24 MONTHLY WEATHER REVIEW
THE WEATHER AND CIRCULATION OF OCTOBER 1960'
J. F. ANDREWS
Extended Forecast Sechon, U.S. Weather Bureau, Washmgton, D.C.
1. INTRODUCTION
Generally fine fall weather prevailed throughout' rllost'
of the United States during October 1960. The days
were pleasantly warm and t,he nigh& cool. There was
very little severe storm activity, and no tropical storms
were observed in the Atlant'ic, Caribbean, and Gulf of
Mexico.
Principal exception to the good weather occurred over
the Southwest where Arizona, New Mexico, and Texas
report'ed record or near record amounts of precipitation
for the month, with flash flooding a frequent occurrence
in Texas.
2. MONTHLYMEAN CIRCULATIONANDWEATHER
MEAN CIRCULATION
The most anomalous feature of October's average
circulation pattern at 700 mb. (fig. 1) was strong blocking
over the North Atlant'ic, where heights averaged as nluch
as 390 ft. above normal. During September [1] blocking
had been centered just north of Scandinavia. As the
blocking moved west,ward, it increased in st'rengt'h and
was associated with development near Ireland of a dcep
mean Low both a t 700 mb. and sea level (figs. 1 and 2).
The presence of a cyclonic cent'er on a monthly mean map
in this area is most unusual, none previously having been
observed during our period of record (since 1932). Aver-
age sea level pressures in this Low were as much as 12
mb. below normal (not shown), while heights at 700 mb.
were 400 ft. below normal.
Retrogression and intensification of the block was also
associated with development oi' a deep full-latitude trough
over central Asia (fig. 1). Perhaps as a result, the mean
troughs near the Asiatic coast, over the mid-Pacific, and
oft' the California coast moved eastward from September
to October. The full-lat'it'ude trough near t'he east coast
of North America during September deepened at middle
latitudes as its lower portion moved slowly eastward in
October. At higher latitudes, however, t'his trough
weakened and retrograded as blocking from t'he n'ort'h
Atlantic spread into eastern Canada, the trough assunling
more of a negative tilt'.
uary 1961 will appear in the February, March, and -4pril 1961 issucs, respectively, of thr
1 Articles on the weat,her and circulation of November 19B0, Dccemher 1960, and Jan-
M c n t h l l ~ Weather Review.
Wind speeds a t 700 mb. also reflected the blocking
cl1ar:tcter of t'he circulation over t8he At'lnnt'ic. Sote in
figure 3A the characterist'ic split jet stream over the
At,lantic and Europe, with wind speeds up to 7 n1.p.s.
above normal at high ltitit'udes and as much as 9 n1.p.s.
above norrnd a t lower lat'itudes (fig. 3B). An extensive
area of subnormal wind speeds, as much as 7 m.p.s., was
observed at middle lat'it'udes. The axis of nlaxirnunl west
winds across the At'lantic was displaced sout'h of normal
(normal position is shown by dashed line) as it result of
the blocking. Elsewhere around the hemisphere, the jet
axis appeared as a well defined current, north of its normal
position over eastern Asia and t'he west,ern Pacific, and
near its normal position over t'he eastern Pacific and across
North America (fig. 3A). T;li"nd speeds in t8he lat'ter two
areas were close to t'heir normal values (fig. 3B). This is
also implied by small departures from nornml of 700-mb.
heights (fig. 1).
AVERAGE UNITED STATES WEATHER
October was generally warm over most of the contiguous
United States, with below normal temperatures observed
only in the Plateau Stat'es, t,he Xortheast,, and in port'ions
of t'he Upper Mississippi Valley (fig. 4). Temperature
departures were rat'her small, 2' F. or less over most of
thc Nat,ion, alt'hough positive departures of as much as
4' F. were observed in southeastern Montana (fig. 4).
The predorninantly mild weather can be related t'o the
weaker t'hm normal ridge over western Canada (fig. 1).
As a result of t'he weakness of this ridge, relatively mild
Pacific air masses dominated the Nation's weather. Over
the Great Basin, however, strong radiational cooling in
the mean sea level High (fig. 2) result'ed in below normal
ternperat'ures. The cool conditions in Arizcma and New
Mexico can be related primarily to southward advection
of Pacific air masses into a stronger than norrnal t'rough
aloft (fig. 1), and also t'o cloudiness and precipit'at'ion from
a very slow moving storm near mid-month. In tthe Xorth-
eltst below normal 700-mb. heights and northerly, anorn-
alous flow result'ed in cool conditions (figs. 1 and 4).
From the Middle Atlant'ic States to the Gulf of hlexico
this flow diminished in strength, and, combined wit'h a
weak confluence zone over the middle United St'ates,
tended to prevent the southward intrusion of cooler
conditions.
JANUARY 1961 MONTHLY WEATHER R1I:VIEW 25
FIQURE 1.-Mean 700-mb. contours (solid) and height departurw from normal (dotted) (both in tens of feet) for October 1960. Blocking
pattern in the Atlantic was the outstanding circulation feature of thcl month.
The outstanding feature of the precipit,at,ion pattern for
October was the large area in the Southwest where anlourlt,s
were far in excess of the mont,hly normal (fig. 5 ). As
much as six times t,he normal amount of precipit'at'ion fell
in portions of southeast,ern Texas. Victoria reported
17.25 inches, an all-time record for any month, while
Corpus Christi, with 10.66 inches at the airport, and 15.49
inches at tthe Weat8her Bureau city office, had its rainiest'
October in a period of record dating back t'o 1887. At
Austin, Tex., rainfall of 12.31 inches was t8he second
heaviest on record for Oct,ober. The heavy precipitation
in t8he Southwest was related t'o the deeper than normal
t,rough in that area (fig. 1) and to cyclonically curved
southeasterly flow of Gulf moisture a t t'he surface (fig. 2).
This weather pattern replaced the upper level ant'icyclone
and generally dry conditions which had prevailed during
September [I].
Near normal amounts of precipitat,ion fell over much of
the East. This was related primarily to cyclonic curvature
of the contours and below normal 700-mb. heights in the
mean trough along t8he east coast.
Less than half the normal amount of precipitation fell
FIGURE 2.--hIean sea level isobars (millibars, hundreds omitted)
for October 1060. Low cells a n d s t o r m t r a c k i n t h e iVotth
Atlantic were displaced well south of normal.
in the Great' Basin, most of California, and the nort'hern
Great Plains (fig. 5 ). No measurable precipitation fell at
Rapid City, S. Dak. during October; none had fallen since
September 22. Anticyclonic curvature and a weak ridge
aloft (fig. 1) contributed most to this precipitation
deficiency.
SOME CHARACTERISTICS OF EUROPEAN WEATHER
In this section specid at)tention will be devoted to Oc-
tober's weather in Europe because of the unusual nature of
tJhe monthly mean circulation observed in that area. The
average weather observed in Europe during October can
be divided roughly int'o three regimes: cool and dry in the
north, cool and wet in the south, and warm and wet in the
middle countries. In figure 6A is shown the average sur-
face temperature and its departure from nornral for se-
lected European cities during October 1960, while figure
6B gives the total precipitat'ion and percentage of normal
for the same cit'ies. These data are from [a ]. Normals
used are based on a 30-year average (1901-30 when avwil-
able) as recornmended b y t h e World Meteorological
Organization.
Unusually heavy amounts of precipitation fell in most
areas, with only the northern portions of the British Tsles
and Scandinavia receiving suhstant'inlly less t'llan norrnal
amounts. Many count'ries received more than t'wice their
normal rainfall for t'he month, while much of Spain had
more than three times the normal. In general, the greatest
falls and percentages were found in areas closest to the
Atlantic Ocean. La Coruna. Soain received 10.62 inc-hcs.
26 MONTHLY WEATHER REVIEW JAK UARY 1961
I
,I . ~
-
~~ ~. . . - ~-~.~---, graphic lilting, droppcd much of their moisture near and
FIGURE :3.-(A) Mran 700-mb. isotitchs and (B) departure from
monthly normal wind speed (both in meters per second) for
October 1960. Solid arrows in (A) indicate axes of primary wind
speed maxima with the normal position dashed. Areas of de-
parturex in (B) greatclr than +4 are hatched, those greater than
-4 are stipplcd.
and Brest m d Bordeaux, France 8.66 inches each. I n
nlany areas t'lris wtts the wettest October in several
d c c d e s , m d flooding was reported througlrout' nruch of
western Europe.
The unusually wet weat'her was well related t'o October's
tnean circulat'ion pattern. Of most importance was the
deep mean trough along the coast of westernEurope and t,he
intense cyclonic center of action near Ireland (figs. 1 and
2 ). Abnormally strong Atlnnt'ic west'erlies, aided by oro-
JAKUARY 1961 MONTHLY WEATHER REVIEW 27
FIGURE 4"Departure of average surface tctmpclrature from ~lornxtl
(" F.) for October 1960. Departures were ger~crally small for
the month. (From [6].)
along coast'al areas, - with somewhat lesser precipitation
amounts further inland. Much of the hand of heaviest
precipitat'ion fell near or to the north of the prinlary jet
axis at' 700 mb. (fig. 3). At sea level, st.orws moving
across the Atlantic reached their rnaximurn interlsity mar
the coast before moving inland and weakening. The path
of these systems was rwll defined by the zonal trough on
the mean sea level chart (fig. 2 ).
The strong upper level ridge near Gredand and the
accompanying lack of c]vclonic activit'J- were rclat'ed to
above norrnal temperatures and a precipitation dcfi-
ciency in Iceland, while stronger t'llan nornlal nortllerly
flow result'ed in below nornlsl t8emperutures tmd subnor-
mal amounts of precipitation t8hroughout most of Scandi-
navia (figs. 1, 2 , 6). A strong onshore flow of relat,ivcly
cool Atlant'ic air, combined with persistent cloudiness R I ~
precipitation, produced cooler t'han normal conditions in
southwestern Europe, where Madrid, Spain, reported t~
temperat'ure departure of "4F. In central and south-
FIGURE 6.-(A) Average surface temperature and departure from
normal (" F.), and (B) total precipitation (inches, approximate)
and percentagc of normal for 0ct)ober 1960 at selected European
stations.
esstern+~urope prevailing sout'lterly flow at sea level and
aloft resulted in generally warmer than normal conditions.
3. WEEK-TO-WEEK VARIABILITY
Rather-marked week-to-week changes occurred in the
circulation and weather over the contiguous United
St'ates during Oct'ober. These changes will be described
28 MONTHLY WEATHER REVIEW
FIGURE 7.--Five-day mean 700-mb. contours (solid) and height
departures from normal (dotted) (both in tens of feet) for October
4-8, 1960.
using a series of 5-day lnean 700-nlb. charts centered one
week apart. The reader is referred to the correspondin6
maps of weekly temperature departure from normal and
total precipitat'ion published in the N'eekly U'eather and
Crop Bulletin [3].
WEEK ENDING OCTOBER 9
The month began with the west'erlics stronger than
nornlal, troughs off both east and west coasts of the Vnitcd
States, and a strong ridge over the West (fig. 7). Another
trough, seemingly out' of place because of high zonal index
conditions and short wavelength, was found over the
Gulf of hlexico. The circulation in the Atlantic was
strikingly similar t'o t>he mean pttt'tern for the rrlont'h (c o n
pare figs. 1 and 7).
Mild Pacific air rnasscs dominated the United States
and resulted in above normd ternpertitures over d l but
the extreme northwestern arld northettst'ern sections of
the country [3]. Greatest weekly departures, as much as
9' F. above normal, were observed in the nort>hern Great
Plains. A temperature of 91' F. at' Bismarck, N. Dak.
on the 4th equalled their previous record high for so late
in the season. This unseasonable \varnlth was relat'ed to
the strong upper level ridge over the West', and to the
extensive area of negative 700-mb. height anorndl- over
western Canada (fig. 7). It' has long been known that
negative height anomdies over west'ern Clanada during
t,he c,ooler seasons are associated with above normal tern-
peratures over most of t'he Cnited States, with the con-
verse also true. Cool weather in the Northeast was re-
lated to stronger than norrnal nort'herly circulation
FIGL-RE S.--Five-day mean 700-mb. contours (solid) and height
departures from norrnal (dotted) (both in tens of feet) for October
11-15, 1960.
around the deep center of action over eastern Canada
Little if A ~I S precipitation fell in the area from the
Rockies to t'he Great Lakes, under the influence of dr?-,
northwcsterl~ flow aloft (fig. 7). The heaviest and most
frequent precipit'ation fell over the southeastern quart,er
of t'he Xiation, with a~nounts of 2 inches or more quite
general. These heavy rains were related to A slow rnov-
ing trough and cyclonic center over Louisiantl and Missis-
sippi. Precipit'ation in the Fur West was rtssociat,ed with
the approac~h of the deep trough off the coust. As this
trough rnoved eastward, a stornl developed over the Far
Southwest lute in the week, bringing heavy precipitation
to that B l ' C R .
WEEK ENDING OCTOBER 16
(fig. 7).
E:tstw-ard nlotion of all trough-ridge sgstmls occurred
from the first) to t'he second weeks under the influence of
continuing fast westerlies. The trough over t h e Gulf of
Mexico and Gulf States filled considerably as it rnoved
eastward (fig. 8). As a result little if' an)- rain fell in the
SOllthCASt'.
Eustwnrd motion was also observed in the tenlpernture
patterns between the two weeks. Cold Pacific air nlasses
scconlpanicd the eastern Pacific trough into the Far West,
where temperatures for the week averaged as rnuch as 9'
F. below normal in southern Nevada and southeastern
Idaho.
Abnorrnally warm weather overspread the East, to in-
clude d l but northern New England, where a persistent
northerly circulation kept temperatures below normal
(fig. 8). Escttnaba, Mich., reported its highest tempera-
FIGURE 9.-Five-day mean 7oO-mb. contours (solid) and height
departurcls from normal (dottcd) (both i n tens of feet) for Octobcr
18-22, 1960.
ture so lat,e in t,he season, 82" F. on t'he 10th. Daily
temperature records were established a t Des Moines, 1ow-a
'(86') and Topeka, Kans. (87") on t'he llt'h, Detroit,
Mich. (81") on the 13th, and Providence, R.I. (81") on
the 15th.
The deep t,rough in the West spread heavy rains from
the lower Great Plains to the Great .I1akes, with gretrtcst
amounts in Texas. As much as 12 inches fell in the south-
ern part of t,hat Stat,e. Precipitation at Denver, Colo.,
on the 13th cnded a 20-day period without rneasur:rble
precipitation and the driest August 1-Octobcr 12 period
' of record. T h e rainfall occurred a s a storm system tle-
veloped over the Far Sout.hw7est and hecame t,rapped by
a massive high pressure area to the nort'h. As :t result,
precipitation persisted in the southern Rocky Mount~airl
States for four to five days, carrying over into the follow-
ing week. Roswell, K. Mcx., reported :a near record 24-
hour amount8 on the 16th-17th. 'rhe cutting off and stag-
nation of this storm was related to tlrnplification of the
circulation in the eastern Pacific near t'he end of the
week.
Western Europe had its most favorable weather of tlle
month during the second week as the trough near the
coast moved eastward int'o central Europe (fig. 8).
WEEK ENDING OCTOBER 23
A complete reversal of circulation and t'ernpcrature
regimes occurred between t'hc second and third weeks in
the United Stat,es. This change was effected primarily
by amplification and eastward motion of t,he trough-
ridge system in the eastern Pacific. As a result a st,rong
full-latitude ridge developed over the coast of west'ern
FI(:I.RE IO.-Five-day mean 700-mb. contours (solid) and height
tl(~ptlrtnrc~s from normal (dotted) (both in tens of feet) for October
25-29, 1 0 G O .
Sorth America, with positivc height anomalies replacing
the ncgutivc field of the previous week (figs. 8, 9). At
the sume time the t'rough over t'he West moved eastward
to the Appalachians, where ridge conditions had prevailed
t l k wcek before. Marked changes also occurred down-
stream, with the circulation reverting t,o t'he same general
pattern as observed during t'he first week (figs. 7, 9).
Stronger t'han normal northwesterly flow over western
Sorth America (fig. 9) deployed cold, continental polar
air masses into the eastern two-thirds of the United
Stwt,es, thus bringing to an abrupt end the warm regirnc
of the week bcfore. Early season minimum temperature
records W C ~A established on the 19th at Bismarck, X.
Dak. (5") and Huron, S. Dak. (11"), and on the 20th at
Sioux City, Iowa (16") and Topeka, Kans. (22'). The
circulation reversal in the West. was also accompanied
by a reversal in temperature regimes, wit'h some areas
:tveraging 10" F. warnwr than the previous week.
(lontinurtion of t,rough conditions in the Southwest
brought additional heavy rains t'o t'he Southern Plains,
with Texas ugain rccciving the heaviest tmounts. Up
to 10 inches fell in the middle Texas coastal region,
resulting in considerable flash flooding. East'ward motion
of the t,rougll in the West also brought substantial amounts
of prwipitution to t'he Atlantic Coastal St'ates.
WEEK ENDING OCTOBER 30
Int,ensification and retrogression of Sorth At'lantic
blocking dominat'ed the circulation changes t'ownrd the
end ol the month. Heights at 700 mb. rose as much as
500 feet over southeastern C'anada, while an increase of
700 feet was observed north of tlle Siberian Peninsula
30 MONTHLY WEATHER JANUARY 1961
I OCTOBER 1960 I I \
FInrrRE 11.-Tracks of Pacific typhoons superimposed upon mean
700-mb. height contours (same as fig. 1) for Octobcr 1960. Open
circles and dates indicate 1200 CMT positions.
(figs. 9, 10). As a result, t'he middle-latitude westerlies
diminished in strength, wit'h the circulation pattern
characterized by a series of t,runcated trough-ridge svsterns
with relatively short wavelengths.
Collapse of the ridge over western Korth America
resulted in milder Pacific air and above normal tenlpera-
tures spreading eastward to the Mississippi Valley. Xiost
of the East continued cool because of stronger than norrnul
nort'herly circultktion (fig. 10).
For the t'hird consecutive week heavy rains fell in
cent,ral and sout'heastern Texas, causing major flooding
along several streams. Amounts of 5 to 10 inches fell
south of San Ant,onio on the 25th and from 7 to 10 inches
in the Austin area on t'he 28th. Heavy amounts also
spread northward into the western Great' Jlakes region.
Much of this precipitation can be related to a developing
lee trough east of the Rockies and to rrmintcnance ol the
southwest'ern trough.
Several slow moving storm systems, deepening in the
trough off the east coast, brought heavy precipitation to
the Middle Atlantic coast and the Xortheast. Some ol
this was in the form of an early season snowfall in Penn-
sylvania, New York, and New Eng1:tnd. Alrlourlts were
generally light, but up t'o 6 inches was reported in S e w
Hampshire.
4. TROPICALACTIVITY
ATLANTIC
There was a complete lack of tropical storm develop-
ment in t'he Atlantic during October 1960. This com-
pares with an average frequency of two such storms for
October for the period 1887-1956. This absence of
tropical activity was quite well related to the anomalous
character of the circulation over t'he Atlantic, i.e., west'er-
lies and subtropical ridge south of normal (figs. 1, 3),
and is in agreenlent~ with the findings of Ballenzweig [4].
PACIFIC
Four typhoons were observed in the Pacific during
Oct'ober 1960. Trwks of these storms superimposed
upon the 700-rnb. monthly mean circulation (same as
fig. 1) are shown in figure 11. I t may be recalled that
during September 1960 [l] four tropical storms were
observed in tlle western Pacific, none reaching typhoon
intensit)-. However, during October all st'orms were of
typhoon st'rengtll. Sortrlally tropicd activity in the
westcrn Pacific. decreases from September to October [5 ].
The relative increase between these two months during
1960 was probably related in part to the northward
displacement of the rnitl-tropospheric westerlies and sub-
tropical ridge (fig. 1). As a result the axis of maximum
west wind a t 700 rnb. WAS some 10' north of normal over
eastern Asia tmd the western Pacific (fig. 3A).
T~-phoons Kit and Ilola developed during the first half
of the month. Both followed similar westward courses,
sout'h of t'he Subtropical ridge axis, as they passed through
tlle Philippines into the South China Sea before dissipat,-
ing over land. Kote how closely their paths followed the
10,300-ft'. contour (dashed) of the monthlv mean 700-mb.
chart (fig. 11). TJ-phoons Mamie and Xina, on the
other lland, developed during the latter half of the nlonth
and recurved northward into the westerlies. Here they
becar~lc severe extratropical systems as they moved
rapitlly eastward, Xarnie reuching a minimum sea level
pressure of 952 m b . in the Gulf of Alaska on the 24t,h,
while Nina deepened to 968 nib. on the 29th and 30th.
REFERENCES
1. C. F. Tisdsle, "The \!-rather and Circulation of September
19CiO-Includirlg a Discussion of Tropical Storm Activity,"
Monthly I.Veather Review, vol. 88, No. 9-12, Sept.-Dec. l9G0,
2. 1J.S. \Yeather Bureau, Monthly Climatic Data f o r the World, vol.
13, No. 10, October 1960.
3. U.S. \\-eather Bureau, W e e k l y W e a t h e r a n d C r o p B u l l e t i n , Na-
t i o n a l S u m m a r y , vol. XLVII, Nos. 41-44, Oct. 10, 17, 24,31,
1960.
4. E. M . Ballenzweig, "Relation of Long-Period Circulation
Ruornalies to Tropical Storm Formation and Motion," Journal
of Meteorology, vol. 16, KO. 2, Apr. 1959, pp. 121-139.
5. G. E. Dunn, "Tropical Cyclones," Compendium of Meteorology,
American Meteorological Society, Boston, 1951, pp. 887-901.
G . U.H. FYeather Bureau, W e e k l y W e a t h e r a n d C r o p B u l l e t i n ,
l\-ational S u m m a r y , vol. XLVII, No. 45, Kov. 7, 1960.
pp. 353-361.
U .S . G O V E R N M E N T P R I N T I N G O F F I C E : 1361