equinox.
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__________________
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···-·-· -- · - - - - - -- - - - - - - ---
� ------------- _____ ._
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A NOVEMBER RAINFALL SINGULARITY
Introduction
Chapter 1.
1.1 Singularities.
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Days \'lith measurable rain at Point Mugu occurred much
more often, from 1946 to 1965,
during the middle ten
days of November than in the ten days preceding or
following.
The values are shmvn in figure 1, from data
in a climatic study for Point Mugu and San Nicolas Island,
California
(de Violini,
1967, ·p. 59).
The 17 years of
precipitation data at San Nicolas Island, 55 miles
south-southwest of Point Mugu,
show a similar peak in the
occurrence of days with measurable precipitation.
The p rominence of the peak in rainfall frequency in the
middle of November led to a search for similar tabulations by periods of ten days or less.
Few precipitation
summaries examine the frequency of rainfall occurrences
or the average amount of rainfall at less than monthly
: intervals.
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McDonald's
(1944) charts of average amounts
of precipitation at weekly interv�ls within the 48
contiguous states suggest a possible increase in precipitation for the middle portion of November in California,
but there are no indications in these of the mean number
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----------- --··---- --
--·---··········-·
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Pi!
20
0
ll:<
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10
�
5o
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1%.
0
a
Fig. 1.
=
1 st
- 1 Oth,
=
11th
- 2oth,
c
=
21st - end of month
Frequency of days with measurable precipitation at
July 1946 - June
1966.,
Point Mugu by ten-day intervals,
N
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··"'-�----------------------·------- .. . --... .
... ... ···-------�---·----�---·------�---��------·-- · ·--··--·····-�-
1
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of days on which ra in occurred.
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The increased frequency of ra in in mid-November appears
to be a climatic s ingularity
--
"A characteristic
meteorological condition which tends to occur on or near
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a s pecific calendar date more frequently than chance
would' indicate, " (Hus chke, ed., 1959, p.51 2 ).
This thesis
is concerned with def1ning the extent, and investigating
the poss ible causes,
of this s ingularity.
1.2 Earlier Studies of Recurring Weather Phenomena.
One of the earliest,
if not the first, compilations of
s ingularities by a meteor o l ogist was by Alexander Buchan
(1869).
His paper
concerned with the irregularities
in the s mooth ris e and fall of mean temperature through
the course of the year, and s howed the existence of s ix
cold and three warm s pells in the Britis h climate.
Brooks
(1946), 'l.·lithout giving a complete reference,
indicated that the work on recurring weather anomalies
in Europe_ by van R ijckevorsel in the early years o f this
century, and by Schmaus s in the thirties , are of more
than pass ing interest.
Brooks
(1946) publis hed what has s ince become
a
s tandard
reference to "spells" and s ingularities o f weather in
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e ffects of recurring periods o f similar pres sure distri-
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butions and compared mean daily pres sure values for a
number of s tations with daily s ynoptic charts for the
5 2-year period,
1889 - 1940.
The res ult of this was a
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listi�g o f s ingularities in European weather as being
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stormy,
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portion o f his paper Brooks discus s ed some o f these in
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anticyclonic,
uns ettled, etc.
In the second
more detail, including ".the stormy period of late
November and early December" which will be re ferred to
later in this paper.
Lamb (1950) looked at the 50 years to 1947 for indications of weather spells in terms of cyclonic or anticyclonic activity and found a typical year has five major
s easons and 20 s horter phas es.
He also observed a
period in late November with a maximum of cyclonic
activity that will be mentioned later.
In the United States little work was done on s ingularities
until recent years , primarily becaus e of the generally
s hort periods o f record available for most meteorological
elements.
Wahl
(19 5 2 ) investigated the reality of the
January Thaw of New England folklore.
He found that
there \vas , indeed, something to the legend of a few days
of above freezing temperatures after the middle of
5
January that were then followed by continually decreasing
temperatures through the remainder of the month.
later paper Wahl
In a
(195 3) related variations o f the
general circulation to variations in the occurrence of
s ingularities in the pattern of daily mean temperature
,! and precipitation occurrences at Boston for three
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dif ferent months.
Wahl's last paper of immediate
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concern here
(1954) is a study of a sudden increase in
the probability of snow in October at three midwestern
u.s.
locations.
He felt this is a first indication of
the transition o f circulation patterns from summer to
winter weather.
J�rgensen's
(1951) study of Cali fornia September rain fall
totals was concerned with long-term changes in the
monthly amounts rather than with occurrences on specific
dates and so does not apply directly to this paper.
He
did mention1however, that early fall rains in central
California are o ften the result of cyclonic circulations
that develop aloft near the California coast re flecting
a major perturbation in the established westerlies.
In the western U. S. , Bryson and Lowry (1955) discussed
the synoptic climatology of a singularity in Ari zona's
s ummer precipitation pattern wherein there is a definite
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nce of rain in the
��;�� � everal
days of July compared to the last few days of June.
They
determined that there is a distinct change of air mas s
type over Arizona a t that time of year, and provided a
s et of mean maps to s how how this comes about
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1 Calendaricity as
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a
more precis e des criptive term for the
s ingularity type of phenomeno n �rvas s uggested by Brier,
Shapiro, and Macdonald
(196 3).
This paper is an
outgrowth of an earlier one by Brier
(1961) in which he
arrived at the conclusion that there was a definite
tendency for rainfall singularities in the United States
to recur on s pecific dates.
In the later paper, after
follmving more rigorous procedures and using a longer
period of record, the earlier premise was reversed.
The
new conclusion was that, in the United States, there is
no nationwide tendency for precipitation to occur on
specific dates.
However, nothing in the second paper
prohibits the occurrence of singularities - - or
calendaricities -- in the climatic pattern of a specific
location,
or of a subnational region.
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Chapter 2.
.
Areal Extent _· of Singularity
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l 2. 1 Extent of the November Rainfall Singularity in
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Ventura County.
Although
tests such as those used by O'Mahony
.
(1962)
on
singularities in Australian rainfall might have been
applie d . to the Point Mugu data, this singularity's
_
visu al prominence was sufficient to warrant furth-er
examination without attempting to subject the data to
statistical analyses.
With the uncovering of this singularity in the Point
Mugu rainfall data, an investigation was begun to
' determine the spatial extent of the occurrence.
Accordingly, rainfall records for eleven additional stations in southern Ventura County were obtained from the
Ventura County Flood Control District for the same
20-year period as used in the Point Mugu study,
1965.
1946 -
For several of the locations there was a choice
of recording stations in the immediate vicinity.
Those
chosen had the most complete period of record for the
20 years, and also had had reliable observers over that
time span.
These stations are indicated in figure 2.
Most of the stations have records going back much
further than 1946, but in order to be s trictly comparable,
.7
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34° 301 ·N
--------+---1
Sat
7ta
Hwy 126
•
Piru
icoy
118
Sia1.
Pacific
Ocean
0
Statute
5
Mi.les
34° oo• N
Fie. 2.
------
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Location of selected Ventura Coun y rainfall stations.
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r·---·
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...... ....
· · ···-·····-
---- ... ..
only data for the same years as were available for
Point Mugu were used.
This temporal homogeneity was
maintained in the data for all the stations brought into
this study.
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The dozen stations have been divided into three groups.
The coastal stations are Point Mugu, Port Hueneme,
Oxnard, and Ventura.
A few miles inland, the intermediate
stations are Saticoy,
Camarillo,
Moorpark.
Santa Paula, and
Hore isolated from the sea, and more likely
to be influenced by adjacent mountains, are Fillmore,
Simi, Piru, and Ojai.
The months had been divided arbitrarily into thirds in
the initial computations for Point Mugu, and later
examination showed that no better ten-day period could
be forced on the data by sliding the end-points of the
period a day or two one way or the other.
Therefore,
in determining precipitation frequencies £or the 11
additional stations in the county, the same fragmentation
o f the month was used.
Observations normally were made within one hour o f
0800 PST except a t Point Mugu and Ojai, and the data are
more likely to reflect precipitation falling on the
previous day and evening than on the date recorded.
The
10
observations at Ojai were made at 1700 PST and the Point
Mugu amounts are totals to 2400 PST each day.
The
importance of this time difference diminishes, however,
when the data are grouped into ten-day intervals.
(Unless specifically mentioned, precipitation totals at
the other stations in this study are 24-hour amounts
measured at midnight each day. )
For each station the percent frequency occurrence of
days with at least 0. 01 inch of rain (rainy days) was
determined for the seven 10-day intervals between 11
October and 20 December.
These frequencies are shown
in f:l gure 3.
The mid-November peak f irst noted in the Point liJ.ugu
data is seen to occur, with varying emphasis, in the
data for all the stations.
At the intermediate stations
there is a somewhat lower frequency of occurrence than
at the other two groups of stations, but the peak is
quite apparent throughout.
2. 2 The Singularity in California.
With this mid-November peak in rainfall occurrence now
more firmly established as a singularity in Ventura
County, it became evident that two actions were
11
20
10
Simi
0
Fillmore
20
I
�
0
Piru
Ojai
10
I
�
0
Saticoy
Camarillo
Santa Paula
Moorpark
20
10
0
0
N
D
Port Hueneme
Oxnard
Ventura
Point Nugu
a = 1st- loth,
Fig. 3.
b
=11th- 20th,
c =21st- end of month
Frequency of days with measurable precipitation at selected
stations in Ventura County, 11 Oct- 20 Dec, 1946- 1965.
12
desirable:
1) to _expand the study to other southern
California locations; and 2) to group the data into finer
time divisions.
To enlarge the areal coverage,
data for the same 20-year
period for four major u.s. Weather Bureau locations along
the California coast were acquired
1946 - 1965).
(U. S. Weather Bureau,
These are the airport stations at San
Diego, Los Angeles,
Santa Barbara, and Santa Maria.
To
accomplish the second item, the data for these stations
as well as for Point Mugu were computed in terms of
pentads
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five-day intervals -- as outlined on page
V. l9 of the Guide to Climatological Practices
(World
Meteorological Organization, 1960), commencing with
pentad 58 and continuing through pentad 7 3.
Inclusive
dates of the pentads for the last quarter of the year
are given in figure 4.
The use of sub-monthly intervals in presenting meteorological data is a long-established practice.
The weekly
Weather and Crop Bulletin of the u.s. Weather Bureau,
Mac Donald's (1944) weekly maps of average precipitation
amounts, and Lahey, Bryson, and Wahl's
(1958) five-day
mean sea level pressure charts are a few examples of
attempts to provide a picture of the state of the
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���:: :���� th:n �===����- ����--==�:h�;·
-
-
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means or totals, but without the overwhelming bulk of
data that results from a daily presentation.
In attempting to determine a northern bound for this
singula
· rity, rea dily availa}:)le data for Scotia, California
{400 miles north-northwest of Santa Maria) were examined.
These new locations, and others brought into the study
later, are shmvn in figure 10.
The data, presented in figure 4,
all six stations.
show this singularity at
The pentad of interest, number 64, is
shaded on ·this and follmv-ing figures.
Note that for
Los Angeles, Santa Maria, and Scotia, the number of
rainy days in this mid-November period is exceeded by
the frequencies in other, later, pentads.
However, as
shown by figure 5, this pentad includes a greater average
total rainfall than any other pentad through the end of
the year.
2. 3 The Singularity in the Mountain States.
Since the singularity does not now seem to be confined
to the southern California region, a search for its
existence in the data of stations farther inland was
made.
Daily precipitation data for three other western
U. S. locations -- Flagstaff,
Salt Lake City,
and Denver
14
r��:�:e = � :: : ��� �� :: �
�
�
b a
�-
�
-
� :=y
e tic l 2
e
Weather Bureau, 1946 - 1965).
ear period
(��. s�. �
The pentadal frequencies
and average amounts were computed; the results are
shown in figure 6.
Again, the frequency of days with
precipitation is greatest at all thre� stations in
pentad 64.
· A peak is also evident in the average amount
of precipitation for pentad 64 at each station,
but that
for Denver is not as definite a maximum as it is at the
other two stations.
This is probably due to some of
the precipitation amounts being the liquid equivalent
of. snowfall.
(For these, and the other stations in the
Nidwest and East, "precipitation days" is a more
\,,
'II
suitable term than rainy days since there is certain to
be some snowfall included in the data. )
60.
Pentad
No.
56
57
58
59
(;JJ
61
October
3- 7
8-12
13-17
18-22
23-'n
28 - 1 NOYo
Pentad
No,.
62
63
64
65
66
67
NO'Ielaber
2- 6
7-11
12-16
17- 21
22-26
27- 1
Deco
Pentad
No.
68
69
70
71
72
73
December
2- 6
7-11
12- 16
17-21
22-26
27-31
CJ)
>­
<(
0
0
D
D
0' N
D
0
D
0. N
SANTA M ARIA
POINT MUGU
SAN DIEGO
SCOTIA
SANTA BARBAR A
LOS ANGELE S
.
.
Fig, 4.
Number of days with at least 0.01 inch of precipitation, by pentad, 13 Oct
-
31 Dec, 1946.- 1965, California stations.
1-'
VI
0. N
. D
SAN DIEGO
Fig.
S.
.
0 N
. D -
0- N
- D
0- N
D
0- N
D
POINT MUGU
SANTA M ARIA
L.OS ANGELES.
SANTA BARBARA
Average amount of precipitation, by pentad, 13 Oct
•
31 Dec, 1946
•
o· N
D
S COTI.A
1965, California stations.
!-'
0\
(J)­
r
<t
0
0 N - D
FL AGSTAFF
0
N
D
FLAGSTAFF
Fig. 6.
D
0- N
SALT LAKE CITY
0
N
D
SALT LAKE CITY
Number of days with precipitation and average amount of precipitation,
by pentad,
D
0 N
DENVER
0- N
D
DENVER
13 Oct - 31 Dec, 1946 - 1965, Hountain States stations.
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Chapter 3.
Precipitation Occurrence by Date
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i 3.1 Examination of Daily Data.
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/ To determine if there was a preferred date for the
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occurrence of this singularity at the nine stations so
far investigated, daily frequencies and average daily
amounts were computed and are shown in figure 7 for four
of the California stations.
(The daily data for Los
Angeles and Santa Barbara were very similar to the plot
presented for· Point :D-1ugu. )
Within the. 12 - 16 November
pentad there is a peak in the occurrence of precipitation
�
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on 14 November at all stations except Scotia where the
peak occurs on both 14 and 15 November.
At Scotia the
observation day is 0800 - 0800 so that a day with rain
most likely occurred on the preceding date.
Thus the
apparent lag of the Scotia peak may be merely a reflection
of the observation time.
In the average daily amounts,
a peak occurs on 14 November at all stations except San
Diego, where the peak average amount occurs on 16
: November.
; At the three inland statio�s
(figure 8) the peak in
;occurrence appears first on 14 November at Salt Lake City,
i
then on 15 November at Flagstaff, and finally on 16
November at Denver.
· However, in the graph of average
18
19
daily amounts,
the peak occurs first at Flagstaff - - a
day ahead of the peak occurrence at that station -- then
at Salt Lake City, a day after the peak occurrence there.
At Denver there is a broad plateau in the average daily
amount at a quite low value with nothing particularly
distinguished in the pattern at any time in this portion
of the year.
This peak in occurrence of rainy days does not imply that
when rain fell it was a single day of rain with dry days
before and after.
Rather, when there has been a rainy
period of several days in mid�November, that period very
l ..
,,,
likely included the date of peak occurrence noted in the
figures.
For example,
at Point Mugu there have been
seven times in the 20 years that rain has fallen on 14
November, but on none of those occasions was that a lone
occurrence.
Each time that date was one of several
consecutive days with rain.
data for Santa Barbara,
This is also true of the
Scotia, Salt Lake City, and
Flagstaff, and in over half the peak date occurrences at
the other stations.
14
z
NOV
DEC
.S COTIA
OCT
NOV
DEC
10[
en
>oct
co
-
I --=-1 -
I
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NOV
Fig, 7.
Number of days with precipitation and average amount of
precipitation,
hy date,
23
Oct
- 31
Dec,
1946 - 1965,
California stations.
N
0
[
�o�Cl��
10 .
16
DEC
[�
�o
��
od [
NOV
OCT
14
10
-
O CT
<{
0
0
NOV
I
NOV
Fig. 8.
DEC
DEC
.20
�
[
00
DENVER
llt\%
OCT
[
15-17
oc������������������
p
.20
�oo
SA LT LAKE CITY
NOV
' �
I
DEC
15
P,��,�N �
OCT
NOV
DEC
[
�oo�Q�pdd
�
.20
FLAGSTAFF
14
OCT
NOV
DEC
Number of days with precipitation and average amount of precipitation, by date, 23 Oct - 31 Dec, 1946 - 1965, Mountain States stations.
N
!--'
Chapter 4-.
Eastward Propagation of the Singularity
4. 1 The European La te November Storminess.
Is this precipitation peak reflected in any other singu­
larity?
Brooks (1946),
in his oft-referenced articles on
singularities in European weather based on the period
1889 - 1940,
included a period of late November storminess.
He provided thi? period with mean beginning and ending
dates of 24 Novewber and 14 December, respectively.
also gave two dates of peak frequency:
9 December.
Later, Lamb
He
25 November and
(1950 )·, indicated two peaks in
cyclonic activity during·the latter part of the year in
the British Isles.
One is from 25 to 29 November, the
other is from 6 to 1 2 December -- thus separating Brooks'
single period of storminess into two.
If we equate Brooks' period of late November storminess
and Lamb's November maximum of cyclonic activity with
occurrences of measurable precipitation, the period near
25 November may be considered as having a peak in the
frequency of precipitation.
We may then investigate
whether the singularity in precipitation occurrence noted
on the California coast on 14 November, and at Denver on
16 November, could also be seen in Europ� near 25
November.
23
r ·..--�·-···------
·
····-----··--···-------··-·-----·--·--·-·····-
·- -- . ····- . .
I
I Given
I
the 105 degrees of longitude that separates Denver
from London, and a time delay of nine days�, is such a
I connection
l
I that
I
I
I
possible?
These differences would require
·
the causative factor of this singularity move at
less than 1 2 degrees of longitude per day, or at about
20 knots.
,
Such a movement is not at all unrealistic.
To
·1 support this movement a peak in the frequency of precipi"'"
!
I
! tating days should be ·found in the Midwest near the 17th,
and on the East Coast near the 19th of the month.
I
! As discussed further in Section 6. 2,
I
i
average speed were maintained on an undisturbed great
circle path around the ea � fh, this singularity, if it
l were to survive such
!
··
if t..�is· 20 knot
a.
trip, would return to the west
_-
I
coast of North America in about 5 2 days.
1
aloft is a series of troughs and ridges rather than
i
Since the flow
circular, several thousand miles are easily added to the
globe-girdling trajectory, and another week or so would
be required to complete the trip.
Therefore, a time of
60 days would be reasonable for completion.
The
histogram of figure 1 has addition�peaks in the
frequency of rainfall occurrence at Point Mugu in
mid-January and mid-March -- 60 and 1 20 days after the
primary peak in mid-November!
. j
24
f' ��---����
!
-·--�-·-·--···------··-�
I
.
���-·-·'--·��---·-�-·-·
-��-n ·�··---·--· -�•
-
--·•"' -��--�-��---·�--�------T--- -----�...:..�-<-'"' ---�-�----�-- --�--.--·-··-•••<-
I 4. 2 November Data at Hidwest and East Coast Stations.
I!November precipitation data for 20 years for two more
..
Ii stations
were : abulated -- Urbana, Illinois and Wood-
!
I
I
I
I!
!
stock,
Maryland
(U. S.
Weather Bureau,
1946 - 1965).
l
i
'
The
daily data for these stations are shown in figure 9.
At Urbana a peak occurs in the frequency graph on both
: 15 and 16 November, the same dates as noted for the
singularity at Flagstaff and Denver.
The maximum average
daily amount occurs on the 1 5 th with a secondary
maximum on the 16th.
In the data for Woodstock a minor
peak in the frequency appears on 17 November, but there
is no supporting maximum in the average amount on that
date.
It would seem that the singularity-producing event has
been waylaid in its cross-country movement, or that its
effect on the frequency pattern has been masked out by
phenomena from other sources.
-\
.
a. llallber
ot daJII
with maasurable
p:Ncipitation
b.
Awrap dai.l.7 a.nmt ot precipitation
.30
10
�
15
0
u
I I
2
I� II
12
'7
17
'22
�
.... ..,
H
v
URBANk
.30
�
�
'T n � n
I
0
I
I I
u
'2
'7
�..
112
17
'22
I
:X:
0
:z:
H
'27
WOCDStOCI.
Figo 9.
November daily precipitation data for Urbt.�, Ill., and Woodstock, Mdo,
1946
-
1965o
N
V1
Chapter 5.
Storm Tracks and Pres$ure Changes
5. 1 November Storm T racks.
In examining the mean storm tracks .for November as
indicated in the maps of Weightman (1945) and Klein
(1957)
(combined in figure 10) a possible reason for· the
disappearance of this singularity becomes apparent.
The storm tracks that are dominant in the western United
States this month do not continue directly across the
country, but rather curve northeastward from the Rockies,
move across the Great Lakes region and into Canada.
Weightman's map has two tracks entering the United States
from the Pacific Coast.
One of these holds to the
northern tier of states while the other crosses through
central California, northern Arizona, and New Mexico
before curving toward the southern shore of Lake
Michigan.
The only tracks that pass near the Woodstock
area that do not originate in Gulf or Atlantic waters
come from southern branches of Weightman's Colorado Low
and Texas Lm" tracks.
Klein • s Northern Hemisphere chart for November shm-1s two
secondary tracks coming into Colorado from the west and
northwest, combining into a primary track in eastern
26
Salt Lake
City•.
-
---
....
Fig.
10.
: 1892 - 1912
: 1899 - 1938
(Weightman, 1945}
(Klein, 1957}
Principal tracks of low pressure centers across the United States in November.
N
-...J
28
Colorado.
This track then curves northeastward in a
manner similar to those of Weightman and passes over
Lakes Michigan and Huron into Canada.
Of interest here
is that these tracks curving to the northeast from the
Denver area are following a great circle course that
passes· through London.
This northeasterly trend of the storm tracks across the
main portion of the United States may explain the lack
of a precipitation peak at Woodstock in November.
addition,
In
the general agglomeration and concentration of
storm tracks in the Great Lakes region is such that any
anomaly that might be responsible for increased
occurrence of precipitation in the western United States
becomes very thoroughly lost in the multitude.
5. 2 Five-day Mean Charts.
To attempt to follow the movement of this singularity
across the United States, into Canada, and possibly to
Europe, the five-day "normal" surface maps of Lahey;
Bryson, and Wahl
provide
a
(1958) are of some help.
These charts
mean surface map for the same pentadal intervals
as used in the present study, and a map of the change in
pressure from one mean map to the next.
Thus one is
able to follow, albeit in rather large time jumps, the
29
shift of possible singularity-causing influences from
the Mountain States and Midwest suddenly into Europe
(see figures lla - llc)
•
Other than slight deepening of the Aleutian and Icelandic
Lows, there are few differences in the mean maps for the·
four pentads from 7 through 26 November,
particularly as
: analyzed from data in a widely spaced grid.
Thus the
charts of pressure change from one mean map to the next
are of assistance in determining how the pressure field
has changed.
Beginning with the pressure change chart reflecting the
difference between pentad 63 and pentad 64 (figure lla) ,
there are pressure falls over Alaska and western Canada,
· with slight pressure rises indicated over the Pacific
i
! Coast and Mountain
StatesQ
.
!
; pressure
America.
·pentad 6 5
The largest area of
falls occurs off the east coast of North
On the pressure change chart for pentad 64 to
(figure llb),
Lhe main region of pressure falls
extends from Alaska and Canada through the central United
:states to the Gulf Coast:
The area of Woodstock is in a
:region of slight pressure rise, while Urbana is in. a
definite pressure fall region.
6 5 and 66
(figure llc)
,
Then, between pentads
the region of largest pressure
·falls shifts from over northern Canada to northern
30
A. Mean sea-level pressure
Pentad 63
7 - 11 November
H = High; L = lDv
Isobaric interval = 3 mb.
(Hjo
Pentad 83
'0
B. Pressure change:
Pentad 63 to Pentad 64
R = Rise; F = Fall
Iaallobaric interval
=
1 mb.
Areas of over 1 millibar
cha nge are shaded.
c. Mean sea-level pressure
Pentad 64
12 - 16 November
Isgend as for Chart A.
(An.r :r.be,-, Brpon,
and Wahl; 1958.)
Fig. 11a. Fiw-da;r mean sea-lewl pressure and pressure change charts;
7 - 16 November.
31
c. Mean sea-level pressure
Pentad 64
16 tlovember
12
-
legend as for Chart A.
Pentad 64
D. Pressure change:
Pentad 64 to Pentad 65
Isgend as for Chart B.
E. Mean sea-level pressure
Pentad 65
17 - 21 Noveml:er
Legend as for Chart A •
Figo 11b. Five-day mean sea-level pressure and pressure change charts;
12 - 21 November.
32
1�0
E. Mean sea-lewl pressure
Pentad 65
17 21 November
I
-
legend as tor Chart A.
Pentad
F. Pressure change:
Pentad 6 5 to Pentad
�
65
l�
66
legend as for Chart B.
\ "'r
V
.
a. Mean sea-level pressure
Pentad 66
22
26 November
-
legend as tor Chart A.
Fig. 11c. Five-day E&n sea leve l pressure and pressure change charts;
17
26 November.
-
-
33
Europe and Scandinavia, indicating lower pressures in
those areas in time for the late November storm periods
of both Brooks
{1946) and Lamb
{1950).
5. 3 Tracking Problems.
Any relations between precipitation occurrence patterns
and mean storm tracks,
or other synoptic features, can
be partially 6bscured b� greatly differing periods of
record.
All precipitation computations used here are
based on the 20 years 1946 through 1965.
Weightman's
(194 5) average tracks are based on 20 years of daily
charts from 1892 through 1912, and Klein's
{1957)
principal tracks on the 40 years of historical maps from
1899 through 19 38.
The five-day 11normaln surface charts
of Lahey, Bryson and l�7ahl
{19 58) were prepared from data
taken at fixed positions of latitude and longitude from
daily charts for b•lO periods totaling 20 years:
through 191 3 and 1925 through 1937.
1907
Finally, Brooks'
(1946) singularities are based on the 5 2-year 1889
through 1940 period, and Lamb's
{1950) maxima stem from
the 50-year period 1898 through 1947.
That the mid-November rainfall singularity cannot be
followed clearly through the various mean charts used
here does not necessarily mean that its movement cannot
34
/'� be traced at all.
Thi s particular singularity may not
/
have existed during the periods used for those charts.
Namias
(1969 p.
57)
states:
" • • •
there is no reason for
assuming that a singularity is a permanent climatological
characteristic.
In other words, there is no reason why
there should not be long-period climatic fluctuations in
the intensity and timing of singularities
• • • " .
I
'
i.
I
I
!
Ii
-I
I
L.·-----------------�---------·
!
·---------------------------
--------�-------- �------ -------- -
-
--------- - -------------,--- - ----------------
Chapter 6.
Possible Causes
6.1 Possible Upper-air Influences on the Singularity.
A possible influence on the occurrence of precipitation
days i·n mid-November is found in a study by Winston
(1954) .
His figure 3 shows the latitudinal position of
the 700 millibar
(about 3 kilometers) geostrophic zonal
wind field through the year based on five-day mean data
for 8 years, 1945 - 1952.
The westerly zonal maximum
(indicated at over 12 meters per second) , near 50° North
latitude in September, moves southward during October,
and by mid-November reaches about 42° North.
In early
December, this wind maximum begins to move northward,
returning to its original latitude by early January.
This southward swing of the westerlies may very well be
reflected in the higher frequency of precipitation at
the approximate time of their most s�utherly reach.
Namias'
(1950) 700 millibar zonal index, using ten-day
averages for 1944 - 1949, shows a minimum in mid-November.
Later, Namias
(1952) found that th.e long-term 700
millibar circulation patterns
(1933 - 1952) changed
markedly from April to May and October to November.
persistence of surface patterns of temperature and
35
The
3�
perturbations in the westerlies.
This in turn results
in anomalies in both the temperature and precipitation
patterns,
one of which could be the mid-November
precipitation peak.
This post-equinoctial drastic shift in the circulation
i
i
I!
I
pattern before it settles down to the more usual
arrangements of s ummer or winter flow has been noted in
I
instance, Yeh,
I
changes in the Northern Hemisphere circulation in the
i
spring and fall of 1956 as seen in the upper atmospheric
I
I!
I
other portions of the world and at other altitudes.
Dao, and Li
(1959) reported on sudden
flow over Asia and the Pacific to 100 millibars
16 kilometers).
For
(about
They suggested that these sudden
changes in the flow may well be a world-�lide phenomenon
and related to a similar change noted by Sutcliffe and
Bannon
(1954) over the Hediterranean and Middle East.
'
!
_________�
- -��------ -·-------·----------� ··-----·-- ------�---- ----- ··-----
····· - ------ - - - - -- ·-
37
At higher altitude13,
Webb
(1966,- pp.l40 - 145) noted
six definite seasons in the stratospheric circulation.
One of these, the "ear � y winter season" of 15 October to
15 December, begins with a rapid shift from the summer
easterly circulation to the westerlies of winter.
Using
data from the Meteorological Rocket Network's Summer 1960
through December 1964 firings at the White Sands Missile
Range, New Mexico, he presented a picture (his figure
4. 4, p. l42) of the zonal circulation in the region of the
stratopause based on mean winds in the layer between 45
and 55 kilometers.
The summer easterlies gradually
!
become less intense until the autumnal equinox when weak
\.,
'"
westerlies usually first appear.
These increase in
intensity rapidly for the next few \\Teeks, peaking at
near 70 to 80 meters per second by the end of October.
The zonal speed decreases slightly to a secondary minimum
around 5 to 10 November, then increases to a greater
peak by early December.
The "winter storm period" then
takes over.
6. 2 Conclusion.
From a simple question concerning a peak in the
frequency of rainy days during November at Point Mugu,
this paper has gone far beyond its initial concern with
Ventura County .
From the original intent to investigate
3B
r:h:- �:-::1-::::�-:-:
f
= ·:
--
i
- --
:�:::�� �i��:�-::
--
November r
ity
! and to attempt some physical explanation for it,
thi-s
paper has expanded io verify the singularity's existence
at other California stations and in the Rockies, traced
it to the Midwest,
and found indications that the
singuiarity might be seen in the late November storminess
j
in Europe.
I
I
. II
I
i
A possible cause of this singularity is suggested in
the rapid decay of the summer circulation in the upper
levels of the atmosphere following the autumnal equinox
1 and the southward shift of the westerly maximum in the
I lower
levels as the wind
'·
�atterns
of the Northern
i
!
Hemisphere begin to acquire the characteristics of a
I
winter
situation.
.
I
I
I
I1 This
I
i
II
1
I
Ii
singularity may be part of a possible global
pattern with a periodicity of about 60 days.
Six 61-day
cycles become a 366-day year; thirteen 60-day cyclep
are surprisingly close to the 26-month "quasi-biennial"
oscillation of the tropics and subtropics.
I
i
Further study would examine precipitation frequencies at
a
greater number of stations in North America for longer
periods of record and differing sequences of years to
39
determine if there have been preferred areas or times
for this singularity to appear.
Additionally, five-day
mean flow data, both surface and aloft, would be
required for the same periods as under study so that
proper spatial and temporal relations can be maintained.
Attempts should also be made to locate the singularity
before it arrives in North America. -- perhaps in
Japanese data -- and to determine if there is any valid
link between the bimonthly cycle hypothesized above and
knovm relationships between both precipitation and
sunshine and the lunar cycle
Lund,
1965).
(Brier and Bradley, 1964;
Brier, G.W., A test of _the reality of rainfall
singularities, Journal of Meteorology, 18:242- 246,
1961.
·
1
•
Brier, G.W., and D.A. Bradley, The lunar synodical period
and precipitation in the United States, Journal of
the Atmospheric Sciences, 21:386- 395, 1964.
I Brier,
I
I
I
G.W., R. Shapiro, and N.J. Macdonald, A search
for rainfall calendaricities, Journal of the
Atmospheric Sciences, 20:529-532, 1963.
I Brooks, C.E.P., Annual recurrences of weather: "Singu­
I
larities", Weather, 1:107-113 and 1:130-134, 1946.
·I
I
Bryson, R.A., and W.P. Lowry, Synoptic climatology of the
Arizona summer precipitation singularity, Bulletin of
the American Meteorological Society, 36: 3 29- 3 39, 1955.
Buchan, A. , Interruptions· in the regular rise and fall
of temperature in the course of the year, Journal of
the Scottish Meteorological Society, 2:4-15, 1869.
de Violini, R., Climatic Handbook for Point Mugu and San
Nicolas Island, Volume I, Surface Data, Pacific
Mi�sile Range M1scellaneous Report PMR-MR-67- 2, 142pp.,
Pacific Hissile Range, Point Mugu, California, 1967.
Huschke, R.E. (ed.), Glossary of Meteorology, 6 38 pp.,
American Meteorolog1cal Soc1ety, Boston, 1959.
Jorgensen, D. L. , A long-term fluctuation in early Fall
precipitation in California, Bulletin of the American
Meteorological Society, 3 2:210-21 3, 1951.
Klein, W.H., Principal Tracks and Mean Frequencies of
Cyclones and Anticyclones in the Northern Hemisphere,
u.s. Weather Bureau Research Paper No. 40, 60 pp.,
U.S. Weather Bureau, Washington, 1957.
Lahey, J.F., R.A. Bryson, and E.W. Wahl, Atlas of
Five-Day Normal Sea-Level Pressure Charts for the
Northern Hemisphere, Scientific Report No. 7, USAF
C ontract AF19(604)-99 2, 75 pp., University of Wisconsin
Press, Madison, 1958.
40
41
Lamb, H.H. , Types and spells of weather around the year
in the British Isles: annual trends, seasonal
structure of the year, singularities, Quarterly Journal
of the Royal t1eteorological Society, 76: 39 3-429, 1950.
Lund, I.A., Indications of a lunar synodical period in
United States observations of sunshine, Journal of
the Atmospheric Sciences, 2 2:24- 39, 1965.
McDonald, W.F., Average Precipitation in the United
States for the Per1od 1906 to 1935 Inclusive, 53 pp.,
U.S. Weather Bureau, Washington, 1944.·
·
Namias, J., The index cycle and its role in the general
circulation, Journal of Meteorology, 7:130-1 39, 1950
•
. , The annual course of month-to-month persistence
in climatic anomalies, Bulletin of the American
Meteorological Society, 3 3: 279-285, 1952.
---.--
, A late November singularity, pp. 55-6 2 in A.
Court, ed., Eclectic Climatology, Oregon State
University Press, Corvallis, 1969.
---.:::---
O'Mahony, G., Singularities in daily rainfall, Australian
Journal of Physics, 15:301- 3 26, 196 2.
Sutcliffe, R.C. and J.K. Bannon, Seasonal changes in
upper-air conditions in the Mediterranean-Middle East
Asia, pp. 3 22- 3 34 in Scientific Proceedings of the
International Associat1on of Meteorology, Rome, 1954.
U.S. Weather Bureau, Climatological Data for Arizona,
California, Colorado, Illinois, Maryland-Delaware,
and Utah, National Weather Records Center, Asheville,
N.C., October, November, December, 1946-1965.
Wahl, E.W., The January tha\·l in Nevl England (an example
of a \veather singularity), Bulletin of the American
.[\'1eteorological Society, 33: 380- 386, 1952.
, Singularities and the .general. circulation,
Journal of Meteorology, 10:42-45, 1953.
---:::---
, A weather singularity over the u.s. in October,
Bulletin of the American Meteorological Society, 35:
351- 356, 1954.
--=-___,.-
Webb, W.L., Structure of the Stratosphere and Mesophere,
(Internat1onal Geophys1cs Ser1es, Volume 9) 382 pp.,
Academic Press, New York, 1966.
42
Weightman, R . H., Average Monthly Tr acks by Types of Lows
in the United States, 1 5 pp. , U. S. Weat.her Bureau,
Washin gton, 1 9 45 .
Winston, J. S. , The annual course o f zonal wind speed at
700 mb, Bulletin of the American Meteorological
Society, 3 5 : 468-471, 1 9 54.
World Meteorolo gical Organization, Guide to Climatological
Practices, . WMO-No. 100 . TP : 44, . Geneva, 1 960.
Yeh, T. C. , S. Y. Dao, and M. T. Li, The abrupt change of
circulation over the Northern Hemisphere during June
and October, pp. 2 49- 267 in B. Bolin, ed. , The
Atmosphere and Sea in · Motion, Oxford Univers1ty Press,
1 9 59 .